Fishery Bulletin 101(1) 



elusions pose two questions. First, do fish from different 

 groups mix extensively? Second, do such groups represent 

 reproductive units or stocks? 



Our analysis was based on a small set of larval para- 

 sites, all of which are known to be long-lived and do not 

 multiply in the host. Other long-lived parasites such as 

 the myxosporeans have been used in stock discrimination 

 but were not included here because of a lack of abundance 

 data. However, the decreased ability to detect differences 

 because of the small data set was offset by an increased 

 ability to detect the host's past activities. Most of these 

 parasites live for at least several years; therefore, the 

 presence and abundance of these parasites may indicate 

 where the host has been over that time period. At least 

 some of the individuals of each of the parasite species, 

 however, were probably short-term acquisitions (lasting a 



few years); thus, there may be some bias in the data of the 

 recent past. 



Our data suggest less extensive movement of Pacific 

 halibut in southern areas. Because parasites are generally 

 more abundant in the south, southern fish may be more 

 easily classified. Nevertheless, if the southern fish mingle 

 extensively with more northern fish, there should be more 

 similarity in the parasite faunas. In particular, central 

 area fish should develop characteristics of southern fish. 

 This did not happen, as is shown by the very low propor- 

 tion of central fish misclassified as southern fish (Table 

 5). Our information cannot completely rule out the move- 

 ment of southern fish to central areas during the spawn- 

 ing season, and then back to southern areas for the feed- 

 ing season. Their long-lived parasite fauna, having been 

 established in the distinct southern areas, would probably 



