Symposium Abstract: Ecological Consequences of Lost Habitat Structure for Commercially Significant Flatfishes: Habitat Choice and Vulnerability to Predators
A. W. Stoner, C. L. Ryer, and R. A. McConnaughey
Numerous field studies, both descriptive and experimental, have shown that fishing gear can have a negative impact on the structural complexity of benthic environment. Impacts in high-relief habitats such as coral reefs, hard-bottom, seagrasses, and cobble are well documented. Soft-bottom habitat can also contain physical structure created by different bedforms, sessile invertebrates such as sponges, anemones, soft corals, and bryozoans, and the empty shells of molluscs. Recent laboratory experiments with Alaska flatfishes show that age-0 and age-1 fish have a strong behavioral affinity for sediments structured with sand waves, sponges, bryozoans, and bivalve shells. Responses were stronger in juvenile Pacific halibut than rock sole. The presence of structured habitat also affected the survivorship of age-0 fishes in the presence of a piscivorous predator, but habitat-mediated predator-prey interactions varied with prey species. Comparisons of trawled and untrawled locations in the Gulf of Alaska and the Bering Sea reveal that densities and biomass of sponges, anemones, bryozoans, gastropod shells, soft corals, and other biota providing structure for small fishes decrease with fishing activity. It follows that loss of structured habitat in low-relief shelf environment can have both direct and indirect impacts on the function of habitat for demersal fishes, particularly during their first year of life. We need a better understanding of how structural complexity in softbottom environment influences abundance and recruitment of fishes and invertebrates, and better characterization of habitat features is probably required.