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examination. Prey remains were identified to species 

 by staff of Allied Whale at the College of the Atlantic, 

 Bar Harbor, Maine. 



High-speed (ISO 400) black-and-white film was used 

 in 35 mm single-lens reflex cameras equipped with 

 telephoto lenses (range 200-400 mm) to photograph 

 whales. When possible, three regions were photo- 

 graphed on each side of a whale: between the tip of the 

 snout and the blowhole, the flank between the blow- 

 hole and dorsal fin, and the dorsal fin. 



Photos were classified as matchable or unmatchable 

 based on the same criteria defined by Seipt et al. (1990) 

 for fin whale photoidentification. Unmatchable photos 

 had poor focus, were not perpendicular to the whale, 

 or were too far from the whale to distinguish marks 

 clearly (generally photos taken at distances >100m 

 from the whale). For photos judged matchable, a whale 

 was classified as a unique individual based on the 

 presence of one or more of the following characters: 

 recognizable scars, a distinctive dorsal-fin shape (in- 

 cluding dorsal-fin notches), or detectable pigmentation 

 on the flank between the blowhole and dorsal fin. If 

 at least one of these features was not present in a 

 photograph, it was discounted. 



Matches of individual whales were made within in- 

 dependent photographic collections of the Atlantic 

 Cetacean Research Center (Gloucester MA), the Center 

 for Coastal Studies (Provincetown MA), and the Ceta- 

 cean Research Unit (Gloucester MA) by personnel ex- 

 perienced in photo-identifying individual humpback or 

 fin whales. The independent catalogs of identified 

 whales from each organization were compared, with 

 matches being confirmed by both other groups, 

 resulting in a single collective catalog of identified 

 whales. Only matches agreed upon by all parties were 

 accepted. 



In order to examine long-range movements of sei 

 whales, photographs were solicited from researchers 

 working in the Gulf of Maine for comparison with the 

 unified catalog described above. Each set of photo- 

 graphs obtained in different geographic areas or years 

 were treated separately. 



Data for this study were stored on PC-based micro- 

 computers and statistical analyses were performed 

 using SPSS (1989) statistical software package for 

 PC's, including calculation of mean values and standard 

 deviations. A two-tailed <-test was used to compare 

 mean values for associated group sizes between dif- 

 ferent parts of the study area, and a x" test was used 

 to test potential differences in group sizes when a 

 mother-calf pair was present in the group (Zar 1984). 



Results 



Photoidentification 



A total of 240 sei whale sightings took place between 

 29 June and 20 September 1986. Photographs were 

 taken on 182 sightings (75.8%). In 51 photographed 

 sightings (28.0% of all photographed sightings) the 

 animal could not be reliably identified because of poor 

 photographic quality. 



Photoidentification of some individual sei whales was 

 possible using variation in dorsal-fin shape, placement 

 of small circular scars on either flank, and light pig- 

 ment swaths behind the dorsal fin (Fig. 2). A total of 

 47 identifiable non-calf sei whales and 4 calves were 

 photographed; of these, 19 were identifiable based on 

 notches in their dorsal fin alone, 4 based on the loca- 

 tions of small circular scars on the flanks, and 10 based 

 on both distinctive dorsal fins and circular scars. No 

 attempt was made to photoidentify calves. Twelve 

 whales were identified based on dorsal-fin shape and 

 pigment swaths behind the blowhole. One sei whale was 

 missing its dorsal fin, and one had a large white scar 

 visible on the lower portion of its right caudal pedun- 

 cle. In 12 cases, animals did not have distinctive marks 

 by which they could be identified reliably. 



Occurrence and occupancy 



The 47 individual sei whales were sighted on as few 

 as 1 and as many as 15 separate days (x 2.4, SD 3.0) 

 (Fig. 3). Seventeen individuals (36.2%) were observed 

 on more than one day; the mean period for resighted 

 animals between first and last sighting was 26.8 days 

 (SD 24.1, median 20.0). No individual sighting record 

 spanned more than 66 days from first to last sighting. 

 Twenty-six individuals (55.3%) were initially photo- 

 graphed on southern Stellwagen Bank, 15 (31.9%) on 

 northern Stellwagen Bank, 4 (8.5%) on Jeffrey's 

 Ledge, 1 (2.1%) in Massachusetts Bay (west of Stell- 

 wagen Bank), and 1 (2.1%) in the Great South Chan- 

 nel. Only 6 animals out of the 17 resighted were 

 photographed in more than one of these areas. Of 

 these, four were first seen on southern Stellwagen and 

 subsequently moved north on the Bank; one animal 

 showed the reverse pattern. The remaining one was 

 first photographed on southern Jeffrey's Ledge and 

 later resighted on northern Stellwagen Bank. One of 

 these whales moved between northern and southern 

 Stellwagen Bank at least five times; this individual also 

 had the greatest number of sightings (15) and the 

 longest period between first and last sighting. 



