PS 58-134
Factors affecting Trochus niloticus populations on Saipan
The sustainable harvest of populations is largely dependent on knowledge of the species ecology and stakeholder involvement. On the island of Saipan, little is known about the factors that affect the populations of a marine gastropod, trochus (Trochus niloticus). Trochus is a local delicacy that is currently protected. In this study, we analyzed factors that may affect trochus populations, including: marine protected area (MPA) designation, predation, substrate cover, and knowledge of regulations among local fishermen.
We compared Trochus size distributions in one MPA and one non-MPA. We analyzed the size distributions of dead Trochus along the barrier reef-flat to shells piled on the beach to represaent predated Trochus. We surveyed 51 local fishermen, to quantify knowledge of current regulation, agreement or disagreement with current management, and suggestions for future management.
Results/Conclusions
Our results suggest that MPAs do not positively affect trochus populations. There were more live and mature trochus at MPAs than non-MPAs and the CPUE at MPAs was below the 60-CPUE harvestable limit. High frequencies of juvenile trochus were predated. Increased rock cover and decreased rubble cover predicted trochus presence. Most (94%) of the fishermen surveyed were aware of current regulations. However, approximately 50% of those surveyed disagreed with current regulations. Controversy with current regulation could lead to non-compliance with the law and ultimately an unsustainable trochus population. Among future management suggestions provided by local fishermen, 70% encouraged more frequent seasons and increased enforcement. Designating MPAs with increased rock cover and decreased rubble cover and enforcing a size-limitation policy could better sustain trochus populaitons.