Behavior and ecology of the Atlantic white-sided dolphin (Lagenorhynchus acutus) in coastal New England waters

Atlantic white-sided dolphins (Lagenorhynchus acutus) are among the most ab undant, and least studied, cetaceans in coastal New England. Between April and October 1984 through 1997 we sighted 1,231 groups of Atlantic white-sid ed dolphins, primarily on Stellwagen Bank and Jeffreys Ledge (two shallow g lacial deposits along the coasts of Massachusetts, New Hampshire, and Maine ). Mean group size was 52 (+/- 90.9), and was significantly larger from Aug ust through October (71.9 +/- 111.4) than April through June (35.0 +/- 45.4 ). Calf sightings were uncommon until June and July, after which they were present in over 50% of groups. Combined with observations of apparent newbo rn calves, this confirms that early summer is an important calving period. The presence of calves did not, however, solely account for the increase in group size. Boat interaction (bow- and stern-wake riding) was the most com monly recorded behavior (47.4% of sightings), followed by traveling (31.4%) , interactions with other cetacean species (27.6%), social interaction (15. 5%), and feeding (9.5%). While feeding was uncommon, one observation of app arently coordinated "ball" feeding was seen with sand lance (Ammodytes spp. ) as the visible prey. Aerial behavior showed a positive correlation with g roup size, although it was often impossible to tell whether the same dolphi ns were leaping repeatedly. Eighty-eight dolphins were photo-identified usi ng either unusual body pigment or a distinctive dorsal fin. While several i ndividuals were reidentified between years and between areas, no reidentifi cations were made within a year in the same area. Unusually pigmented indiv iduals were much more likely to be reidentified than those with distinctive dorsal fins, most likely due to higher visibility. We suggest that Atlanti c white-sided dolphins are generally using the study area as transients in what appears to be a large home range.