Recovery potential and conservation options for elasmobranchs

Abstract

Many elasmobranchs have experienced strong population declines, which have been largely attributed to the direct and indirect effects of exploitation. Recently, however, live elasmobranchs are being increasingly valued for their role in marine ecosystems, dive tourism and intrinsic worth. Thus, management plans have been implemented to slow and ultimately reverse negative trends, including shark-specific (e.g. anti-finning laws) to ecosystem-based (e.g. no-take marine reserves) strategies. Yet it is unclear how successful these measures are, or will be, given the degree of depletion and slow recovery potential of most elasmobranchs. Here, current understanding of elasmobranch population recoveries is reviewed. The potential and realized extent of population increases, including rates of increase, timelines and drivers are evaluated. Across 40 increasing populations, only 25% were attributed to decreased anthropogenic mortality, while the majority was attributed to predation release. It is also shown that even low exploitation rates (2-6% per year) can halt or reverse positive population trends in six populations currently managed under recovery plans. Management measures that help restore elasmobranch populations include enforcement or near-zero fishing mortality, protection of critical habitats, monitoring and education. These measures are highlighted in a case study from the south-eastern U.S.A., where some evidence of recovery is seen in Pristis pectinata, Galeocerdo cuvier and Sphyrna lewini populations. It is concluded that recovery of elasmobranchs is certainly possible but requires time and a combination of strong and dedicated management actions to be successful.

Evidence for rapid recovery of shark populations within a coral reef marine protected area

“…This uncertainty is largely due to the ubiquitous nature of fishing in coral reef ecosystems worldwide (Newton et al 2007). These issues are pertinent to the establishment of management strategies such as marine protected areas (MPAs) (Bond et al 2012;White et al 2017) and shark sanctuaries (Ward-Paige et al 2012) that have been promoted as a means of ensuring the conservation and recovery of shark populations. They add to other unanswered questions about this approach to management and its efficacy (Davidson 2012), such as the optimal size and placement of MPAs, whether they are useful for all components of a shark fauna including wide-ranging apex predators (Ward-Paige et al 2012) and mesopredators (White et al 2017), and the level of enforcement that is required to have desired effects for shark populations (Ward-Paige 2017).…”

“…These issues are pertinent to the establishment of management strategies such as marine protected areas (MPAs) (Bond et al 2012;White et al 2017) and shark sanctuaries (Ward-Paige et al 2012) that have been promoted as a means of ensuring the conservation and recovery of shark populations. They add to other unanswered questions about this approach to management and its efficacy (Davidson 2012), such as the optimal size and placement of MPAs, whether they are useful for all components of a shark fauna including wide-ranging apex predators (Ward-Paige et al 2012) and mesopredators (White et al 2017), and the level of enforcement that is required to have desired effects for shark populations (Ward-Paige 2017). It is generally agreed that strict enforcement is paramount to the success of an MPA Dulvy 2006;Edgar et al 2014;Gill et al 2017), although even well-managed parks such as the Great Barrier Reef Marine Park have seen declines in common species of reef sharks due to illegal fishing in no-take zones ).…”

Shark recreational fisheries: Status, challenges, and research needs

“…Given the potential significance of recreational fishing practices for shark mortality or fitness, fundamental questions remain related to the effectiveness of different management actions related to recreational shark fisheries (indeed all sectors) (see Francis 1998;Ward-Paige et al 2012) as they do for many species that have been actively managed for even longer periods than sharks. To what extent do protected areas (and what type across the spectrum) serve as a relevant tool in shark management?…”

Landings Composition of the Northeast U.S. Skate, Rajidae, Wing Fishery and the Effectiveness of Prohibited Species Regulations

“…This is particularly challenging in elasmobranch fi sheries that often include species of similar appearance (Stone et al, 1998;Machado et al, 2004;Figueiredo et al, 2007;Stevenson and Lewis, 2010;Silva et al, 2012). Without accurate species composition information, it is difficult to assess the impacts of fi shing on each stock and determine if the exploitation rate is sustainable (Stevens et al, 2000;Figueiredo et al, 2007;Morgan et al, 2009;Ward-Paige et al, 2012). The majority of the skates landed for the wing fi shery are processed (wings removed, carcasses discarded) at sea, making species identifi cation even more diffi cult.…”