Fish-habitat associations on a deep reef at the edge of the Oregon continental shelf

Heceta Bank is a large reef on the edge of the central Oregon continental shelf that supports a wide variety of commercial fisheries. Using the research submersible Delta, we studied fish abundances on Heceta Bank and the relationship between species composition of fish assemblages and bottom types. Cluster analysis indicated that fish assemblages were most unique on mud, boulder, rock ridge, mud and cobble, and mud and boulder substrates. Rockfishes, particularly pygmy Sebastes wilsoni, sharpchin S. zacentrus, rosethorn S. helvomaculatus, and yellowtail S. flavidus, were the most abundant fishes and dominated all substrates except mud, where Dover sole Microstomus pacificus and zoarcids Lycodes pacificus were most abundant. Principal component analysis (PCA) and canonical correlation analysis (CCA) were used to determine the sources of variation within the data. PCA demonstrated that habitat variability was a fundamental cause of heterogeneity among fish assemblages. In contrast, CCA showed how species occurrences were related to specific substrates. Ontogenetic shifts in behavior and substrate preference occurred in pygmy rockfish. Small juveniles often formed dense schools above the bank's shallower rocky ridges. Larger individuals occurred in non-polarized assemblages on the bottom in cobble and boulder fields