Abstract. — Little information 

 exists on the biology of the demer- 

 sal shark, Squalus mitsukurii . Re- 

 cently, large numbers of this spe- 

 cies were taken incidentally during 

 research surveys conducted at 

 Southeast Hancock Seamount in 

 the central North Pacific Ocean. 

 The information collected during 

 1985 to 1988 from these surveys is 

 used to describe the life history, 

 depth distribution, and biology of 

 S. mitsukurii. 



Bathymetric distributional pat- 

 terns of female and male S. mitsu- 

 kurii differed slightly, although 

 bottom longline catches revealed a 

 depth distribution extending from 

 the summit (260 m) to 740 m for 

 both sexes. Males generally were 

 found deeper than females. In ad- 

 dition, the size of males generally 

 increased with depth whereas no 

 apparent trend was observed for 

 females. 



Reproductive parameters for 

 both sexes are presented. Males 

 tended to reach maturity at smaller 

 sizes than did females. Gravid fe- 

 males had broods of up to six uter- 

 ine embryos. Length of young close 

 to parturition was 21-26 cm. 



Tentative estimates of age and 

 growth were made from dorsal 

 spine increment counts. Maximum 

 ages were 27 years for females and 

 18 years for males. Females exhib- 

 ited more rapid growth than males 

 after about age 9. 



The diet of S. mitsukurii in- 

 cluded both benthic and mesope- 

 lagic prey. Fishes, cephalopods, and 

 crustaceans were the major compo- 

 nents of the diet. 



Comparison of the biological 

 characteristics suggest that this 

 species is probably typical of other 

 slow-growing, low fecund members 

 of the genus Squalus. The 50% de- 

 cline in catch rates observed dur- 

 ing this study suggests that the 

 number of S. mitsukurii on the sea- 

 mount declined dramatically, pos- 

 sibly as a result of overfishing. 



Biology and population 

 characteristics of Squalus 

 mitsukurii from a seamount in 

 the central North Pacific Ocean 



Christopher D. Wilson 



Alaska Fisheries Science Center. National Marine Fisheries Service. NOAA 

 7600 Sand Point Way NE, Seattle. Washington 98 1 I 5 



Michael R Seki 



Honolulu Laboratory, Southwest Fisheries Science Center 



National Marine Fisheries Service. NOAA 



2570 Dole Street. Honolulu. Hawaii 96822-2396 



Manuscript accepted 23 February 1994. 

 Fishery Bulletin 92:851-864. 



The discovery of large stocks of the 

 pelagic armorhead, Pseudopenta- 

 ceros wheeleri, on seamounts of the 

 southern Emperor-northern Hawai- 

 ian Ridge by Soviet fishermen in 

 1967 signaled the inception of a 

 large, intense foreign trawl fishery 

 for this species during the early 

 1970s (Uchida and Tagami, 1984). 

 During 1967-75, for example, 

 nearly one million metric tons of 

 pelagic armorhead were taken from 

 this area by Japanese and Russian 

 trawlers (Boehlert and Genin, 

 1987). By the mid-1970's, catch 

 rates of pelagic armorhead had de- 

 clined dramatically, and commercial 

 fishing for the species effectively 

 ceased by 1984. The National Ma- 

 rine Fisheries Service (NMFS) ini- 

 tiated research stock-surveys of the 

 area in 1985, and in August 1986 a 

 six-year fishing moratorium was 

 enacted (NMFS, 1986). 



Results from the NMFS surveys 

 provided information to describe the 

 population dynamics of P. wheeleri 

 (Somerton and Kikkawa, 1992). 

 However, the population biology of 

 several other fish species which 

 were caught incidentally in large 

 numbers during the NMFS surveys 

 was largely unknown. One example 

 was the demersal shark, Squalus 



mitsukurii, which represented the 

 largest bycatch in the NMFS sur- 

 vey data (Somerton 1 ). 



Little is known about the life his- 

 tory and population dynamics of S. 

 mitsukurii (Compagno, 1984) in 

 contrast to the more cosmopolitan 

 congener S. aeanthias which has 

 been extensively studied (Com- 

 pagno, 1984; Ketchen, 1986). Squa- 

 lus mitsukurii is broadly distributed 

 in the Pacific and Indian Oceans 

 (Compagno, 1984; Parin, 1987). 

 Specimens resembling S. mitsu- 

 kurii have also been taken in the 

 Atlantic although their taxonomic 

 status is unclear (Compagno, 1984). 

 Squalus mitsukurii is known to in- 

 habit the waters around various is- 

 lands and seamounts in addition to 

 coastal waters (Parin, 1987; Tan- 

 iuchi et al., 1993). Litvinov (1990) 

 reported on several aspects of the 

 biology of S. mitsukurii from 117 

 specimens taken from the Sala-y- 

 Gomez Seamounts in the Southeast 

 Pacific. Off southeast Africa, Bass 

 et al. (1976) presented limited in- 

 formation on the life history of S. 

 mitsukurii, which had earlier been 

 identified as S. blainvillei (Bass et 



1 Somerton, D. National Marine Fisheries 

 Service, Seattle, WA 98115. Personal 

 commun., 1992. 



851 



