196 



Fishery Bulletin 98(1) 



Very few individuals of three species of relatively 

 large squalid sharks iCentrophorus squamosus, Scym- 

 nodon plunketi, and Dalatias licha) were captured on 

 Chatham Rise. These three species also happen to 

 have liver oil that is high in squalene, or that has 

 a high diacyl glycerol ether to triglycerol ratio, and 

 the liver oil of these sharks is thus of high quality for 

 industrial purposes (Bakes and Nichols, 1995; Weth- 

 erbee, 1998). Because each of these species formed 

 less than 1% of the total shark catch in all fishing, 

 targeting of any of these species by commercial fisher- 

 ies on Chatham Rise does not appear to be practical. 

 However, these species have been captured in greater 

 numbers in fishing that was conducted at shallower 

 depths and that targeted different fishes at locations 

 other than Chatham Rise in New Zealand (Clark and 

 Kingi). 



The consistency in catch rate, regardless of time 

 of day, indicates that there are few changes in the 

 distribution of the deep-sea shark community on a 

 diurnal basis. However, capture in a trawl may not 

 provide information on activity patterns or feeding 

 periodicity. For example, Kobayashi (1986) found 

 that capture rate of sharks was higher at night than 

 during the day in deep-sea fishing with baited lines. 

 The present study was conducted over a three-month 

 period and does not provide much information on 

 seasonal differences in the distribution of deep-sea 

 sharks. Some studies have suggested that there is 

 continual movement of reproductive groups, or age 

 classes, out of a particular area (Yano, 1991; Weth- 

 erbee, 1996). Other studies have maintained that 

 community structure, temperature, and salinity of 

 the deep-sea environment vary little throughout the 

 year (Kobayashi, 1986; Clark and KingM. 



Orange roughy appear to be common prey of two 

 species of sharks (E. granulosus and C. owstoni) and 

 are also consumed by two of the less common, large 

 squalids (C. squamosus and D. licha ). Centroscymnus 

 owstoni may exert the greatest predation pressure on 

 orange roughy populations because both species are 

 found in large numbers on the north of Chatham Rise. 

 An expanded investigation of the feeding habits of 

 sharks would provide more information on the relation- 

 ship between sharks and commercially important tele- 

 osts on Chatham Rise. 



Abundance 



Differences in abundance of sharks between the 

 orange roughy and oreo surveys appear to be attrib- 

 utable to the location at which fishing was concen- 

 trated in each survey. For the oreo survey, fishing 

 was restricted to the south of Chatham Rise, and 

 during the orange roughy survey, fishing was con- 



centrated on the north of Chatham Rise (although 

 trawls were made throughout Chatham Rise). The 

 observation that there were no significant differences 

 between the catches in areas common to both surveys 

 indicates that overall differences between the sur- 

 veys were probably not due to differences in fishing 

 methods (duration of trawls and net specifications) 

 or time (season or year). The contribution of sharks 

 to total biomass of each survey was also remarkably 

 similar. 



The composition of the shark community was 

 dependent upon the area of Chatham Rise that was 

 sampled. Moving from west to east on the north 

 of Chatham Rise, the dominant species in trawls 

 changed from C. owstoni to D. calcea. Fishing areas 

 at the eastern tip of Chatham Rise were the most 

 diverse. There, the highest densities (kg/km^) were 

 recorded for six of the eight species of sharks and for 

 all sharks combined. Etmopterus granulosus was the 

 most abundant shark on the south of Chatham Rise, 

 completely dominating the catch in the westernmost 

 areas. Variation in the composition of the deep-sea 

 shark community with location has been observed in 

 other areas off New Zealand, and also in Japan and 

 southern Africa (Kobayashi, 1986; King and Clark, 

 1987; Compagno et al., 1991). In several studies, the 

 community of deep-sea sharks was thought to vary 

 with latitude (Merrett and Marshall, 1981; Nakaya 

 and Shirai, 1992; Yano and Kugai, 1993). The distri- 

 bution of sharks on Chatham Rise may be influenced 

 by a number of physical and biological factors. How- 

 ever, the lack of information on the deep-sea envi- 

 ronment in this area precluded examination of the 

 relationship between shark abundance and either 

 biotic or abiotic factors; in contrast to other studies 

 (Graham and Hastings, 1984; Bianchi, 1991; 1992; 

 Garcia et al., 1998). Large portions of Chatham Rise 

 are as shallow as 500 m, and sharks with fairly 

 deep distributions might not move freely between 

 the north and south slopes. Thus, the patterns of 

 distribution observed for several species of sharks 

 near Chatham Rise may be related to this physical 

 barrier. 



In this study, shark abundance also varied with 

 depth. The depth range at which maximum shark 

 density was recorded in the present study ( 700—800 

 m) was deeper than that reported by Kobayashi 

 (1986) (300-500 m), and shallower than that found 

 by Yano and Kugai ( 1993 ) ( 1100-1200 m). Depth dis- 

 tributions of sharks caught on Chatham Rise are 

 characterized by several patterns. Some of the larger 

 species were rare at depths greater than 1100 m. 

 which may approximate their maximum depth of 

 occurrence. The density of other species declined 

 abruptly beyond 1200 m, and the proportion of Apris- 



