Abstract.— Sei whales Balenop- 

 tera horealis are noted for major 

 fluctuations in distribution, often in 

 response to local availability of prey. 

 An influx of sei whales occurred in 

 the southern Gulf of Maine during 

 summer 1986. Forty-seven individ- 

 uals (including four mothers with 

 calves) were photographically iden- 

 tified using natural markings, in- 

 cluding dorsal-fin notches, placement 

 of small circular scars on the ani- 

 mal's flank, and natural variation in 

 dorsal-fin shape and pigment swaths 

 along the dorsal surface behind 

 the blowholes. Seventeen of these 

 whales (36.1%) were photographed 

 on more than one day, and the period 

 between first and last sighting of 

 individuals ranged from one to 66 

 days. Only six animals were sighted 

 in more than one region in the south- 

 ern Gulf of Maine. Observed behav- 

 ior included traveling, nearsurface 

 skim feeding, lunge feeding, and 

 (rarely) "milling" or breaching. Group 

 sizes were small and variable. Two 

 individuals were matched to photo- 

 graphs taken in other regions in or 

 near offshore Gulf of Maine waters. 

 We hypothesize that the southern 

 Gulf of Maine represents a short- 

 term feeding site. The occurrence of 

 individuals without sufficient marks 

 for individual recognition suggests 

 that photoidentification is of limited 

 value in the study of this species. 



Behavior of individually- identified 

 sei whales Balaenoptera borealis 

 dun'ng an episodic influx into the 

 southern Gulf of Maine in 1986 



Mark R. Schilling 



Cetacean Research Unit, P.O. Box 159, Gloucester, Massachusetts 01930 



Irene Seipt 



Cetacean Research Program, Center for Coastal Studies 

 Provincetown, Massachusetts 02657 



Mason T. Weinrlch* 



Cetacean Research Unit, P.O. Box 159. Gloucester, Massachusetts 01930 



Steven E. Frohock 



Atlantic Cetacean Research Center, P.O Box 1413, Gloucester, Massachusetts 01930 



Anne E. Kuhlberg 



Cetacean Research Unit, PO Box 159, Gloucester, Massachusetts 01930 



Phillip J. Clapham 



Cetacean Research Program, Center for Coastal Studies 



Provincetown, Massachusetts 02657 

 Department of Zoology, University of Aberdeen, Aberdeen AB9 2TN, Scotland 



Most species of baleen whales under- 

 take seasonal migrations between 

 high-latitude feeding grounds and 

 warmer breeding areas (Kellogg 1929, 

 Slijper 1962, Mackintosh 1965). Pop- 

 ulations often show annual variations 

 in local spatial distribution within 

 these areas (Wursig et al. 1985). 

 While the factors causing these varia- 

 tions are not well defined for breed- 

 ing grounds, it has been suggested 

 that they are explained on feeding 

 grounds by differences in prey distri- 

 bution (Whitehead and Carscadden 

 1988, Payne et al. 1990). Because of 

 the energetic demands upon large 

 whales (Lockyer 1981) and the unpre- 

 dictable distribution of their prey, 

 such areal variation would be ex- 

 pected if the animals were seeking to 



Manuscript accepted 5 July 1992. 

 Fishery Bulletin, U.S. 90:749-755 (1992). 



* Author to whom reprint requests should be 

 sent. 



maximize their feeding efficiency. 



Sei whales Balaenoptera borealis 

 have been reported to have greater 

 variation in distribution on their feed- 

 ing grounds than most baleen whale 

 species (Horwood 1987). Sei whales 

 have been reported in considerable 

 numbers for brief periods outside of 

 their regular range in Norway (1885, 

 1898, and 1919), Finland (1885), and 

 Scotland (1906) (Tomilin 1957, Jons- 

 gard and Darling 1977). Ingebrigtsen 

 (1929) reported large annual changes 

 in distribution off the Faroe Islands. 

 These changes are hypothesized to be 

 related to local increases in plank- 

 tonic productivity (International 

 Whaling Commission 1977, Horwood 

 1987). 



Sei whales off the northeastern 

 United States and southeastern Can- 

 ada have been little studied. Mitchell 

 and Chapman (1977) hypothesized 



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