Varying reef shark abundance trends inside a marine reserve: evidence of a Caribbean reef shark decline

Abstract

Spatial comparisons of reef shark abundance inside and outside marine protected areas (MPAs) are common and generally report positive MPA effects, yet few studies have tracked abundance trends over long time periods. This is problematic because inside:outside comparisons at a single point in time cannot evaluate whether populations are declining. In Belize, the Caribbean reef shark Carcharhinus perezi is one of the most fished shark species and is more abundant inside MPAs. Although the relative abundance of C. perezi was stable inside Glover’s Reef Marine Reserve (GRMR) from 2001 to 2013, using standard baited remote underwater video station surveys, we document a decline in relative abundance inside the no-take marine reserve from 2009 to 2019. We used a negative binomial generalized linear model and model averaging to test the effect of year, depth, and water temperature on C. perezi and nurse shark Ginglymostoma cirratum relative abundance. While model-averaged results indicated a C. perezi decline, G. cirratum remained stable from 2009 to 2019. We hypothesize that the C. perezi decline is a result of fishing along the edge of GRMR, while G. cirratum stability is related to their behavior and nationwide protection. Given the dynamic nature of fisheries regulations, economic pressures, and site-specific environmental conditions, our results emphasize the need for standardized long-term monitoring of reef sharks inside and around MPAs globally.

Assessing the effects of coral reef habitat and marine protected areas on threatened megafauna using aerial surveys

“…Indeed, shark and ray catches are historically low in all New Caledonian waters (Juhel et al, 2017) while commercial and recreational fishing in coral lagoons are limited to finfish and invertebrates (Léopold et al, 2014). So, the positive statistical effect reported here cannot be due to the release of fishing pressure on elasmobranchs, as observed in no-take MPAs within heavily fished regions (Osgood, McCord & Baum, 2019; Espinoza et al, 2020;Jabado et al, 2021;Flowers et al, 2022). A more plausible explanation is that the ban on fishing inside the Poé MPA may have led to locally enhanced availability of prey for sharks and Myliobatidae (i.e.…”

“…Both techniques are invasive and provide information on a limited number of tagged individuals. Visual underwater censuses from scuba divers and baited remote underwater videos systems are commonly employed to count sharks and rays (and more rarely, sea turtles) inside and around MPAs (Jaiteh et al, 2016; MacNeil et al, 2020; Jabado et al, 2021; Flowers et al, 2022). However, some individuals or species remain unseen owing to natural rarity or elusiveness (Juhel et al, 2017; Boussarie et al, 2018).…”

“…While many studies have investigated the effect of MPAs on the abundance of megafauna species (Bond et al, 2012; Espinoza et al, 2014; Dwyer et al, 2020; Jabado et al, 2021; Flowers et al, 2022), few have simultaneously accounted for the effect of habitat, i.e. how the spatial heterogeneity of habitat influences species abundance (Osgood, McCord & Baum, 2019; Albano et al, 2021).…”

Two thirds of species in a global shark fin trade hub are threatened with extinction: Conservation potential of international trade regulations for coastal sharks

“…National prohibition on targeted catch and trade of certain threatened species or all sharks (i.e., “shark sanctuaries”) are unlikely to work by themselves in nations where longlines, gillnets, and trawls are widely used to fish for other taxon, as it will likely result in dead discard or illegal retention rather than substantially reduced mortality. Mortality reduction can be achieved in several ways, including gear modifications, to reduce shark catch (e.g., Senko et al., 2022) or targeted spatial or time‐area closure for longline, gillnets, and trawls in specific areas, where threatened shark species are caught (e.g., Flowers et al., 2022). Although applying stock assessment‐based catch limits may be challenging in some low‐capacity nations, recent advances and expanding efforts in documenting catch (Jaiteh et al., 2016; Quinlan et al., 2021), conducting data limited stock assessments (Cortés & Brooks, 2018), and implementing scalable shark abundance surveys (MacNeil et al., 2020) suggest that catch limits‐based management could be more tractable in low‐capacity nations than is popularly assumed.…”

Extinction risk, reconstructed catches and management of chondrichthyan fishes in the Western Central Atlantic Ocean

“…Notably, abundance is often highest in heavily managed Exclusive Economic Zones (EEZs; MacNeil et al, 2020), marine reserves (Bond et al, 2012; MacNeil et al, 2020), shark sanctuaries (Clementi et al, 2021) and remote areas far from human population centres (Ward‐Paige et al, 2010). There are, however, signs of recent stability and/or recovery in some better‐studied shark populations in the United States (Carlson et al, 2012; Peterson et al, 2017), The Bahamas (Hansell et al, 2018; Talwar et al, 2020) and Belize (Bond et al, 2017; Flowers et al, 2022), largely due to targeted management that began in the 1990s (Castro, 2013; Ward‐Paige, 2017). Otherwise, a lack of data has challenged the assessment of shark population trends.…”