754 



Fishery Bulletin 90(4), 1992 



having scars change with age (Shevchenko 1977) might 

 make identification over a prolonged period difficult. 



The lack of distinctive markings on some individuals 

 indicates that while photoidentification is useful in 

 studies of sei whales, it is not likely to allow identifica- 

 tion of all members of the population. Because we were 

 unable to determine the sex and/or age of the animals 

 involved, it is impossible to indicate whether distinc- 

 tive markings were related to age or sex. 



The photographic matches of sei whales in the 

 southern Gulf of Maine to both Georges Bank and the 

 Scotian Shelf lend some support to the idea that whales 

 in the 1986 influx were from the closest-known geo- 

 graphic stock. However, given the dearth of knowledge 

 concerning the biogeography of this species, and 

 Brown's (1977) record of a sei whale moving 4000km 

 in 10 days, many or all of the animals reported here 

 may come from other locations in the North Atlantic. 

 During the year of the southern Gulf of Maine influx, 

 abnormally high levels of Calanus finmarchicus were 

 present on Stellwagen Bank (Payne et al. 1990). Our 

 findings therefore lend support to the hypothesis that 

 sei whales show annual areal fluctuations to take 

 maximal advantage of changes in local productivity 

 throughout their range. Whether each individual in- 

 dependently found the increased copepod productivity, 

 or whether social factors were involved in the influx, 

 remains an open question which our data do not 

 address. 



Most of the sei whales in 1986 were seen during late 

 July and early August, with a secondary peak in early 

 September (Fig. 3). This suggests that the local pro- 

 ductivity provided a brief stop-over point during the 

 summer feeding season. Repeated resightings of a few 

 individuals during the study suggest that a small 

 number of animals found prey levels adequate to allow 

 a prolonged occupancy period. 



Observed behavior of sei whales was similar to that 

 previously described (Tomilin 1957, International 

 Whaling Commission 1977, Horwood 1987). The rela- 

 tively small variation around the mean breath interval 

 shows a departure from the standard balaenopterid 

 pattern of hyperventilation, e.g., several breaths taken 

 in rapid succession followed by a longer diving period 

 (Gunther 1949, Leatherwood et al. 1976). The rolling 

 we observed during apparent feeding behavior differs 

 from that described by Tomilin (1957) who did not 

 observe this species roll during feeding. 



Social groups observed in this study are similar to 

 those reported by studies of other balaenopterids, with 

 individuals being sighted either alone or in small groups 

 (Nemoto 1964, Dorsey 1983, Whitehead and Carlson 

 1988). Lockyer (1977) reported a mean associated 

 group size of 2.4, slightly higher than the 1.8 reported 

 here. Since she did not define an associated group, 



however, direct comparisons are difficult. Further, if 

 there is a correlation between the associated group-size 

 and prey patch-size (such as that described for hump- 

 back whales by Whitehead 1983), it is possible that the 

 larger group size observed could be explained by the 

 more productive Antarctic waters. Our limited data 

 also suggest that, as in other baleen whales, cow/calf 

 pairs were more solitary than other animals, both in 

 frequency of association with other individuals and in 

 overall group size. This has previously been docu- 

 mented in humpback whales (Clapham and Mayo 1987), 

 gray whales Eschrichtius robustus (Swartz 1986), and 

 right whales Eubalaena australis (Payne 1986). 



Acknowledgments 



Many people helped gather field data including Cindy 

 Belt, Carole Carlson, Peggy Christian, Lisa Frohock, 

 David Mattila, Sharon Pittman, and many interns. 

 Polly Hamlin (CCS), Maribel Marcy (CRU), and Lisa 

 Frohock (ACRC) helped considerably in compiling raw 

 data. Scott Kraus (New England Aquarium), Nancy 

 Miller, Fred Wenzel, and Dave Wiley all provided 

 photographs of sei whales for comparison with our 1986 

 sightings. Dr. Steven Katona and his colleagues at the 

 College of the Atlantic generously took their time to 

 examine the fecal material. We thank the owners and 

 crews of the Dolphin Fleet, Cape Ann Whale Watch, 

 Cap't Bill and Sons Whale Watch, and Gloucester 

 Whale Watch for their logistical help and support. 

 Funding for this study came from the National Marine 

 Fisheries Service, the American Cetacean Society/Los 

 Angeles Chapter, the Essex County Ecologj' Center, 

 and Gloucester Whale Watch: we are indebted to 

 them all. 



Citations 



Agler. B.A., J. A. Beard, R.S. Bowman, H.D. Corbett, 



S.E. Frohock, M.P. Hawvermale. S.E. Katona. S.S. Sadove, 

 and I.E. Seipt 



1990 Finback whale. Balaenoptera physalus, photographic 

 identification: Methodology and preliminary results from the 

 western North Atlantic. Rep. Int. Whaling Comm. (Spec. 

 Issue 12):349-356. 

 Brown, S.G. 



1977 Some results of sei whale marking in the Southern 

 Hemisphere. Rep. Int. WTialing Comm. (Spec. Issue l):39-43. 

 CETAP (Cetacean and Turtle Assessment Program) 



1982 A characterization of marine mammals and turtles in the 

 mid- and north Atlantic areas of the U.S. outer continental 

 shelf. Final Report of the Cetacean and Turtle Assessment 

 Program, University of Rhode Island, to the Bureau of Land 

 Management, Washington D.C. Kingston, 450 p. 



