BEHAVIOR AND SEGREGATION OF THE DALL ' S PORPOISE IN THE NORTHWESTERN NORTH PACIFIC OCEAN
To improve knowledge of the life history of Dall's porpoise, Phocoenoides dalli (True, 1885) that are incidentally caught by the Japanese salmon mothership fishery in the northwestern North Pacific, a 34-day cruise was conducted during August-September, 1982, after the fishing season. A total of 710 Dall's porpoise were sighted and 80 were caught using hand-held harpoons. The species' southern limit was at 41°N latitude, at a surface water temperature of l8°-l9°C, and overlapped the range of Lissodelphis and Lagenorhynchus. Distribution of the truei-type was limited to the Japanese coastal waters and the number sighted was negligible east of 155°E. Density of Dall's porpoise was higher in the western and northern parts of the research area, and somewhat lower in the southeast. More Dall's porpoise rode the ship's bow wave during mid-day than in the morning or evening, and in areas where the surface water temperature was 11°C or above. In areas with a surface water temperature of 11°C or below, most of the Dall's porpoise avoided the ship. The latter areas had a high number of mother-calf pairs and calves possibly weaned, none of which rode the bow wave. Adults not accompanying calves were sighted in both areas. School size was not different between the two areas. Most of the specimens were taken in the southern part of the study area. Males predominated and most were 2 to 6 years old, around the age of attainment of sexual maturity. Lactating individuals were significantly scarce in the sample. The dalli-type reached sexual maturity at a smaller body length than the truei-type. Based upon comparisons of results from this cruise with those obtained from the salmon mothership fishery since 1978, we conclude that, during the season from June through September, (I) females in the state of late pregnancy, lactation, or pregnancy and simultaneous lactation are mainly distributed in the northern area, and (2) the southern area is mainly occupied by males and some females not accompanied by calves. 1 Present address: Far Seas Fisheries Research Laboratory, 5-7-1 Orido, Shirnizu-shi, Shizuoka-ken 424, Japan. Sci. Rep. Whales Res. Inst., No. 35, 1984, 107-128 108 KASUYA AND JONES
Abundance and Seasonality of Dall’s Porpoise (Phocoenoides dalli) in Southeast Alaska.
Little is known about Dall’s porpoise (Phocoenoides dalli) population biology in Southeast Alaska. Here we present the first abundance estimates for Dall’s porpoise in the waters of Southeast Alaska. We studied the density and abundance of Dall’s porpoise during 19 line-transect vessel surveys covering the major inland waters of Southeast Alaska between the months of April and September, from 1991 to 2012. Dall’s porpoise was the most frequently encountered odontocete (toothed cetacean) within the study area and abundance was estimated with multiplecovariate distance sampling methods. Highest abundance was recorded in spring months (N = 5,381, CV = 25.4%), with lower numbers in summer (N = 2,680, CV = 19.6%), and lowest in fall (N = 1,637, CV = 23.3%). Peak density in spring months (31.6 porpoises/100 km2) was the highest ever reliably recorded for inshore areas of the species’ range. Estimates of abundance for comparable areas (i.e., those surveyed consistently in each study year) showed strong yearly fluctuations, and demonstrate that this species is a common inhabitant of these waters from at least spring to early fall.
On a new species of porpoise, Phocaena dalli , from Alaska
gion, and lower tail coverts, rich vinaceous-cinnamon, lighter and more buffy on the abdomen, duller and more olivaceous on the tibiae. Lining of the wing dull black ; edge of wing buff", becoming jialer on the carpometacarpal region. Sides and flanks blackish-slate, with a strong glau. cous or chalky cast in certain lights. Gray of the back separated from the light drab or grayish-buff' of the neck by a narrow bar of black. Wing, 10.50; tail, 4.80; culmeu, 3.20; depth of bill, .95; width of bill, 1.75 ; tarsus, 2.75 ; middle toe, 2.35. Twelve examples, from various parts of southern and western Mexico, Guatemala, Nicaragua, Costa Rica, and Veragua, differ constantly and conspicuously from two South American specimejns (one from the mouth of the Amazon, the other from British Guiana) in the characters pointed out above. The specimen described and selected as the type of the new species is the lightest colored example among the twelve. A binomial appellation is in this case preferred to a trinomial, for the reason that there is no indication of i^robable intergradation, the most southern specimen of the Central American form. (from Veragua) being, on the contrary, the darkest of the whole lot. The species is named in honor of Senor Don Jose C. Zeledon, the accomplished ornithologist, of San Jose, Costa Rica.