670 



Abstract — We summarize the life his- 

 tory characteristics of silvergray rock- 

 fish (Sebastes brevispinis) based on 

 commercial fishery data and biologi- 

 cal samples from British Columbia 

 waters. Silvergray rockfish occupy 

 bottom depths of 100-300 m near the 

 edge of the continental shelf. Within 

 that range, they appear to make a 

 seasonal movement from 100-200 m 

 in late summer to 180-280 m in late 

 winter. Maximum observed age in 

 the data set was 81 and 82 years 

 for females and males, respectively. 

 Maximum length and round weight 

 was 73 cm and 5032 g for females 

 and 70 cm and 3430 g for males. The 

 peak period of mating lasted from 

 December to February and parturi- 

 tion was concentrated from May to 

 July. Both sexes are 50% mature by 

 9 or 10 years and 90% are mature by 

 age 16 for females and age 13 years 

 for males. Fecundity was estimated 

 from one sample of 132 females and 

 ranged from 181,000 to 1,917,000 

 oocytes and there was no evidence 

 of batch spawning. Infection by the 

 copepod parasite Sarcotaces aretieus 

 appears to be associated with lower 

 fecundity. Sexual maturation appears 

 to precede recruitment to the trawl 

 fishery; thus spawning stock biomass 

 per recruit analysis (SSB/R) indicates 

 that a F 50 r r harvest target would cor- 

 respond to an F of 0.072, 20% greater 

 than M (0.06). Fishery samples may 

 bias estimates of age at maturity 

 but a published meta-data analysis, 

 in conjunction with fecundity data, 

 independently supports an early age 

 of maturity in relation to recruitment. 

 Although delayed recruitment to the 

 fishery may provide more resilience 

 to exploitation, managers may wish 

 to forego maximizing economic yield 

 from this species. Silvergray rockfish 

 are a relatively minor but unavoid- 

 able part of the multiple species trawl 

 catch. Incorrectly "testing" the resil- 

 ience of one species may cause it to 

 be the weakest member of the species 

 complex. 



Life history characteristics for silvergray rockfish 

 (Sebastes brevispinis) in British Columbia waters 

 and the implications for stock assessment 

 and management 



Richard D. Stanley 



Allen R. Kronlund 



Fisheries and Oceans, Canada 



Pacific Biological Station 



Nanaimo, British Columbia, Canada V9T 6N7 



Email address (lor R D Stanley) stanleyngipac dfo-mpo.gc ca 



Manuscript submitted 6 April 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 31 March 2005 by the Scientific Editor. 



Fish. Bull. 103:670-684 (2005). 



Silvergray rockfish (Sebastes brevispi- 

 nis) range from the Gulf of Alaska to 

 central Baja California (Love et al., 

 2001) and are a minor part of the trawl 

 and hook-and-line fisheries catch from 

 northern Washington to the Gulf of 

 Alaska (Alaska Fisheries Information 

 Network. 1 Pacific Fisheries Informa- 

 tion Network, 2 Pacific Biological Sta- 

 tion 3 ). Coastwide commercial landings 

 averaged 2600 metric tons (t) from 

 1990 to 2000, and about two-thirds 

 of these landings came from British 

 Columbia (B.C.) waters, mostly from 

 bottom trawling. Hook-and-line land- 

 ings are the most common type in 

 Alaskan waters (mostly from south- 

 eastern Alaska) and have averaged 

 less than 20 t. Combined annual 

 trawl landings from Washington and 

 Oregon peaked at over 1000 t from 

 1977 to 1979, declined to an average 

 of 210 t from 1990 to 1998, and since 

 1999 have further declined to negli- 

 gible levels. 



The B.C. bottom trawl fishery is 

 currently managed through individual 

 vessel quotas (IVQs) whereby a fixed 

 proportion of the annual quota for 

 each stock is allocated to each quota- 

 holder. Because silvergray rockfish 

 are currently assessed and managed 

 as four separate stocks (Fig. 1: Pacific 

 Marine Fisheries Commission areas 

 3CD, 5AB, 5CD, and 5E), a vessel 

 may possess up to four area-specific 

 quotas for silvergray rockfish. All bot- 

 tom trawlers on the outer coastal wa- 

 ters of British Columbia are required 

 to have an independent observer on 

 the vessel. Once vessels have reached 



their IVQ for one area and species, 

 and have exhausted their limited op- 

 portunity to temporarily lease quota 

 from other lease-holders, they must 

 cease all bottom trawling even though 

 they may still have IVQ remaining 

 for other species in that area. 



The quotas for silvergray rockfish 

 are relatively small compared with 

 those for other species in the fishery; 

 thus fishermen can fully fill their sil- 

 vergray rockfish IVQs as they target 

 other species. However, if silvergray 

 rockfish become difficult to avoid 

 through increased abundance or avail- 

 ability, or if the silvergray rockfish 

 quota is reduced, even though catch 

 rates remain constant, they become 

 a nuisance in that fishermen cannot 

 fulfill their IVQs for other species 

 without exceeding their silvergray 

 rockfish IVQ. Therefore, the quotas 

 for minor species, such as silvergray 

 rockfish, now assume more impor- 

 tance than would be gained from 

 their landed value. Finally, the en- 

 actment of species-at-risk legislation 

 in Canada has led to the requirement 



1 Alaska Fisheries Information Network. 

 2000. AKFIN Support Center, 612 W 

 Willoughby Ave. Suite B. Juneau, Alaska 

 99801. 



2 Pacific Fisheries Information Network. 

 2000. Pacific States Marine Fisheries 

 Commission, 205 SE Spokane Street, 

 Suite 100, Portland, Oregon 97202. 



3 Pacific Biological Station. 2000. Un- 

 publ. data. Fisheries and Oceans Can- 

 ada. Nanaimo, British Columbia V9T 

 6N7, Canada. 



