Declining grouper spawning aggregations in Western Province, Solomon Islands, signal the need for a modified management approach.

A T Hughes,R J Hamilton,K L Rhodes,J H Choat,Heather M Patterson

doi:10.1371/journal.pone.0230485

A T Hughes, R J Hamilton + Show 3 more

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https://doi.org/10.1371/journal.pone.0230485

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Abstract

Globally, groupers (Epinephelidae) that form fish spawning aggregations (FSAs) are highly vulnerable to overfishing and often require site-specific approaches to management. Over 5-years (2009–2013), we conducted underwater visual censuses (UVC) at a well-known spawning site at Njari Island, Gizo, Western Province, Solomon Islands, that supports aggregations of squaretail coralgrouper (Plectropomus areolatus), camouflage grouper (Epinephelus polyphekadion) and brown-marbled grouper (E. fuscoguttatus). Findings show that while there were species-specific variations in the duration and timing of the spawning season, aggregation densities peaked from March to June, representing the main spawning season for all three species. For P. areolatus, gonad analysis from samples taken from 2008 to 2011 confirmed reproductive activity in support of density trends observed through UVC. Over the 5-year UVC monitoring period, FSA densities declined for P. areolatus and E. polyphekadion. Conversely, following the first year of monitoring, E. fuscoguttatus densities increased. These inter-specific differences may reflect variable responses to fishing as shown elsewhere, or for example, differences in recruitment success. In response to known declines in FSAs of these species, in 2018 the Solomon Islands government placed a nationwide ban on these species’ harvest and sale between October and January. As this study shows, this ban does not encompass the peak aggregation period at Njari and will offer limited protection to other FSAs of these species that are known to vary in reproductive seasonality across the Solomon Islands. A more biologically meaningful and practical management strategy would be to implement a nationwide ban on the harvest and sale of these groupers each month between full and new moons when these FSAs form consistently throughout the country. Since effective management of FSAs typically requires a combined approach, spatial management that protects both spawning sites and reproductive migratory corridors is warranted.

Highlights

Coral reef fisheries provide a valuable source of protein and income for coastal communities throughout the tropics and subtropics, yet these fisheries have come under increasing threat from overfishing, commercialization, habitat loss, population growth and climate change, among other impacts [1,2,3,4]
The site is located on the seaward edge of a reef promontory on the northwestern tip of the barrier reef system, where P. areolatus, E. polyphekadion and E. fuscoguttatus form overlapping spawning aggregations, similar to other sites in the region
Similar to E. polyphekadion, peaks in E. fuscoguttatus density occurred in April and May

Summary

Introduction

Coral reef fisheries provide a valuable source of protein and income for coastal communities throughout the tropics and subtropics, yet these fisheries have come under increasing threat from overfishing, commercialization, habitat loss, population growth and climate change, among other impacts [1,2,3,4]. Heavy fishing on the FSAs of some species, such as the Critically Endangered (CR) Nassau grouper (Epinephelus striatus) [15], has led to several aggregations becoming economically extinct, with other historical aggregations fully extirpated [10, 16,17] These declines have come from a combination of small-scale, large-scale and subsistence fishing [13, 18,19,20,21,22,23], including the Southeast-Asia live reef food fish trade that target FSAs throughout the Indo-Pacific [17]

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