408 



Fishery Bulletin 93(2), 1995 



most important family by number (36.8%), and the 

 orangeback squid, Sthenoteuthis pteropus, was the 

 most important species (20.6%, Table 4). 



Eighteen fish were counted from spinal columns 

 and otoliths with an index of numerical importance 

 of 32.10% (Table 2). Fish were found together with 

 cephalopods in 19.0% of the stomachs containing food. 

 In zone A the numbers of free lenses offish and cepha- 

 lopods were similar. However, only 32 cephalopod lenses 

 were found in zone B; fish lenses were not found. 



Zone C A total of 46 cephalopods were found in 

 stomachs from zone C. The family Ommastrephidae, 

 represented solely by Sthenoteuthis pteropus, was the 

 most important species by number (41.6%) and esti- 

 mated weight (Table 4). The Onychoteuthidae ranked 

 second in importance by number but not by weight. 

 In the combination of all three zones, the Om- 

 mastrephidae, Onychoteuthidae, Histioteuthidae, 

 and Thysanoteuthidae were the most important 

 cephalopod families by number in swordfish diet 

 (67.9%); other families are probably occasional prey. 

 The most important species was Sthenoteuthis 

 pteropus (28.3%, Table 4). The S. pteropus collected 

 were mostly females, as evidenced by their large ML's 

 (females can reach 650 mm ML and males 280 mm 

 ML, Zuev et al., 1985) and by the presence of large 

 oviducts. Moreover of the "Unknown A" species, five 

 cephalopod species (Braehioteuthis sp., Grim- 



alditeuthis bomplandi, Megalocranchia sp., Octopo- 

 teuthis rugosa, and Spirula spirula) were identified 

 for the first time in swordfish stomach contents. 



Comparative analysis of hard structure 

 degradation 



Otoliths (sagittae) of Scomber japonicus were dis- 

 solved after an average time of 6 hours and 47 min- 

 utes (% decrease of otolith length=2.121 + 14.424T, 

 SD=5 min; Fig. 3). Otolith length decreased signifi- 

 cantly over a period of one hour (ANOVA, df=14, 

 P=5.0425 x 10" 5 ). 



Otoliths of Micromesistius poutassou showed a sig- 

 nificant decrease in length after an interval of 12 

 hours (ANOVA, df=8, P=1.7605 x 10" 2 ). After 48 

 hours, they had lost 40%' of their length (% decrease 

 of otolith length=1.932 + 0.843T, Fig. 3) but still 

 maintained their original shape. 



Lower rostral length and upper rostral length did 

 not differ significantly after 48 hours in acid (ANOVA, 

 df=24, P=0. 95588 and df=24, P=0. 93221, respec- 

 tively). In addition, wing length of the lower beak 

 did not differ significantly after 48 hours (ANOVA, 

 df=24, P=0. 97319). No significant differences were 

 found for fish and cephalopod eye lense diameter af- 

 ter 48 hours (ANOVA, df=4, P=0.50454 and df=4, 

 P=0.89424, respectively). 



Scomber japonicus 



% decrease otol'th length = 2 121 + 14 424T 

 t - 9697 



, -1 



: 



- -• 



- ". Micromesistius poutassou 



% decrease otolith length = I 932 + 483T 



^ = 9419 



Time (h) 

 Figure 3 



Decrease in otolith length of chub mackerel, Scomber japonicus, and blue 

 whiting, Micromesistius poutassou (measured on the longest axis) after 

 immersion in hydrochloric acid (pH=l.l) for 48 hours. 



