UC Santa Cruz

Three quarters of the world’s fisheries are classified as overexploited or depleted. Management programs have mainly focused on reducing the fishing pressure on these stocks. However, some stocks fail to rebound even after fishing effort is reduced and hatchery programs may be used to facilitate population recovery. Despite substantial investment in hatchery supplementation, failed programs outnumber successful ones. It therefore seems vital to explore the abiotic and biotic factors that hinder their success. This thesis addresses the performance of several active recovery policies through the use of multispecies microcosms. Specifically, I ask 1) whether one or several supplementation efforts are needed before a sustainable stock population is established and 2) what factors influence the success or failure of recovery in these microcosms. My results show that the community within an ecosystem may strongly influence a recovery program’s likelihood of success and that multiple small additions may offer a better chance of success than one or several large additions. My results support previously made arguments that community ecology is an important framework for fisheries management. Moreover, commercial fishing alters community structure and this may happen in a way that inhibits population recovery. I suggest reconceiving population recovery as ‘facilitated invasion’ may provide useful guidance for designing future recovery programs.