Seipt et al.: Identification of Balaenoptera physalus in Massachusetts Bay 



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left side was photographed. Because fin whales gener- 

 ally have less marked variations in their features than 

 do humpback or right whales, and because a series of 

 photographs of high quality are generally required to 

 successfully identify an individual, we adopted a con- 

 servative approach in our matching: only photos of ex- 

 cellent quality were used, and a match was considered 

 confirmed only if three features were common in photo- 

 graphs of both sightings. 



Photographs were taken with a 35-mm camera 

 equipped with a 200-mm, 300-mm or 400-mm lens, 

 power winder, and recording databack. Kodak Tri-X 

 or T-Max film (both rated at ISO 400) was used. Copies 

 of photographs were sent to the North Atlantic Fin 

 Whale Catalogue at College of the Atlantic in Bar Har- 

 bor, Maine, for analysis of the movement of individual 

 whales outside our study area. 



Definitions 



The following terms are used in this report: 



Occupancy The sum of the resighting intervals of an 

 individual whale within years, i.e., the number of days 

 between the first and last sighting of a whale in a par- 

 ticular year. We do not assume that an individual was 

 necessarily present in the study area for all or part of 

 the period between sightings. 



Occurrence The temporal distribution of an indivi- 

 dual whale in the study area, expressed as the total 

 number of separate days on which the whale was 

 observed. 



Resighting interval The interval, in days, between 

 successive sightings of an individual whale within a par- 

 ticular year. 



Results 



During the period 1980-87, a total of 156 fin whales 

 were individually identified. While many other animals 

 were photographed, this number represents only those 

 whales that were sufficiently well-marked and well- 

 photographed to ensure that the file contained no dup- 

 licates. A total of 98 individuals (62.8%) were observed 

 more than once, 70 (44.9%) of which were photo- 

 graphed in more than one year. The photographs 

 shown in Figure 2 provide one example of the features 

 used to identify an individual whale in two different 

 years. 



Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



While fin whales were sometimes observed between 

 the beginning of November and the end of February, 

 none were photographed during this period in any year. 

 (In 1979, only two fin whales were photographed, both 

 of which were subsequently resighted). 



Table 1 shows the number of individuals observed for 

 each year of the study period, the percentage of these 

 animals that were photographed on more than one day 

 in that year, and that were reidentified in each subse- 

 quent year. The occurrence of identified fin whales dur- 

 ing 1987 (the year with the largest number of cruises) 

 is shown in Figure 3. This temporal distribution is 

 broadly representative of other years with a similar 

 level of effort. Table 2 summarizes resighting intervals, 

 grouped by 10-day periods, for 1985, 1986 and 1987 

 combined (the 3 years with the greatest vessel effort). 



Occupancy was calculated for each whale that had 

 been observed more than once in a year (individuals 

 seen only once or not at all in the year were excluded). 

 Observed occupancies (n = 159, including two or more 

 occupancy periods for individuals who were resighted 

 in more than one year) ranged from 1 to 197 days (mean 

 46.1 days, SD 47.407). The mean number of days in a 

 year that individual fin whales were photographed 

 (occurrence) was calculated (including individuals ob- 

 served on only one day, but excluding individuals not 

 observed in the year). Observed values {n = 264) ranged 

 from 1 to 12 days (mean 2.5 days, SD 2.011). 



Of the 70 individual fin whales photographed in more 

 than one year, 26 were observed in 2 years, 15 in 3 

 years, 14 in 4 years, 7 in 5 years, 3 in 6 years, 3 in 7 

 years, and 2 in 8 years. (These figures include the two 

 individuals identified in 1979.) Table 3 summarizes the 

 sighting histories of these whales. 



Discussion 



A major problem confounding interpretation of the 

 data presented here is the relatively low level of effort 

 involved in this study. An appreciation of the difference 

 in effort directed at fin whales and at humpback whales 

 (the whalewatching vessels' preferred species) can be 

 gained by comparing the respective ratios of sightings 

 to individual identifications, i.e., the total number of 

 whales recorded (whether photographed or not) ver- 

 sus the number of sightings for which not only was a 

 photograph taken, but where the photograph was good 

 enough to positively identify the individual. For hump- 

 back whales, this ratio is consistently about 1.2:1 for 

 all years. For fin whales, however, the ratio ranged 

 from 11:1 in 1986 (a year with unusually low numbers 

 of humpback whales) to 83:1 in 1981. The mean for all 

 years was 32:1. These ratios reflect two factors. First- 

 ly, far fewer fin whales were approached than hump- 



