Habitat associations and determinants of refuge use in post-settlement lingcod (Ophiodon elongatus)

Graduation date: 2006Lingcod are an overexploited fish species in the Pacific Northwest and although there\ud has been extensive study of the habitat requirements of adults, particularly during\ud spawning, relatively little is known regarding the habitat requirements of post-settlement\ud juveniles. Many juvenile fish use structural components of habitat to\ud alleviate the risk of predation, as well as for foraging. Laboratory experiments and a\ud field tagging study were performed in order to investigate habitat preference in\ud juvenile lingcod, as well as factors that govern habitat use. Initial laboratory\ud experiments demonstrated an affinity by juvenile lingcod for structure over bare sand\ud habitats, whether the structure was rock, shell or seagrass. Body size, nutritional\ud state, and light level were also found to be determinants of the extent to which\ud juvenile lingcod use structural refuges. In the laboratory, older, larger individuals\ud exhibited a higher propensity for structure use than did smaller juvenile fish. In fish\ud of both body sizes, increasing hunger levels caused fish to emerge more readily from\ud refuges than did those that were satiated. Die! patterns of ambient illumination were\ud simulated in the laboratory, and refuge use decreased significantly in response to lower nocturnal light levels, a pattern that was not observed in the smaller size class.\ud An acoustic tagging study conducted in Yaquina Bay, Oregon corroborated the basic\ud habitat preferences seen in laboratory experiments. Juvenile lingcod showed a high\ud degree of site fidelity, remaining in discreet areas of significant structural complexity,\ud as revealed by underwater video of benthic habitat. The way in which an animal\ud utilizes structural refuges adds or detracts from individual fitness, making this\ud investigation into the habitat requirements of post-settlement lingcod an important\ud step in understanding the life history and ecology of an important recreational and\ud commercial species