Influence of Sea Surface Temperature and Chlorophyll-a on abundance and body size of black skipjack (Euthynnus lineatus) in the Mexican South Pacific

Influence of Sea Surface Temperature and Chlorophyll-a on abundance and body size of black skipjack (Euthynnus lineatus) in the Mexican South Pacific | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Influence of Sea Surface Temperature and Chlorophyll-a on abundance and body size of black skipjack (Euthynnus lineatus) in the Mexican South Pacific Yuliesky Garcés-Rodríguez, Yadian Israel La Rosa-Izquierdo, Emilio Alejandro Alemany-Rodriguez This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9558665/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract This study investigates the relationship between oceanographic variability, specifically sea surface temperature ( SST ) and chlorophyll- a (Chl- a ) concentration, and the abundance and size structure of Euthynnus lineatus (black skipjack) along the southern Pacific coast of Mexico from October 2022 to October 2024. The region experiences two distinct seasons: a dry season with strong “Tehuano” winds causing upwelling, and a rainy season influenced by the Costa Rica Coastal Current. High-resolution satellite data were integrated with biometric and catch data from local artisanal fisheries. Seasonal catch patterns peaked between April and July, following increased productivity and rising SST. The highest catches coincided with SST around 31.0°C, suggesting a thermal preference that enhances aggregation and catchability. Significant interannual variability was observed; 2023 catches were more than double those of 2024, likely associated with the presence of a warm pool in 2023 and varying environmental conditions. Morphometric analysis indicated larger individuals during cooler, productive months (October–March) and smaller fish during warmer periods, possibly due to temperature-driven metabolic responses. Principal component analysis (PC1: 38.4%; PC2: 27.7%) confirmed a strong seasonal modulation of environmental and biological variables. These findings suggest that monthly SST and Chl- a variability are primary drivers of E. lineatus dynamics in Oaxaca, providing essential data for sustainable fisheries management and assessing the impacts of climate change and extreme events on artisanal fisheries. Tuna Artisanal fishery MODIS Mexican Pacific Euthynnus lineatus Figures Figure 1 Figure 2 Figure 3 Figure 4 1 Introduction Understanding the dynamics of pelagic species of commercial importance in the Eastern Tropical Pacific requires a rigorous analysis of the oceanographic variables that modulate their habitat. Among these parameters, sea surface temperature ( SST ) is one of the most critical factors determining the distribution and behavior of tunas in tropical regions (Lehodey et al. 1997 ; Zainuddin 2011 ; Wang et al. 2025; Godinez-Padilla 2025). Studies have shown that SST not only influences metabolic and growth rates but also acts as a thermal barrier defining migratory routes and aggregation zones (Bertignac et al. 1998 ). However, the observed association between tunas and ocean thermal structures cannot be explained solely by temperature. This phenomenon involves complex mechanisms linked to highly productive areas where organisms search for food in oceanic fronts, eddies, or upwelling systems (Schaefer 1987 ; Brill and Lutcavage 2001 ; Zainuddin et al. 2017 ; Garcés-Rodriguez et al. 2023). The use of satellite data to estimate chlorophyll-a ( Chl-a ) concentration has allowed researchers to more accurately predict feeding zones and potential habitats for various tuna species (Polovina et al. 2001 ; Zainuddin et al. 2009; IATTC. 2022). In the case of the black skipjack, Euthynnus lineatus , its epipelagic ecology places it mainly in waters where surface temperatures exceed 24°C (Muhlia-Melo 1980 ; Forsbergh 1989 ; Godinez-Padilla 2025). This species is distributed from southern Baja California to Peru, maintaining a close association with continental shelf areas, unlike other tunas that perform large-scale transoceanic migrations (Fiedler and Bernard 1987 ; Collette et al. 2023 ). In the Mexican South Pacific, particularly along the coasts of Oaxaca, the black skipjack is one of the primary resources exploited by artisanal fisheries (Sandoval-Ramírez 2020; DOF 2023 ). The socioeconomic importance of this fishery for coastal communities highlights the need to evaluate how oceanographic parameters affect the species' abundance and size structure. The Oaxaca coast is recognized for its high biological productivity, driven by processes such as coastal upwelling and the formation of anticyclonic gyres in the Gulf of Tehuantepec (Lavín et al. 1992; Trasviña et al. 2003 ). These conditions make the region a hotspot for biological activity, favoring migration, feeding, and reproduction for numerous marine species (Ayala-Duval et al. 1988 ). Despite its importance, the fisheries face challenges related to sustainability, overfishing, and global climate change (Abudarda et al. 2021 ). Fluctuations in catches and specimen size are often attributed to environmental variations that alter resource availability in traditional fishing grounds. Therefore, analyzing oceanographic variables is fundamental to understanding the uncertainties associated with migratory processes and population dynamics of the black skipjack in the region. This study aims to evaluate the relationship between key oceanographic variables ( SST and Chl-a concentration) and the abundance and body size of Euthynnus lineatus in the coastal waters of Oaxaca, Mexico. The research seeks to characterize the environmental drivers of population dynamics to inform sustainable management strategies for this ecologically and economically significant species in the Mexican South Pacific. 2 Materials and Methods 2.1 Study Area The study region is located in the Eastern Tropical Pacific, covering the coastal zone of Oaxaca, Mexico (Fig. 1 ). This marine ecosystem is part of a highly dynamic oceanographic system influenced by converging regional currents, seasonal upwelling events, and terrestrial nutrient inputs, which together sustain high biological productivity (Lara-Lara et al. 2008 ; Martínez-Santos 2014). The Oaxacan coastal area is characterized by a complex underwater topography, including rocky reefs, sandy bottoms, and estuarine-lagoon systems that play critical ecological roles for marine biodiversity (Ruiz-Pérez et al. 2016), while supporting populations of species such as Euthynnus lineatus . Oceanographic conditions in the region are strongly modulated by two predominant seasons: the dry season (November to April) and the rainy season (May to October). During the dry season, strong "Tehuano" winds blow intensely from the Gulf of Mexico toward the Pacific through the Isthmus of Tehuantepec, triggering intense upwelling that transports nutrient-rich subsurface waters to the photic layer (Lavín et al. 1992; Fiedler 1994 ). This process fertilizes surface waters, reducing temperature and drastically increasing phytoplankton biomass. Conversely, the rainy season is marked by weakening winds and the dominance of the Costa Rica Coastal Current, introducing warmer, less productive waters alongside organic matter from terrestrial runoff (Kessler 2006 ). 2.2 Sea Surface Temperature and Chlorophyll-a Data To characterize the pelagic environment during the study period (October 2022 to October 2024), SST data were obtained from the Level 4 Multi-scale Ultra-high Resolution ( MUR ) Foundation SST version 4.1 product. Produced by the Group for High Resolution Sea Surface Temperature (GHRSST), this product offers a global spatial resolution of 0.01° x 0.01°, allowing for detailed analysis of small-scale features in coastal and oceanic environments (Chin et al. 2017 ). Chlorophyll-a concentration was determined using data from the Moderate-Resolution Imaging Spectroradiometer ( MODIS ) sensor aboard the AQUA satellite. Level 3 Chl-a products provide monthly global data at a resolution of 0.04° x 0.04°. These data were used as an indicator of primary productivity, allowing for the correlation of biological production peaks with catch events. 