Graduation date: 1981 / Best scan available for figures and pages listing computer code. Original is a photocopy.

The oceans are essential for humanity, yet these systems continue to be degraded and suffer from pollution, habitat destruction and overexploitation. The Costa Rican Gulf of Nicoya is a productive gulf that is fished by both large-scale industrial fisheries and small-scale artisanal fishermen. However, the gulf is profoundly overfished and there has been a shift in both the type of species and size of fishes being targeted, which has had devastating economic and ecological effects in the region. To improve their livelihoods, artisanal fishermen have together with governmental agencies instituted partially protected marine protected areas, known as AMPRs which are intended to give artisanal fishermen exclusive fishing rights and to better the health of the ecosystems. However, these AMPRs can vary greatly within and between each other in aspects such as what types of fishing gear is allowed. To investigate how fishing techniques impact the health of the fish stocks and the wellbeing of fishermen within an AMPR, the size of a target fish, Spotted Rose Snapper (Lutjanus guttatus) and the number of undesired fish caught, was compared based on the number of approved fishing methods such as nets, longlines and commercial scuba diving, between different zones. This was conducted by identifying and measuring catch in collaboration with the National University of Costa Rica, who contributed with databases and field assistance, and artisanal dead bait longline fishermen (bottom long line) in the Paquera-Tambor AMPR. The results showed that in areas where fishing gear is more restricted, the mean weight of Spotted Rose Snapper was higher, but the relative proportion bycatch was not different. Furthermore, there was no difference in legal capture or breeding lengths between areas with high and low restriction of fishing gear. This indicates that the effects of overfishing are less predominant in zones where fewer fishing methods are permitted. The restriction of fishing methods could increase biodiversity and size in fish by exploiting less cohorts of populations. The preservation of size in fish species is very important regarding reproductive success, and it is therefore paramount that larger individuals are protected. This could be accomplished by for example, restricting the amount of allowed fishing gear or introducing maximum catch sizes. However, an improvement of the fish stocks, and therefore human wellbeing cannot be achieved in the Gulf of Nicoya without a revision of the strategies of two influential governmental bodies, the Costa Rican coast guard and the Costa Rican Institute of Fisheries and Aquaculture.