Shark Declines: Fuel for a Decade of Conservation Effort
Scientists have been studying the population status of sharks for years and while the vulnerability, threatened status and biological importance of sharks has long-been well-recognized and documented by the research community (1), ten years ago, shark conservation was catapulted in the public spotlight after the highly publicized report, titled “Collapse and conservation of shark populations in the northwest Atlantic” by Baum and colleagues (2), in the journal Science. By using fisheries logbook data, this paper presented shocking and significant changes in abundance for many species of shark off the Northwest Atlantic over multiple decades.
While the data-analysis and magnitude of the declines reported within Baum et al. (2), and the subsequent Baum and Myers (3), have been challenged (4), the former article has been cited in the scientific literature a total of 685 times since its publication (Google Scholar, 17 Sept 2013). The paper was the beginning of a series of similar studies, to name just a few, showing patterns of shark declines in the Indian (5), Pacific (6, 7), Northwest Atlantic and Gulf of Mexico (8, 9) and Mediterranean ocean basins (10), while sharks have also been reported to be largely absent throughout the Caribbean (11). Moreover, recent work utilizing different data sources assessing changes in abundance has documented similar patterns of declines in the Gulf of Mexico (12), as well as shifting baselines of predator biodiversity in the Central Pacific (13). The declines in many shark populations over the past decades have also generated species-specific risk and threat analyses (i.e., ecological risk assessment, stock assessment, IUCN Red Listing (14, 15, 16).
Paralleling the pace in the research community has been the rise of the global shark conservation advocacy movement, a social phenomenon fueled by increased digital access to science and interactions via social media (17). Due to the magnitude and increased awareness of shark declines reported by various studies over the past decade as well as the media attention that has been generated from these publications, the take home message that has seemed to resonate with the public is that populations of shark species are drastically declining globally, despite not all shark populations being a cause for concern.
As the threats imposed on shark species continue to become better understood, technologies for studying shark behavior and conservation also continue to evolve rapidly. For example, there continues to be development of non-lethal methodologies for studying threatened shark species (18). Collaborations between national authorities, the public and scientific communities have also been creating shark-specific marine protected areas known as shark sanctuaries. In addition, there is a recent push towards utilizing sharks as a non-consumptive resource through diving ecotourism, a widespread and economically important industry that is now one of the strongest contemporary arguments for their protection (19). Over the next decade, shark conservation efforts will continue to shift its focus from largely describing shark declines to finding and implementing tangible solutions.
1) Stevens JD, Bonfil R, Dulvy NK, Walker PA. 2000. The effects of fishing on sharks, rays, and chimaeras (chondrichthyans), and the implications for marine ecosystems. ICES J Mar Sci 57:476–494.
2) Baum JK, Myers RA. 2004. Shifting baselines and the decline of pelagic sharks in the Gulf of Mexico. Eco Lett 7:135–145.
3) Baum JK, et al. 2003. Collapse and conservation of shark populations in the Northwest Atlantic. Science 299:389–392.
4) Burgess GH, et al. 2005. Is the collapse of shark populations in the Northwest Atlantic Ocean and Gulf of Mexico real? Fisheries 30:19–26.
5) Graham NAJ, Spalding MD, Sheppard CRC. 2010. Reef shark declines in remote atolls highlight the need for multi-faceted conservation action. Aquat Cons: Mar Fresh Ecosyst 20:543-548.
6) Robbins WD, Hisano M, Connolly SR, Choat JH. 2006. Ongoing collapse of coral-reef shark populations. Curr Biol 16:2314-2319.
7) Nadon MO, et al. 2012. Re‐creating missing population baselines for pacific reef sharks. Cons Biol 26:493-503.
8) Shepherd TD, Myers RA. 2005. Direct and indirect fishery effects on small coastal elasmobranchs in the northern Gulf of Mexico. Eco Lett 8:1095–1104
9) Myers R A, Baum JK, Shepherd TD, Powers SP, Peterson CH. 2007. Cascading effects of the loss of apex predatory sharks from a coastal ocean. Science 315:1846-50.
10) Ferretti F, Myers RA, Serena F, Lotze HK (2008) Loss of large predatory sharks from the Mediterranean Sea. Cons Biol 22:952–64
11) Ward-Paige CA, Mora C, Lotze HK, Pattengill-Semmens C, McClenachan L, et al. 2010. Large-scale absence of sharks on reefs in the greater-Caribbean: a footprint of humanpressures. PloS ONE 5:e11968.
12) Powers SP, et al. 2013. Gulf-wide decreases in the size of large coastal sharks documented by 10) Ferretti F, Myers RA, Serena F, Lotze HK (2008) Loss of large predatory sharks from the Mediterranean Sea. Cons Biol 22:952–64
13) Drew J, Phillip C, Westneat MW. 2013. Shark tooth weapons from the 19th century reflect shifting baselines in Central Pacific predator assemblies. PLoS ONE 8:e59855.
14) Dulvy N, et al. .2008. You can swim but you can’t hide: the global status and conservation of oceanic pelagic sharks and rays. Aquat Cons: Mar Fresh Ecosyst 482:459–482.
15) Cortés E., et al. 2010 Ecological risk assessment of pelagic sharks caught in Atlantic pelagic longline fisheries. Aquat Liv Res 23:25–34.
16) Gallagher AJ, Kyne PM, Hammerschlag N. 2012. Ecological risk assessment and its application to elasmobranch conservation and management. J Fish Biol 80:1727–1748.
17) Darling E, Shiffman D, Drew J, Cote I. 2013. The role of twitter in the life cycle of a scientific publication. Ideas Eco Evo 6:32-43.
18) Hammerschlag N, Sulikowski J. 2011. Killing for conservation: the need for alternatives to lethal sampling of apex predatory sharks. Endang Spec Res 14:135-140.
19) Gallagher AJ, Hammerschlag N. 2011. Global shark currency: The distribution, frequency, and socio-economics of shark ecotourism. Curr Issues Tour 14:797-812.