Overfishing and Climate Change Elevate Extinction Risk of Endemic Sharks and Rays in the Southwest Indian Ocean Hotspot and Adjacent Waters

Overfishing and Climate Change Elevate Extinction Risk of Endemic Sharks and Rays in the Southwest Indian Ocean Hotspot and Adjacent Waters | 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 Overfishing and Climate Change Elevate Extinction Risk of Endemic Sharks and Rays in the Southwest Indian Ocean Hotspot and Adjacent Waters Riley Pollom, Jessica Cheok, Nathan Pacoureau, Katie S. Gledhill, and 16 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-984080/v2 This work is licensed under a CC BY 4.0 License Status: Posted Version 2 posted You are reading this latest preprint version Show more versions Abstract The southwest Indian Ocean (SWIO) is a hotspot of endemic and evolutionarily distinct sharks and rays. We summarise the extinction risk of the sharks and rays endemic to coastal, shelf, and slope waters of the SWIO and adjacent waters (Namibia to Kenya, including SWIO islands). Thirteen of 70 species (19%) are threatened: one is Critically Endangered, five are Endangered, and seven are Vulnerable. A further seven (10%) are Near Threatened, 33 (47.1%) are Least Concern, and 17 (24.2%) are Data Deficient. While the primary threat is overfishing, there are the first signs that climate change is contributing to elevated extinction risk through habitat reduction and inshore distributional shifts. By backcasting their status, few species were threatened in 1980, but this changed soon after the emergence of targeted shark and ray fisheries. South Africa has the highest national conservation responsibility, followed by Mozambique and Madagascar. Yet, while fisheries management and enforcement have improved in South Africa over recent decades, drastic improvements are urgently needed elsewhere. To avoid extinction and ensure robust populations of the region’s endemic sharks and rays and maintain ecosystem functionality, there is an urgent need for the strict protection of Critically Endangered and Endangered species and sustainable management of Vulnerable, Near Threatened, and Least Concern species, underpinned by species-level data collection and reduction of incidental catch. Environmental Engineering Ocean Engineering Climatology marine conservation Convention on Biological Diversity elasmobranch IUCN Red List Index biodiversity indicator Sustainable Development Goals Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 2 posted You are reading this latest preprint version Show more versions 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-984080","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":62827476,"identity":"1d1cd9aa-0194-49fb-8e1f-3dac4ce1f9af","order_by":0,"name":"Riley Pollom","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAvklEQVRIiWNgGAWjYHACxgMPGBjk2BgYDIjXcyCBgcGYdC2JDURrMZ/dfOBAQsW29D7p5m2SPypsGPjbuxPwapG5cyzhQMKZ27ltMsfKJCTOpDFInDm7Aa8WCYkcgwOJbUAtEjlmEoZthxkMJHKJ05LOBtKSSIqWBLCWg0RpkYH4xbBNIq3YsuFMGg9hv0g3H3zwoeK2vPyM5I03gSEmx9/ei18LgwSCyQJi8+BXjqaF+QNh5aNgFIyCUTASAQB3E0h+CYHcygAAAABJRU5ErkJggg==","orcid":"","institution":"Simon Fraser University, British Columbia","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Riley","middleName":"","lastName":"Pollom","suffix":""},{"id":62827477,"identity":"d45fe184-3a81-4355-b049-c2ddf99c74a3","order_by":1,"name":"Jessica Cheok","email":"","orcid":"","institution":"Simon Fraser University, British Columbia","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jessica","middleName":"","lastName":"Cheok","suffix":""},{"id":62827478,"identity":"c1ae11cb-5ca3-47fa-b44f-f94c2a4aff9e","order_by":2,"name":"Nathan Pacoureau","email":"","orcid":"","institution":"Simon Fraser University, British Columbia","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Nathan","middleName":"","lastName":"Pacoureau","suffix":""},{"id":62827479,"identity":"84d87040-21b6-4ef9-803b-2f4ea534a89d","order_by":3,"name":"Katie S. 