711 



Abstract — As nearshore fish popu- 

 lations decline, many commercial 

 fishermen have shifted fishing effort 

 to deeper continental slope habitats 

 to target fishes for which biological 

 information is limited. One such fish- 

 ery that developed in the northeastern 

 Pacific Ocean in the early 1980s was 

 for the blackgill rockfish (Sebastes 

 melanostomits), a deep-dwelling 

 (300-800 mi species that congre- 

 gates over rocky pinnacles, mainly 

 from southern California to southern 

 Oregon. Growth zone-derived age esti- 

 mates from otolith thin sections were 

 compared to ages obtained from the 

 radioactive disequilibria of 210 Pb, in 

 relation to its parent, 226 Ra, in otolith 

 cores of blackgill rockfish. Age esti- 

 mates were validated up to 41 years, 

 and a strong pattern of agreement 

 supported a longevity exceeding 90 

 years. Age and length data fitted 

 to the von Bertalanffy growth func- 

 tion indicated that blackgill rockfish 

 are slow-growing (A' = 0.040 females. 

 0.068 males I and that females grow 

 slower than males, but reach a greater 

 length. Age at 509c maturity, derived 

 from previously published length-at- 

 maturity estimates, was 17 years for 

 males and 21 years for females. The 

 results of this study agree with gen- 

 eral life history traits already recog- 

 nized for many Sebastes species, such 

 as long life, slow growth, and late 

 age at maturation. These traits may 

 undermine the sustainability of black- 

 gill rockfish populations when heavy 

 fishing pressure, such as that which 

 occurred in the 1980s, is applied. 



Radiometric validation of age, growth, 

 and longevity for the blackgill rockfish 

 (Sebastes melanostomus) 



Melissa M Stevens 



Allen H. Andrews 



Gregor M. Cailliet 



Kenneth H. Coale 



Moss Landing Marine Laboratories 



8272 Moss Landing Road 



Moss Landing, California 95039 



E-mail address ((or A. H Andrews, contact author): andrewsiS'mlml calstate.edu 



Craig C Lundstrom 



Department of Geology 



University of Illinois— Urbana Champaign 



255 Natural History Bldg. 



1301 W.Green Street 



Urbana, llmois 61801 



Manuscript submitted 9 June 2003 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 18 June 2004 by the Scientific Editor. 



Fish. Bull. 102:711-722 (20041. 



The blackgill rockfish (Sebastes mela- 

 nostomus) is a deep-water rockfish 

 that is found mainly along the conti- 

 nental slope between 300 and 800 m 

 depth off central and southern Cali- 

 fornia (Moser and Ahlstrom. 1978; 

 Cross, 1987; Williams and Ralston, 

 2002). Although not as heavily tar- 

 geted in relation to other commercially 

 important rockfish species, a directed 

 commercial fishery for blackgill rock- 

 fish has existed since the mid-1970s, 

 beginning off southern California 

 (Point Conception area) and spreading 

 northward ( Monterey area) as stocks 

 of other heavily fished rockfishes 

 declined (Butler et al., 1999). Using 

 acoustic sonar and set nets, the com- 

 mercial fleet was able to catch large 

 aggregations of previously unexploited 

 blackgill rockfish. Landings peaked in 

 1983 with 1346 metric tons (t) caught 

 coast-wide, but declined over the next 

 decade, presumably because of the dis- 

 appearance of the large concentrations 

 that could be located with acoustical 

 gear (Butler et al., 1999). In 2001, 

 141 t were reportedly landed along 

 the entire west coast (PacFIN 1 ) — less 

 than half of the allowable catch (343 t; 



NOAA, 2001) for blackgill rockfish 

 that year. 



The first stock assessment of black- 

 gill rockfish was made by Butler et 

 al. (1999). One objective of this as- 

 sessment was to determine age and 

 growth characteristics, which were 

 then applied to estimate age-at-ma- 

 turity, natural mortality, and stock 

 biomass. Using conventional aging 

 methods (i.e., otolith increments), 

 we estimated that blackgill rockfish 

 live at least 87 years and reach full 

 (100%) maturity from 13 to 26 years 

 for females, and from 13 to 24 years 

 for males. Although such estimates 

 are useful and should be considered 

 whenever available, validation of the 

 age-estimation procedure is needed to 

 be certain of accurate age estimates 

 (Beamish and McFarlane, 1983; 

 Campana, 2001). Inaccurate age de- 

 terminations in some cases have led 

 to overharvesting of stocks such as 

 Pacific ocean perch (Sebastes alutus) 



1 PacFIN (Pacific Fisheries Information 

 Network). 2002. Commercial fisher- 

 ies landing data. http://www.PacFIN. 

 org. [Accessed 9 August 2002]. 



