Gaskin et al Phocoena phocoena in the coastal waters of northern Japan 



445 



N = 3), 7(147.4, 158cm, iV = 2), 8 (145.5cm, TV = 2), to 

 11 (149.5cm, N = 1) (Table 2). Testis samples were 

 available for eight mature males of known age. All 

 were captured in March, April or May, 1983-1986, and 

 all specimens had inactive testes. 



Females 



Including those examined by Miyazaki et al., 1987), 

 females ranged in length from 92.4 to 185 cm (N = 25); 

 in addition, one fetus of 62 cm was obtained. Ages were 

 determined for 14 specimens, ranging through 0.5 

 (92.4 cm, AT =1), 2-2.5 (121-143. 5cm, N = 6), 3 (131.5- 

 140 cm, N = 3), 4 (140 cm, N = 1), 8-8.5 (162-166 cm, 

 N = 2) to 9 years (173 cm, N = 1) (Table 3). Seven 

 animals were mature, with one or more corpora al- 

 bicantia. Four of these specimens were pregnant, but 

 none were lactating, based on the non-distended nipples 

 and gross sections of mammary gland which revealed 

 no traces of milk. 



Fetuses 



These were collected on 03 March 1986 (30 cm, N = 1) 

 by the Otaru Aquarium (one other was not retained 

 and not measured), at Otaru on the west coast of 

 Hokkaido, and on 24 April 1986 (58.5, 62 cm, N = 2), 

 at Usujiri on the Pacific coast of southern Hokkaido. 

 Miyazaki et al. (1987) recorded a 73 cm fetus on 3 May 

 1986, from a female taken at 42°37'N, 144°28'E. 



Immature animals of both sexes 



Samples (Tables 2 and 3) from Wakkanai, Nemuro, 

 Habomai, Aomori, Usujiri, Shizukari, Iwanai, and Taiji 

 and in all months sampled other than March (Janu- 

 ary, April, May, October, and December) showed evi- 

 dence of immature animals of both sexes. All were 

 <143.5cm in length (N = 25). Although seven animals 

 were collected from Otaru in March, and one in April, 

 there were no immature animals in the samples. 



Length-Age relationships 



Miyazaki et al. (1987) plotted the age/length relation- 

 ships of nine males and six females from Japanese 

 waters against those from other regions. We have 

 replotted these data (Fig. 2), incorporating the new 

 specimens obtained in the present study, giving a total 

 28 specimens (14 males and 14 females) of known age 

 from Japanese waters. The small samples and cluster- 

 ing still preclude valid statistical comparison and le- 

 gitimate calculation of age-length curves, but female 

 porpoises from Japan are still shown to be larger than 

 females from the North Sea at given ages, as Miyazaki 

 etal. (1987) observed. 



Stomach contents 



We examined the stomachs of 16 porpoises from trap 

 nets near Usujiri and were given samples from four 

 more taken from gill nets by staff at the Otaru 

 Aquarium near Otaru, in April-May of 1985 and 1986. 

 Fifteen stomachs were nearly empty All contained 

 varying numbers of round worms, Ascaris spp. A 

 small quantity of seaweed was found in one 129 cm 

 male; a large quantity of seaweed and a 1-m length of 

 0.25 cm fishing gear twine were found in a 139-cm 

 male in poor condition (sunken dorsal musculature 

 and blubber only about 1cm in thickness). The 

 twine was caught distally at the entrance to the 

 oesophagus and stretched into the second stomach 

 compartment. Food items in the remaining five por- 

 poises were similar. They included small squid 

 beaks (probably Ommastrephidae) and eroded oto- 

 liths in varying quantities, tentatively identified as 

 herring Clupea sp., anchovy Engraulis sp., and hake 

 Merluceius sp. The condition of the remains was 

 poor, and because stomach contents from porpoises from 

 trap nets probably represent only coincident prey 

 trapped with them, we do not report these items in 

 detail. 



Discussion 



Body length at birth and probable season 

 of parturition 



Lengths of three fetuses collected from females caught 

 off Japan were compared with fetal growth curves from 

 the western and eastern Atlantic populations (Fig. 2 

 in Gaskin, 1984). Their lengths fell on or just above 

 the growth curves for Atlantic porpoises. Length at 

 birth in the Hokkaido population, therefore, is prob- 

 ably close to 80 cm, and parturition in northern Japa- 

 nese waters is probably in May-June, judged not only 

 by comparison with the neonatal growth curve of 

 Gaskin et al. (1984) and coincident length/month rela- 

 tionship but also by the parallel degree of develop- 

 ment of the fetuses examined from Usujiri and the 

 North Atlantic. 



Life history pattern 



Based on published literature, there is considerable 

 synchrony in the seasonal breeding of the harbor por- 

 poise throughout its range (Gaskin, 1984). From the 

 limited data presently available from Japanese waters 

 (eg., sizes of fetuses in spring and state of mature 

 testes), we expect the timing of the cycle in the north- 

 ern Japanese population to be similar to the North 



