Abstract — The use of parasites as in- 

 dicators of the stock structure of Pacific 

 hahbut {Hippoglossus stenolepis) in the 

 northeast Pacific was investigated by 

 using 328 adult (>55 cm fork length) 

 hahbut from 15 composite localities 

 ranging from northern California to 

 the northern Bering Sea and 96 ju- 

 venile (10-55 cm) halibut from five 

 localities ranging from the northern 

 Queen Charlotte Islands to the Bering 

 Sea. Counts of eight selected parasite 

 species (the juvenile acanthocephalans 

 Corynosoma strumostim and C. vil- 

 losum, the metacestode Nyhelinia sur- 

 menicola, the digenean metacercaria 

 Otodistnmum sp., and the larval nema- 

 todes Anisakis simplex, Pseudoterra- 

 noi'a decipiens, Contracaecum sp., and 

 Spirurid gen. sp.) that produce infec- 

 tions of long duration, do not multiply 

 in the host, and that have a relatively 

 high abundance in at least one geo- 

 graphic locality were subjected to dis- 

 criminant function analysis. Juvenile 

 Pacific halibut showed no separation 

 and, even though they were not heav- 

 ily infected with parasites, the analysis 

 suggested that juveniles could be a 

 mixed stock. Three groups of adults 

 were identified: fish from California to 

 the southern Queen Charlotte Islands, 

 those from the northern Queen Char- 

 lotte Islands to the central Bering Sea, 

 and those from the central and north- 

 ern Bering Sea. These groups suggest 

 that the single stock concept be more 

 thoroughly evaluated. 



The use of parasites in discriminating stocks 

 of Pacific halibut (Hippogiossus stenolepis) 

 in the northeast Pacific 



Reginald B. Blaylock 



Department of Biological Sciences 

 University of Alberta 

 Edmonton, AB T6G 2E9, Canada 



and 



Department of Fisheries and Oceans 

 Pacific Biological Station 

 Nanaimo, B.C. V9R 5K6, Canada 

 Present address: College of Manne Sciences 



The University of Southern Mississippi 



703 East Beach Blvd 



PO Box 7000 



Ocean Spnngs, Mississippi 39566-7000 

 E-mail address: reg blaylock@usm.edu 



Leo Margolis (deceased) 



Department of Fishenes and Oceans 

 Pacific Biological Station 

 Nanaimo, B.C. V9R 5K6, Canada 



John C. Holmes 



Department of Biological Sciences 

 University of Alberta 

 Edmonton, AB T6G 2E9, Canada 



Manuscript accepted 10 July 2002. 

 Fish. Bull. 101: 1-9(2003). ' 



The Pacific halibut (Hippogiossus steno- 

 lepis ) is an Arctic-Boreal Pacific pleuro- 

 nectid flatfish ranging throughout the 

 North Pacific from southern California 

 to northern Japan, but is most abun- 

 dant in the Gulf of Alaska, The halibut 

 supports one of the top five commercial 

 fisheries in North America, with aver- 

 age annual landings of approximately 

 25,000 metric tons from 1991 to 1995 

 (IPHC, 1996), and is also widely sought 

 in the sport fishery, thus contributing 

 significantly to west coast economies. 

 The International Pacific Halibut Com- 

 mission (IPHC) is responsible for man- 

 agement of the resource. From the 

 1930s through the 1950s the IPHC re- 

 cognized at least three stocks of hali- 

 but from tagging experiments, egg and 

 larval drift, anatomical differences, 

 and differences in growth rate: 1) those 

 in the Bering Sea; 2) those from the 

 Gulf of Alaska south to Cape Spencer, 



Alaska; and 3) those south of Cape 

 Spencer (Skud, 1977). These bound- 

 aries roughly followed the zoogeo- 

 graphic zonation in the North Pacific. 

 Skud (1977) re-analyzed the data and 

 concluded that there was extensive 

 intermingling of fish among areas and 

 that there was no evidence to indicate 

 that fish north and south of Cape 

 Spencer, Alaska, constituted different 

 stocks. Available biochemical evidence 

 (Tsuyuki et al., 1969; Grant et al., 

 1984), although limited in scope and by 

 sampling effort, suggests little genetic 

 variation throughout the northeast 

 Pacific. As a result, the IPHC manages 

 halibut as a single population, but with 

 statistical divisions for management of 

 data. 



Parasites have been used successfully 

 to distinguish populations or stocks of 

 fishes and, as a result, provide informa- 

 tion useful in fisheries management ( see 



