Identifying Conservation Strategies for Group-Spawning Coral Reef Fish in the Indo-Pacific, Using a Case Study of a Protogynous Giant Wrasse

Abstract

Fish reproducing in group-spawning aggregations face intense fisheries during spawning events due to increased ease of capture. Other traits often associated with group spawning, such as late sexual maturation and sequential hermaphroditism, cause group-spawning species to be especially vulnerable to population declines, either because fishermen target large, reproductively mature specimens or because they target juveniles that would otherwise have reached sexual maturity and contributed to reproduction. In group-spawning species that are protogynous hermaphrodites, including species of grouper, snapper, and the giant wrasse (Cheilinus undulates) fishing large specimens skews sex ratios towards females, thereby interfering with reproduction through sperm limitation. Unprecedented sex ratio skew could cause aggregations to disappear from their historical sites, with potential evolutionary implications. In this paper, I review the unique threats afflicting group-spawning species, as well as possible resolutions to these threats. I use the highly endangered humphead wrasse as a case study in the deleterious effects of overfishing on population dynamics, in the effectiveness of trade regulations and conservation strategies already in place, and in potential solutions not yet applied. Using the conclusions of this analysis, I extrapolate trends likely to continue in the Indo-Pacific region, where aggregation spawning is unfamiliar to fisheries scientists but familiar to local fishermen, and where aggregation-forming species are apt to benefit most from the implementation of effective conservation strategies.