2.3 Biological Sampling and Data Analysis Biological data for Euthynnus lineatus were collected from the small-scale artisanal fishing fleet operating in Puerto Angel, Oaxaca. Monthly sampling was conducted at landing sites over two consecutive years. For each captured organism, the following metrics were recorded: Fork Length ( FL ): Measured to the nearest centimeter using a standard ichthyometer following FAO protocols for tunas (FAO 1982 ). Total Weight ( TW ): Determined using a calibrated digital scale with a precision of ± 10 grams. Catch data ( C ), expressed in tons ( t ), were obtained from official records of the National Commission of Aquaculture and Fisheries ( CONAPESCA ). These records, analyzed in conjunction with the number of active vessels in the area as a measure of fishing effort, served as a proxy for the relative abundance and availability of the species. The artisanal fleet consists of approximately 250 small vessels (less than 12 meters) utilizing traditional gear such as handlines or trolling. To identify significant differences in the variability of weights and lengths, the non-parametric Kruskal-Wallis ( KW ) test was applied, as distributions did not meet normality assumptions. A principal component analysis ( PCA ) was performed using Python (version 3.12) to synthesize common variability between environmental and biological variables. Results were visualized via a biplot, differentiating observations by season and representing variable influence through vectors. In compliance with modern ethical standards, it is declared that large language models ( LLMs ) were not used for original data generation or primary statistical analysis. 3 Results 3.1 Environmental Conditions (2022–2024) Monthly average SST along the Oaxaca coastal zone showed marked variability, ranging from 27.2°C to 31.5°C, with an average of 29.3°C. Two distinct thermal phases were identified: a warm period (May–October) and a cold period (November–April). In 2023, SST increases began in May, peaking in June and July at approximately 31.5°C. In contrast, the cold period showed a marked decline starting in October 2022, reaching its lowest value in February 2023 (27.2°C) (Fig. 2 ). Spatial analysis revealed distinct thermal patterns. In July 2023, a "warm pool" was observed along the Oaxaca coast, with the 31.0°C isotherm situated between Puerto Escondido and Puerto Angel. In comparison, July 2024 recorded cooler waters, with the 30.0°C isotherm predominating in the same area (Fig. 3 a, b). Chlorophyll-a concentration followed an inverse pattern to temperature. The highest values were recorded during winter and spring (October–April) (Fig. 2 ), coinciding with upwelling events. In July 2024, Chl-a filaments (> 0.5 mg m − 3 ) were observed along the coast, while July 2023 presented mostly oligotrophic conditions (< 0.2 mg m − 3 ) (Fig. 3 c, b). 3.2 Abundance and Size Structure of Black Skipjack Catch records of E. lineatus in Oaxaca show a recurring seasonal pattern, with abundance increasing in March and peaking in July. During the study period, monthly catches fluctuated between 11 and 130 tons (Table 1 ). A significant finding was the interannual difference: 2023 total catch reached 743.4 tons, more than double the 359.9 tons recorded in 2024. The highest catch volumes were recorded between April and July, with the highest catches occurring in May (~ 115 t) and July (~ 130 t) of 2023. Conversely, the lowest catches occurred between August and October, with the lowest value observed in September 2024. This seasonal pattern aligns with the historical availability of E. lineatus in the region, typically marked by increased abundance during the spring and summer. Monthly trends in 2023 showed a steady increase from February to July, followed by a decline. In contrast, 2024 exhibited a downward trend beginning in April, with catch volumes consistently below the historical monthly average. Table 1 Monthly summary of fishery and biological parameters for black skipjack ( Euthynnus lineatus ) off the coast of Oaxaca, Mexico, from October 2022 to October 2024. Catch is expressed in tons (t), Mean FL represents the average fork length in centimeters (cm), and Mean TW is the average total weight in kilograms (kg). SD indicates the standard deviation for length and weight measurements. Year Month Catch (t) Mean FL (cm) Length SD (cm) Mean TW (kg) Weight SD (kg) 2022 October 28.9 45.4 1.9 1.6 0.2 2022 November 106.8 45.9 3.3 1.8 0.5 2023 February 36.8 48.4 2.8 1.7 0.3 2023 March 47.4 49.5 1.7 1.6 0.2 2023 April 55.2 48.6 3.1 1.9 0.3 2023 May 115.1 48.2 1.7 1.9 0.2 2023 June 56.6 48.5 2.5 1.8 0.3 2023 July 130.5 47.2 2.3 1.7 0.3 2023 August 37.8 45.9 2.7 1.6 0.2 2023 September 41.4 47.5 2.6 1.8 0.3 2023 October 37.7 45.7 2.9 1.6 0.3 2024 February 51.1 48.4 2.9 1.9 0.4 2024 March 29.1 49.0 4.5 2.0 0.4 2024 April 53.5 45.2 4.3 1.6 0.3 2024 May 35.9 46.9 3.3 1.7 0.3 2024 June 30.9 46.9 3.3 1.5 0.2 2024 July 22.3 44.9 4.6 1.5 0.3 2024 August 23.6 46.4 2.5 1.6 0.1 2024 September 11.5 47.4 4.0 1.7 0.2 2024 October 18.9 46.3 3.4 1.6 0.2 Biometric analysis of 2,099 sampled organisms revealed a fork length range between 36.2 and 62.0 cm (average 47.1 cm). Specimens caught in cooler months (February–March) were significantly larger (> 48.5 cm) than those caught in summer. The lowest monthly FL averages, on the other hand, did not show a defined pattern, as the minimum values ​​observed (between 44.8 and 45.4 cm) corresponded to different times of the year. Furthermore, significant differences in FL were observed by sampling month (Table 1 ), revealing temporal variations in the body size composition of E. lineatus catches in the southern Mexican Pacific. The FL frequency histogram of E. lineatus showed that sizes between 44 and 50 cm were the most abundant (1,708 individuals). In addition, low frequencies were observed for individuals larger than 50 cm (191 individuals) and smaller than 42 cm. Average total weight was 1.7 kg (range 0.9–4.0 kg). The highest weights were observed between February and May (> 1.9 kg), while the lowest ( 1.9 kg), while the lowest values ​​(< 1.6 kg) were recorded between June and August (Table 1 ). Statistical analysis also showed significant differences in total weight (Kruskal-Wallis, H = 85.13, P < 0.05) between all seasons, except between summer and autumn. All other interactions were statistically significant (P < 0.05). 3.3 Multivariate Analysis of Environmental-Biological Interactions The PCA explained 66.2% of the total variance with the first two components (Fig. 4 ). The first component ( PC1 , 38.4%) showed a strong positive loading for body size variables and a pronounced negative loading for temperature ( r = -0.77). The second component ( PC2 , 27.7%) was primarily associated with catch volume ( r = 0.85). The PCA biplot identified clear seasonal patterns. Winter samples were associated with higher chlorophyll concentrations and larger organisms. Summer observations reflected higher temperatures and smaller organisms. Spring served as a transitional phase, while autumn was linked to increased population availability and catch volume (Fig. 4 ). The low contribution of the "year" variable suggests that seasonal climatic cycles are more influential than specific interannual variations in structuring the biology of E. lineatus in the region. 