‘Fatal attraction’: Death of a false killer whale by an Indo-Pacific sailfish bill

‘Fatal attraction’: Death of a false killer whale by an Indo-Pacific sailfish bill | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 24 February 2026 V1 Latest version Share on ‘Fatal attraction’: Death of a false killer whale by an Indo-Pacific sailfish bill Authors : Beatriz Queiroz , Lucas Santos , Diego Pinheiro , Larissa Oliveira 0000-0002-5735-3697 [email protected] , Vicente Faria , and Vitor Carvalho Authors Info & Affiliations https://doi.org/10.22541/au.177192732.23740111/v1 159 views 107 downloads Contents Abstract *Correspondence author Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Here we document an exceptional and previously unreported event: the stranding of a false killer whale, Pseudorca crassidens, neonate in northeastern Brazil resulting from a fatal collision with an Indo-Pacific sailfish, Istiophorus platypterus. Detailed necropsy, pathological examination, and genetic identification of the embedded foreign structure demonstrate unequivocally that the trauma was caused by the bill of I. platypterus. To our knowledge, this represents the first confirmed case of interaction between these two species for the Brazilian coast, and one of the very few documented worldwide, providing valuable insight into the ecological dynamics of pelagic predators in the Southwestern Atlantic. This case also underscores the importance of long-term beach monitoring programs for detecting unusual biological events and improving our understanding of marine mammal ecology, behavior, and mortality sources. ‘Fatal attraction’: Death of a false killer whale by an Indo-Pacific sailfish bill Queiroz, B. 1,2 ; Santos, L. 1 ; Pinheiro, D.R.M. 1 ; Oliveira, L.R. 1,2,3,4,5* ; Faria, V.V. 2 ; Carvalho, V.L. 1 1 Associação de Pesquisa e Preservação de Ecossistemas Aquáticos (NGO Aquasis), Caucaia and Icapuí, Brazil 2 Marine Vertebrate Evolution and Conservation Lab (EvolVe), Departamento de Biologia, Universidade Federal do Ceará (UFC), Fortaleza, Brazil 3 Universidade do Vale do Rio dos Sinos (UNISINOS), São Leopoldo, Brazil 4 Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul (GEMARS), Torres, Brazil 5 Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil *Correspondence author Larissa Rosa de Oliveira Associação de Pesquisa e Preservação de Ecossistemas Aquáticos Icapuí, Ceará Email: [email protected] [email protected] This study reports the stranding of a false killer whale, Pseudorca crassidens (Owen, 1846), in northeastern Brazil, as a result of a fatal encounter with an Indo-Pacific sailfish, Istiophorus platypterus (Shaw, 1792) . The false killer was a female neonate measuring 163 cm in total length and weighing 49.9 kg (Fig. 1), and it was found dead on December 12, 2021, at Canoa Quebrada Beach, Aracati, Ceará (4°31’4.80”S; 37°42’35.66”W) (Fig. 2). The presence of fetal folds, a partially open umbilicus, rostral vibrissae (Fig. 3), and a flexible, laterally positioned dorsal fin was observed, suggesting that the specimen was a neonate. A penetrating injury was observed in the caudal portion of the left mandible (Fig. 3) with a pointed structure protruding near the right ear (Fig. 4A). Necropsy revealed a hematoma in the mandibular region, with local perforation caused by the foreign body, which affected the pterygoid and occipital bones, causing multiple fractures in the right periotic-tympanic complex (Figs. 4A, 4B). The cause of death was attributed to cranial trauma associated with the foreign object. Other pathological findings included brownish gastric fluid, edematous content in the trachea and bronchi, and hemorrhagic pulmonary parenchyma. The heart was friable and showed diffuse congestion. Regarding the central nervous system, the brain was autolyzed, the meninges exhibited diffuse congestion, and the spinal cord was hemorrhagic. The other organs and internal parts showed post-mortem alterations. During necropsy, the penetrating foreign body of animal origin was recovered from the skull, and a 1 cm³ bone fragment was preserved in absolute ethanol at –20 °C for genetic analysis. DNA was extracted using the Qiagen DNeasy Blood & Tissue Kit, after which cytochrome c oxidase subunit I (coxI) was amplified following Ward et al. (2005). The 610 bp sequence obtained (GenBank accession PZ025216) matched 23 sequences assigned to an Indo-Pacific sailfish, Istiophorus platypterus (Shaw 1792) (Perciformes: