Abstract. — A total of 707 common 

 dolphins, Delphinus delphis Linnaeus, 

 (376 males and 331 females) taken in 

 Japanese, Korean, and Taiwanese drift 

 nets in the central North Pacific Ocean 

 from February to November 1990 and 

 1991 were examined. Sex, total length, 

 date, and location of capture were re- 

 corded. Biological samples were col- 

 lected from 152 of the dolphins exam- 

 ined (93 males and 59 females). Ages 

 were determined by counting dentinal 

 layers. Female reproductive status was 

 determined by macroscopic examina- 

 tion of ovaries (n=43). Eight females 

 were mature, two were pregnant, three 

 were resting, two were lactating, and 

 one was of unknown condition. Testes 

 and epididymes were examined for evi- 

 dence of spermatogenesis (rc=70); 21 

 males were mature. A preliminary es- 

 timate of gestation period was 11.1 

 months. The sex ratio appeared to fa- 

 vor males; segregation during the sam- 

 pling period may be responsible for dif- 

 ferences from 1.0. Male average age at 

 sexual maturation was estimated to be 

 10.5 years. The largest sexually imma- 

 ture male was 179 cm; the smallest 

 sexually mature was 182 cm. Mature 

 testis weights ranged from 273.2 g to 

 1,190 g. Females reached sexual matu- 

 ration at about 8.0 years; estimates of 

 length at sexual maturation were 172.8 

 and 170.7 cm. Predicted asymptotic 

 lengths for males and females were 

 188.1 cm and 179.4 cm, respectively. 

 Calving appeared to peak in May and 

 June. Sampling effort moved north- 

 ward through September; infrequent 

 sampling of parturient females and 

 neonates during the projected calving 

 mode suggests they were segregated 

 outside the fishing area at that time. 



Growth and reproduction of the 

 common dolphin, Delphinus delphis 

 Linnaeus, in the offshore waters 

 of the North Pacific Ocean 



Richard C. Ferrero 

 William A. Walker 



National Marine Mammal Laboratory, Alaska Fisheries Science Center 



National Marine Fisheries Service, NOAA 



7600 Sand Point Way, NE, Seattle, Washington, 981 15 



Manuscript accepted 12 December 1994. 

 Fishery Bulletin 93:483-494 (1995). 



The common dolphin, Delphinus 

 delphis Linnaeus, is an oceanic spe- 

 cies widely distributed throughout 

 the tropical and temperate seas of 

 the world. In the western North 

 Pacific Ocean, published accounts 

 have dealt almost exclusively with 

 taxonomy, distribution, and sea- 

 sonal movements (Ogawa, 1937; 

 Nishiwaki, 1967; Kasuya, 1971; 

 Ohsumi, 1972). The common dol- 

 phin has been studied most exten- 

 sively in the eastern North Pacific 

 Ocean where research has focused 

 primarily on species distribution, 

 herd movements, reproductive sea- 

 sonality, stock differences, and be- 

 havior (Norris and Prescott, 1961; 

 Brownell, 1964; Hui, 1979; Evans, 

 1982; Perrin et al., 1985; Perryman 

 and Lynn, 1993; Heyning and 

 Perrin, 1994; Walker and Cowan 1 ; 

 Walker et al. 2 ). 



Two morphotypes of common dol- 

 phin, a short-beaked form and a 

 long-beaked form, differing in ros- 

 tral length, overall size, and color 

 pattern, have been described from 

 southern California waters (Banks 

 and Brownell, 1969; Evans, 1975). 

 Heyning and Perrin (1994) de- 

 scribed two species of Delphinus 

 from the eastern North Pacific 

 Ocean, a short-beaked form which 

 is referable to D. delphis Linnaeus 

 and a long-beaked form assigned to 

 the nominal species D. bardaii Dall, 



1893. Recent studies of molecular 

 genetics confirm the morphologic 

 findings and support distinction of 

 these two morphotypes of common 

 dolphin as separate species (Rosel 

 et al., 1994). 



Despite the abundance of D. 

 delphis in the eastern North Pacific 

 Ocean, little biological information 

 on age, growth, and reproductive 

 condition exists in the literature. 

 Ridgway and Green (1967) and 

 Harrison et al. (1972) present go- 

 nadal data for a total of 30 male and 

 25 female specimens collected over a 

 16-year period from single strandings 

 or live-capture. Correlations with 

 age were not incorporated in either 

 study. Hui (1979) correlated age, 

 reproductive condition, and flipper 

 bone development and summarized 



1 Walker, W. A., and D. F. Cowan. 1981. Air 

 sinus parasitism and pathology in free- 

 ranging common dolphins, Delphinus 

 delphis, in the eastern tropical Pacific. 

 Southwest Fish. Sci. Cent., Natl. Mar. 

 Fish. Serv., NOAA, 8604 La Jolla Shores 

 Dr., La Jolla, CA 92038. Admin. Rep. LJ- 

 81-23C, 19 p. 



2 Walker, W. A., F. G. Hochberg, and E. S. 

 Hacker. 1984. The potential use of para- 

 sites Crassicauda (Nematoda) and Nasi- 

 trema (Platyhelminthes) as biological tags 

 and their role in the natural mortality of 

 common dolphins, Delphinus delphis, in 

 the eastern North Pacific. Southwest Fish. 

 Sci. Cent., Natl. Mar. Fish. Serv., NOAA, 

 8604 La Jolla Shores Dr., La Jolla, CA 

 92038. Admin Rep. LJ-84-08C, 31 p. 



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