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Ecological redundancy between coral reef sharks and predatory teleosts

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Abstract

Reef sharks may be ecologically redundant, such that other mesopredatory fishes compensate for their functions when they decline in number, preventing trophic cascades. Oral jaw gape, hereafter referred to as gape, determines maximum prey size in many piscivores and therefore affects the size structure of prey assemblages. Here, we examine whether gape and maximum prey size differ between five species of reef shark and 21 species of teleost (n = 754) using data collected from 38 reefs in the Indo-Pacific. Sharks displayed relatively small gape dimensions compared to most teleost species and, at smaller sizes, the giant trevally Caranx ignobilis and other teleosts may be able to consume larger prey than similar-sized sharks. However, ecological redundancy between reef sharks and teleosts appears to decline at larger sizes, such that the grey reef shark Carcharhinus amblyrhynchos, for example, may be capable of consuming larger prey than any other reef predator at its largest sizes, regardless of prey body shape. Moreover, sharks may be able to consume proportionally larger prey as they grow, in contrast to reef teleosts, which may largely be limited by their gapes to ever-smaller prey as a proportion of their body size. Our results also suggest that reef sharks may be unable to swallow whole prey that are > 36% of their length, consistent with gut-content studies. Conservation of reef ecological function may therefore depend not only on the protection of sharks but also particular size classes and key components of the mesopredatory guild.

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Funding

This research was supported by the donation of ship time on the M/Y Pangaea by Outpost Expedition Pacific Ltd (OEP), and funded through a gift from Teach Green to The University of Western Australia (UWA) to support conservation-related marine research in the Indo-Pacific Ocean under the Pangaea Initiative. TDC is the recipient of an Australian Research Council Future Fellowship (Project Number FT180100154) funded by the Australian Government.

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SB conceived the ideas and designed methodology; SB collected the data; JJM obtained the funding; SB, JJM and TDC analysed the data; SB led the writing of the manuscript with JJM and TDC contributing critically to the drafts and final manuscript.

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Correspondence to Shanta C. Barley.

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Barley, S.C., Clark, T.D. & Meeuwig, J.J. Ecological redundancy between coral reef sharks and predatory teleosts. Rev Fish Biol Fisheries 30, 153–172 (2020). https://doi.org/10.1007/s11160-019-09588-6

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  • DOI: https://doi.org/10.1007/s11160-019-09588-6

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