Giant coral reef fishes display markedly different susceptibility to night spearfishing

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.

Assessing and managing charismatic marine megafauna in Palau: Bumphead parrotfish (Bolbometopon muricatum) and Napoleon wrasse (Cheilinus undulatus)

“…In many locations, bumphead parrotfish show strong ontogenetic shifts with age, moving out of lagoon systems as they reach sexual maturity and seeking out exposed reef habitats where cyanobacteria are abundant (Hamilton et al, 2017; Pearse et al, 2018). Habitats in Palau show high connectivity owing to the configuration of the reef system (Colin, 2009) and, as a result, movement among habitats is common and therefore may not show the same strong ontogenetic shifts as observed in other locations.…”

Lessons from a global remote sensing mapping project. A review of the impact of the Millennium Coral Reef Mapping Project for science and management

“…Using MCRMP to define coral reef habitat types but also design their sampling strategy, Pearse et al (2018) were able to determine the present habitat preference of these two species, their abundances and distributions.…”