Releases of cultured sub-adult Trochus niloticus generate broodstock for fishery replenishment in Vanuatu

Abstract

The over-fished topshell Trochus niloticus ('trochus ') was cultured in Vanuatu and grown to sub-adult size (~40 mm) in sea cages. We released 200 of these trochus at each of five reef sites managed through Customary Marine Tenure (CMT) to test the utility of this approach for restocking. The trochus were individually tagged, measured and placed into crevices behind the reef crest. Searches at the sites after 6 months yielded conservative recapture estimates of 36-47% of tagged individuals at sites. Average growth rates were >2.3 rom per month, allowing the trochus to reach shell sizes of 50-60 rom, known to be the onset of sexual maturity. Small, yet significant differences in growth rates between release sites (P < 0.001) suggest that this restocking approach could be optimised if the ecological correlates to growth rates are identified. Under community-based management through CMT, release of sub-adult trochus can be a successful, final step in promoting hatchery-produced juveniles to maturity to allow natural restocking of different types of depleted reefs.