Hideyoshi Yoshida

POPULATION STRUCTURE OF FINLESS PORPOISES (NEOPHOCAENA PHOCAENOIDES) IN COASTAL WATERS OF JAPAN BASED ON MITOCHONDRIAL DNA SEQUENCES

Abstract To clarify population structure of finless porpoises (Neophocaena phocaenoides) in Japan, we examined mitochondrial DNA sequences of 174 animals. All individuals except for a female were collected in 5 geographically discrete coastal waters where Japanese porpoises are mainly distributed: Sendai Bay–Tokyo Bay, Ise–Mikawa Bays, Inland Sea–Hibiki Nada, Omura Bay, and Ariake Sound–Tachibana Bay. We analyzed 345 base pairs of the control region for all animals and detected 10 haplotypes. Two of those were shared by animals from > 1 area, whereas the other 8 were each found only in 1 area. The most common haplotype in Ise–Mikawa Bays and Ariake Sound–Tachibana Bay was not found at other locations. Analysis of the frequency distribution of haplotypes quantified genetic differentiation, and measurements of gene flow indicated limited dispersal of animals among locations. We conclude that finless porpoises in each of the 5 locations belong to distinct populations.

Finless porpoise abundance in Omura Bay, Japan : estimation from aerial sighting surveys

We used aerial surveys and line-transect methods to estimate the abundance of the finless porpoise (Neophocaena phocaenoides) in Omura Bay, Japan. We conducted 4 surveys once each season from August 1993 to May 1994. We surveyed 621.5 km and sighted 54 porpoise groups (87 animals). In the spring survey, we detected porpoises offshore as well as inshore, whereas porpoises were mostly inshore in all other seasons. The abundance of porpoises was estimated to be 187 animals (0.6 individuals/km 2 , CV = 20%).

A population size estimate of the finless porpoise,Neophocaena phocaenoides, from aerial sighting surveys in Ariake Sound and Tachibana Bay, Japan

We estimated the population size of the finless porpoise (Neophocaena phocaenoides) in Ariake Sound and Tachibana Bay of western Kyushu, southwestern Japan, from aerial sighting surveys using line transect methods. All 12 surveys were conducted from May 1993 to May 1994 (8 in Ariake Sound and 4 in Tachibana Bay). In addition to these, 14 surveys were also carried out to obtain information on porpoise occurrence in Tachibana Bay (5 surveys) and in neighboring Sumo Nada (5) and Yatsushiro Sound (4). In Ariake Sound, 225 porpoise groups (369 animals) were detected during all flights totalling 1,694.4 km. In Tachibana Bay, a total of 997.8 km was surveyed and 55 groups (290 animals) were sighted. However, no sightings were recorded in Sumo Nada (distance searched = 148.7 km) and Yatsushiro Sound (208.4 km). In Ariake Sound, few sightings were recorded from waters shallower than 5 m in depth. In Tachibana Bay all animals were detected from waters of less than 50 m depth. The population size was estimated as 1,983 animals in Ariake Sound (95% CI = 1,382-2,847), 1,110 in Tachibana Bay (95% CI = 642-1,920), and 3,093 in the 2 waters (1.3 individuals/km2, 95% CI = 2,278-4,201).

FOOD HABITS OF FINLESS PORPOISES NEOPHOCAENA PHOCAENOIDES IN WESTERN KYUSHU, JAPAN

Abstract We examined the stomach contents of 87 finless porpoises (Neophocaena phocaenoides) in the Ariake Sound–Tachibana Bay area and Omura Bay in western Kyushu, Japan, between 1987 and 1992. Fish (Gobiidae and Atherinidae) were the most numerous and most frequently occurring prey in Omura Bay, whereas both cephalopods (Octopodidae, Sepiidae, Sepiolidae/Sepiidae, and Loliginidae) and fishes (Clupeidae, Engraulidae, and Sciaenidae) were equally important in Ariake Sound–Tachibana Bay. Species compositions in the commercial catch differed between the 2 waters, suggesting that differences in prey availability may explain the geographical variation in diet. Finless porpoises in Ariake Sound–Tachibana Bay showed ontogenetic and seasonal variations in diet. The mean length at weaning was estimated to be 101 cm, corresponding to approximately 6 months of age. Calves fed on small-sized demersal fish and cephalopods. The predominant prey species for sexually mature individuals (including lactating females) consisted of konoshiro gizzard shad (Konosirus punctatus) and cephalopods. Seasonal availability of these organisms may be related to births in the fall–winter season in Ariake Sound–Tachibana Bay. Size-dependent prey selectivity was equivocal. Day–night difference in foraging time was not indicated by the index of stomach fullness.

Abundance estimates of dalli-type and truei-type of Dall’s porpoise Phocoenoides dalli in the western central part of the Sea of Okhotsk, July–September between 1990 and 2010

The abundance of dalli- and truei-types of Dall’s porpoise Phocoenoides dalli was assessed based on the multicovariate distance sampling method, using line-transect survey data collected in the western central part of the Sea of Okhotsk between 1990 and 2010. The estimated abundance are 77,856 individuals in 1990, 72,303 in 2009 and 111,402 in 2010 for dalli-type, and 120,198 individuals in 1990 and 101,173 in 2009 for truei-type. Abundance was not estimated for truei-type in 2010 because of small sample size. During this period, abundance seemed to fluctuate, but statistically significant trends could not be detected in abundance. Considerable small numbers of sightings of truei-type in 2010 could be attributed to insufficient survey effort in the southeastern region and warmer temperature in the southwestern region. We surmise that the abundance of Dall’s porpoise migrating into the Sea of Okhotsk during summer depends on interannual shifts in environmental conditions and resulting prey availability.