Shark Fisheries & Conservation

Sharks in the Eastern Tropical Pacific Corridor

Having persisted for at least 400 million years, sharks are part of one of the oldest extant vertebrate groups (elasmobranchs) on the planet. However, increased fishing pressure coupled with relatively slow growth and low fecundity has resulted in the progressive depletion of populations worldwide. The removal of a top predator, such as sharks, from any ecosystem may have profound environmental consequences, triggering cascade effects that can result in ecosystem collapse (Baum & Worm 2009; Estes et al. 2011; Ferretti et al. 2010; Heithaus et al. 2012; Myers et al. 2007). Recent estimates indicate a 50 to more than 90% decline in shark stocks depending on species and area (Camhi et al. 2009; Worm et al. 2013), this rapid depletion has propelled sharks to the top of worldwide conservation concerns. In 2004, the Eastern Tropical Marine Pacific Corridor (ETPC) was established.

The main objective of this agreement is the conservation and sustainable development of a 211 million hectare oceanic region from Costa Rica to Ecuador, including five marine protected areas (MPA’s): Galapagos Islands and Marine Reserve (Ecuador), Cocos Island (Costa Rica), Coiba National Park (Panama), Malpelo Fauna and Flora Sanctuary (Colombia) and Gorgona (Colombia). As top predators, sharks are an essential part of the ETPC ecosystem, but their populations have been steadily declining due to increases in commercial fishing (Arauz et al. 2004; Buckley & Hile 2007; Ramirez & Medina 1999; Teplitzky 2005; Watts & Wu 2005). Despite the rising concern regarding population sustainability and conservation of many of the commercially important shark species inhabiting the area, population structure and behavioral and reproductive properties remain unclear for most species. While effective conservation and management strategies for sharks require a fundamental understanding of their population structure and life history strategies such as reproductive behavior (Ahonen et al. 2009; Laikre et al. 2005; McCook et al. 2009; Palsbøll et al. 2006). The ETPC provides a framework within which to address the need for regional research and cooperation in the management of shark stocks. Rebuilding depleted shark stocks is possible, and can occur where a number of conservation management instruments are combined to reduce mortality to an appropriately low level (Ward-Paige et al. 2012).

The Scalloped Hammerhead Shark – Sphyrna lewini
Sphyrna lewini is a viviparous shark with a circumtropical distribution along continental margins and around mid-oceanic islands (Compagno et al. 2005). But animals are tied to coastal areas for reproduction and utilize near shore nurseries throughout their range. Age of first reproduction is ±15 years (Castro 1993; Clarke 1971; Compagno 1984; Duncan & Holland 2006). Movements are limited by deep ocean expanses and females show fidelity to parturition areas (Chapman et al. 2009; Duncan et al. 2006). The schooling nature of S. lewini makes it vulnerable to fisheries because they concentrate in often predictable locations and are thus easily caught in large numbers (Abercrombie 2005).

In addition to the ‘Globally endangered’ and ‘Endangered (A4bd) in the Eastern Central and Southeast Pacific’ assessments (http://www.iucnredlist.org), in March 2013 S. lewini was included in CITES Appendix 2 (www.cites.org). The appendix lists species, which may become threatened with extinction unless trade is closely controlled. In addition to the high demand for its fins (Abercrombie et al. 2005; Chapman et al. 2009; Watts & Wu 2005), shark, including S. lewini, has become a typical consumption fish in the ETPC countries (Teplitzky 2005; Watts & Wu 2005). It has recently been shown that, by diminishing population size, chronic overfishing may have fragmented its range into smaller locally isolated populations and has likely resulted in fewer migrants and lower ecological connectivity throughout its Eastern Pacific range (Nance et al. 2011). Preliminary data suggests that S. lewini used to be far more abundant throughout the ETPC and has recently formed into a series of separate and potentially very small populations.

We intend to provide critical baseline information to inform and improve the development of conservation measures and facilitate targeted conservation, management and sustainable use of S. lewini in the ETPC. The key issue is the identification and prioritization of local population conservation units (CU’s). Identifying CU’s is an essential first step in conservation in order to know the boundaries of the populations that need to be conserved (Funk et al. 2012). And moreover, to identify critical habitat, such as nursery areas and migration pathways linked to important ecological processes such as mating, pupping and foraging.

If you would like more information on this study please contact Judith Bakker.