Istiophoridae) in the BOLD Systems database (Barcode of Life Data System; https://www.boldsystems.org), seven of which had a high percent identity of 99.84% (GBAAY43711-24, GBAAY43713-24, GBAAY43717-24, GBAAY43718-24, GBAAY43737-24, GBAAY43751-24, and GBMTG4710-16 [BOLD:ABZ5149]). The sequence was also analyzed using the Basic Local Alignment Search Tool (BLAST) in GenBank (Altschul et al., 1990; BLASTn: https://blast.ncbi.nlm.nih.gov/Blast.cgi). This resulted in a total of 100 matches, all assigned to I. platypterus , with the highest percent identity value of 99.84% observed in 25 DNA matches (KR067401.1, NC_022478.1, OP404092.1–OP404106.1, OP404108.1, OP404110.1, OP404112.1, OP404114.1, OP404118.1, OP404120.1, OP404122.1, and OP404123.1). All BLASTn matches had an E-value of 0.0, indicating that the probability of random alignment is negligible. Notably, both databases yielded the same maximum identity value (99.84%). The assigned species identity obtained in both DNA-based analyses is in accordance with the available morphological evidence, as the rostrum fragment obtained (Fig. 5) is compatible with that of an I. platypterus specimen (e.g., Häge et al., 2022). Therefore, the available evidence suggests that the unidentified rostrum fragment belongs to I. platypterus . To our knowledge, this represents the first report of interaction between I. platypterus and P. crassidens on the Brazilian coast. We speculate that this fatal encounter between a false killer whale neonate and an Indo-Pacific sailfish was accidental, occurring during foraging when both species targeted the same prey. The neonate may have accompanied its mother into a school of fish, leading to an incidental collision with I. platypterus amid the frenzy of hunting. Isotopic analyses indicate that false killer whales and billfish likely feed on similar prey species (Ortega-Ortiz et al., 2014), and their spatial distributions overlap (Santana-Hernández et al., 2009; Ortega-Ortiz et al., 2014). Still, we cannot dismiss the possibility that the mother was chasing the sailfish, since this species is prey to false killer whales (Baird, 2018). In this case, the sailfish accidentally collided with the calf. Any of the potential scenarios implies an accidental collision that killed the neonate, given that Indo-Pacific sailfish can reach 68–70 mph (110–113 km/h) in short hunting bursts. This exceptional speed places the sailfish among the fastest known marine predators (Logan et al., 2023). Nevertheless, evidence also points to direct and aggressive interactions. A false killer whale was observed with a billfish beak fragment embedded in its back in the Mexican Central Pacific (Ortega-Ortiz et al., 2014). Aggressive encounters between whales and billfishes, both unidentified, were described near Oahu in the Hawaiian Archipelago (Major, 1979). Bills of marlin fishes embedded in the jaws of Antarctic minke whales were recorded at 64°06’S, 87°14’E and 64°52’S, 91°l8’E (Ohsumi, 1973). All of these cases were interpreted as attacks by billfishes. False killer whales are widely distributed in tropical to warm-temperate waters, usually offshore but occasionally nearshore (Stacey et al., 1994; Zaeschmar, 2014; Baird et al., 2018). In Brazil, most of the species records are from strandings and few from onboard sightings (Andrade et al., 2001; Alves et al., 2002; Santos et al., 2010; ICMBio, 2025). They are gregarious, traveling in groups of 20–100 individuals with strong social bonds (Baird et al., 2008), and are known to form mixed-species associations, especially with bottlenose dolphins ( Tursiops truncatus ) (Flores et al., 2003; San Martín et al., 2023), possibly for cooperative foraging and protection (Zaeschmar, 2014). Their diet consists of cephalopods and pelagic fish (Odell & McClune, 1999), and although their foraging behavior is not fully understood, they are observed foraging cooperatively (Acevedo-Gutierrez et al., 1997; Baird et al., 2009). The Indo-Pacific sailfish is an epipelagic predator inhabiting tropical and subtropical waters (Collette & Graves, 2019), with distribution in the Atlantic ranging from 40º N and 50° N in the western and eastern North Atlantic, respectively, and 40º S in the western and eastern South Atlantic (Beardsley et al., 1975; Nakamura, 1985). In southeastern Brazil, satellite tagging has shown preference for surface waters (Mourato et al., 2014). Billfishes don’t rely on extreme speeds but use their elongated bill and