Seasonal changes in abundance and compelling evidence of migration for 2 rockfish species (Sebastes auriculatus and S. caurinus) inhabiting a nearshore, temperate-water artificial reef

Abstract

We used scuba over fixedwidth strip transects to monitor seasonal abundances of brown rockfish (Sebastes auriculatus) and copper rockfish (S. caurinus) on a nearshore artificial reef in Puget Sound, Washington, over a 7-year period. Spring and fall abundances were intermediate and marked transitional phases between seasons of highest (summer) and lowest (winter) abundance for both species. Analyses of length classes indicated that the numbers of seasonal juvenile recruits were not sufficient to account for the marked differences in abundance between summer and winter. For both species, the proportion of large fish (≥20 cm in total length) to the total number observed in summer and winter was significantly greater during the winter. Late-stage gravid brown rockfish occurred in greatest abundance during the spring and late-stage gravid copper rockfish were observed only in the summer. We examined auxiliary data from a genetics study of brown rockfish that was conducted concurrently at the reef and interpreted the results, along with our survey findings, as providing compelling evidence of seasonal migrations on and off the reef.