NOAA Fisheries West Coast. The Mako Shark is one of the species most commonly found in commercial fisheries’ bycatch.
The shark finning industry has become so lucrative that fishing vessels incidentally catching sharks end up retaining their fins in numbers nearly equivalent to the targeted fish species (Camhi, 1999; Pawson and Vince, 1999). Two mechanisms expose sharks to overfishing, one of which is through direct exploitation, where sharks are intentionally hunted and captured for the Asian delicacy shark fin soup. The other and more dangerous mechanism exposing sharks to overfishing is bycatch.
Bycatch, the unwanted marine life caught during commercial fishing for a specific species, is becoming one of the leading factors contributing to the extinction risk of open-ocean shark species. It is an often dominant source of shark mortality across various fisheries and is considered by ecologists to be a critical factor that could impair shark conservation efforts (Worm et al., 2013, Oliver et al., 2015). However, very few people are even aware of the word bycatch, this lack of awareness may doom sharks in the long term.
Bycatch is a frequently listed threat for sharks by the IUCN (IUCN, 2013). However, it is a heavily under-researched topic. Meanwhile, much progress has been made to identify practical, commercially viable, and even efficient methods to significantly reduce seabird and sea turtle bycatch in longline fisheries (Gilman et al., 2007; Watson & Kerstetter, 2006).
For example, in the western Pacific, shark species comprise 27% of total bycatch and, in subtropical fisheries, 18% (Bailey et al., 1996; Heberer and McCoy, 1997). Between 1992 and 2003, sharks constituted 25% of the total catch in the US Atlantic longline swordfish and tuna fisheries (Abercombie et al., 2005). It is well documented that high-seas longline vessels targeting tuna frequently catch the endangered great white shark (Bailey et al. 1996; Camhi et al. 1998).
Shark bycatch is increasing in occurrence as commercial fishing techniques evolve (Camhi et al., 2008). Gill nets—long nets set at the surface or bottom of the ocean—are common off the coast of Mozambique, which is dangerous for the vulnerable whale sharks that frequently inhabit the area (Rohner et al., 2018). Trawling has occurred in the Mediterranean sea for over a century and has since wiped out 16 shark species in the Tyrrhenian and Adriatic seas (Ferretti et al., 2010). Pelagic sharks are threatened by bycatch in every ocean they frequent.
Robert Engberg. An unlucky Mako Shark caught by Tuna fishers.
The demand for shark fins, which do not require much refrigeration space and take up minimal storage, has increased, particularly in Asia (Bonfil 1994). Shark fin demand remains high today, as growing upperclassmen in Asian countries appreciate shark fin soup as a status symbol. Therefore, fishers have a higher incentive not to discard bycaught sharks.
Sharks are unable to sustain high levels of harvesting (Baum et al. 2003, Baum and Myers 2004, Beerkircher et al. 2002). There is already a notion that commercial shark fisheries and Illegal, Unreported, and Unregulated (IUU) fishing overfish shark populations. The added threat of shark bycatch exacerbates the danger for sharks as it is under-researched.
Bycatch may be a more significant threat than targeted exploitation because it escapes the regulation of catch limits, unsustainably depletes shark populations in critical habitats, and it is thoroughly underresearched. North America conducts the most shark bycatch research (~40%), while glaringly less research is conducted in regions where shark bycatch is particularly common, the Indopacific (Molina & Cooke, 2012).
Research needs in the field of shark bycatch, per Molina and Cooke., include a need for studies that combine approaches, studies that focus on shark repellents, studies that explore the handling component of bycatch, studies that examine the fate of discarded sharks, and research that covers fisheries, and species in more regions.
References
Abercrombie DL, Balchowsky HA, Paine AL (2005) 2002 and 2003 annual summary: large pelagic species. NOAA Technical Memorandum, NMFS SEFSC-529, 33 pp
Bailey, K., Williams, P.G. and Itano, D. 1996. By-catch and discards in Western Pacific tuna fisheries: A review of SPC data holdings and literature. Technical Report 34. Oceanic Fisheries
Baum JK, Myers RA, Kehler DG, Worm B, Harley SJ, Doherty PA. 2003. Collapse and conservation of shark populations in the northwest Atlantic. Science 299: 389–392.
Beerkircher LR, Cortes E, Shivji M. (2002). Characteristics of shark bycatch observed on pelagic longlines off the southeastern United States, 1992–2000. Marine Fish Review 64: 40–49.
Bonfil, R. (1994) Overview of World Elasmobranch Fisheries. FAO Fisheries Technical Paper No. 341.
Camhi, M. (1999) Sharks on the Line II: An Analysis of Pacific State Shark Fisheries. Living Oceans Program, National Audubon Society, Islip, NY, 116 pp
Camhi, M. et al. (2008) Sharks of the open ocean: biology, fisheries, and conservation. Blackwell Science.
Gilman EL (2011) Bycatch governance and best practice mitigation technology in global tuna fisheries.
Ferretti, F., Worm, B., Britten, G. L., M.R., H., & Lotze, H. K. (2010). Global Consequences of Shark Declines.
IUCN (2013) Bycatch a problem for the sharks and rays in the Mediterranean and Black sea. Retrieved from https://www.iucn.org/content/bycatch-problem-sharks-and-rays-mediterranean-and-black- sea
Oliver S., Braccini M., Newman S.J., Harvey E.J. (2015) Global patterns in the bycatch of sharks and rays, Mar. Policy 54 86–97.
Pawson, M. and Vince, M. (1999) Management of shark fisheries in the Northeast Atlantic. In: Case Studies of the Management of Elasmobranch Fisheries (ed. R. Shotton). FAO Fisheries
Molina, J. M., & Cooke, S. J. (2012). Trends in shark bycatch research: Current status and research needs. Reviews in Fish Biology and Fisheries,22(3), 719-737. doi:10.1007/s11160-012-9269-3
Rohner, C. A. et al. (2018) ‘Satellite tagging highlights the importance of productive Mozambican coastal waters to the ecology and conservation of whale sharks’, PeerJ. PeerJ Inc., 6, p. e4161. doi: 10.7717/peerj.4161.
Watson JW, Kerstetter DW. 2006. Pelagic longline fishing gear: a brief history and review of research efforts to improve selectivity. Marine Technology Society Journal 40: 6–11.
Worm, B. et al. (2013) Global catches, exploitation rates, and rebuilding options for sharks, Mar. Policy