FISHERY BULLETIN: VOL. 76. NO. 3 



Cephalopods were collected primarily with two 

 types of nets: a 3-m opening-closing modified 

 Tucker trawl and a 3-m Isaacs-Kidd midwatej- 

 trawl (IKMT). Details of the trawling with the 

 Tucker trawl are given by Walters (1976). When 

 the Tucker trawl failed to close or close com- 

 pletely, the trawl was considered an open tow. 

 Tows usually were made at 5 to 6 km/h for a period 

 of 3 h. Twilight periods were generally avoided. 

 Tows made with net closed indicated the catch 

 contained almost no contamination. Contamina- 

 tion from previous tows was minimized by care- 

 fully cleaning the net after each tow. The trawl 

 tended to wander vertically when open; this was 

 most severe in deep tows. During the latter part of 

 the program, acoustic depth telemeters allowed 

 trawl depths to be continuously adjusted and 

 greatly reduced wandering. The distribution 

 figures indicate the extent of this wandering. 

 Trawl depths usually were determined with a 

 time-depth recorder attached to the trawl. 



Clarke ( 1973) discussed trawling methods with 

 the IKMT. The trawl was lowered quickly then 

 towed horizontally at 5 to 6 km/h for usually 2 h. 

 Retrieval was rapid with the ship moving slowly 

 ahead. Vertical wandering of the net was not as 

 serious as with the Tucker trawl. All specimens 

 captured with the IKMT were assumed to come 

 from the modal trawling depth of the net, or if no 

 clear mode was present, from the midpoint of the 

 effective vertical range of the tow. The occasional 

 capture of a specimen during setting or retrieval of 



a net results in an anomalous depth record below 

 the animal's normal habitat. Contamination of 

 the catch by animals from previous tows occasion- 

 ally occurred with the IKMT. This contamination 

 is especially serious as the error may be impossible 

 to detect. 



IKMT data for a few of the most abundant 

 species are presented both as catch per trawling 

 effort and as actual catch figures (Table 1). The 

 remaining distribution figures are designed to 

 show animal size vs. depth relationships and to 

 indicate the precision and reliability of the data 

 (e.g., fishing range of the tow, open or opening- 

 closing tow). As a result, corrections in the data for 

 unequal sampling at various depths could not be 

 made. This bias was especially critical at depths 

 <400 m during the day and at depths > 1,000 m 

 during the day and night where sampling was low. 

 The magnitude of this error can be determined 

 from Table 2, which lists sampling time in each 

 100-m depth interval. 



Depth data for most species taken over the en- 

 tire trawling period have been combined. There- 

 fore, short-term variation in depth distributions 

 may be obscured. Where sufficient data exist to 

 determine general distribution patterns based on 

 Tucker trawls alone, these data are presented 

 separately. For species with insufficient data, data 

 from both trawls are combined in the figures. In 

 most cases larvae, which usually have a different 

 vertical distribution than adults, have been 

 excluded from the distribution figures and the 



Table l. — Depth distribution, capture rates, and numbers of the most abundant cephalopod species captured by the Isaacs-Kidd 

 midwater trawl. Day captures for Pterygioteuthis giardi are included in Figure 4. R = capture rate in numbers per 1,000 m^ of water 

 sampled. N = actual number captured. ND = no data. 



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