NOTE Clarks and Kaimmer: Estimates of commercial longllne gear selectivity for Hippoglossus stenolepis 



467 



targeting certain size groups and 

 thereby producing a different selec- 

 tivity schedule. In area 2B, for ex- 

 ample, the best catch rates may be 

 achieved by targeting smaller fish; 

 whereas in Alaska it may be more 

 profitable to target larger fish. 



If the decline in selectivity in area 

 2B were the result of the commer- 

 cial fishery targeting areas where 

 the fish are smaller, one would ex- 

 pect to see the decline in data from 

 survey releases (which are done over 

 the whole area), but not in data 

 from releases at spot fishing loca- 

 tions (most of which are customary 

 commercial fishing locations). How- 

 ever, the mark-recapture data show 

 the opposite pattern, if anything; 

 therefore ground selection does not 

 appear to be the explanation. 



When length-specific selectivity 

 is allowed to be dome-shaped in the 

 stock assessment model (rather than 

 forced to be asymptotic), the esti- 

 mated commercial selectivities turn 

 out to be quite similar in pattern 

 to the mark-recapture estimates, 

 including the differences among ar- 

 eas. But the selectivities estimated 

 for the IPHC systematic setline sur- 

 vey are asymptotic or ramp-shaped, 

 rather than dome-shaped. They in- 

 dicate that ground selection by the 

 commercial fishery really does have 

 an effect on the form of commercial 

 selectivity, contrary to what the 

 mark-recapture data may indicate. 



Literature cited 



) I 



80 100 120 140 160 180 



Fork lengtti (cm) 



Area 2B (18589 releases, 2760 recoveries) 



80 100 120 140 160 180 



Fork lengtti (cm) 



Area 3A (33952 releases, 2479 recoveries) 



o 



l.t 



80 100 120 140 160 

 Fork lengtti (cm) 



] \ 1 1 — 



80 100 120 140 160 

 Fork length (cm) 



Area 2C (15220 releases, 1422 recoveries) Area 3B (9399 releases. 464 recoveries) 



Figure 2 



Estimates of length-specific commercial selectivity (±1 standard deviation) 

 for Pacific halibut ^Hippoglossus stenolepis) based on all releases 1960-90, 

 by regulatory area. The scale was set by defining selectivity to be 1.0 at 

 120 cm, so that value has no standard deviation, and other values can and 

 do exceed 1.0. 



Huse, I., S. Lokkeborg, and A. V. Soldal. 



2000. Relative selectivity in trawl, longline and gilnet 



fisheries for cod and haddock. ICES J. Mar. Sci. 



57:1271-1282. 

 Kaimmer, S. M. 



1999. Direct observations on the hooking behavior of 

 Pacific halibut, Hippoglossus stenolepis. Fish. Bull. 

 97:873-883. 



2000. Pacific halibut tag release programs and tag release 

 and recovery data, 1925 through 1998. Int. Pac. Halibut 

 Comm. Tech. Rep. 41, 31 p. 



Lokkeborg, S., and A. Bjordal. 



1992. Species and size selectivity in longline fishing: a 

 review. Fish. Res. 13:311-322. 

 Millar, R. B., and R. J. Fryer. 



1999. Estimating the size-selection curves of towed 

 gears, traps, nets, and hooks. Rev. Fish. Biol. Fish. 

 9:89-116. 



Myers, R. A., and J. M. Hoenig. 



1997. Direct estimates of gear selectivity from mul- 

 tiple tagging experiments. Can. J. Fish. Aquat. Sci. 

 54:1-9. 

 Myhre, R. J. 



1969. Gear selection and Pacific halibut. Int. Pac. Hali- 

 but Comm. Tech. Rep. 51, 35 p. 

 Sigler, M. 



1999. Estimation of sablefish, Anop/opoma fimbria, abun- 

 dance off Alaska with an age-structured population 

 model. Fish. Bull. 97:591-603. 

 Sullivan, P. J., A. M. Parma, and W. G. Clark. 



1999. The Pacific halibut stock assessment of 1997. Int. 

 Pac. Halibut Comm. Sci. Rep. 79. 

 Woll, A., J. Boje, R. Hoist, and A. C. Gundersen. 



2001. Catch rates and hook and bait selectivity in long- 

 line fishery for Greenland halibut {Reinhardtius hip- 

 poglossoides. Walbaumi at East Greenland. Fish. Res. 

 51:237-246. 



