SUMMER FEEDING-HABITS OF DALL PORPOISE, PHOCOENOIDES-DALLI, IN THE SOUTHERN SEA OF OKHOTSK

Stomach contents were analyzed from 85 Dall's porpoises, Phocoenoides dalli, taken in the southern Sea of Okhotsk during the summer of 1988. Thirteen species of fish and five species of cephalopods were identif ied. Fishes comprising 9 families were predominant and made up 79.9% o f the total number of prey, with an overall occurrence in the stomachs of 100%. Three families of cephalopods made up 20.1% of the total num ber of prey ingested, with an overall occurrence of 74%. The Japanese pilchard, Sardinops sagax melanostictus, was the primary prey and repr esented 72.0% of the total prey in 97.3% of the stomachs examined. The gonatid squid, Berryteuthis magister, ranked second and made up 16.9% of the total prey in 61.6% of the stomachs. Walleye pollock, Theragra chalcogramma, was the third most abundant prey item consumed and repr esented 6.0% of the total, with an occurrence of 53.4%. Composition of the sample by the calculated total mass and caloric intake supports t he numeric findings on the relative importance of the three major prey species to the Dall's porpoise diet. The Japanese pilchard was dearly dominant using these indices and constituted 65.4% of the total mass and 80.7% of the caloric intake. Berryteuthis magister made up 26.8% o f the mass and 15.5% of the caloric intake. Walleye pollock contribute d the least to the diet with 7.9% of the total mass and 3.8% of the ca loric intake. Volumetric data indicate that porpoises are feeding heav ily on Japanese pilchard throughout the daylight hours. Berryteuthis m agister was probably fed upon in the late night or early morning hours . Occurrence of both Dall's porpoise and Japanese pilchard in the coas tal waters of the southern Sea of Okhotsk is seasonal. The summer move ments of Dall's porpoise into this region may be related to the season al migration and abundance of the Japanese pilchard.