Expanding dead zones lead to pelagic habitat traps more prone to overfishing
Dr Rui Rosa1, Dr Nuno Queiroz2,3, Ms Marisa Vedor2, Mr Gonzalo Mucientes2, Ms Ana Couto1,2, Dr. Frederic Vandeperre4, Dr. Pedro Afonso4, Dr. Nicolas Humphries3, Dr David Sims3,5,6
1MARE, Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Cascais, Portugal, 2CIBIO/InBIO, Universidade do Porto, Porto, Porto, 3arine Biological Association of the United Kingdom, Plymouth , UK, 4IMAR, University of the Azores, Department of Oceanography and Fisheries, Horta, Portugal, 5Ocean and Earth Science, National Oceanography Centre Southampton, Southampton, UK, 6University of Southampton, Southampton, UK
Climate-driven expansions of permanent oxygen minimum zones (OMZs) resulting in shallower upper boundaries (shoaling) are expected to concentrate large pelagic fish further in surface waters potentially making them more vulnerable to surface fisheries. But how OMZ expansion, surface warming and fisheries may interact to impact oceanic fish populations in the future has never been quantified, which is particularly crucial for threatened pelagic sharks exposed to unregulated fishing exploitation in oceanic waters where OMZs occur. Here we show that electronic-tagged blue sharks interact horizontally and vertically with the eastern tropical Atlantic OMZ, remaining associated with the area for longer than expected, suggesting it may represent preferred foraging habitat. Maximum dive depths (MDD) of blue sharks entering the OMZ area shifted shallower compared to adjacent well-oxygenated habitats, and such MDD decrease was significantly associated with decreasing dissolved oxygen (DO) at depth and increasing sea surface temperature (SST). From this model relationship we predict further vertical habitat compression for blue shark of 30 – 50 m depth in the next 50 years, when we estimate sharks may encounter longline hook depths ~30% more often during dives than at present. Furthermore, analysis of satellite-tracked surface longline vessels shows fishing intensity is greater directly above OMZs compared to adjacent areas. We argue that this future environmental setting will lead to a ‘habitat trap’ for pelagic sharks with more rapid overfishing above OMZs as a consequence of expanding hypoxia driven by climate change, and in the absence of strict fishery catch controls.
Biography:
Rui Rosa graduated in Marine Biology by Faculty of Sciences, University of Lisbon (FCUL), in 1999 and completed a PhD degree in Biology by the same institution in 2005. Subsequently, Rosa carried out his post-doctoral activities on Climate Change research at Univ. Rhode Island (USA), funded by FCT and US National Science Foundation.
Rosa lab (http://www.ruirosalab.com) seeks to understand how future environmental changes, such as ocean deoxygenation (dead zones), warming and ocean acidification, affect marine biodiversity.
Rosa has authored 170 papers in international peer reviewed journals, many published in top-ranked journals such as Nature Geoscience, PNAS, Proc. Royal Soc. London, Global Ecology and Biogeography, Global Change Biology, and Biology Letters, among others, as well as highlighted in renowned media – e.g. BBC News (three times), Discovery Channel, National Geographic (two times), The New York Times, The Times – and in European Commission Alerts. He has also been engaged in internationally-renowned evaluation programs, including those of US National Science Foundation, NERC (UK), ANR (FR), National Geographic, and US MIT Sea-Grants.