4 Discussion 4.1 Influence of Thermal Variability on Population Dynamics The results underscore the importance of SST as a critical modulator of black skipjack distribution and catchability in the Mexican South Pacific. Maximum catches of Euthynnus lineatus occur when isotherms exceeding 30.5°C are located near the coast, suggesting a potential thermal association favoring aggregation in areas accessible to the artisanal fleet (Stretta 1991 ). This is particularly evident from May to July, when seasonal warming of the mixed layer promotes higher metabolic activity and, possibly, higher feeding rates. The catch discrepancy between 2023 and 2024 highlights the species' sensitivity to larger-scale environmental fluctuations. In July 2023, the presence of a warm pool with temperatures above 31.0°C coincided with the maximum catch peak (130 t), whereas in 2024, with temperatures below 30.0°C, landings were significantly lower. This relationship suggests SST acts as an indicator of an optimal "habitat window"; when conditions deviate, schools may move to deeper or offshore areas (Punsly et al. 1994 ; Zainuddin et al. 2017 ). 4.2 Biological Productivity and Trophic Lag The relationship between chlorophyll-a and black skipjack catches reveals a lagged response common in upwelling ecosystems. Peaks in E. lineatus abundance occur approximately two to three months after Chl-a maximums. This lag represents the time required for primary production energy to transfer through intermediate trophic levels to top predators (Stretta 1991 ; Zainuddin et al. 2017 ). During the dry season, Tehuano winds inject nutrients, triggering phytoplankton blooms (high Chl-a between December and March) (Fiedler 1994 ; Trasviña et al. 2003 ). This explosion of life sustains the prey of E. lineatus , whose abundance peaks later, coinciding with the most successful artisanal fishing season in spring and summer. 4.3 Size Structure and the Temperature-Size Rule A significant finding is the seasonal variation in body size, which appears to follow the "Temperature-Size Rule" ( TSR ). Larger specimens consistently predominate during cooler months, while smaller individuals are more frequent in summer. This can be explained by two mechanisms: cooler winter temperatures are associated with higher food availability from upwelling, allowing individuals to reach higher biomass (Fiedler 1994 ). Second, higher summer temperatures increase metabolic demands; for larger fish, the energetic cost of maintaining homeostasis in warm water may lead them to migrate to deeper, cooler strata (Lowerre-Barbieri et al. 2011 ). Consequently, the fraction remaining in warm coastal waters consists mostly of younger or smaller individuals with higher thermal tolerance. 4.4 Implications for Fisheries Management The artisanal nature of the E. lineatus fishery in the Mexican South Pacific makes it inherently dependent on coastal resource accessibility. Identifying oceanographic indicators, such as the 31.0°C thermal threshold and chlorophyll-a peaks, allows for the prediction of high-vulnerability periods. It is essential to consider high interannual catch variability when setting management strategies. The > 100% difference between 2023 and 2024 catches indicates that available biomass is highly stochastic and environment dependent. Integrating satellite oceanographic monitoring into regional fishery assessments will allow decision-makers and fishing communities to adapt with greater resilience to an uncertain, transforming ocean. 5 Conclusions This study demonstrates that the abundance and size structure of Euthynnus lineatus off the Oaxaca coast are intrinsically linked to seasonal oceanographic variability in the Mexican South Pacific. Catch peaks follow nutrient enrichment events with a two-to-three-month lag relative to chlorophyll-a maximums. SST acts as a determinant of catchability, with a marked thermal preference toward values near 31.0°C during summer. Furthermore, seasonal body size modulation was confirmed, where cooler, productive winter conditions favor larger organisms, while summer warming is associated with smaller specimens. These findings suggest that black skipjack is a highly sensitive indicator of climate change effects on tropical artisanal fisheries. Declarations Acknowledgments This work was supported by the artisanal fishers of Puerto Angel, Oaxaca. Biological data were obtained through the Fishery Improvement Project (FIP) " Mexico-Oaxaca Artisanal Skipjack and Black Skipjack Tuna - Handline ". We thank the Walton Family Foundation, the David & Lucile Packard Foundation, and the Ocean Innovation Challenge for their financial support. Authors contributions Yuliesky Garcés-Rodriguez: Conceptualization, methodology, investigation, writing -Original draft preparation. Yadian Israel La Rosa-Izquierdo: Investigation, writing -reviewing and editing. Emilio Alejandro Alemany-Rodriguez: Investigation, writing -reviewing and editing. Funding Declaration This research and the publication of this article did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. 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Jurnal Ilmu dan Teknologi Kelautan Tropis 3(1):82–90, https://doi.org/10.29244/jitkt.v3i1.7837 Zainuddin M, Farhum A, Safruddin S et al (2017) Detection of pelagic habitat hotspots for skipjack tuna in the Gulf of Bone-Flores Sea, southwestern Coral Triangle tuna, Indonesia. Plos One 12(10). https://doi.org/10.1371/journal.pone.0 185601 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 01 May, 2026 Editor assigned by journal 01 May, 2026 Submission checks completed at journal 30 Apr, 2026 First submitted to journal 28 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9558665","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":637334978,"identity":"211d2402-6ebe-4949-81b2-03b3a89e0615","order_by":0,"name":"Yuliesky Garcés-Rodríguez","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABC0lEQVRIiWNgGAWjYFAC5oYDDAwJDPwQnhwPgwRBLYwQLZINIE6CMXFaQEoZDA5AtDAQ1GJwI7HxwIc/aYmbz59O/Fz5w0BGfnbzww8MFffsGnBraTg4sy0ncduN3M2SZxIMeAzuHDOWYDhTnIxPy2HehgqgFt4Nkg0Jf3gMJBLMGBjbEpLxOKzh8J8/FYmb+89u/tkAtEV+Rvo3wloY2HISNzDkbpMEaWG4kQO2xQ6XFskzDxsO9ralGc+4kbvNsiEN6JcbOcUSCWcSEnBp4TuefPjDjz/Jsv1Ah91ssDGwBzps44cPFQn2uLQoHIDQjg0owkArEhsYsAN5qASmmThtGQWjYBSMghEHABrnZPPnwlYnAAAAAElFTkSuQmCC","orcid":"","institution":"SmartFish Rescate de Valor, A.C.","correspondingAuthor":true,"prefix":"","firstName":"Yuliesky","middleName":"","lastName":"Garcés-Rodríguez","suffix":""},{"id":637334979,"identity":"c535539e-b7c8-41b0-af08-522829773e52","order_by":1,"name":"Yadian Israel La Rosa-Izquierdo","email":"","orcid":"","institution":"Instituto Mexicano de Investigación en Pesca y Acuacultura Sustentable","correspondingAuthor":false,"prefix":"","firstName":"Yadian","middleName":"Israel La","lastName":"Rosa-Izquierdo","suffix":""},{"id":637334980,"identity":"fe0c57d1-1f91-4669-a3f4-a955bfbc21f4","order_by":2,"name":"Emilio Alejandro Alemany-Rodriguez","email":"","orcid":"","institution":"Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional","correspondingAuthor":false,"prefix":"","firstName":"Emilio","middleName":"Alejandro","lastName":"Alemany-Rodriguez","suffix":""}],"badges":[],"createdAt":"2026-04-28 23:23:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9558665/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9558665/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109091741,"identity":"4e6e3e7c-d12f-433c-81f6-d68b2ed8dc6b","added_by":"auto","created_at":"2026-05-12 13:37:56","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":183048,"visible":true,"origin":"","legend":"\u003cp\u003eMap of the study area along the southern Pacific coast of Mexico, highlighting the state of Oaxaca and the Gulf of Tehuantepec. The black dots indicate the primary landing sites for fishery data: Puerto Escondido, Puerto Ángel, and Salina Cruz; biological samples were specifically obtained from Puerto Ángel. The upper inset shows the location of Oaxaca within the Mexican territory.