Tags: Threats,  Bycatch 

Bycatch

bycatchBrian.jpg

The term ‘bycatch’ is used for fish caught unintentionally in a fishery that is designated to catch other fish. Many fishing techniques and gear are not very selective and result in catching and discarding millions of tons of marine life that was not the target species, accounting for over 40% of the estimated total marine catch (Davies et al. 2009). Longline fishing, typically used to catch tuna, employs miles of fishing line with thousands of hooks that indiscriminately catches whatever comes along to eat the bait, including turtles, seabirds and sharks. In addition to longlines, gear such as bottom trawlers and gillnets also produce large numbers of shark bycatch (Bonfil 2000).

An estimated 50 million sharks are caught as bycatch in commercial fisheries each year.

Until recently, shark ‘bycatch’ was considered a nuisance and sharks were cut loose and disposed of overboard, sometimes still alive. However, as shark fins have become increasingly valuable, these fleets have little incentive to take measures to reduce shark bycatch. It is easier and more profitable to cut off the fins and discard the bodies at sea.

The term ‘bycatch’, in reference to sharks, may be a misnomer. Despite available means to decrease bycatch of sharks, the strong economic incentive to keep the fins reduces the likelihood of implementing these methods. Simple gear changes, such as switching from steel to nylon leaders, have demonstrated a reduction of shark bycatch while improving catch of ‘target’ species (Ward et al. 2007). New hook designs, weak or smart hooks, as well as new shark derrents and fishing methods could greatly reduce shark bycatch while also resulting in higher yields of target fish, saving time and money for the crews (Gilman et al. 2008).

New methods my reduce bycatch but some may still end up on a hook. The good news is greater than 95% of the species of shark most commonly caught as bycatch can be released if fishing crews can use safe and efficient release practices and for species such as the blue shark, the most commonly caught shark as bycatch, survival rates are high when released (Moyes et al. 2006). If it wasn’t for the valuable fins, these sharks would probably not be retained!

References

Bonfil, R. 2000.  The problem of incidental catches of sharks and rays, its likely consequences, and some possible solutions.  Shark Conference 2000, Honolulu, Hawaii, February 21-24.

 

Davies, R.W.D., Cripps, S.J., Nickson, A., and Porter, G. 2009. Defining and estimating global marine fisheries bycatch. Marine Policy, 33(4): 661-672.

 

Diop, M., and Dossa, J. 2011.  30 years of shark fishing in West Africa: development of fisheries, catch trends, and their conservation status in Sub-Regional Fishing Commission member countries.  CSRP/SRFC, 51 pp.

 

Dudley, S.F.J. and Cavanagh, R.D. 2006. Rhynchobatus djiddensis In: IUCN 2011.  IUCN Red List of Threatened Species Version 2011.2. www.iucnredlist.org. Downloaded on 03 February 2012.

 

Gilman, E., Clarke, S., Brothers, N., Alfaro-Shigueto, J., Mandelman, J., Mangel, J., Peterson, S., Piovano, S., Thomson, N., Dalzell, P., Donoso, M., Goren, M., Wener, T. 2008. Shark interactions in pelagic longline fisheries. Marine Policy, 32(1): 1-18.

 

Lack, M. and Meere, F. 2009. Pacific Islands Regional Plan of Action for Sharks: guidance for Pacific Island Countries and Territories on the conservation and management of sharks. Forum Fisheries Agency Secretariate fo the Pacific Community and Secretariat of the Pacific Regional Environment Programme.

 

Moyes, C. D., Fragoso, N., Musyl, M.K., and Brill, R.W. 2006. Predicting post-release survival in large pelagic fish. Transactions of the American Fisheries Society, 135: 1389-1397.

 

Pascoe, S., Okey, T.A. and Griffiths, S.  2008. Economic and ecosystem impacts of illegal, unregulated and unreported (IUU) fishing in Northern Australia.  The Australian Journal of Agriculture and Resource Economics, 52: 433-452.

 

Smith, B., 2011, “The Coming Green Wave: Ocean Farming to Fight Climate Change”, The Atlantic, Nov. 23, 2011, http://www.theatlantic.com/health/archive/2011/11/the-coming-green-wave-ocean-farming-to-fight-climate-change/248750/

 

Suzuki, T. 2002. Development of Shark Fisheries and Shark Fin Export in Indonesia: Case Study of Karansong Village, Indramayu, West Java.  Elasmobranch biodiversity, conservation and management: Proceedings of the International Seminar and Workshop, Sabah, Malaysia, July 1997.

 

Tull, M. 2009.  The History of Shark Fishing in Indonesia: A HMAP Asia Project Paper, Sept. 2009.  Associate Professor Malcolm Tull, Murdoch Business School and Asia Research Centre, Murdoch University.

 

Varkey, D.A., Ainsworth, C.H., Pitcher, T.J., Goram, Y., and Sumaila.  2010.  Illegal, unreported and unregulated fisheries catch in Raja Ampat Regency, Eastern Indonesia.  Marine Policy, 34: 228-236.

 

Ward, P., Lawrence, E., Darbyshire, R., Hindmarsh, S.  2007.  Large-scale experiment shows that banning wire leaders help pelagic sharks and longline fishers.  Western and Central Pacific Fisheries Commission, Scientific Committee Third Regular Session, Honolulu, 13-24 August.

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