852 



Fishery Bulletin 92(4). 1994 



al., 1986). Whether populations of S. mitsukurii from 

 different geographic areas exhibit the high variabil- 

 ity in life history characteristics reported for S. 

 acanthias (Ketchen, 1972, 1986; Compagno, 1984; 

 Nammack et al., 1985) is unclear. The aim of the 

 present study was to provide information on the bi- 

 ology and population characteristics of S. mitsukurii 

 using a larger number of specimens than had previ- 

 ously been available, and thus elucidate its role as a 

 member of the unique fauna associated with sea- 

 mounts in the central North Pacific Ocean. 



Methods 



Squalus mitsukurii specimens were collected aboard 

 the NOAA ship Townsend Cromwell during nine 

 cruises to Southeast (SE) Hancock Seamount from 

 January 1985 to November 1988 (Table 1). The sea- 

 mount is located on the northern Hawaiian Ridge in 

 the central North Pacific Ocean at lat. 29°48'N and 

 long. 179°04'E (Fig. 1). It has a circular, flat-topped 

 summit with an area of about 4.5 km 2 at a depth of 



260 m. The seamount flanks have an average slope 

 of 0.22 and reach bottom depths of 5,200 m about 22 

 km away from the summit (Brainard, 1986). Water 

 temperatures generally are 13°-15°C at 260 m depth 

 (i.e. summit) and decrease to 4°-6°C by 750 m 

 (Brainard, 1986). 



Most S. mitsukurii were collected with bottom 

 longline gear (Somerton and Kikkawa, 1992; 

 Shiota 2 ), although a few specimens were also taken 

 by bottom trawl, handline, vertical longline, and one 

 set with a 25-mm square mesh bottom gill net (Table 

 1). Only data from hook-caught specimens were used 

 (except for the food habits portion of the study) to 

 avoid any bias due to differences in gear selectivity. 

 Sets were conducted primarily during daylight hours, 

 between the summit depth and 744 m. 



All specimens of S. mitsukurii from a set, or a ran- 

 dom subsample from large catches, were processed. 

 Fish were sexed and weighed to the nearest 10 g. 



2 Shiota, P. M. 1987. A comparison of bottom longline and deep- 

 sea handline for sampling bottom fishes in the Hawaiian archi- 

 pelago. Honolulu Lab., Southwest Fish. Cent. Natl. Mar. Fish. 

 Cent. Admin. Rep. H-87-5, 18 p. 



35°N- 



30° 



25°- 



20°- 



% 



SE Hancock Seamount 



CD 



%. Colahan Smt 

 a » 



Kure Atoll 



, % Midway Island 



**•>»* 





PACIFIC OCEAN 



179-03'E OS 



•S., 



•5 



Main Hawaiian Islands 



175°E 



180° 



175°W 



1 m 



165° 



160° 



155° 



Figure 1 



Location of SE Hancock Seamount. 



