Blaylock et al.: Use of parasites in discriminating stocks of Hippog/ossus slenolepis 



Bering Sea (SB) was included in the northern group (not 

 shown). Inclusion of the northern Queen Charlotte Islands 

 (NQC) in the southern group had little effect (81% cor- 

 rect classification) (not shown). These analyses indicated 

 a southern (OR-SQC) group, a central (NQC-SB) group, 

 and a northern (PI-SMI) group. 



Classification into two categories (with SQC as the di- 

 viding line) provided no substantial improvement (87'^ 

 correct) (not shown). Inclusion of NQC in the southern 

 group had little effect (88% correct classification). 



Discrimination of juveniles was poor with any organi- 

 zation of localities. The "best fit" classification correctly 

 classified only 66% of the fish and there was substantial 

 misclassification among the localities (Tables 6 and 7). 

 Fish from the northern Queen Charlotte Islands (NQC) 

 through Nagai Island (NI) separated reasonably well, but 

 the majority of fish from the northernmost locality were 

 also misclassified to this group. Note that parasite num- 

 bers and prevalences were low in the juveniles (Table 2). 



Discussion 



Our results show four things: 1) parasites clearly differen- 

 tiate a group of southern adults; 2) parasites provide some 



evidence for a separation of the northernmost adults; 3) 

 the differentiation is not always unequivocal; and 4) para- 

 sites do not differentiate groups of juvenile fish. 



Skud (1977) concluded that southern and northern 

 groups mixed extensively at all ages of their life history 

 and that, although populations of adults may be largely 

 discrete in the summer, any such discreteness was tempo- 

 rary because tagging evidence suggested more extensive 

 winter migrations associated with spawning. Our data, on 

 the other hand, suggest that there is some merit to the 

 IPHC's early recognition of three stocks of adult halibut. 

 Parasite data support the existence of two major groups 

 of halibut and suggest the possibility of a third group in 

 the central and northern Bering Sea. The high proportion 

 of correct classifications based on parasites suggest that 

 these differences are well established. 



Recognition of three such groups is also supported 

 by several of Skuds (1977) observations. He presented 

 data suggesting that after fish home to spawning areas, 

 southern and northern fish maintain reasonably separate 

 migration circuits between feeding and spawning grounds. 

 Data from Skud (1977) and more recent tagging data 

 (Geernaert, 1996) also suggest that southern fish move 

 less than their northern counterparts. Skud also recog- 

 nized a resident population in the Bering Sea. These con- 



