A pilot study of the distribution and abundance of rockfishes in relation to natural environmental factors and an offshore oil and gas production platform off the coast of Southern California.

Abstract

Platform Hidalgo is located in 123 m of water off Point Arguello, California. A pilot study was conducted to examine the distribution and abundance of rockfishes around Hidalgo and at eight adjacent natural reefs. To test for differences in fish assemblages among reefs using factorial ANOVA, the natural reefs were classified according to two levels each of three factors: “low” (0.2–0.5 m) versus “high” (>1 m) relief height; “nearfield” (<3 km from Hidalgo) versus “farfield” (>3 km from Hidalgo) proximity to the platform; and “shallow”(113–160 m) versus “deep” (195–213 m) reef depth. Fishes were also tagged over natural reefs with breakaway hook tags. Surveys and tagging studies were conducted from July to October 1990. During surveys in July and August, large numbers of young-of-the-year (YOY)rockfishes (primarily Sebastes entomelas, S. flavidus and S. hopkinsi) were found in the surface and midwaters around Hidalgo. At the base of the platform, 1+ yr rockfishes (mainly S. entomelas and S. flavidus) were very abundant. When the platform was resurveyed in October, following the first gale of the year, nearly all the YOY rockfishes had disappeared, thought the 1+ yr fishes were still abundant at the platform’s base. While the ultimate fate of the YOY rockfishes is not known, our preliminary data suggest the hypothesis that Platform Hidalgo acts as producer of fish biomass by providing habitat for pelagic larvae to settle and grow before dispersing as small juveniles.