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Fishery Bulletin 93(3), 1995 



April and the other in June). In the waters off Que- 

 bec, one pair (adult and calf) was observed in late 

 July (Perkins and Whitehead, 1977). Similarly, calves 

 have not been reported in the waters off the west 

 coast of the United States (Dorsey, 1983) and are also 

 not commonly observed on the high-latitude feeding 

 grounds in the Southern Hemisphere (Kasamatsu et 

 al., 1988). 



In the North Atlantic, the majority of minke whale 

 calf sightings have occurred in lower latitudes. In 

 the southwestern North Atlantic, calves have been 

 sighted in the waters between Bermuda and the 

 Antilles (Mitchell, 1991) as well as in the northern 

 Leeward Islands (Mattila and Clapham, 1989). 



One possible explanation for the absence of calves 

 in higher latitudes is that minke whales wean their 

 calves before entering these waters. According to 

 Jonsgard (1951), North Atlantic minkes are thought 

 to calve between November and March, and nursing 

 is believed to last for only four to five months. This 

 information would concur with reports of no or few 

 lactating females found during the summer off both 

 Norway (Jonsgard, 1951) and Newfoundland (Ser- 

 geant, 1963; Mitchell and Kozicki, 1975). 



In the Southern Hemisphere, it also appears that 

 females wean their calves before reaching higher lati- 

 tudes (Best, 1982; Kato and Miyashita, 1991). How- 

 ever, there is evidence (at least in the Southern Hemi- 

 sphere) that pairs (mother and calf) may remain in 

 low or middle latitudes until weaning occurs (Kato 

 and Miyashita, 1991), which suggests that some minke 

 whale populations segregate by reproductive class. 



Segregation by both sex and age class has been 

 described in many minke whale populations. Whal- 

 ing data from the North Atlantic, the North Pacific, 

 and the Southern Hemisphere suggest that minke 

 whales segregate by sex during their summer mi- 

 gration (Jonsgard, 1980; Kasamatsu and Ohsumi, 

 1981; Sigurjonsson, 1982; Larsen and 0ien, 1988; 

 Wada, 1989) as well as on their feeding grounds 

 (Jonsgard, 1980; Ohsumi, 1983; Larsen and 0ien, 

 1988; Wada, 1989; Kato et al., 1990a). Segregation 

 by maturational class has also been recorded in 

 minke whales (Best, 1982; Ohsumi, 1983; Wada, 

 1989; Kato et al., 1990a). Jonsgard (1951) suggested 

 that newly weaned calves and juveniles off Norway 

 probably do not migrate north together with larger 

 animals, which is in agreement with data reported 

 by Wada (1989) for areas off the Pacific coast of Japan. 



Neither the sex nor age class of the minke whales 

 in the waters of Cape Cod and Massachusetts Bay 

 areas is known because it is not currently possible 

 to determine either in the field. Stranding data from 

 this area give a mean length for minke whales of 

 505 cm (n=35, SD= 140.3 cm); comparison of this fig- 



ure with data on lengths of individuals caught in 

 North Atlantic whaling operations (Jonsgard, 1951; 

 Sergeant, 1963; Mitchell and Kozicki, 1975; 

 Christensen, 1981) would suggest that the majority 

 of animals that have stranded here were immature. 

 The sex ratio of stranded animals was approximately 

 even. Whether this sample is representative of the 

 general population or only of those more likely to 

 strand is unknown. 



Group size 



In this study approximately 95% of all minke whale 

 sightings were singletons. Single animals appear to 

 predominate in other studied areas, although there 

 is evidence of group size changing by season, lati- 

 tude, sex and age class, and when prey is present. In 

 some cases, however, it is unclear whether animals 

 reported in large groups (particularly when feeding) 

 are actually associated with or are simply attracted 

 to a common location by the presence of prey. 



Data from the Mingan Islands in the Gulf of Saint 

 Lawrence show that minke whales are usually soli- 

 tary, although they are seen in large coordinated 

 groups of five to fifteen animals when actively feed- 

 ing. 3 Aerial surveys conducted off Iceland in June 

 and July reported a mean school size of 1.1 (Gunn- 

 laugsson et al., 1988). Jonsgard (1951) found that 

 minke whales tend to travel alone off the western 

 coast of Norway, noting only a few sightings consist- 

 ing of pairs; in the Arctic, single animals were pre- 

 dominant in catches, although groups of three to ten 

 animals were more common than pairs. In the west- 

 ern North Pacific off the Chukotka coast, sightings 

 were usually of single animals. However, when po- 

 lar cod arrive in late June and in July, minke whales 

 are often observed in groups of five or six animals 

 (Ivashin and Votrogov, 1981); again, it is not clear 

 whether such groups are truly associated according 

 to the definition of 'group' used here. Information on 

 minke whales in the Southern Hemisphere also in- 

 dicates variabilty in group size with changes in lati- 

 tude and season as well as with differences in matu- 

 rational class (Williamson, 1975; Best, 1982; Kato et 

 al., 1989; Kato et al., 1990b). 



The group size frequency of minke whales observed 

 in the Massachusetts Bay and Cape Cod Bay areas 

 did not appear to change with time of year or with 

 the presence of prey (on the basis of sightings where 

 confirmed feeding occurred). Because the majority 



3 Sears, R., F. W. Wenzel, and J. M. Williamson. 1981. Behavior 

 and distribution observations of Cetaeea along the Quebec north 

 shore (Mingan Islands), summer-fall 1981. Mingan Islands 

 Cetacean Study, Montreal, Unpubl. Rep., 72 p. 



