Radiometric age validation of the bocaccio rockfish, Sebastes paucispinis

Investigators: Allen H. Andrews, Erica J. Burton, Gregor M. Cailliet, and Kenneth H. Coale

The bocaccio rockfish (Sebastes paucispinis) has been an important component of the long history of California rockfish fisheries (Lenarz 1987). Landings of bocaccio during the 1970’s and early 1980’s remained quite high and frequently exceeded 6000 tons in annual landings. More recently, landings have been down and an assessment of the bocaccio fishery in the Conception/Monterey/Eureka INPFC areas indicate the current stock size of the fishery is probably not greater than 15-20% of the 1970 level and may be closer to 10% of that level (Ralston et al. 1996). Current recommendations are that harvests be held to minimal levels until there is some evidence of recovery.

To properly manage this fishery, the age structure and growth characteristics of the bocaccio must be known along with other life history parameters. Some life history aspects are known (Phillips 1964, Moser 1967, Gunderson et al. 1980, Moser and Boehlert 1991, Woodbury and Ralston 1991), but longevity estimates remain controversial. Recent and historic longevity estimates based on a variety of traditional techniques (scales, otolith surface ageing, break and burn, transverse sectioning) range from less than 20 yr to greater than 50 yr (Phillips 1964, Wilkins 1980; Donald Pearson, NMFS, Southwest Fisheries Science Center at Tiburon Laboratories, personal communication; Paul Reilly, California Department of Fish and Game in Monterey, personal communication).

Otoliths of bocaccio are inherently difficult to read using traditional techniques and attempts to validate the periodicity of annulus formation have been unsuccessful (marginal increment analysis, oxytetracycline; Donald Pearson, NMFS, Southwest Fisheries Science Center at Tiburon Laboratories, personal communication). Because the growth structure of otoliths suggests the bocaccio is long-lived, we propose to test hypotheses about age, growth rates, and longevity by applying the radiometric ageing technique to the otoliths of bocaccio.

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