An ocean habitat trap? Impacts of global oxygen-minimum zone expansions on threatened apex predator ecology
Lead Research Organisation:
Marine Biological Association of the United Kingdom
Department Name: Marine Biology
Abstract
Permanent oxygen minimum zones (OMZs) that extend to over 10 million km3 of ocean (ca. 8% of ocean volume) are expanding geographically and vertically due to climate-driven reductions in dissolved oxygen (DO). Potential impacts on marine animal distributions and abundance may be particularly significant for high-oxygen-demand apex predators, such as oceanic pelagic sharks, by reducing habitat volumes through OMZ shoaling and concentrating them further in surface waters where they become more vulnerable to fisheries. But predictions of how exploited oceanic fish actually respond to OMZ expansions are not based on mechanistic understandings, principally because direct measurements of oxygen tolerances during normal behaviour have not been determined for large predatory fish in the open ocean. The proposed research will bring about a step change in our understanding of OMZ impacts on oceanic ecology by applying our existing expertise in animal movement studies and by deploying new telemetry technologies for measuring oxygen environments actually encountered by free-living oceanic sharks moving above/within OMZs. This will enable major unknowns to be addressed concerning how oceanic sharks respond physiologically and behaviourally to OMZs, how oceanic shark habitats change with predicted OMZ expansion, and whether this will increase shark vulnerability to fishing gear. The project will achieve its objectives through linked field and modelling studies on two Red-Listed species, the warm-bodied (endothermic) shortfin mako, Isurus oxyrinchus, and the ectothermic blue shark, Prionace glauca, that are the two pelagic shark species most frequently caught in high seas fisheries. By focusing in depth on key processes underlying shark responses to DO in situ, our new modelling approaches will establish effects of future warming and OMZ shoaling on fish niches and determine how these shift distributions and alter capture risk by fisheries. The project represents a discipline-spanning approach linking physiology to ecology and oceanography, with wide-ranging outcomes for understanding global biotic responses to warming and ocean deoxygenation with direct relevance to sustainable fisheries and species conservation.
Planned Impact
There are two main potential science outcomes of the proposed research that may lead to significant impacts. Firstly, vertical space-use of oceanic blue and shortfin mako sharks may be shifted to shallower depths by the expanding eastern tropical Atlantic OMZ and sharks may remain that region for long periods of time due to greater foraging opportunities (as prey are similarly habitat compressed). As a result, the vulnerability of oceanic sharks to capture by fisheries may be much greater in the OMZ than in normoxic waters elsewhere in the Atlantic. This would identify the need to consider OMZs as areas requiring consideration of special management measures with respect to oceanic sharks and perhaps other pelagics (e.g. tunas, swordfish). OMZs may be particularly important areas that support large catches of sharks but that have gone undetected as major sources because of poor reporting of catches and the lack of regulation. Therefore, the proposed research may be of great interest to the International Commission for the Conservation of Atlantic Tunas (ICCAT) for informing plans to develop sustainable exploitation of oceanic sharks in the Atlantic. Similarly, the International Union for the Conservation of Nature (IUCN) World Commission on Protected Areas (WCPA) are interested in the project results because they address an emerging interest in assessing the status and global impacts of ocean deoxygenation. Furthermore IUCN WCPA are interested in exploring the potential of OMZs as a network of high seas Marine Protected Areas (MPA).
In the proposed research we plan to engage directly with ICCAT regarding shark catch limits in OMZs and with the IUCN WCPA on upper-trophic level impacts of ocean deoxygenation and to explore a potential role of OMZs as high seas MPAs. We plan to present the results of the proposed research formally to ICCAT as part of the annual intersessional meetings of the shark species group in addition to the species data preparatory meetings and stock assessment sessions (which the P.I. and Project Partner have attended as part of the EU delegation). A potential outcome will be bringing new data and understanding on shark movements, electronic tag recapture rates to estimate potential fishing mortality between different ocean areas, and the effects of environmental changes on risk of shark capture from fisheries, into the shark stock assessment process to inform recommendations for management. The proposed project may contribute results that identify OMZs as areas at particular risk from overfishing.