\u003c/p\u003e","description":"","filename":"floatimage1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9558665/v1/1ff7ecd6ec3e2c04477abc75.jpg"},{"id":109091649,"identity":"e15c6315-1524-4571-912e-57fb79ac1190","added_by":"auto","created_at":"2026-05-12 13:37:32","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":68611,"visible":true,"origin":"","legend":"\u003cp\u003eInterannual variability in monthly averages of chlorophyll-\u003cem\u003ea\u003c/em\u003econcentration, sea surface temperature (SST), and black skipjack (\u003cem\u003eEuthynnus lineatus\u003c/em\u003e) catch along the coast of Oaxaca from October 2022 to October 2024. The solid black line represents monthly chlorophyll-\u003cem\u003ea\u003c/em\u003econcentrations (mg m⁻³), and the dashed black line indicates SST (°C). Gray bars show the monthly catch volumes (tons).\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9558665/v1/df5304e37422e02b0b268bcf.jpeg"},{"id":109091653,"identity":"d45a4935-79cd-4936-9b48-9c0581e2027d","added_by":"auto","created_at":"2026-05-12 13:37:33","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":116350,"visible":true,"origin":"","legend":"\u003cp\u003eSpatial and temporal distribution of Sea Surface Temperature (\u003cem\u003eSST\u003c/em\u003e) and chlorophyll-a (\u003cem\u003eChl-a\u003c/em\u003e), along the southern Pacific coast of Mexico for July 2023 and July 2024. Panels (a) and (b) show average \u003cem\u003eSST\u003c/em\u003e (°C), while panels (c) and (d) represent average \u003cem\u003eChl-a\u003c/em\u003e concentration (mg m\u003csup\u003e-\u003c/sup\u003e³). Black dashed contour lines delineate the 30.5 and 31.0 °C isotherms and the sea surface chlorophyll concentrations of 0.2, 0.5, and 1.0 mg m\u003csup\u003e-\u003c/sup\u003e³.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9558665/v1/d8dfe79e3d48f6714ef9ca87.jpeg"},{"id":109091659,"identity":"b7d5c808-97bb-493e-89ff-90c3f1cf0986","added_by":"auto","created_at":"2026-05-12 13:37:34","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":65218,"visible":true,"origin":"","legend":"\u003cp\u003ePrincipal Component Analysis (PCA) biplot of environmental and biological variables for Euthynnus lineatus. The axes PC1 and PC2 account for 38.4% and 27.7% of the total variance, respectively. Symbols represent seasonal sampling groups: Autumn (orange circles), Winter (blue squares), Spring (green triangles), and Summer (pink diamonds). Vectors indicate the direction and strength of influence for environmental factors (Temperature, Chlorophyll), biological parameters (Captures, Length, Weight), and temporal variables (Month, Year)\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9558665/v1/fd71af37baabd9343f33c805.jpeg"},{"id":109204435,"identity":"40ef245d-2284-45a1-8bf5-049a47a854fc","added_by":"auto","created_at":"2026-05-13 14:59:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":710467,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9558665/v1/224c15cf-c0d0-4913-9dee-bc3d95f60217.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Influence of Sea Surface Temperature and Chlorophyll-a on abundance and body size of black skipjack (Euthynnus lineatus) in the Mexican South Pacific","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eUnderstanding the dynamics of pelagic species of commercial importance in the Eastern Tropical Pacific requires a rigorous analysis of the oceanographic variables that modulate their habitat. Among these parameters, sea surface temperature (\u003cem\u003eSST\u003c/em\u003e) is one of the most critical factors determining the distribution and behavior of tunas in tropical regions (Lehodey et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Zainuddin \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Wang et al. 2025; Godinez-Padilla 2025). Studies have shown that \u003cem\u003eSST\u003c/em\u003e not only influences metabolic and growth rates but also acts as a thermal barrier defining migratory routes and aggregation zones (Bertignac et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). However, the observed association between tunas and ocean thermal structures cannot be explained solely by temperature. This phenomenon involves complex mechanisms linked to highly productive areas where organisms search for food in oceanic fronts, eddies, or upwelling systems (Schaefer \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Brill and Lutcavage \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Zainuddin et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Garc\u0026eacute;s-Rodriguez et al. 2023).\u003c/p\u003e \u003cp\u003eThe use of satellite data to estimate chlorophyll-a (\u003cem\u003eChl-a\u003c/em\u003e) concentration has allowed researchers to more accurately predict feeding zones and potential habitats for various tuna species (Polovina et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Zainuddin et al. 2009; IATTC. 2022). In the case of the black skipjack, \u003cem\u003eEuthynnus lineatus\u003c/em\u003e, its epipelagic ecology places it mainly in waters where surface temperatures exceed 24\u0026deg;C (Muhlia-Melo \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1980\u003c/span\u003e; Forsbergh \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Godinez-Padilla 2025). This species is distributed from southern Baja California to Peru, maintaining a close association with continental shelf areas, unlike other tunas that perform large-scale transoceanic migrations (Fiedler and Bernard \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Collette et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the Mexican South Pacific, particularly along the coasts of Oaxaca, the black skipjack is one of the primary resources exploited by artisanal fisheries (Sandoval-Ram\u0026iacute;rez 2020; DOF \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The socioeconomic importance of this fishery for coastal communities highlights the need to evaluate how oceanographic parameters affect the species' abundance and size structure. The Oaxaca coast is recognized for its high biological productivity, driven by processes such as coastal upwelling and the formation of anticyclonic gyres in the Gulf of Tehuantepec (Lav\u0026iacute;n et al. 1992; Trasvi\u0026ntilde;a et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). These conditions make the region a hotspot for biological activity, favoring migration, feeding, and reproduction for numerous marine species (Ayala-Duval et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1988\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite its importance, the fisheries face challenges related to sustainability, overfishing, and global climate change (Abudarda et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Fluctuations in catches and specimen size are often attributed to environmental variations that alter resource availability in traditional fishing grounds. Therefore, analyzing oceanographic variables is fundamental to understanding the uncertainties associated with migratory processes and population dynamics of the black skipjack in the region.\u003c/p\u003e \u003cp\u003eThis study aims to evaluate the relationship between key oceanographic variables (\u003cem\u003eSST\u003c/em\u003e and \u003cem\u003eChl-a\u003c/em\u003e concentration) and the abundance and body size of \u003cem\u003eEuthynnus lineatus\u003c/em\u003e in the coastal waters of Oaxaca, Mexico. The research seeks to characterize the environmental drivers of population dynamics to inform sustainable management strategies for this ecologically and economically significant species in the Mexican South Pacific.