292 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 14. — Number of fish families and categories of organisms taken in the central Pacific, by trawl and latitude, 



1953-56 



[Basic data In appendii tables 7 and 8; see P. 286 for description of faunal zonesj 



the North Equatorial Current and the Aleutian 

 Current. As might be expected, this relation also 

 holds true generally for the number of fish fami- 

 lies represented in the catch. Although these data 

 are variable, partly because there were more hauls 

 in some areas than in others, they do show a gen- 

 eral reduction in the variety of the fauna in a 

 tropics-to-arctic direction, a well-known phenom- 

 enon (Hesse, Allee, and Schmidt, 1947: p. iii). 



In table 15 we have attempted to classify the 

 major groups of organisms according to their 

 probable trophic level, based on information de- 

 rived from a number of sources with MacGinitie 

 and Mac Ginitie (1949) and Marshall (1954) 

 being among the more useful. If we are not too 



greatly in error in our food-habit evaluations, it 

 would appear that the Isaacs-Kidd trawls sample 

 principally the primary carnivores, some of which 

 are also herbivores and detritus feeders, such as 

 the shrimps, and other animals which are second- 

 ary carnivores as well, such as the majority of the 

 fishes. Very few, if any, of the fishes captured can 

 be classed as herbivores. 



TRAWL CATCHES AS ECOLOGICAL 

 INDICATORS 



The staff of the Bureau of Commercial Fisheries 

 Biological Laboratory, Honolulu, has attempted 

 to maintain an ecological approach in its investi- 

 gations on the causes of variation in the abundance 



Table 1.5. — Major categories, probable trophic level, and latitudinal variation in abundance of organisms taken in the 



Isaacs-Kidd trawl catches, central Pacific, 1953-56 



' Faunal zones referred to are those Indicated in appendix tables 7 and 8; see also p. 286. 



