California Sea Grant College Program

In this dissertation, I address fundamental ecological issues concerning widow rockfish (Sebastes entomelas) habitat use and distribution, which can be used as the foundation for appropriate marine reserve design. Although widow rockfish is one of the most commercially important rockfish species on the US West Coast, no previous work has specifically addressed the habitat requirements of this species. In Chapter One, I identify significant habitat associations between widow rockfish and three habitat variables; bottom depth. vertical depth of fish in the water column, and temperature. My results indicate that the average significant habitat association for widow rockfish includes bottom depths between 136-298 m. vertical depths between 101-197 m. and temperatures between 7.1-8.1°C. These results provide useful insights towards the definition of essential fish habitat (EFH) for this species.

In Chapter Two. I address fluctuations in habitat use through time. I detected no significant interannual, seasonal. or intraannual variation in the range of bottom depths preferred by widow rockfish, but I did detect a significant correlation between bottom depth and vertical depth. Fish are further off the bottom at deeper bottom depths, and this relationship varies significantly by season. Understanding the ecological phenomenon affecting this behavior could provide us with additional insight into the ecology and habitat requirements of this species. Finally, in Chapter Three, I investigated widow rockfish distribution, and changes through time. I detected three significant annual shifts in the spatial distribution within an 11-year time series (1988-1998), corresponding to the two major El Niño events that occurred within this time frame.

My results have the following implications for marine reserves design. First, the habitat encompassed in any marine reserve(s) designed for widow rockfish conservation must include the range of bottom depths and temperatures significantly associated with its distribution. Second, the marine reserve(s) should encompass both the inshore and offshore components of widow rockfish habitat. Finally, a single reserve may not afford equal protection to this species, particularly with regard to El Niño versus non-El Niño years. Therefore, in addition to seasonal habitat use, one must consider interannual shifts in distribution.