Engagement with the IUCN will be in collaboration with our Project Partner Prof Dan Laffoley who is the Marine Vice-Chair of the IUCN WCPA. We will work with Prof Laffoley in two linked areas. First, the WCPA are to produce an authoritative report on the impacts of ocean deoxygenation that will be launched at a future meeting of the World Conservation Congress. The proposed research will form the key source of new information detailing how IUCN Red-Listed oceanic sharks will respond to the combined effects of ocean deoxygenation, warming and fishing exploitation. Secondly, as part of the collaborative reporting of the effects of deoxygenation on sharks, we will explore with IUCN the potential for identifying OMZs as candidate high seas MPAs in the event that they are identified as key shark habitats that appear to be undergoing overfishing. We aim to feed project results into focused meetings with IUCN to determine whether there is scope and opportunity for proposing OMZs as MPAs as part of their Global Plan of Action.
In the proposed research we plan to engage directly with ICCAT regarding shark catch limits in OMZs and with the IUCN WCPA on upper-trophic level impacts of ocean deoxygenation and to explore a potential role of OMZs as high seas MPAs. We plan to present the results of the proposed research formally to ICCAT as part of the annual intersessional meetings of the shark species group in addition to the species data preparatory meetings and stock assessment sessions (which the P.I. and Project Partner have attended as part of the EU delegation). A potential outcome will be bringing new data and understanding on shark movements, electronic tag recapture rates to estimate potential fishing mortality between different ocean areas, and the effects of environmental changes on risk of shark capture from fisheries, into the shark stock assessment process to inform recommendations for management. The proposed project may contribute results that identify OMZs as areas at particular risk from overfishing.
Engagement with the IUCN will be in collaboration with our Project Partner Prof Dan Laffoley who is the Marine Vice-Chair of the IUCN WCPA. We will work with Prof Laffoley in two linked areas. First, the WCPA are to produce an authoritative report on the impacts of ocean deoxygenation that will be launched at a future meeting of the World Conservation Congress. The proposed research will form the key source of new information detailing how IUCN Red-Listed oceanic sharks will respond to the combined effects of ocean deoxygenation, warming and fishing exploitation. Secondly, as part of the collaborative reporting of the effects of deoxygenation on sharks, we will explore with IUCN the potential for identifying OMZs as candidate high seas MPAs in the event that they are identified as key shark habitats that appear to be undergoing overfishing. We aim to feed project results into focused meetings with IUCN to determine whether there is scope and opportunity for proposing OMZs as MPAs as part of their Global Plan of Action.
People |
ORCID iD |
David Sims (Principal Investigator) | |
Nicolas Humphries (Researcher) |
Publications
Womersley FC
(2023)
Four steps to curb 'ocean roadkill'.
in Nature
Womersley FC
(2022)
Global collision-risk hotspots of marine traffic and the world's largest fish, the whale shark.
in Proceedings of the National Academy of Sciences of the United States of America
Waller MJ
(2023)
Direct measurement of cruising and burst swimming speeds of the shortfin mako shark (Isurus oxyrinchus) with estimates of field metabolic rate.
in Journal of fish biology
Vedor M
(2021)
Oceanic Diel Vertical Movement Patterns of Blue Sharks Vary With Water Temperature and Productivity to Change Vulnerability to Fishing
in Frontiers in Marine Science
Sims DW
(2021)
Shortfin mako sharks speeding to the brink.
in Science (New York, N.Y.)
Sequeira A
(2019)
Overhauling Ocean Spatial Planning to Improve Marine Megafauna Conservation
in Frontiers in Marine Science
Queiroz N
(2021)
Reply to: Shark mortality cannot be assessed by fishery overlap alone.
in Nature
Queiroz N
(2021)
Reply to: Caution over the use of ecological big data for conservation.