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Pollock","email":"","orcid":"","institution":"IUCN Red List Unit","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Caroline","middleName":"M.","lastName":"Pollock","suffix":""},{"id":62827494,"identity":"f305c486-ff51-409b-9ae9-23d927afe7f5","order_by":18,"name":"Cassandra L. Rigby","email":"","orcid":"","institution":"James Cook University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Cassandra","middleName":"L.","lastName":"Rigby","suffix":""},{"id":62827495,"identity":"6007a0b2-de18-4604-8f18-f595db540821","order_by":19,"name":"Nicholas K. Dulvy","email":"","orcid":"","institution":"Simon Fraser University, British Columbia","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Nicholas","middleName":"K.","lastName":"Dulvy","suffix":""}],"badges":[],"createdAt":"2021-10-16 19:59:03","currentVersionCode":2,"declarations":"","doi":"10.21203/rs.3.rs-984080/v2","doiUrl":"https://doi.org/10.21203/rs.3.rs-984080/v2","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":19411039,"identity":"9d16d344-686e-4e85-a16f-f4b2199cabb9","added_by":"auto","created_at":"2022-03-21 00:09:40","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":110001,"visible":true,"origin":"","legend":"\u003cp\u003eEndemic species richness of (a) sharks and rays (n = 70), (b) threatened (Critically Endangered, Endangered or Vulnerable, according to the IUCN Red List Categories) sharks and rays (n = 13), (c) threatened sharks (n = 8), and (d) individual distributions of threatened rays (n = 5) across the SWIO+ region.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-984080/v2/11cbd92ba4146d862bb3696a.png"},{"id":19411036,"identity":"14f73cae-2c4b-417b-bc8e-a2f5a2248143","added_by":"auto","created_at":"2022-03-21 00:06:40","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":99051,"visible":true,"origin":"","legend":"\u003cp\u003eSpecies population time-series (expressed as a proportion) modelled from demersal research trawl surveys in commercially fished areas (line) and shore-based research angling surveys (dashed line) off the west and south coasts of South Africa. Lines and dashed lines denote the mean, and shaded regions represent the 95% credible intervals. Time-series are divided by their initial values and start at one. Silhouette colours indicate Red List status: dark green is Least Concern, light green is Near Threatened, yellow is Vulnerable, orange is Endangered.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-984080/v2/dad34d3ec6de4b0f146920e2.png"},{"id":19410913,"identity":"52e3a5fe-9ff8-4b88-a599-6c31c1799f67","added_by":"auto","created_at":"2022-03-20 23:57:40","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":11614,"visible":true,"origin":"","legend":"\u003cp\u003eCount of reported threat categories in the 20 threatened (Critically Endangered, Endangered and Vulnerable) and Near Threatened SWIO+ shark and ray species.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-984080/v2/e7432e73e8736248b905f804.png"},{"id":19410917,"identity":"ea644ea4-480d-4aab-a958-f936db7944fb","added_by":"auto","created_at":"2022-03-20 23:57:40","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":264560,"visible":true,"origin":"","legend":"\u003cp\u003eSpatial and temporal change in density (ln kg per km-2) between 20°E and 27°E longitude for 1991 and 2016 for (a) Lesser Guitarfish (Acroteriobatus annulatus; Vulnerable), (b) Bluntnose Spurdog (Squalus acutipinnis; Near Threatened), and (c) Twin-eye Skate (Raja ocellifera; Endangered).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-984080/v2/f0448bc9fd0ee0b77645baa0.png"},{"id":19410988,"identity":"f061a107-9780-49db-9c33-64144270044a","added_by":"auto","created_at":"2022-03-21 00:00:40","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":20771,"visible":true,"origin":"","legend":"\u003cp\u003eRed List Index (RLI) for SWIO+ endemic sharks and rays (n = 70). (a) The decline in RLI across assessment years 1980, 2005, and 2020. Country-specific declines in RLI from (b) 1980—2005 and (c) 2005—2020. Calculations of RLI exclude Data Deficient (DD) species.