Evaluating rabbitfish restocking potential in support of Guam’s coastal fisheries

Aquaculture-based fisheries enhancement (i.e., restocking) involves releasing hatchery-reared fish into the wild to support depleted populations and sustain fisheries. However, the benefits of these activities can be difficult to detect. We created a theoretical model to evaluate the potential benefits of restocking initiatives for a prominent forktail rabbitfish (Siganus argenteus) fishery in Guam. Forktail rabbitfish have three distinct life stages making them ideal for a discrete stage-structured modeling approach: mañahak (recruits), dagge (juveniles), and hiteng kahlao (adults). We modelled restocking scenarios whereby mañahak were harvested for grow-out and subsequently reintroduced into the population as dagge, thereby reinforcing the life stage transition with the lowest natural survival probability. We found that restocking had variable impacts on the population structure and resilience that were dependent on the intensity of exploitation. Under full exploitation, restocking improved resilience by shifting the most sensitive life-stage transition from mañahak-to-dagge to dagge-to-hiteng kahlao. Only under low-to-intermediate fishing could restocking reverse the population trajectory from a declining trend to a growing one. Restocking 2–10 % of the unfished biomass (B0) allowed the population to sustain 12–25 % higher yields while still maintaining the 50 % B0 benchmark. Overall, fishing and natural reproduction were consistently the strongest determinants of population structures, transitions, and trajectories; however, restocking augmented population resilience and improved fisheries yields. This study demonstrates the potential viability of restocking in combination with fishing regulations to enhance fisheries yield in a culturally important fishery.