Sigler: Estimation of abundance of Anoplopoma fimbria off Alaska 



599 



60,000 t were unreasonably low because during the 

 same period, the longline relative abundance index 

 was stable even though annual commercial catches 

 were 20,000-30,000 t (Clausen et al., 1997). 



Eggers et al. (1982) described a quantitative 

 method of estimating the effective radius of a baited 

 hook or pot by comparing catch rates between gear 

 with different spacings between baits. They applied 

 this method to a hook-spacing experiment for sable- 

 fish longline gear and estimated that the bottom area 

 fished per hook was 4.8 ni". I applied this estimate 

 to the time series of longline relative abundance in- 

 dices, which implied that sablefish absolute biomass 

 in Alaska ranged from 7 to 16 million t during 1979 

 to 1996, a range that seems improbably high because 

 catches of about 50,000 t in the early 1970s subse- 



Table 2 



Log-likelihood, estimated values of exploitable biomass 

 (thousands metric tons, age 2+) for 1995. the fishable frac- 

 tion of the total population in numbers for 1995, age at 

 50'7( vulnerability, vulnerability of the last age class fs,^^^^, 

 where s^^,^^^^ < 1 implies a dome-shaped selectivity function), 

 and projected allowable biological catch for 1996 (ABC^g). 

 Values were estimated from the original data. Log-likeli- 

 hood is the value of the objective function. Selectivity, re- 

 cruitment, and initial age composition always were esti- 

 mated. Asterisk (*) indicates results where survey 

 catchability was estimated and natural mortality was fixed. 

 No * indicates results where survey catchability and natu- 

 ral mortality were fixed. 



Fishable fraction 



4.17 



6.85 



8.70 0.772 



10.61 0.673 0.833* 



13. .59 0.837* 0.801 



Age at 50<^ 



4.17 



6.85 



8.70 

 10.61 

 13,59 



4.17 

 6.85 

 8,70 

 10,61 

 13,59 



ABC,, 



4,17 



6,85 



8,70 



10,61 



13,59 



availability 



4,0 

 3.9* 



3.9 



4.0* 

 4.5 



4.0 



4.0* 



4.3 



4.0 



4.1* 



4.4 



22.7 

 23.0 12.8* 

 6.4* 10.1 



33.4 



19.6* 



16.2 



68.5 



30.2* 



24.0 



4.2* 

 4.6 



62.9* 

 39.0 



