Abstract
In recent decades, spearfishing with SCUBA has emerged as an efficient method for targeting reef fish in deeper waters. However, deeper waters are increasingly recognised as a potential source of refuge that may help sustain fishery resources. We used a combination of historical catch data over a 20-year time period and fishery-independent surveys to investigate the effects of SCUBA spearfishing on coral reef fish populations in the southern Mariana Islands. Two jurisdictions were studied; Guam, where SCUBA spearfishing is practiced, and the nearby Commonwealth of Northern Mariana Islands (CNMI), where SCUBA spearfishing has been banned since 2003. Fishery-independent data were collected using baited remote underwater stereo-video systems (stereo-BRUVs) stratified by depth, marine protected area status and jurisdiction. Herbivores (primary consumers) dominated spearfishing catches, with parrotfish (scarines) and surgeonfish/unicornfish (acanthurids) the main groups harvested. However, the large, endangered humphead wrasse (Cheilinus undulatus) was the main species by weight landed by SCUBA spearfishers. SCUBA spearfishing was associated with declining size of scarines over time and catches shifting from a dominance of large parrotfishes to a mixed assemblage with increasing proportions of acanthurids. Comparisons between Guam and the nearby CNMI revealed differences in the assemblage of fished species and also greater size of scarines and acanthurids in deep water where SCUBA fishing is banned. These results suggest that SCUBA spearfishing impacts reef fish populations and that the restriction of this fishing method will ensure refuge for fish populations in deeper waters. We recommend a ban on SCUBA spearfishing to preserve or aid the recovery of large, functionally important coral reef species and to improve the sustainability of coral reef fisheries.
Highlights
Spearfishing is an important method for harvesting reefassociated fish worldwide
The single species that contributed the greatest biomass to selfcontained underwater breathing apparatus (SCUBA) spearfishing catch was the humphead wrasse (Cheilinus undulatus)
95% of the total spearfishing catch of C. undulatus was caught with SCUBA
Summary
Spearfishing is an important method for harvesting reefassociated fish worldwide. Like other fishing methods, spearfishing has undergone significant modifications through time, evolving from handmade spears and basic skin-diving equipment to highpowered guns, underwater lights and the utilisation of selfcontained underwater breathing apparatus (SCUBA) to maximise catches. Spearfishing has been regarded as an unsustainable fishing technique when unregulated [1,2,3], management regulations such as protecting certain species or introducing size and catch limits could work positively with the inherently high selectivity of the method [4,5]. Apart from direct consumption needs, spearfishing is commercially valuable, with 75% of marketed reef fish in Micronesia sourced from night-time spearfishing [9]. When combined with access to commercial markets and no catch restrictions, spearfishing at night can quickly deplete inshore fish resources [3,10]. Herbivorous fish play an important functional role in regulating algal growth on coral reefs [12,13] and effective ecosystem-based management may warrant restrictions on the use of spear guns when coral reefs are dominated by algae [6,8]. Despite spearfishing presenting a number of concerns for management, Gillet and Moy [1] concluded in their comprehensive assessment of spearfishing in the Pacific Islands that the single most important management measure was to prohibit the use SCUBA for spearfishing and the effective enforcement of such bans
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