Date of Award
Doctor of Philosophy (PhD)
Oceanography and Coastal Sciences
Charles A. Wilson
Behavioral responses of young-of-the-year red snapper, Lutjanus campechanus, to alterations in water flow were examined in the laboratory and the field in an effort to facilitate their release from shrimp trawls. Experiments with red snapper, collected by divers, were conducted in a racetrack flume. Four vertical and two horizontal mesh and solid panel types were examined. Four snapper (out of 96) escaped with vertical panels and thirteen fish (out of 48) exited with horizontal panels. Escapes occurred primarily with solid panels containing 0.95-cm holes drilled at 5-cm intervals. However, snapper that escaped with solid horizontal panels frequently went back into the net. The reduced water flow areas created by the panels appeared to trigger a territorial response in the juvenile snapper. Frequently, individuals that were behind the panel would attack other snapper, thus limiting access to the escape openings. Based on these experiments, panels do not appear to be an effective mechanism to induce young-of-the-year red snapper to exit trawls. Other experiments examined the behavior of red snapper in response to increasing and constant fish density, the presence of a trawl-webbing reef, and water flow. Agonistic activity increased as fish density increased, peaked at a density of 11 snapper per 0.16 m$\sp3$ of water, then declined. The presence of a reef under no-flow conditions increased agonistic encounters when one or two snapper defended the territory. Agonistic behavior increased with water flow over no flow conditions because fish defended reduced-flow areas. The snapper appeared to form dominance hierarchies in the absence of a reef, and when excluded from the reef by the resident snapper. Disruptions by the resident snapper may have prevented the dominance hierarchy among nonresident snapper from stabilizing, since the number of agonistic acts remained high. In contrast, agonistic activity among a constant number of snapper declined over time. These snapper appeared to establish a dominance hierarchy quickly and required little subsequent agonism to maintain the hierarchy. Agonistic behavior may reduce the ability of young-of-the-year red snapper to escape from bycatch reduction devices that create areas of reduced water flow near escape openings.
Rogers, Donna Reeve, "Behavior of Red Snapper, Lutjanus Campechanus, in Relation to Trawl Modifications to Reduce Shrimp Trawler Bycatch." (1998). LSU Historical Dissertations and Theses. 6757.