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Fishery Bulletin 98(1) 



part of the catch, but the catch of C. owstoni declined 

 substantially, and D. calcea began to dominate the 

 shark catch. Along the eastern tip and southeast 

 portion of Chatham Rise (areas 6 and 7), D. calcea 

 accounted for the highest percentage of the catch, 

 but E. granulosus was also prominent, and these 

 two species formed over 85% of the shark catch by 

 weight. Etmopterus granulosus dominated catches 

 in areas along the south of Chatham Rise (areas 

 8-10); the proportion of the total catch increased 

 with proximity to New Zealand (Fig. 3). The three 

 large squalids (C. squamosus, S. plunketi, D. licha) 

 were sporadically caught in areas 1-8, each with a 

 peak density in area 6, but no squalids were recorded 

 from the southwest of Chatham Rise (areas 9 and 

 10). Apristurus spp. were caught in small numbers 

 throughout Chatham Rise, but their presence was 

 more dependent upon depth than location (Fig. 3). 



Composition of the catch also varied with depth 

 (Fig. 4) and several natural divisions were apparent. 

 The three large squalids (C. squamosus, S. plunketi, 

 D. licha ) appeared to have shallow distributions, and 

 were not captured deeper than 1100 m (with the 

 exception of one S. plunketi caught at 1170 m, and 

 one C. squamosus at 1201 m). Densities (kg/km-) 

 of the other species were fairly high at depths of 

 700-1200 m, although D. calcea was most abundant 

 at depths of less than 1000 m, E. granulosus peaked 



1,200, 



1,000 



Depth (m) 



Figure 4 



Density (kg/km^) of sharks collected at all locations on Chatham Rise, New Zea- 

 land, at various depth intervals for both surveys combined. For abbreviations of 

 species see Figure 3. For each species, P -values are given in parentheses for 

 ANOVA comparisons of densities among depth intervals. 



at 900-1200 m, and Apristurus spp. densities were 

 highest at depths greater than 1000 m (Fig. 4). At 

 depths greater than 1200 m, Apristurus spp. were 

 the only sharks regularly caught in the trawls. There 

 was a significant difference among three depth inter- 

 vals (700-1000 m, 1000-1300 m, and 1300-1- ml for 

 mean densities (kg/km^) of each species in the orange 

 roughy survey, but only for the three most abun- 

 dant species iD. calcea, C. crepidater, and E. granu- 

 losus) in the oreo survey (ANOVA, P<0.05). Density 

 (kg/km^) for all sharks combined gradually declined 

 with depth between 700 and 1200 m, but was low at 

 depths greater than 1200 m (Fig. 5). 



Distribution 



Diversity (number of species per trawl) was signif- 

 icantly higher for the orange roughy survey than 

 for the oreo survey (Mest, P=0.0003), but diversity 

 in areas common to both surveys (areas 6, 8, 9, 

 10) did not differ (Mest, P=0.14, 0.77, 0.81, and 

 0.63 respectively). There was a significant differ- 

 ence among areas for mean diversity values in both 

 surveys (ANOVA, P<0.01). Area 3 had the highest 

 mean diversity value (4.2, SD=1.6) and area 10 

 had the lowest value (1.1, SD=0.9). Diversity dif- 

 fered significantly among the three major depth 

 intervals (700-1000 m, 1000-1300 m, 1300-(- m) 

 for the oreo survey (ANOVA, 

 P=0.007), but not for the orange 

 roughy survey (ANOVA, P=0.50). 

 The total number of species of 

 shark caught in trawls was 

 inversely proportional to depth, 

 and declined by half from a max- 

 imum often (800-900 m) to only 

 five species at depths of 1200- 

 1300 m (Fig. 5). 



The index of similarity (S) 

 between the two surveys was high 

 (0.89), and for each survey there 

 was a high degree of similarity 

 between areas, except for those 

 most distant from each other, par- 

 ticularly between area 10 and other 

 areas (Table 2). Indices of similar- 

 ity between depth intervals were 

 very similar for both surveys: high 

 (0.80 for the orange roughy survey 

 and 0.81 for the oreo survey) for 

 the two shallowest depth intervals 

 ( 700-1000 m versus 1000-1300 m), 

 moderate (0.57 and 0.63) for the 

 1000-1300 m vs 1300-1- m intervals, 

 and much lower (0.42 and 0.47) for 



S D.l. 10.270) 



 C.s. (0.0021 

 n S.p. (0.711) 



 A.s. (0-769) 

 H D.c. (0.001) 

 n C.c (0.001) 



 Co. (0.006) 

 □ E.g. (0.364) 



