Habitat associations of deep-water rockfishes in a submarine canyon: an example of a natural refuge


Yoklavich, Mary M., H. Gary Greene, Gregor M. Cailliet, Deidre E Sullivan, Robert N. Lea, and Milton S. Love
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A multidisciplinary assessment of benthic rockfishes (genus Sebastes) and associated habitats in deep water was conducted in Soquel Submarine Canyon, Monterey Bay, California. Rock habitats at depths to 300 m were identified by using bathymetric and side-scan sonar imaging, verified by visual observations from a manned submersible, mapped and quantified. Species composition, abundance, size, and habitat specificity of fishes were determined by using a video camera and parallel laser system along transects made by a submersible. We counted 6208 nonschooling fishes representing at least 52 species from 83 10-min strip transects that covered an estimated 33,754 m2. Rockfishes represented 77% of the total number of individuals, and included a minimum of 24 species. Six distinct habitat guilds of fishes were manifest from habitat-based clustering analysis: small species were associated with mud and cobble substrata of low relief, and larger species of rockfishes were associated with high-relief structures such as vertical rock walls, ridges, and boulder fields. There was remarkable concordance between some of the guilds identified in Soquel Canyon and the results of other habitat-specific assessments of fishes along the west coast of the United States from central California to Alaska. These generalities are valuable in predicting community structure and evaluating changes to that structure, as well as in applying small-scale species-habitat relationships to broader-scale fishery resource surveys. Additionally, establishment of these groups is critical when incorporating the concept of essential fi sh habitat (EFH), and negative impacts to it, into the management of fi sheries in relatively deep water, as required by the Sustainable Fisheries Act of 1996. High numbers of large rockfishes (e.g. Sebastes chlorostictus, S. levis, S. rosenbblatti, and S. ruberrimus) were locally associated with rock ledges, caves, and overhangs at sites having little or no evidence of fishing activity. Abundance and size of several species were lower at fi shed than at unfished sites. We suggest that rock outcrops of high relief interspersed with mud in deep water of narrow submarine canyons are less accessible to fishing activities and thereby can provide natural refuge for economically important fishes, as exemplified in Soquel Canyon.