References

Abercrombie, D.L., Clarke, S.C., Shivji, M.S. (2005) Global-scale genetic identification of hammerhead sharks: Application to assessment of the international fin trade and law enforcement. Conservation Genetics 6: 3
Ahonen, H., Harcourt, R.G., Stow, A.J. (2009) Nuclear and mitochondrial DNA reveals isolation of imperiled grey nurse shark populations (Carcharhinus taurus). Molecular Ecology 18: 4409-4421
Arauz, R.M., Cohen, Y., Ballestero, J., Bolaños, A., Pérez, M. (2004) Decline of shark populations in the Exclusive Economic Zone of Costa Rica.
Proceedings of the International Symposium on Quantitative Ecosystem Indicators for Fisheries Management. Paris, France
Baum, J.K., Worm, B. (2009) Cascading top-down effects of changing oceanic predator abundances. Journal of Animal Ecology 78: 699-714
Buckley, L., Hile, J. (2007) The end of the line? Global threats to sharks (second edition) WildAid
Camhi, M.D., Valenti, S.V., Fordham, S.V., Fowler, S.L., Gibson, C. (2009) The conservation status of pelagic sharks and rays. Report of the IUCN Shark Specialist Group. Pelagic Shark Red List Workshop, IUCN Species Survival Commission Shark Specialist Group. Newbury, UK. 78 pp
Castro, J. I. (1993) The shark nursery of Bulls Bay, South Carolina, with a review of the shark nurseries of the southeastern coast of the United States. Environmental Biology of Fishes 38: 37–48
Chapman, D.D., Pinhal, D., Shivji, M.S. (2009) Tracking the fin trade: genetic stock identification in western Atlantic scalloped hammerhead sharks Sphyrna lewini. Endangered Species Research 9: 221–228
Clarke ,T. A. (1971) The ecology of the scalloped hammerhead shark, Sphyrna lewini, in Hawaii. Pac. Sci. 25: 133-144
Compagno, L. J. V. (1984) FAO Species Catalogue. Vol. 4. Parts 1 & 2, Sharks of the world. FAO Fisheries Synopsis, p. 125.
Compagno, L. J. V., Dando, M, Fowler, S. (2005) Sharks of the world, Princeton field Guides. Princeton University Press.
Duncan, K.M., Holland, K.N. (2006) Habitat use, growth rates and dispersal patterns of juvenile scalloped hammerhead sharks (Sphyrna lewini) in a nursery habitat. Marine Ecology Progress Series 312: 211-221
Duncan, K.M., Martin, A.P., Bowen, B.W., De Couet, H.G. (2006) Global phylogeography of the scalloped hammerhead shark (Sphyrna lewini). Molecular Ecology 15: 2239-2251
Estes, J.A., Terborgh, J., Brashares, J.S., Power, M.E., Berger, J., Bond, W.J. et al. (2011) Trophic downgrading of planet Earth. Science 333: 301-306
Ferretti, F., Worm, B., Britten, G., Heithaus, M.R., Lotze, H.K. (2010) Patterns and ecosystem consequences of shark declines in the ocean. Ecol. Lett. 13: 1055-1071
Funk, W.C., McKay, J.K., Hohenlohe, P.A., Allendorf, F.W. (2012) Harnessing genomics for delineating
conservation units. Trends in Ecology & Evolution 27: 498-496
Heithaus, M.R., Wirsing, A.J., Dill, L.M. (2012) The ecological importance of intact top predator populations: a synthesis of fifteen years of research in a seagrass ecosystem. Mar. Freshwater Res. 63: 1039-1050
Laikre, L., Palm, S., Ryman, N. (2005) Genetic population structure of fishes: implications for coastal zone management. Ambio 34: 111–119
McCook, L.J., Almany, G.R., Berumen, M.L., Day, J.C., Green, A.L., Jones, G.P., Leis, J.M., Planes, S., Russ, G.R., Sale, P.F., Thorrold, S.R. (2009) Management under uncertainty: guide-lines for incorporating connectivity into the protection of coral reefs. Coral Reefs 28: 353-366
Myers, R.A., Baum, J.K., Shepherd, T., Powers, S.P., Peterson, C.H. (2007) Cascading effects of the loss of apex predatory sharks from a coastal ocean. Science 315: 1846-1850
Nance, H.A., Klimley, P., Galván-Magaña, F., Martínez-Ortíz, J., Marko, P.B. (2011) Demographic processes underlying subtle patterns of population structure in the scalloped hammerhead shark, Sphyrna lewini. PLoS ONE 6 (7): e21459. doi:10.1371/journal.pone.0021459
Palsbøll, P.J., Bérubé, M., Allendorf, F.W. (2006) Identification of management units using population genetic data. Trends in Ecology and Evolution 22: 11-16
Ramírez, R., Medina, E. (1999) Diagnóstico pesquero del recurso tiburón en Panamá. Informe Téchnico, Autoridad Marítima de Panamá. Dirección General de Recursos Marinos y Costeros
Teplitzky, K. (2005) Fishing for a management strategy: The threat to Panamanian Pacific shark populations. Temple University, School for International Training Panamá: Conservation and Development
Ward-Paige, C.A., Keith, D.M., Worm, B., Lotze, H.K. (2012) Recovery potential and conservation options for elasmobranchs. Journal of Fish Biology 80: 1844-1869
Watts, S., Wu, V. (2005) At rock bottom: The declining sharks of the Eastern Tropical Pacific. WildAid report
Worm, B., Davis, B., Kettemer, L., Ward-Paige, C.A., Chapman, D., Heithaus, M.R., Kessel, S.T., Gruber, S.H. (2013) Global catches, exploitation rates and rebuilding options for sharks. Marine Policy 40: 194-204