Abstract
The humphead wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum) are two of the largest, most iconic fishes of Indo‐Pacific coral reefs. Both species form prized components of subsistence and commercial fisheries and are vulnerable to overfishing. C. undulatus is listed as Endangered and B. muricatum as Vulnerable on the IUCN Red List of Threatened Species. We investigated how night spearfishing pressure and habitat associations affected both species in a relatively lightly exploited setting; the Kia fishing grounds, Isabel Province, Solomon Islands. We used fisheries‐independent data from underwater visual census surveys and negative binomial models to estimate abundances of adult C. undulatus and B. muricatum as a function of spearfishing pressure and reef strata. Our results showed that, in Kia, night spearfishing pressure from free divers had no measurable effect on C. undulatus abundances, but abundances of B. muricatum were 3.6 times lower in areas of high spearfishing pressure, after accounting for natural variations due to habitat preferences. It is likely the species’ different nocturnal aggregation behaviors, combined with the fishers’ use of night spearfishing by spot‐checking underpin these species’ varying susceptibility. Our study highlights that B. muricatum is extremely susceptible to night spearfishing; however, we do not intend to draw conservation attention away from C. undulatus. Our data relate only to the Kia fishing grounds, where human population density is low, the spot‐checking strategy is effective for reliably spearing large numbers of fish, particularly B. muricatum, and fisheries have only recently begun to be commercialized; such conditions are increasingly rare. Instead, we recommend that regional managers assess the state of their fisheries and the dynamics affecting the vulnerability of the fishes to fishing pressure based on local‐scale, fisheries‐independent data, where resources permit.
Highlights
The humphead wrasse (Cheilinus undulatus) and the bumphead parrotfish (Bolbometopon muricatum) are two of the largest coral- reef fish in the Indo-Pacific (Donaldson & Dulvy, 2004; Hamilton & Choat, 2012; Sadovy et al, 2003)
Our results demonstrate that B. muricatum is more vulnerable to night spearfishing compared to C. undulatus in the Kia fishing grounds
This contrasts with the catch composition from the nearby, but more heavily fished Nusabanaga fishing grounds, where B. muricatum made up 56% of the catch and C. undulatus made up 5.6% of the catch (Hamilton, 2005)
Summary
The humphead wrasse (Cheilinus undulatus) and the bumphead parrotfish (Bolbometopon muricatum) are two of the largest coral- reef fish in the Indo-Pacific (Donaldson & Dulvy, 2004; Hamilton & Choat, 2012; Sadovy et al, 2003). B. muricatum is a major bioeroder on coral reefs (Bellwood, Hoey, & Choat, 2003) It scavenges protein by consuming sessile animals (including coral), detritus, and endolithic autotrophs from shallow reef surfaces exposed to wave action, which is processed in the pharyngeal mill before digestion (Hamilton & Choat, 2012). Both species are inactive at night; a characteristic of labrids
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