in Nature
Description | Climate-driven expansions of ocean hypoxic zones are predicted to concentrate pelagic fish in surface layers, but how expanding hypoxia and high-seas fisheries will interact to affect threatened pelagic sharks has not been studied. In this research we have analysed the movements and behaviour of satellite-tracked blue and shortfin sharks - two of the most fished pelagic sharks - and longline fishing vessels above the eastern tropical Atlantic oxygen minimum zone (OMZ). The results showed that there was a 40% reduction in the maximum daily dive (MDD) depths of blue sharks above the mesopelagic OMZ, findings consistent with hypothesised habitat compression due to low dissolved oxygen (DO) at depth. Our behaviour/environmental model demonstrated that MDD depths were reduced due to combined effects of decreasing DO at depth, high sea surface temperatures, and increased surface-layer net primary production. The observed shifts in vertical habitat extent were significant, potentially increasing shark vulnerability to surface fisheries. We found greater intensity of longline fishing effort occurred above the OMZ compared to well-oxygenated adjacent waters. In OMZ areas blue shark catches were two to three times higher and were associated with strong DO gradients, suggesting potential aggregation of sharks along suitable DO gradients contributed to habitat compression and higher fishing-induced mortality. The implications of our results are that stricter fisheries controls in OMZ areas to counteract deoxygenation effects on shark catches will be needed as oceans continue warming. |
Exploitation Route | There are two main ways the science results may lead to significant impacts. The demonstration that the vertical space-use of pelagic sharks is shifted to shallower depths above the eastern tropical Atlantic OMZ leading to habitat compression of sharks and estimated increases in susceptibility to capture by fisheries, shows sharks will be at greater risk of exposure to fisheries capture above the eastern tropical Atlantic OMZ than in adjacent normoxic waters and most areas elsewhere in the North Atlantic. These results will be of interest to fisheries management bodies tasked with the management of sharks in International Waters of the Atlantic, such as the International Commission for the Conservation of Atlantic Tunas (ICCAT). This is because shark habitat compression above OMZs with progressing ocean deoxygenation will alter catch rates and the distribution of longline fisheries, which predicts further regional declines in abundance without mitigating management measures. This may require ICCAT to consider management measures in the light of climate change effects, something which has yet to be incorporated into any shark management measure anywhere in the world. Furthermore, global conservation bodies with an interest in climate change effects on apex predators and in high seas Marine Protected Areas, such as the IUCN World Commission on Protected Areas (WCPA), will be interested in the results to inform proposals for protected large-scale areas of the ocean as MPAs for sharks and associated biodiversity. |
Sectors | Environment Government Democracy and Justice |
URL | http://www.globalsharkmovement.org |
Description | The research has contributed to a major IUCN (International Union for the Conservation of Nature) report entitled "Ocean Deoxygenation - Everyone's Problem: Causes, Impacts, Consequences and Solutions", edicted by D. Laffoley and J. Baxter, which is due for publication in 2019. Our research contributed the entire chapter on the effects of ocean deoxygenation on sharks, skates and rays. It is anticipated that this IUCN report will be a landmark publication to galvanise interest, support and international action on the issue of ocean deoxygenation. |
First Year Of Impact | 2019 |
Sector | Environment |
Impact Types | Economic Policy & public services |
Description | OCEAN DEOXYFISH - Ocean deoxygenation effects on threatened top predators: New understanding and predictions from novel bio-logging instruments and data |
Amount | € 3,110,000 (EUR) |
Organisation | European Research Council (ERC) |
Sector | Public |
Country | Belgium |
Start | 09/2020 |
End | 09/2025 |
Title | Global Shark Movement and Environment Database |
Description | The Global Shark Movement Project Database holds satellite tracking locations and associated data of over 2,000 pelagic sharks (23 species) with environmental data (17 variables) extracted for each shark daily location. It holds approximately 300,000 track days of shark movements. The shark movement tracking data were contributed by 40 research groups in over 100 institutes in 26 countries. The GMSP Database is managed by the P.I. |
Type Of Material | Database/Collection of data |
Year Produced | 2019 |
Provided To Others? | No |
Impact | The GSMP Database is being used widely across the 40 research teams to address key questions in shark ecology, conservation and interactions with fisheries. Research publications are currently in review and preparation. It seems likely that the first paper will be published in time to have an impact at the CITES (Convention on International Trade in Endangered Species) Conference of Parties in May 2019. |
URL | https://www.globalsharkmovement.org/ |