large dorsal fins to improve prey capture through slashing maneuvers (Domenici et al., 2000, 2014; Oliver et al., 2013). The sailfish have the largest dorsal fin among billfishes, which improves bill control during maneuvers (Domenici et al., 2014). Given the overlapping ecological niches of the false killer whale and the Indo-Pacific sailfish, there is potential for more frequent interspecific encounters, as both species inhabit the epipelagic zone, raising the possibility of competition for prey or direct predation. To investigate the probability of such interactions, we utilized AquaMaps, a global species distribution modeling framework (Ready et al. 2010), which generates probability maps of species occurrence by combining environmental suitability models with known occurrence records. AquaMaps incorporates environmental parameters such as water temperature, salinity, depth, primary productivity, and associations with sea ice or coastal zones to predict suitable habitats at a global scale. Pixel-wise correlation analysis of the predicted occurrence layers revealed a significant positive relationship between both species (Pearson’s r = 0.51, p < 0.001), indicating that suitable habitats tend to coincide. The mean probability of co-occurrence was 0.36 ± 0.25, suggesting moderate spatial overlap, particularly along the northeastern Brazilian continental shelf. These results are illustrated by the probability of co-occurrence across the Southwestern Atlantic Ocean (Fig. 2, with a color gradient highlighting regions of higher and lower likelihood of overlap). Overall, the findings suggest that potential interactions, such as competition for prey or opportunistic predation, may be more frequent in this region due to higher ecological overlap and a narrower shelf environment, highlighting areas where monitoring and conservation efforts could be prioritized. This case represents the first record of interaction between a false killer whale and an Indo-Pacific sailfish in Brazil, documented over three decades of stranding monitoring in the region. This study highlights the importance of long-term monitoring studies based on beach surveys as valuable tools for understanding the biology of marine species. It provides an opportunity to examine the interspecific behavior that led to the accident, death, and stranding of false killer whales, thereby contributing to the knowledge of the species’ ecology. Acknowledgments Samples were collected under the Potiguar Basin Beach Monitoring Program (PMP‑BP), an environmental licensing requirement coordinated by IBAMA for Petrobras’ activities. We thank Mika Holanda (NGO Aquasis) for assistance with image editing. Data availability statement All data supporting the findings are included within the manuscript. The DNA sequence generated has been deposited in GenBank (accession number PZ025216) References Acevedo-Gutierrez, A., Brennan, B. J., Rodriguez, P., & Thomas, M. (1997). Resightings and behavior of false killer whales ( Pseudorca crassidens ) in Costa Rica. Marine Mammal Science , 13 (2), 307–314. https://doi.org/10.1111/j.1748-7692.1997.tb00634.x Altschul, S. F., Gish, W., Miller, W., Myers, E. W., & Lipman, D. J. (1990). Basic local alignment search tool. Journal of Molecular Biology , 215 (3), 403–410. https://doi.org/10.1016/S0022-2836(05)80360-2 Alves, M. D. O., Meirelles, A. C. O., Barros, H. M. D. R., Silva, C. P. 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Keywords behavioral ecology marine natural history vertebrate Authors Affiliations Beatriz Queiroz Associacao de Pesquisa e Preservacao de Ecossistemas Aquaticos View all articles by this author Lucas Santos Associacao de Pesquisa e Preservacao de Ecossistemas Aquaticos View all articles by this author Diego Pinheiro Associacao de Pesquisa e Preservacao de Ecossistemas Aquaticos View all articles by this author Larissa Oliveira 0000-0002-5735-3697 [email protected] UNISINOS View all articles by this author Vicente Faria Universidade Federal do Ceara - Campus do Pici View all articles by this author Vitor Carvalho Associacao de Pesquisa e Preservacao de Ecossistemas Aquaticos View all articles by this author Metrics & Citations Metrics Article Usage 159 views 107 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Beatriz Queiroz, Lucas Santos, Diego Pinheiro, et al. ‘Fatal attraction’: Death of a false killer whale by an Indo-Pacific sailfish bill. 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