\u003c/p\u003e"},{"header":"2 Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 \u003cem\u003eStudy Area\u003c/em\u003e\u003c/h2\u003e \u003cp\u003eThe study region is located in the Eastern Tropical Pacific, covering the coastal zone of Oaxaca, Mexico (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This marine ecosystem is part of a highly dynamic oceanographic system influenced by converging regional currents, seasonal upwelling events, and terrestrial nutrient inputs, which together sustain high biological productivity (Lara-Lara et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Mart\u0026iacute;nez-Santos 2014). The Oaxacan coastal area is characterized by a complex underwater topography, including rocky reefs, sandy bottoms, and estuarine-lagoon systems that play critical ecological roles for marine biodiversity (Ruiz-P\u0026eacute;rez et al. 2016), while supporting populations of species such as \u003cem\u003eEuthynnus lineatus\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eOceanographic conditions in the region are strongly modulated by two predominant seasons: the dry season (November to April) and the rainy season (May to October). During the dry season, strong \"Tehuano\" winds blow intensely from the Gulf of Mexico toward the Pacific through the Isthmus of Tehuantepec, triggering intense upwelling that transports nutrient-rich subsurface waters to the photic layer (Lav\u0026iacute;n et al. 1992; Fiedler \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). This process fertilizes surface waters, reducing temperature and drastically increasing phytoplankton biomass. Conversely, the rainy season is marked by weakening winds and the dominance of the Costa Rica Coastal Current, introducing warmer, less productive waters alongside organic matter from terrestrial runoff (Kessler \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e2.2 Sea Surface Temperature and Chlorophyll-a Data\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eTo characterize the pelagic environment during the study period (October 2022 to October 2024), \u003cem\u003eSST\u003c/em\u003e data were obtained from the Level 4 Multi-scale Ultra-high Resolution (\u003cem\u003eMUR\u003c/em\u003e) Foundation SST version 4.1 product. Produced by the Group for High Resolution Sea Surface Temperature (GHRSST), this product offers a global spatial resolution of 0.01\u0026deg; x 0.01\u0026deg;, allowing for detailed analysis of small-scale features in coastal and oceanic environments (Chin et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eChlorophyll-a concentration was determined using data from the Moderate-Resolution Imaging Spectroradiometer (\u003cem\u003eMODIS\u003c/em\u003e) sensor aboard the AQUA satellite. Level 3 \u003cem\u003eChl-a\u003c/em\u003e products provide monthly global data at a resolution of 0.04\u0026deg; x 0.04\u0026deg;. These data were used as an indicator of primary productivity, allowing for the correlation of biological production peaks with catch events.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e2.3 Biological\u003c/b\u003e \u003cb\u003eSampling and Data Analysis\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eBiological data for \u003cem\u003eEuthynnus lineatus\u003c/em\u003e were collected from the small-scale artisanal fishing fleet operating in Puerto Angel, Oaxaca. Monthly sampling was conducted at landing sites over two consecutive years. For each captured organism, the following metrics were recorded:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eFork Length (\u003cem\u003eFL\u003c/em\u003e): Measured to the nearest centimeter using a standard ichthyometer following FAO protocols for tunas (FAO \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1982\u003c/span\u003e).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eTotal Weight (\u003cem\u003eTW\u003c/em\u003e): Determined using a calibrated digital scale with a precision of \u0026plusmn;\u0026thinsp;10 grams.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eCatch data (\u003cem\u003eC\u003c/em\u003e), expressed in tons (\u003cem\u003et\u003c/em\u003e), were obtained from official records of the National Commission of Aquaculture and Fisheries (\u003cem\u003eCONAPESCA\u003c/em\u003e). These records, analyzed in conjunction with the number of active vessels in the area as a measure of fishing effort, served as a proxy for the relative abundance and availability of the species. The artisanal fleet consists of approximately 250 small vessels (less than 12 meters) utilizing traditional gear such as handlines or trolling. To identify significant differences in the variability of weights and lengths, the non-parametric Kruskal-Wallis (\u003cem\u003eKW\u003c/em\u003e) test was applied, as distributions did not meet normality assumptions. A principal component analysis (\u003cem\u003ePCA\u003c/em\u003e) was performed using Python (version 3.12) to synthesize common variability between environmental and biological variables. Results were visualized via a biplot, differentiating observations by season and representing variable influence through vectors.\u003c/p\u003e \u003cp\u003eIn compliance with modern ethical standards, it is declared that large language models (\u003cem\u003eLLMs\u003c/em\u003e) were not used for original data generation or primary statistical analysis.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Environmental Conditions (2022\u0026ndash;2024)\u003c/h2\u003e \u003cp\u003eMonthly average \u003cem\u003eSST\u003c/em\u003e along the Oaxaca coastal zone showed marked variability, ranging from 27.2\u0026deg;C to 31.5\u0026deg;C, with an average of 29.3\u0026deg;C. Two distinct thermal phases were identified: a warm period (May\u0026ndash;October) and a cold period (November\u0026ndash;April). In 2023, \u003cem\u003eSST\u003c/em\u003e increases began in May, peaking in June and July at approximately 31.5\u0026deg;C. In contrast, the cold period showed a marked decline starting in October 2022, reaching its lowest value in February 2023 (27.2\u0026deg;C) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSpatial analysis revealed distinct thermal patterns. In July 2023, a \"warm pool\" was observed along the Oaxaca coast, with the 31.0\u0026deg;C isotherm situated between Puerto Escondido and Puerto Angel. In comparison, July 2024 recorded cooler waters, with the 30.0\u0026deg;C isotherm predominating in the same area (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b).\u003c/p\u003e \u003cp\u003eChlorophyll-a concentration followed an inverse pattern to temperature. The highest values were recorded during winter and spring (October\u0026ndash;April) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), coinciding with upwelling events. In July 2024, \u003cem\u003eChl-a\u003c/em\u003e filaments (\u0026gt;\u0026thinsp;0.5 mg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) were observed along the coast, while July 2023 presented mostly oligotrophic conditions (\u0026lt;\u0026thinsp;0.2 mg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, b).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Abundance and Size Structure of Black Skipjack\u003c/h2\u003e \u003cp\u003eCatch records of \u003cem\u003eE. lineatus\u003c/em\u003e in Oaxaca show a recurring seasonal pattern, with abundance increasing in March and peaking in July. During the study period, monthly catches fluctuated between 11 and 130 tons (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A significant finding was the interannual difference: 2023 total catch reached 743.4 tons, more than double the 359.9 tons recorded in 2024. The highest catch volumes were recorded between April and July, with the highest catches occurring in May (~\u0026thinsp;115 t) and July (~\u0026thinsp;130 t) of 2023. Conversely, the lowest catches occurred between August and October, with the lowest value observed in September 2024. This seasonal pattern aligns with the historical availability of \u003cem\u003eE. lineatus\u003c/em\u003e in the region, typically marked by increased abundance during the spring and summer. Monthly trends in 2023 showed a steady increase from February to July, followed by a decline. In contrast, 2024 exhibited a downward trend beginning in April, with catch volumes consistently below the historical monthly average.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMonthly summary of fishery and biological parameters for black skipjack (\u003cem\u003eEuthynnus lineatus\u003c/em\u003e) off the coast of Oaxaca, Mexico, from October 2022 to October 2024. Catch is expressed in tons (t), Mean \u003cem\u003eFL\u003c/em\u003e represents the average fork length in centimeters (cm), and Mean \u003cem\u003eTW\u003c/em\u003e is the average total weight in kilograms (kg). SD indicates the standard deviation for length and weight measurements.