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Fishery Bulletin 90(4)^ 1992 



the existence of a "stock" of sei whales centered 

 around Nova Scotia. During the spring these animals 

 are thought to occur on the southern edge of George's 

 Bank (Mitchell and Chapman 1977, CETAP 1982). Dur- 

 ing June and July, they move north to the southern 

 Scotian Shelf, then onto Brown's, Bacarro, and Rose- 

 way Bank from August to October (Sutcliffe and Brodie 

 1977). The lack of sightings in these areas, plus late- 

 winter/early-spring strandings in South Carolina, Loui- 

 siana, and Mississippi suggest a southward movement 

 after October (Mead 1977). The inshore waters of the 

 southern Gulf of Maine are rarely used by sei whales 

 (CETAP 1982, Payne et al. 1990). 



In this paper, we report on the photoidentification, 

 occupancy patterns, surface behavior, and social 

 behavior of individual sei whales found in the Gulf of 

 Maine during an unexpected summer influx of this 

 species in 1986, documented through daily shipboard 

 surveys. We also report results of photographic iden- 

 tification of individual sei whales, and evaluate the 

 feasibility of such techniques for investigations of this 

 species. 



Methods 



Non-systematic surveys of the southern Gulf of Maine 

 were conducted daily (weather permitting) from mid- 

 April through October on commercial whale-watching 

 and research vessels operating out of Provincetown 

 and Gloucester, Massachusetts during 1980-91. In 

 1986, the only year of sei whale abundance, the number 

 of vessels collecting data varied. There were usually 

 six to nine 4-hr cruises daily from each port. Vessels 

 were 18-30 m long diesel-powered whale-watching 

 vessels and 6.7-14 m long research vessels powered by 

 sail, diesel, or outboard engines. Whale-watch cruises 

 were typically 4-5 hr in duration, while research-vessel 

 cruises often lasted from dawn until dusk. 



Search effort by whale-watching vessels was concen- 

 trated on the southern and northern edges of Stell- 

 wagen Bank and the southern edge of Jeffrey's Ledge 

 because of the concentrations of whales there (Fig. 1). 

 Stellwagen Bank is a shallow glacial deposit with a sand 

 substrate, at 20-40m. Southern Jeffrey's Ledge has 

 a mean depth of 48 m, and is a mixture of sand, gravel, 

 and rocks. Depths surrounding both areas extend to 

 182 m. In both areas there is upwelling, caused by steep 

 topography which enriches the biological productivity 

 of the area, providing food for whales (Kenney and 

 Winn 1986). 



For each sighting data included location, direction 

 and speed of animal movement (based on LORAN-C 

 readings taken every 5-10 min), environmental condi- 

 tions, behavioral information including respiration in- 



CLOUCESTER 



JEFFREY'S LEDGE 



STELLWAGEN BANK 



-7r, 05w 



Figure 1 



Study area in the Gulf of Maine. 



tervals (to the nearest second) of individuals recog- 

 nizable by natural marks, notable non-respiratory sur- 

 face behavior, and associations among whales. Two or 

 more whales were considered associated if they were 

 in close proximity and consistently coordinated in the 

 timing and direction of their surfacings. 



Cow/calf pairs were treated as single animals for an 

 analysis of occupancy periods (the time between first 

 and last sighting), assuming that the calf's movements 

 are determined by those of its mother. Calves were 

 designated based on the animal being considerably 

 smaller than any other animals, and on the continuous 

 association between two individuals for at least 30 min 

 or on more than one day. Personnel were experienced 

 in observing mother-calf pairs of humpback Megaptera 

 novaeangliae and fin Balaen.optera physalus whales. To 

 determine mean associated group size, mother and calf 

 pairs were counted as two individuals. 



Fecal samples were scooped from the surface in a 

 5-gallon bucket on two days in August 1986 near north- 

 ern Stellwagen Bank. The material was frozen until 



