858 



Fishery Bulletin 92(4), 1994 



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20 



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fall 88 



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fall 86 



n = 40 



win 88 



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n = 23 



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spr 87 



n = 25 



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-sum 86 



n = 61 



4 8 12 16 20 24 28 



Total Length (cm) 



Figure 6 



Size-frequency composition of 

 Squalus mitsukurii uterine em- 

 bryos during 1986-88. 



major components of the diet (Table 4). Fishes 

 were found in 63.7% of the stomachs with 

 prey and numerically accounted for 36.8% of 

 the total prey while making up 74.5% of the 

 total aggregate weight. Micronektonic 

 stomiiform and myctophid fishes, and file- 

 fishes (family Monacanthidae) were the most 

 commonly identified fishes; however, most 

 fishes were in an advanced stage of diges- 

 tion and thus unidentifiable to a lower taxon. 

 Crustaceans were present in 32.3% of the 

 stomachs and represented 30.3%> of the prey 

 organisms, but only 3.6% of the total aggre- 

 gate weight. In particular, euphausiids and 

 the lophogastrid mysid Gnathophausia longi- 

 spina, were commonly found. Cephalopods, 

 predominantly digestion-resistant squid 

 beaks and eye lenses, were present in 45.1% 

 of the stomachs, representing 26.4% of the 

 total prey items and 19.9% of the prey weight. 

 Remaining prey items included pelagic tuni- 

 cates, coelenterates, and unidentified remains. 

 Gut fullness was evaluated as a function 

 of diel feeding activity and gear type. For longline 

 data, no significant difference was found between the 

 two daytime (x~=0.001, P>0.1) or two nighttime 

 blocks (x 2 =3.822, P>0.1). However, when longline 

 data from daytime blocks were pooled and compared 

 with pooled nighttime blocks, the proportion of empty 

 stomachs was significantly greater during the night 

 ( 87% ) than during the day (46% ; x 2 =26.250, P<0.001 ). 

 Longline-caught fish had a significantly greater pro- 

 portion of empty stomachs than did fish caught by 

 bottom gill net <x 2 =5.081, P<0.05). 



Discussion 



Size and abundance 



Squalus mitsukurii was the second most abundant 

 species sampled by bottom longline gear at SE 

 Hancock Seamount in 1985-88 (Somerton 4 ). How- 

 ever, the large apparent decline in catch rates for S. 

 mitsukurii during this period suggests that the re- 

 search fishing may have had a major impact on stock 

 size which is (i.e. in 1988) at only 20% of its 1985 

 value. It is likely that populations of this species, 

 like other elasmobranchs ( Holden, 1974 ), are particu- 

 larly sensitive to overfishing. In addition, seamount 

 populations of S. mitsukurii may be at further risk 

 to overexploitation because of the limited habitat 



4 Somerton, D. National Marino Fisheries Service. Seattle, WA 

 98115. Personal commun., 1992. 