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYear\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMonth\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCatch (t)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean \u003cem\u003eFL\u003c/em\u003e (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLength SD (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMean \u003cem\u003eTW\u003c/em\u003e (kg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eWeight SD (kg)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOctober\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e28.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNovember\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e106.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFebruary\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e36.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e48.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMarch\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e47.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e49.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eApril\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e55.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e48.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMay\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e115.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e48.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eJune\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e56.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e48.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eJuly\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e130.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e47.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAugust\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e37.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSeptember\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e41.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e47.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOctober\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e37.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFebruary\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e51.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e48.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMarch\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e49.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eApril\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e53.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMay\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e35.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e46.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eJune\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e46.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eJuly\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e22.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e44.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAugust\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e23.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e46.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSeptember\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e47.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOctober\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e46.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eBiometric analysis of 2,099 sampled organisms revealed a fork length range between 36.2 and 62.0 cm (average 47.1 cm). Specimens caught in cooler months (February\u0026ndash;March) were significantly larger (\u0026gt;\u0026thinsp;48.5 cm) than those caught in summer. The lowest monthly \u003cem\u003eFL\u003c/em\u003e averages, on the other hand, did not show a defined pattern, as the minimum values ​​observed (between 44.8 and 45.4 cm) corresponded to different times of the year. Furthermore, significant differences in \u003cem\u003eFL\u003c/em\u003e were observed by sampling month (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), revealing temporal variations in the body size composition of \u003cem\u003eE. lineatus\u003c/em\u003e catches in the southern Mexican Pacific. The \u003cem\u003eFL\u003c/em\u003e frequency histogram of \u003cem\u003eE. lineatus\u003c/em\u003e showed that sizes between 44 and 50 cm were the most abundant (1,708 individuals). In addition, low frequencies were observed for individuals larger than 50 cm (191 individuals) and smaller than 42 cm.\u003c/p\u003e \u003cp\u003eAverage total weight was 1.7 kg (range 0.9\u0026ndash;4.0 kg). The highest weights were observed between February and May (\u0026gt;\u0026thinsp;1.9 kg), while the lowest (\u0026lt;\u0026thinsp;1.6 kg) were recorded in summer.\u003c/p\u003e \u003cp\u003eThe \u003cem\u003eTW\u003c/em\u003e data showed that the highest values ​​of monthly averages were found between February and May (\u0026gt;\u0026thinsp;1.9 kg), while the lowest values ​​(\u0026lt;\u0026thinsp;1.6 kg) were recorded between June and August (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Statistical analysis also showed significant differences in total weight (Kruskal-Wallis, H\u0026thinsp;=\u0026thinsp;85.13, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between all seasons, except between summer and autumn. All other interactions were statistically significant (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Multivariate Analysis of Environmental-Biological Interactions\u003c/h2\u003e \u003cp\u003eThe \u003cem\u003ePCA\u003c/em\u003e explained 66.2% of the total variance with the first two components (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The first component (\u003cem\u003ePC1\u003c/em\u003e, 38.4%) showed a strong positive loading for body size variables and a pronounced negative loading for temperature (\u003cem\u003er\u003c/em\u003e = -0.77). The second component (\u003cem\u003ePC2\u003c/em\u003e, 27.7%) was primarily associated with catch volume (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.85).\u003c/p\u003e \u003cp\u003eThe \u003cem\u003ePCA\u003c/em\u003e biplot identified clear seasonal patterns. Winter samples were associated with higher chlorophyll concentrations and larger organisms. Summer observations reflected higher temperatures and smaller organisms. Spring served as a transitional phase, while autumn was linked to increased population availability and catch volume (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The low contribution of the \"year\" variable suggests that seasonal climatic cycles are more influential than specific interannual variations in structuring the biology of \u003cem\u003eE. lineatus\u003c/em\u003e in the region.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 Discussion","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Influence of Thermal Variability on Population Dynamics\u003c/h2\u003e \u003cp\u003eThe results underscore the importance of \u003cem\u003eSST\u003c/em\u003e as a critical modulator of black skipjack distribution and catchability in the Mexican South Pacific. Maximum catches of \u003cem\u003eEuthynnus lineatus\u003c/em\u003e occur when isotherms exceeding 30.5\u0026deg;C are located near the coast, suggesting a potential thermal association favoring aggregation in areas accessible to the artisanal fleet (Stretta \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1991\u003c/span\u003e). This is particularly evident from May to July, when seasonal warming of the mixed layer promotes higher metabolic activity and, possibly, higher feeding rates.