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

Abstract

There is limited evidence on the rate at which the shark populations of coral reefs can rebound from over-exploitation, the baselines that might signify when recovery has occurred and the role of no-take Marine Protected Areas (MPA) in aiding this process. We surveyed shark assemblages at Ashmore Reef in Western Australia using baited remote underwater video Stations in 2004 prior to enforcement of MPA status and then again in 2016 after eight years of strict enforcement. We found an increase in the relative mean abundance of Carcharhinus amblyrhynchos from 0.16 ± 0.06 individuals/hr -1 in 2004 to 0.74 ± 0.11 individuals/hr -1 in 2016, a change that was also accompanied by a shift in the assemblage of sharks to greater proportions of apex species (from 7.1% to 11.9%) and reef sharks (from 28.6% to 57.6%), and a decrease in the proportional abundance of lower trophic level species (from 64.3% to 30.5%). Abundances and trophic assemblage of sharks at Ashmore Reef in 2004 resembled those of the Scott Reefs, where targeted fishing for sharks still occurs, whereas in 2016, abundances and trophic structures had recovered to resemble those of the Rowley Shoals, a reef system that has been a strictly enforced MPA for over 25 years. The shift in abundance and community structure coincident with strict enforcement of the MPA at Ashmore Reef has occurred at a rate greater than predicted by demographic models, implying the action of compensatory processes in recovery. Our study shows that shark communities can recover rapidly after exploitation in a well-managed no-take MPA.

Protection from illegal fishing and shark recovery restructures mesopredatory fish communities on a coral reef

“…As the composition and abundance of reef fish communities change with depth (e.g., Asher, Williams, & Harvey, ; Brokovich, Einbinder, Shashar, Kiflawi, & Kark, ; Fitzpatrick et al, ), we restricted our analyses to deployments on shallow reef habitats within a depth range of 10–30 m, although some shallower (<10 m) and deeper (>30 m) deployments were originally completed as part of a parallel study on elasmobranchs (Speed et al, ). Cross‐habitat comparisons of reef predator communities in 2004 and 2016 at Ashmore Reef included both reef habitat (hard and soft corals) and near‐reef habitat (sand, rubble, and consolidated limestone pavement) (Figure ).…”

“…The “large” size class of mesopredatory fishes (>100 cm TL) may occupy a size refuge from predators (at least at adult sizes) and will likely compete with sharks for prey (Roff et al, ). Despite the occurrence of apex species at Ashmore Reef (Speed et al, ), these typically occurred in off‐reef (>1.5 km from reef edge) locations in deep water (>30 m). The focal group of sharks for our current study were considered to be reef residents (Heupel, Papastamatiou, Espinoza, Green, & Simpfendorfer, ) and were species that are site attached and can be found on reefs all year round.…”

“…Habitats were initially classified from a still reference image taken from the beginning of each BRUVS deployment video, as per Speed et al (2018). Visual estimates of coral cover (0%-100% rounded to the nearest 5%), complexity (low, medium, and high), and habitat type (sand, reef, or other) were estimated by eye, similar to other studies, (Espinoza et al, 2014;Malcolm, Jordan, & Smith, 2011;Speed et al, 2018;Tickler, Letessier, Koldewey, & Meeuwig, 2017) and replicated three times by independent recorders. Coral cover was then averaged across the three estimates to create an average percentage cover for each image.…”

“…As the composition and abundance of reef fish communities change with depth (e.g., Asher, Williams, & Harvey, 2017;Brokovich, Einbinder, Shashar, Kiflawi, & Kark, 2008;Fitzpatrick et al, 2012), we restricted our analyses to deployments on shallow reef habitats within a depth range of 10-30 m, although some shallower (<10 m) and deeper (>30 m) deployments were originally completed as part of a parallel study on elasmobranchs (Speed et al, 2018). Cross-habi- (Bray & Gomon, 2018) and FishBase www.fishb ase.org (Froese & Pauly, 2011), where regional TL estimates were unavailable (~22% of species).…”

“…Such studies avoid many of the confounding effects that may be introduced by comparisons across space, where reefs can vary in oceanographic setting, histories of exploitation, habitat structure, and biogeography (Casey et al, 2017;Valdivia, Cox, & Bruno, 2017). Although many populations of reef sharks are declining (e.g., Graham, Spalding, & Sheppard, 2010;Robbins, Hisano, Connolly, & Choat, 2006;Ward-Paige, Mora, et al, 2010), in a few circumstances, changes in management strategies or better enforcement of existing regulations have allowed numbers of reef sharks to recover (e.g., Espinoza, Cappo, Heupel, Tobin, & Simpfendorfer, 2014;Speed, Cappo, & Meekan, 2018). These offer a unique opportunity to gain insights into the importance of sharks in reef environments and a means to test predictions generated by spatial comparisons through comparisons of the structure of fish communities prior to and after recovery of shark populations.…”