Title | Animal-attached electronic tag for recording dissolved oxygen, depth, temperature and animal heading and body movements |
Description | The new tag developed in collaboration with this project provides unparalleled detail of fish movements, behaviour and environment in hypoxic ocean regions. The tag contains tri-axial accelerometer, pressure, water temperature, optical dissolved oxygen and heading sensors. The optical DO sensor maintains calibration for long periods of time (months). The printed circuit boards (PCBs) contain a low-power accelerometer, magnetometer, depth and temperature sensors enabling fine-scale 3D movements of tagged animals to be recorded; the tag is recovered after it releases from a predator and can be re-used. Given the large amounts of data typically produced by accelerometers, the sampling rate is configurable and varies between 1 and 50 Hz, with a mini-storage device (microSD card) incorporated to enable environmental data to be collected at very high temporal resolution (1s) allowing 3D movements to be linked with oxygen gradients during dives ('casts'). Furthermore, the tag can record subtle body movements associated with tail beat frequency, power-glide cycles, and overall dynamic body acceleration (ODBA) that can be used as a proxy for energy expenditure in the wild (field metabolic rate; see next section). A timed-release device releases the tag from the fish and a GPS unit allows tag recovery when it floats to the surface. The tag will enable short, 1-3 d data-rich deployments on free-ranging sharks and tunas that potentially dive to 1,700m. A second version incorporating a video camera (DVL2000M; Little Leonardo, Tokyo) has been built that records prey concentrations encountered at different depth and DO environments (down to 2000 m and incorporating red LED lights for recording in the dark). |
Type Of Technology | New/Improved Technique/Technology |
Year Produced | 2019 |
Impact | The tag has been tested in the lab and in large aquaria, and has been trialled on ocean sunfish at sea where it collected data on dissolved oxygen, depth and temperature along the swimming paths of fish for 4 days. The tags will be deployed on large pelagic sharks to gain novel insights into behaviour in environments undergoing deoxygenation. |
Title | Source code for global analysis of pelagic shark spatial density and fishing effort |
Description | The source code can be used to undertake analyses and to prepare figures, in addition to the derived data underlying global maps of shark relative spatial density, longline-fishing effort and shark-longline-fishing overlap and fisheries exposure index (FEI) and plots of spatial overlap and FEI. Freely available on GitHub (https://github.com/GlobalSharkMovement/GlobalSpatialRisk). |
Type Of Technology | Software |
Year Produced | 2019 |
Impact | The code was used to undertake analyses contributing to the 2019 paper in NATURE by Queiroz et al., Sims which received worldwide media coverage. |
URL | https://www.nature.com/articles/s41586-019-1444-4 |
Description | BBC Radio 'Naked Scientists' - The Secret Lives of Sharks |
Form Of Engagement Activity | A broadcast e.g. TV/radio/film/podcast (other than news/press) |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | BBC Radio Cambridge and BBC Radio 5 - The Naked Scientists "Secret Lives of Sharks" (20th June 2021) Here is the link to my piece, and the entire 1 hour show. https://www.thenakedscientists.com/articles/interviews/sharks-are-dire-straits-how-you-can-help https://www.thenakedscientists.com/podcasts/naked-scientists-podcast/secret-lives-sharks |
Year(s) Of Engagement Activity | 2021 |
URL | https://www.thenakedscientists.com/articles/interviews/sharks-are-dire-straits-how-you-can-help |
Description | Save Our Seas Foundation's 'The Whole Tooth' Podcast |
Form Of Engagement Activity | A broadcast e.g. TV/radio/film/podcast (other than news/press) |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | SaveOurSeas - The Whole Tooth Podcast - "Can sharks adapt to changing seas?" (3rd March 2022) The Whole Tooth is an interactive, informal video blog and podcast series aimed at connecting a general audience to top marine researchers in an accessible and engaging way. "Our oceans are changing dramatically - not just with climate change, but also in how it is being used and exploited by humans. In this episode, we ask shark movement experts Prof. David Sims and Freya Womersley, who work on the Global Shark Movement Project, what these changes mean for sharks and how their distribution and behaviour might change in response. Can sharks adapt? Or will it spell further trouble for our elasmobranchs?" |
Year(s) Of Engagement Activity | 2022 |
URL | https://saveourseas.com/worldofsharks/thewholetooth/can-sharks-adapt-to-changing-seas |
Description | Young Marine Biologists (YMB) Summit |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Schools |
Results and Impact | Young Marine Biologists (YMB) Summit 2021 (27 Nov 2021) Introductory presentation "Ocean Predator Research: Past, Present and Future" (From 48.46 min in) https://www.youtube.com/watch?v=3DSraW58N7s Over 150 young people listened to the presentation and engaged with the other talks and activities during the 2-day summit. They asked many questions in the Q&A sessions. |
Year(s) Of Engagement Activity | 2021 |
URL | https://www.youtube.com/watch?v=3DSraW58N7s |