\u003c/p\u003e \u003cp\u003eThe catch discrepancy between 2023 and 2024 highlights the species' sensitivity to larger-scale environmental fluctuations. In July 2023, the presence of a warm pool with temperatures above 31.0\u0026deg;C coincided with the maximum catch peak (130 t), whereas in 2024, with temperatures below 30.0\u0026deg;C, landings were significantly lower. This relationship suggests \u003cem\u003eSST\u003c/em\u003e acts as an indicator of an optimal \"habitat window\"; when conditions deviate, schools may move to deeper or offshore areas (Punsly et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Zainuddin et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Biological Productivity and Trophic Lag\u003c/h2\u003e \u003cp\u003eThe relationship between chlorophyll-a and black skipjack catches reveals a lagged response common in upwelling ecosystems. Peaks in \u003cem\u003eE. lineatus\u003c/em\u003e abundance occur approximately two to three months after \u003cem\u003eChl-a\u003c/em\u003e maximums. This lag represents the time required for primary production energy to transfer through intermediate trophic levels to top predators (Stretta \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1991\u003c/span\u003e; Zainuddin et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). During the dry season, Tehuano winds inject nutrients, triggering phytoplankton blooms (high \u003cem\u003eChl-a\u003c/em\u003e between December and March) (Fiedler \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Trasvi\u0026ntilde;a et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). This explosion of life sustains the prey of \u003cem\u003eE. lineatus\u003c/em\u003e, whose abundance peaks later, coinciding with the most successful artisanal fishing season in spring and summer.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Size Structure and the Temperature-Size Rule\u003c/h2\u003e \u003cp\u003eA significant finding is the seasonal variation in body size, which appears to follow the \"Temperature-Size Rule\" (\u003cem\u003eTSR\u003c/em\u003e). Larger specimens consistently predominate during cooler months, while smaller individuals are more frequent in summer. This can be explained by two mechanisms: cooler winter temperatures are associated with higher food availability from upwelling, allowing individuals to reach higher biomass (Fiedler \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). Second, higher summer temperatures increase metabolic demands; for larger fish, the energetic cost of maintaining homeostasis in warm water may lead them to migrate to deeper, cooler strata (Lowerre-Barbieri et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Consequently, the fraction remaining in warm coastal waters consists mostly of younger or smaller individuals with higher thermal tolerance.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Implications for Fisheries Management\u003c/h2\u003e \u003cp\u003eThe artisanal nature of the \u003cem\u003eE. lineatus\u003c/em\u003e fishery in the Mexican South Pacific makes it inherently dependent on coastal resource accessibility. Identifying oceanographic indicators, such as the 31.0\u0026deg;C thermal threshold and chlorophyll-a peaks, allows for the prediction of high-vulnerability periods. It is essential to consider high interannual catch variability when setting management strategies. The \u0026gt;\u0026thinsp;100% difference between 2023 and 2024 catches indicates that available biomass is highly stochastic and environment dependent. Integrating satellite oceanographic monitoring into regional fishery assessments will allow decision-makers and fishing communities to adapt with greater resilience to an uncertain, transforming ocean.\u003c/p\u003e \u003c/div\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003eThis study demonstrates that the abundance and size structure of \u003cem\u003eEuthynnus lineatus\u003c/em\u003e off the Oaxaca coast are intrinsically linked to seasonal oceanographic variability in the Mexican South Pacific. Catch peaks follow nutrient enrichment events with a two-to-three-month lag relative to chlorophyll-a maximums. \u003cem\u003eSST\u003c/em\u003e acts as a determinant of catchability, with a marked thermal preference toward values near 31.0\u0026deg;C during summer.\u003c/p\u003e \u003cp\u003eFurthermore, seasonal body size modulation was confirmed, where cooler, productive winter conditions favor larger organisms, while summer warming is associated with smaller specimens. These findings suggest that black skipjack is a highly sensitive indicator of climate change effects on tropical artisanal fisheries.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e This work was supported by the artisanal fishers of Puerto Angel, Oaxaca. Biological data were obtained through the Fishery Improvement Project (FIP) \u0026quot;\u003cem\u003eMexico-Oaxaca Artisanal Skipjack and Black Skipjack Tuna - Handline\u003c/em\u003e\u0026quot;. We thank the Walton Family Foundation, the David \u0026amp; Lucile Packard Foundation, and the Ocean Innovation Challenge for their financial support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contributions\u0026nbsp;\u003c/strong\u003eYuliesky Garc\u0026eacute;s-Rodriguez: Conceptualization, methodology, investigation, writing -Original draft preparation.\u0026nbsp;Yadian Israel La Rosa-Izquierdo: Investigation, writing -reviewing and editing. Emilio Alejandro Alemany-Rodriguez: Investigation, writing -reviewing and editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Declaration\u0026nbsp;\u003c/strong\u003eThis research and the publication of this article did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interests\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no financial or non-financial competing interests that are relevant to the content of this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u0026nbsp;\u003c/strong\u003eThe data supporting the findings of this study are available from the corresponding author upon reasonable request. Data are not publicly available due to privacy and confidentiality considerations related to the artisanal fleet.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbudarda AR, Zainuddin M, Safruddin (2021) Impact of increasing sea surface temperature on potential fishing zone of skipjack tuna \u003cem\u003ekatsuwonus pelamis\u003c/em\u003e in makassar strait. Jurnal Ilmu Dan Teknologi Kelautan Tropis, 13(3), 427-437. https://doi.org/10.29244/jitkt.v13i3.35692 \u003c/li\u003e\n\u003cli\u003eAyala-Duval E, Maldonado-Monroy MC, Becerril-Mart\u0026iacute;nez JA et al (1988) Distribuci\u0026oacute;n de algunos componentes del ictioplancton y su relaci\u0026oacute;n con la biomasa zooplanct\u0026oacute;nica 8: 93-102. ISBN 970-654-348-1.\u003c/li\u003e\n\u003cli\u003eBertignac M, Lehodey P, Hampton J (1998) A spatial population dynamics simulation model of Tropical tunas using a habitat index based on environmental parameters. 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Updated February 2023; available March 2022. https://www.iattc.org/en-us/Publication/Commission/Fishery-Status-Report.\u003c/li\u003e\n\u003cli\u003eKessler WS (2006) The circulation of the eastern tropical Pacific: A review. \u003cem\u003eProgress in \u003c/em\u003eOceanography 69: 181-217.\u003c/li\u003e\n\u003cli\u003eLara-Lara JR, Arenas Fuentes V, Baz\u0026aacute;n Guzm\u0026aacute;n C (2008) Los ecosistemas costeros, insulares y epicontinentales, en Capital natural de M\u0026eacute;xico, vol. I: Conocimiento actual de la biodiversidad. CONABIO M\u0026eacute;xico 109-134. \u003c/li\u003e\n\u003cli\u003eLavin MF, Robles JM, Argote ML (1992) F\u0026iacute;sica del Golfo de Tehuantepec. Revista Ciencia y Desarrollo XVIII 103: 97-108.\u003c/li\u003e\n\u003cli\u003eLehodey P, Bertignac M, Hampton J et al (1997) El Ni\u0026ntilde;o Southern Oscillation and tuna in the western Pacific. Nature 389:715-718.\u003c/li\u003e\n\u003cli\u003eLowerre-Barbieri S, Konstantinos G, Saborido-Rey F et al (2011) Reproductive Timing in Marine Fishes: Variability, Temporal Scales, and Methods. Mar Coast Fish Dyn Manag Ecos Sci Manag 71-91. https://doi.org/10.1080/19425120.2011.556932.