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.
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