VERTICAL DISTRIBUTION AND OTHER ASPECTS OF THE ECOLOGY OF 

 CERTAIN MESOPELAGIC FISHES TAKEN NEAR HAWAII 



Thomas A. Clarke^ and Patricia J. Wagner- 



ABSTRACT 



Data on abundance, size, depth and time of capture, and sexual development are presented for 37 

 species of 15 families of rare to moderately abundant mesopelagic fishes taken in the central Pacific. 

 These exhibit a wide variety of patterns of vertical distribution and diel migration. Several undertake 

 migrations similar in extent to those of most myctophids and migrating stomiatoids, while others 

 remain at depth both day and night. In between are species where occurrence or extent of migration are 

 related to size. A trend for juveniles to occur shallower than adults, already noted in myctophids and 

 stomiatoids, is present in most species covered here regardless of migration pattern. Sexual differences 

 in adult size and uneven sex ratios are indicated for several species. The interplay between sexual 

 dimorphism, size difference, and sex ratio and the consequences to reproductive strategy are briefly 

 discussed. 



Most ecological studies of mesoplagic fishes have 

 dealt primarily or exclusively with the two groups 

 which dominate the fauna in most parts of the 

 ocean— the family Myctophidae and the stomiatoid 

 fishes. Because other forms are generally collected 

 in small numbers, our knowledge of their ecology 

 is limited to minor parts of general reports (e.g., 

 Badcock 1970) or short notes on a few new 

 specimens. Systematic or zoogeographic studies 

 have assembled data from earlier collections, but 

 in most cases the ecological value of such data is 

 limited because sampling programs were not 

 designed with ecological objectives in mind. Also 

 the gear used was in many cases undoubtedly 

 ineff"ective at sampling many forms and was 

 fished without really good knowledge of depth of 

 tow. 



Recent, ecologically designed collections in the 

 central Pacific Ocean near Hawaii by our program 

 and that of R. E. Young have yielded a large 

 amount of material involving some 225-250 species 

 of mesopelagic fishes. Data on the myctophids and 

 certain stomiatoids have already been reported 

 (Clarke 1973, 1974), and material including many 

 of the remaining species, which has been passed to 

 other investigators, will eventually be covered in 

 broader reports, e.g., family revisions, etc. 



'University of Hawaii, Hawaii Institute of Marine Biologv, 

 P.O. Box 1346, Kaneohe, HI 96744. 



^University of Hawaii, Hawaii Institute of Marine Biology; 

 present address: University of Alaska, Institute of Marine 

 Science, Fairbanks, AK 99701. 



Manuscript accepted March 1976. 



FISHERY BULLETIN: VOL. 74, NO. 3, 1976. 



In this paper we report on a rather heterogen- 

 eous group of rare to moderately abundant fishes 

 taken in these collections. Included are represen- 

 tatives of several families which are present and 

 often moderately abundant in most parts of the 

 world ocean, but of which knowledge of even the 

 depth distribution is rather poor. Even though we 

 are able to consider only a few other ecological 

 parameters in detail for most of these, we feel that 

 presentation of this data contributes to a broader 

 understanding of the patterns of life history 

 exhibited by the diverse mesopelagic fauna. 



MATERIALS AND METHODS 



Most of the specimens considered herein were 

 taken near Oahu, Hawaii in a series of collections 

 described in detail in Clarke (1973). These included 

 six approximately quarterly series of extended 

 horizontal tows with 2-m (one series) and 3-m 

 Isaacs-Kidd midwater trawls (IK) and a series of 

 samples in the upper 250 m with the larger Cobb 

 Pelagic Trawl (CT). Because the program was 

 designed primarily for study of vertically migrat- 

 ing species, the upper 250 m at night and the 

 400-1,200 m zone by day were covered most thor- 

 oughly; effort in the deeper zone at night was 

 roughly one-fourth that by day. Thus for some of 

 the nonmigrating species considered here, we have 

 examined deep night collections made by R. E. 

 Young with an opening-closing Tucker Trawl 

 (TT). We have also examined collections from 



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