Masters Thesis

The effect of local fishing pressure on the size and age structure of fishes associated with rocky habitats along California’s north coast

Groundfish stocks are typically managed on a regional scale delineated by geographical or geopolitical boundaries. However, fleet and stock dynamics often operate on finer spatial scales, thereby leading to variable impacts of fishing within regional boundaries, which may be evident in the size and age structure of some fishes. This study is designed to examine the validity of the assumption that historic fishing effort on rocky reefs along California’s North Coast is inversely correlated with distance-from-port. Data collection involved hook-and-line sampling at randomly selected “rocky habitat” cells within each of six depth by distance-from-port strata associated with each of three ports: Crescent City Harbor, Trinidad Bay, and Noyo River Harbor. Size structure effects were assessed for six species of rockfish (Sebastes spp.: black, blue, yellowtail, China, gopher, and canary) and two species of Hexagrammidae: lingcod, and kelp greenling. Age data, based on reading sagittal otoliths, were generated for the two most abundant species, black rockfish and blue rockfish. Analysis results suggested a significant positive effect of distance-from-port on the lengths and ages of black rockfish. This effect was variable among ports. Results for species other than black rockfish, which were limited by smaller sample sizes, suggested that the response of length and age data to historic fishing pressure is also variable among species. These findings support an assumption that distance-from-port may act as a proxy for historic fishing pressure within the study region, but the effect of distance-from-port on lengths and ages of species varies by port and by species due to a variety of possible factors. Results from this study may be useful for localized management of black rockfish.