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-984080/v2/3d7a57787d6dbda00536a5af.png"},{"id":19410991,"identity":"4aa47367-3f40-4dbd-8787-cd2f6b40f34a","added_by":"auto","created_at":"2022-03-21 00:03:40","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":30849,"visible":true,"origin":"","legend":"\u003cp\u003eNational conservation responsibility of nine range countries for all 70 endemic shark and ray species in the SWIO+ region for which Red List Status is known.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-984080/v2/55d52341946c55b5fab2f6ae.png"},{"id":19411040,"identity":"2e83a819-8ef7-4710-a073-68ef477c5204","added_by":"auto","created_at":"2022-03-21 00:09:54","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":549990,"visible":true,"origin":"","legend":"","description":"","filename":"SAendemicV11220318.pdf","url":"https://assets-eu.researchsquare.com/files/rs-984080/v2_covered.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eOverfishing and Climate Change Elevate Extinction Risk of Endemic Sharks and Rays in the Southwest Indian Ocean Hotspot and Adjacent Waters\u003c/p\u003e","fulltext":[{"header":"Full Text","content":"This preprint is available for \u003ca href='/article/rs-984080/latest.pdf' target='_blank'\u003edownload as a PDF\u003c/a\u003e."}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"marine conservation, Convention on Biological Diversity, elasmobranch, IUCN Red List Index, biodiversity indicator, Sustainable Development Goals","lastPublishedDoi":"10.21203/rs.3.rs-984080/v2","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-984080/v2","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe southwest Indian Ocean (SWIO) is a hotspot of endemic and evolutionarily distinct sharks and rays. We summarise the extinction risk of the sharks and rays endemic to coastal, shelf, and slope waters of the SWIO and adjacent waters (Namibia to Kenya, including SWIO islands). Thirteen of 70 species (19%) are threatened: one is Critically Endangered, five are Endangered, and seven are Vulnerable. A further seven (10%) are Near Threatened, 33 (47.1%) are Least Concern, and 17 (24.2%) are Data Deficient. While the primary threat is overfishing, there are the first signs that climate change is contributing to elevated extinction risk through habitat reduction and inshore distributional shifts. By backcasting their status, few species were threatened in 1980, but this changed soon after the emergence of targeted shark and ray fisheries. South Africa has the highest national conservation responsibility, followed by Mozambique and Madagascar. Yet, while fisheries management and enforcement have improved in South Africa over recent decades, drastic improvements are urgently needed elsewhere. To avoid extinction and ensure robust populations of the region’s endemic sharks and rays and maintain ecosystem functionality, there is an urgent need for the strict protection of Critically Endangered and Endangered species and sustainable management of Vulnerable, Near Threatened, and Least Concern species, underpinned by species-level data collection and reduction of incidental catch.\u003c/p\u003e","manuscriptTitle":"Overfishing and Climate Change Elevate Extinction Risk of Endemic Sharks and Rays in the Southwest Indian Ocean Hotspot and Adjacent Waters","msid":"","msnumber":"","nonDraftVersions":[{"code":2,"date":"2022-03-20 23:57:38","doi":"10.21203/rs.3.rs-984080/v2","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}},{"code":1,"date":"2021-11-11 15:25:38","doi":"10.21203/rs.3.rs-984080/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d501c768-9639-44c1-90e4-b6f26600666b","owner":[],"postedDate":"March 20th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":11194856,"name":"Environmental Engineering"},{"id":11194857,"name":"Ocean Engineering"},{"id":11194858,"name":"Climatology"}],"tags":[],"updatedAt":"2021-12-24T05:59:14+00:00","versionOfRecord":[],"versionCreatedAt":"2022-03-20 23:57:38","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v2","identity":"rs-984080","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-984080","identity":"rs-984080","version":["v2"]},"buildId":"-HB7Z8yhvgn0wM9Nzuekk","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}