\u003c/li\u003e\n\u003cli\u003eMart\u0026iacute;nez\u0026ndash;Santos HD (2014) Distribuci\u0026oacute;n espacial de la biomasa zooplanct\u0026oacute;nica en el Pacifico sur de M\u0026eacute;xico (entre Puerto Escondido, Oaxaca y Puerto Chiapas, Chiapas) y su relaci\u0026oacute;n con la hidrograf\u0026iacute;a durante julio de 2009. Tesis de licenciatura, Universidad del Mar, Campus Puerto \u0026Aacute;ngel, Oaxaca.\u003c/li\u003e\n\u003cli\u003eMuhlia-Melo Arturo (1980) The Mexican tuna fishery. Revista de la comisi\u0026oacute;n Permanente del Pacifico Sur, (11).\u003c/li\u003e\n\u003cli\u003ePolovina JJ, Howell E, Kobayashi DR et al (2001) The transition zone chlorophyll front, a dynamic global feature defining migration and forage habitat for marine resources. Prog Ocean, 49(1\u0026ndash;4): 469\u0026ndash;483. https://doi.org/10.1016/S00796611(01)00036-2.\u003c/li\u003e\n\u003cli\u003ePunsly RG, Tomlinson PK, Mullen AJ (1994) Potential tuna catches in the eastern Pacific Ocean from schools not associated with dolphins. Fishery Bulletin. 92: 132-143.\u003c/li\u003e\n\u003cli\u003eRu\u0026iacute;z-P\u0026eacute;rez NE, Cerdenares-Ladr\u0026oacute;n de Guevara G, L\u0026oacute;pez-Herrera DL et al (2016) Relaciones tr\u0026oacute;ficas entre cinco especies de peces pel\u0026aacute;gicos que cohabitan en las costas de Oaxaca, M\u0026eacute;xico. Hydrobiological, 26 (1): 69-77.\u003c/li\u003e\n\u003cli\u003eSandoval-Ram\u0026iacute;rez A, Cerdenares-Ladr\u0026oacute;n de Guevara G, Rojas-Herrera AA, Violante- Gonz\u0026aacute;lez J, Garc\u0026iacute;a-Ib\u0026aacute;\u0026ntilde;ez S, Hern\u0026aacute;ndez-G\u0026oacute;mez JC (2020) Feeding Habits of the Fishes Euthynnus lineatus and Scomberomorus sierra (Perciformes: Scombridae) in the Eastern Tropical Pacific.\u0026rdquo; Revista de Biolog\u0026iacute;a Tropical 68, no. 4: 1073\u0026ndash;1083.\u003c/li\u003e\n\u003cli\u003eStretta JM (1991) Forecasting models for tuna fishery with aerospatial remote sensing, International Journal of Remote Sensing, 12:4, 771-779, DOI:10.1080/01431169108929693\u003c/li\u003e\n\u003cli\u003eSchaefer KM (1987) Reproductive biology of black skipjack, \u003cem\u003eEuthynnus lineatus\u003c/em\u003e, an eastern Pacific tuna. Int Am Trop Tuna Commission Bull 19:169-260.\u003c/li\u003e\n\u003cli\u003eTrasvi\u0026ntilde;a A, Barton ED, Velez HS et al (2003) Frontal subduction of a cool surface water in the Gulf of Tehuantepec, M\u0026eacute;xico. \u003cem\u003eGeof Int\u003c/em\u003e 42(1): 101\u0026ndash;114 p.\u003c/li\u003e\n\u003cli\u003eWang Y, Xiaoming Y, Jiangfeng Z (2005) Exploring spatiotemporal non-stationarity of the marine environmental impact on skipjack fishery under different climate conditions in the Western and Central Pacific, Fisheries Research, Volume 286, https://doi.org/10.1016/j.fishres.2025.107398.\u003c/li\u003e\n\u003cli\u003eZainuddin M (2009) Estimating Total Allowable Catch and Mapping Potential Pelagic Fishing Ground in Selayar Waters Using AQUA/MODIS Satellite Imagery. Journal of Torani 19(1):36\u0026ndash;42.\u003c/li\u003e\n\u003cli\u003eZainuddin M (2011) Skipjack tuna in relation to sea surface temperature and chlorophyll-a concentration of Bone Bay using remotely sensed satellite data. Jurnal Ilmu dan Teknologi Kelautan Tropis 3(1):82\u0026ndash;90, https://doi.org/10.29244/jitkt.v3i1.7837\u003c/li\u003e\n\u003cli\u003eZainuddin M, Farhum A, Safruddin S et al (2017) Detection of pelagic habitat hotspots for skipjack tuna in the Gulf of Bone-Flores Sea, southwestern Coral Triangle tuna, Indonesia. Plos One 12(10). https://doi.org/10.1371/journal.pone.0 185601\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"thalassas-an-international-journal-of-marine-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"thal","sideBox":"Learn more about [Thalassas: An International Journal of Marine Sciences](http://link.springer.com/journal/41208)","snPcode":"41208","submissionUrl":"https://submission.nature.com/new-submission/41208/3","title":"Thalassas: An International Journal of Marine Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Tuna, Artisanal fishery, MODIS, Mexican Pacific, Euthynnus lineatus","lastPublishedDoi":"10.21203/rs.3.rs-9558665/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9558665/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the relationship between oceanographic variability, specifically sea surface temperature (\u003cem\u003eSST\u003c/em\u003e) and chlorophyll-\u003cem\u003ea\u003c/em\u003e (Chl-\u003cem\u003ea\u003c/em\u003e) concentration, and the abundance and size structure of \u003cem\u003eEuthynnus lineatus\u003c/em\u003e (black skipjack) along the southern Pacific coast of Mexico from October 2022 to October 2024. The region experiences two distinct seasons: a dry season with strong \u0026ldquo;Tehuano\u0026rdquo; winds causing upwelling, and a rainy season influenced by the Costa Rica Coastal Current. High-resolution satellite data were integrated with biometric and catch data from local artisanal fisheries. Seasonal catch patterns peaked between April and July, following increased productivity and rising \u003cem\u003eSST.\u003c/em\u003e The highest catches coincided with \u003cem\u003eSST\u003c/em\u003e around 31.0\u0026deg;C, suggesting a thermal preference that enhances aggregation and catchability. Significant interannual variability was observed; 2023 catches were more than double those of 2024, likely associated with the presence of a warm pool in 2023 and varying environmental conditions. Morphometric analysis indicated larger individuals during cooler, productive months (October\u0026ndash;March) and smaller fish during warmer periods, possibly due to temperature-driven metabolic responses. Principal component analysis (PC1: 38.4%; PC2: 27.7%) confirmed a strong seasonal modulation of environmental and biological variables. These findings suggest that monthly \u003cem\u003eSST\u003c/em\u003e and Chl-\u003cem\u003ea\u003c/em\u003e variability are primary drivers of \u003cem\u003eE. lineatus\u003c/em\u003e dynamics in Oaxaca, providing essential data for sustainable fisheries management and assessing the impacts of climate change and extreme events on artisanal fisheries.\u003c/p\u003e","manuscriptTitle":"Influence of Sea Surface Temperature and Chlorophyll-a on abundance and body size of black skipjack (Euthynnus lineatus) in the Mexican South Pacific","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-12 13:08:59","doi":"10.21203/rs.3.rs-9558665/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-05-01T12:28:48+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-01T12:27:33+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-01T02:37:07+00:00","index":"","fulltext":""},{"type":"submitted","content":"Thalassas: An International Journal of Marine Sciences","date":"2026-04-28T23:10:32+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"thalassas-an-international-journal-of-marine-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"thal","sideBox":"Learn more about [Thalassas: An International Journal of Marine Sciences](http://link.springer.com/journal/41208)","snPcode":"41208","submissionUrl":"https://submission.nature.com/new-submission/41208/3","title":"Thalassas: An International Journal of Marine Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0c098c9e-0bab-46c3-81dc-57ba8dfe82bf","owner":[],"postedDate":"May 12th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewersInvited","content":"12","date":"2026-05-01T12:28:48+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-01T12:27:33+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-01T02:37:07+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-12T13:08:59+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-12 13:08:59","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9558665","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9558665","identity":"rs-9558665","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}