Anthropogenic pressures on reef-associated sharks in jurisdictions with and without directed shark fishing

Abstract

Shark populations have declined across the Caribbean region, with negative associations between shark abundance and human population density, open access to fishing, and proximity to large markets (‘market gravity’). This decline is frequently attributed to fishing mortality, which increases in areas closer to humans and outside marine reserves. Although it is difficult to disentangle the effects of fishing mortality from other anthropogenic pressures on sharks, comparing shark abundance and diversity in jurisdictions with near zero fishing mortality versus prevalent shark fishing can demonstrate the role of overfishing. We used baited remote underwater video systems to compare shark abundance and diversity on coral reefs in 2 Caribbean nations with contrasting levels of shark exploitation: Belize (shark fishing) and The Bahamas (shark sanctuary). The abundance of targeted shark species and diversity were significantly higher in The Bahamas than in Belize. Caribbean reef and nurse shark abundance in Belize were best predicted by fishing-related factors (marine reserves, market gravity, their interaction). In The Bahamas, abiotic factors (depth, sea surface temperature) best predicted nurse shark abundance, while depth, market gravity, and its interaction with marine reserves predicted Caribbean reef shark abundance. These results indicate that fishing mortality reduces shark abundance and diversity in Belize, while lower fishing mortality in The Bahamas has greatly reduced but not eliminated human impacts on sharks. Future work should elucidate the indirect effects of humans to develop holistic shark conservation plans. We suggest minimizing shark fishing through multinational management plans to improve shark abundance and diversity, especially on reefs near densely populated areas.

Nation-wide assessment of the distribution and population size of the data-deficient nurse shark (Ginglymostoma cirratum)

“…Large and old MPAs stood out as having a fairly higher nurse shark abundance than all other MPA categories, and similar or higher abundance than non-protected sites. These results are in apparent concordance with the findings of Bond and colleagues [ 52 ], who found Caribbean reef sharks ( Carcharhinus perezi ) to be more abundant in protected areas, and of Clementi [ 48 ], who also recorded a significantly higher CPUE of nurse sharks within protected areas than at fished sites in Belize. Bothe these studies focused on fairly large and old MPAs, and in concomitance with study further demonstrate the importance of area and time of enforcement for the positive effects of spatial protection to emerge [ 34 , 35 ].…”

“…It is thus likely that the higher ER at LRA is a better indicator of local relative abundance than MaxN. MaxN at sites along the barrier reef of Belize was also found to be intermediate between LRA and GLO in a study by Clementi and colleagues [48], although the areas surveyed by the study differed from those explored here.…”

“…The abundance of nurse sharks at GLO had previously been highlighted by a fisheries-independent survey, which found nurse sharks to constitute 68% of the elasmobranch catches made from longlines here [ 18 ]. Another study also reported GLO as the area of highest relative abundance (measured as number of sharks per hour from BRUV deployments) in Belize [ 48 ]. GLO is an internationally recognised key area for marine conservation (Designated as a UNESCO world heritage site in 1996), hosting some of the reefs of highest diversity in the Caribbean [ 49 , 50 ].…”

“…longlines here [18]. Another study also reported GLO as the area of highest relative abundance (measured as number of sharks per hour from BRUV deployments) in Belize [48]. GLO is an internationally recognised key area for marine conservation (Designated as a UNESCO world heritage site in 1996), hosting some of the reefs of highest diversity in the Caribbean [49,50].…”

Movements and residency of Caribbean reef sharks at a remote atoll in Belize, Central America

“…Reef-associated sharks have faced sharp declines in recent decades, especially in the Caribbean, with abundance negatively correlated to anthropogenic factors [ 1 – 4 ]. Recent analysis has found that abundance and species diversity of reef sharks was significantly lower in Belize, where shark fishing occurs, than in The Bahamas, where sharks are fully protected [ 5 ]. Despite the economic importance of reef shark species to several tourism-based economies [ 6 – 8 ] and fisheries [ 9 – 11 ], many species remain understudied in tropical seas, especially in low- and middle-income countries.…”