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Fishery Bulletin 89(3). 1991 



found only in large bulls from the higher latitudes. 

 Group C comprises four helminths (P. grandis, Mono- 

 rygma grimaldii (Moniez, 1889) Baylis, 1919, Diphyl- 

 lobothrium sp., and Placentonema gigantissima Guba- 

 nov, 1951) found only in female whales captured in the 

 lower latitudes. 



Discussion 



The prediction that, "When a species of host is divided 

 into two or more population groups separated geo- 

 graphically in different environments, their respective 

 parasite faunas will exhibit differences" (Noble and 

 Noble 1964) is particularly true for helminths that 

 generally require more than one host to complete their 

 life history. The occurrence of a particular parasite in 

 any geographic locality depends upon the presence of 

 a suitable definitive host, suitable intermediate host(s), 

 and complex biological factors which impart a strict 

 interdependency on the organisms comprising the host- 

 parasite complex. 



Knowledge of host dietary composition 

 is very important in studying cetacean 

 helminth zoogeography. Over any area as 

 large as the Antarctic Ocean, widely sep- 

 arated stocks of whales may exploit dif- 

 ferent food organisms. 



Kawamura's (1974) report on the feed- 

 ing ecology of southern hemisphere sei 

 whales recognized a latitudinal succession 

 of major food species. In its southward 

 migration, the sei whale exploits several 

 major food organisms: euphausiids at 

 high latitudes, pelagic amphipods at low 

 latitudes, and copepods at intermediate 

 latitudes (Gaskin 1982). Kawamura 

 (1974) also recognized longitudinal varia- 

 tions in the availability of prey species. 

 Euphausiid crustaceans comprise the 

 bulk of this host's diet in sectors IV 

 through VI while amphipods are more 

 prevalent in their diet in sectors III and 

 IV. Calanoid copepods are of considerable 

 supplementary importance in sectors V 

 and VI. As a species, the sei whale is the 

 most euryphagous balaenopterid whale 

 (Klumov 1963). Budylenko (1978) lists 

 over 80 prey species for this host. Yet 

 Kawamura (1974) indicates that individ- 

 ual sei whales are stenophagous feeders, 

 where stomachs containing more than 

 one prey species are rare. 



Since the prey species are, in all prob- 

 ability, the intermediate hosts of cetacean 

 helminths, variable dietary compositions within species 

 of whales will manifest themselves in their respective 

 helminth faunas. Thus, individual stocks of whales 

 may be distinguishable by regional helminthofaunal 

 peculiarities. 



Seventeen species of helminth have been reported 

 from the sei whale (Table 5). Two of these helminths, 

 the acanthocephalan Bolbosoma turbinella and cestodes 

 of the genus Tetrabothrius, were found in all sei whales 

 sampled in the 1976-77 season. Skrjabin (1968) also 

 found a very high prevalence and intensity of these 

 worms in sei whales throughout the Antarctic. 



The tetrabothriids obtained from sei whales in 

 1976-77 represent two distinct species and one am- 

 biguous form (Table 2). Two (T. wilsoni, T. sp.) have 

 a very high prevalence of infection and the other (T. 

 affinis) occurs less frequently. 



The remaining helminths are encountered less fre- 

 quently in sei whales and several have a very restricted 

 geographical distribution (Table 5). Skrjabin (1975) 

 reported several helminth species whose distributions 

 were limited to specific geographical localities. He 



