Reef‐wide evidence that the presence of sharks modifies behaviors of teleost mesopredators

Abstract

The idea that the presence of sharks impacts the behavior of mesopredatory reef fishes is controversial and lacks clear evidence at reef‐wide scales. We compared the abundance and behavior of these reef fishes in response to the presence of reef sharks using Baited Remote Underwater Video System (BRUVS) deployments in two adjacent reef systems where sharks have either been exclusively targeted by fishing or protected by a no‐take marine reserve. For a subset of videos, we also compared the behavior of mesopredatory reef fishes immediately before and after the appearance of sharks in the video. On reefs where sharks were more abundant, mesopredatory fishes spent less time swimming in midwater (i.e., away from shelter) and guarding bait compared to reefs where sharks have been selectively removed. The same responses occurred after the appearance of sharks in the video. Reactions to sharks varied both in strength and type among species of mesopredator and were mediated by the availability of shelter on the reef and, for one species, by the levels of activity of the reef sharks. In contrast, we did not find that the presence of sharks influenced the abundance of mesopredators at either reef system across hour‐long videos or immediately before and after a shark appeared in the video. Collectively, our findings show that the presence of sharks reduces the propensity of mesopredatory fish to engage in potentially risk‐prone behaviors over large spatial scales and that these interactions are mediated by the behavioral characteristics of both predators and prey, and the environment in which they co‐occur. Our results are consistent with the idea that sharks as predators or larger competitors initiate changes in the behavior of mesopredatory reef fishes likely to affect trophic structuring within coral reef ecosystems.

Relative influence of predators, competitors and seascape heterogeneity on behaviour and abundance of coral reef mesopredators

“…Instead, our results support the recent evidence that metrics such as MaxN are not subtle enough to detect behavioural dynamics that occur over short time scales (i.e. seconds -minutes) (Coghlan et al 2017, Speed et al 2019, Lester et al 2021a). As a result, such metrics may be robust to any effect of the presence of both apex and reef sharks on the abundance of smaller fishes over long (i.e.…”

“…Because sharks are highly mobile (Vianna et al 2013, Ferreira et al 2015, responses by mesopredators may only occur when larger predators/competitors appear in close proximity to the bait bag and when they are recognised as an immediate threat. Recent work by Lester et al (2021a) shows that this is likely to be the case -mesopredators showed significant antithreat behaviours on stereo-BRUV deployments immediately following the appearance of sharks. This analysis found that the response to predators was both species and context-specific, depending on the behaviour of both the mesopredator and the shark, and the amount of shelter offered by the reef Figure 3.…”

“…However, marine systems such as coral reefs are characterised by diverse and abundant communities of predatory fishes ranging in size from larger apex sharks and reef sharks to guilds of smaller mesopredatory species, notably serranids, lethrinids, lutjanids and some labrids. Earlier studies and reviews of behavioural interactions between sharks and mesopredators in these environments have largely focused on the role of reef sharks as predators of mesopredatory fishes (Rizzari et al 2014, Desbiens et al 2021, Lester et al 2021a), but have yet to assess the behavioural interactions between apex sharks, such as tiger sharks Galeocerdo cuvier or great hammerhead sharks Sphyrna mokarran, and teleost fishes. This is largely because these apex species have been removed from many coral reef ecosystems usually via fishing (Dulvy et al 2014, Roff et al 2018.…”

“…Recent studies have used BRUVs to examine the tradeoff between the opportunity to forage presented by a BRUV and the need to exercise vigilance behaviours in response to the presence of a predatory fish. In areas with an increased predator encounter rate, fishes exercise more vigilance and are less likely to approach and feed from a BRUV (Bond et al 2019, Phenix et al 2019, Shea et al 2020, Sherman et al 2020, Lester et al 2021a. There is scope to expand this framework and develop a suite of standardized behavioural metrics that can be applied across multiple studies.…”

Drivers of fine‐scale diurnal space use by a coral‐reef mesopredatory fish

“…Nonetheless, it is possible that C. cruentata on reefs with higher predation risk have larger diurnal home ranges to provide a range of refuges or maximize foraging opportunities outside of crepuscular periods when threats from transient predators are greater (Papastamatiou et al ., 2015). Because home ranges are established and develop over the lifespan of a fish, this result may provide further evidence of chronic responses of fishes to predation risk in addition to the more instantaneous acute responses to immediate risk (Lester et al ., 2021; Madin et al ., 2010).…”