Typical group size, according to Black, is 30 or fewer, especially when the dolphins are feeding and socializing. When travelling or resting, though, they sometimes swim in herds of several hundred to a thousand or more. They often keep company with northern right whale dolphins, Risso's dolphins and, occasionally, bottlenose dolphins and California sea lions. Using the technique of radio tracking, Black has found that Pacific white-sided dolphins are probably daytime feeders.
Within the large, scattered groups, Black has tried to photograph "white" Pacific white-sided dolphins - mainly white individuals that have dinstinctive markings - as well as others with nicks on their dorsal fins. She calls such individuals "herd markers" and has reidentified them up to five times, finding that some white-sided dolphins spend from early summer to early winter in the offshore Monterey Bay, California, area. From January through May, the dolphins move farther offshore or to other areas.
Lagenorhynchus obliquidens
Size: 1.9 to 2.3 m, 150 kg. Males slightly larger than females
Calves at birth: 102 to 124 cm
Teeth: 21 to 28 small, pointed, slightly curved teeth on each side
of upper and lower jaws
Food: Fish (anchovies, hake and pilchards) and small squid
Habitat: Mainly off the continental shelf to deep offshore waters
Range: Temperate North Pacific
Status: Population unknown