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

Abstract

The recovery of communities of predatory fishes within a no‐take marine reserve after the eradication of illegal fishing provides an opportunity to examine the role of sharks and other large‐bodied mesopredatory fishes in structuring reef fish communities. We used baited remote underwater video stations to investigate whether an increase in sharks was associated with a change in structure of the mesopredatory fish community at Ashmore Reef, Western Australia. We found an almost fourfold increase in shark abundance in reef habitat from 0.64 hr−1 ± 0.15 SE in 2004, when Ashmore Reef was being fished illegally, to 2.45 hr−1 ± 0.37 in 2016, after eight years of full‐time enforcement of the reserve. Shark recovery in reef habitat was accompanied by a two and a half‐fold decline in the abundance of small mesopredatory fishes (≤50 cm TL) (14.00 hr−1 ± 3.79 to 5.6 hr−1 ± 1.20) and a concomitant increase in large mesopredatory fishes (≥100 cm TL) from 1.82 hr−1 ± 0.48 to 4.27 hr−1 ± 0.93. In contrast, near‐reef habitats showed an increase in abundance of large mesopredatory fishes between years (2.00 hr−1 ± 0.65 to 4.56 hr−1 ± 1.11), although only smaller increases in sharks (0.67 hr−1 ± 0.25 to 1.22 hr−1 ± 0.34) and smaller mesopredatory fishes. Although the abundance of most mesopredatory groups increased with recovery from fishing, we suggest that the large decline of small mesopredatory fish in reef habitat was mostly due to higher predation pressure following the increase in sharks and large mesopredatory fishes. At the regional scale, the structure of fished communities at Ashmore Reef in 2004 resembled those of present day Scott Reefs, where fishing still continues today. In 2016, Ashmore fish communities resembled those of the Rowley Shoals, which have been protected from fishing for decades.

Monitoring elasmobranch assemblages in a data-poor country from the Eastern Tropical Pacific using baited remote underwater video stations

“…These findings further highlight the efficiency of using BRUVS to survey and monitor elasmobranch species at remote and isolated islands from the ETP, some of which are recognized as UNESCO World Heritage sites. www.nature.com/scientificreports/ Numerous studies have demonstrated that shark abundances are generally greater inside than outside not-take MPAs 19,22,54 , which is in agreement with our findings. However, BRUVS deployed at Caño and Murciélago islands had significantly less species and lower abundances compared to Cocos Island.…”

“…In contrast, BRUVS provide a relatively cost-effective survey method that enhances predator detection by using bait and overcomes fish avoidance issues with divers 25,49,50 . Moreover, permanent footage generated through BRUVS can be used to answer specific behavioral questions 51 or shared with other researchers to support regional and global conservation efforts such as the one lead by the Global FinPrint Project 22 .…”

“…BRUVS have been widely recognized as a suitable sampling method to answer key questions on elasmobranchs 19,22,51 ; however there are some biases associated that are important to recognize. For example, BRUVS are less effective in turbid waters with low visibility, they attract large predators, which may reduce detectability of smaller species, their bait plume dispersion is unknown, and thus our knowledge of the sampling area, and they tend to have a restricted field of view compared to observers in the water 14 .…”

A Time-Extended (24 h) Baited Remote Underwater Video (BRUV) for Monitoring Pelagic and Nocturnal Marine Species

“…The strong attractiveness of bait to sharks [9], has also made BRUVs efficient tools for assessing shark populations. For example, a recent worldwide project (see www.globalfinprint.com) [10] deployed thousands of BRUVs across the globe, and allowed drivers-such as heavy fishing pressure or illegal fishing-for diversities and densities of coastal sharks, to be identified [11,12].…”

The complete mitochondrial genome of a gray reef shark, Carcharhinus amblyrhynchos (Carcharhiniformes: Carcharhinidae), from the Western Indian Ocean

“…The gray reef shark, Carcharhinus amblyrhynchos (Carcharhinidae), has a broad tropical distribution ranging from the Western Indian to the Central Pacific Oceans. This large-bodied shark is commonly associated with coral reefs where it can constitute a major proportion of the high trophic-level predator biomass, and likely plays an important role in structuring reef communities (Friedlander et al 2014;Speed et al 2019). Stemming recent declines in reef shark species caused by overfishing requires urgent management and conservation measures, with concomitant information on the genetic dynamics of reef shark populations to guide these efforts (Heupel et al 2019).…”