Stanley and Kronlund: Life history characteristics for Sebastes brevispmis 



671 



136°W 134°W 132°W 130'W 128 3 W 126°W 12-f : W 122 5 W 



54>N 



52°N' 



50'N' 



Moresby Trough 

 Reed Trough 



__^.Sea Otter Trough 



5 -_ V^Sfefe- ' 



48'N- 



50 100 200 



i Kilometers 



3CD 

 Site A 1 Meter Station 



Figure 1 



Coastal waters of British Columbia showing boundaries of silvergray rockfish [Sebastes 

 brevispinis) stocks, trawl capture locations of silvergray rockfish (black dots) for 

 1996-2000, mooring site for the oceanographic metering of temperature at-depth 

 (Al meter station), and 500-. 1000-, and 1500-m depth contours. 



to assess and protect the status of any species affected 

 by fishing, regardless of its commercial value. 



Research on silvergray rockfish is an example of an 

 area that has been neglected owing to the lack of eco- 

 nomic importance of this species in the commercial 

 fisheries. Even the data that are available have been 

 collected incidentally during fishing operations target- 

 ing other species or during generic sampling programs. 

 Nevertheless, we show in the present article that these 

 data, in conjunction with detailed commercial catch and 

 effort data, can be used to provide insight into the biolo- 

 gy, assessment, and management of silvergray rockfish. 

 This article summarizes this information and provides 

 estimates of the various life history parameters needed 

 for stock assessment. Some of the estimates represent 

 updates from previous work, but we also for the first 

 time present estimates of fecundity and maturity at age 

 and size. Using these values, we also derive a target 

 reference point. 



Materials and methods 



Data sources 



Data for silvergray rockfish were collected from B.C. 

 waters during port sampling, at-sea observer programs, 

 and research cruises from 1977 through 2000. These 



data reside at the Pacific Biological Station, Nanaimo, 

 B.C., Fisheries and Oceans, Canada. As of June 2000, 

 the database contains information on over 40,000 speci- 

 mens. Of these specimens, we aged 13,671 representing 

 most of the specimens from which we obtained otoliths, 

 in addition to documenting length, sex, and maturity 

 stage. We, also used catch observations from the com- 

 mercial trawl observer program from 1996 through 

 2000. 



Habitat 



Preferred depth distributions of silvergray rockfish were 

 inferred from analyzing catch rates in the commercial 

 data. We used all bottom tows that contained silvergray 

 rockfish and included tow duration. Bottom depth of the 

 tows was determined as the midpoint between beginning 

 and end depth of the tows. We applied a nonparametric 

 locally weighted regression smoothing function (LOESS) 

 (Cleveland, 1979) to log-CPUE observations grouped by 

 20-m intervals. 



Depth of peak catch rates by month were compared 

 with temperature-at-depth estimates based on data col- 

 lected from the site Al meter station on the west coast 

 of Vancouver Island (Fig. 1: 48°32"N by 126°12"W). 

 These data, collected from 1986 to 2000 (excluding El 

 Nino years), were taken from 35-, 100-, 175-, and 400-m 

 depths. The temperatures at fixed depths were then 



