SOME ASPECTS OF THE ECOLOGY OF STOMIATOID FISHES 

 IN THE PACIFIC OCEAN NEAR HAWAII 



Thomas A. Clarke' 



ABSTRACT 



Forty-seven species of eight families of stomiatoid fishes were collected in the upper 1,000 m near 

 Hawaii. Most species appear to undertake diurnal vertical migrations; only two definitely did not. 

 Many of the abundant species showed changes in size composition within both day and night depth 

 ranges, the smaller fish occurring shallower. All sizes of several other species appeared to occur 

 throughout their depth ranges. Seasonal changes in the size composition of several species indicated 

 that they spawn principally in the summer. Several species appear to avoid the Isaacs-Kidd trawl 

 better during the day than at night. Some species appeared to avoid the Isaacs-Kidd more than a larger 

 trawl, but many were sampled as well or better by the former. Absence or rarity of mature individuals 

 of several species indicated that the larger fish avoided both trawls. 



Relationships between vertical distribution and morphology of some species are proposed, and 

 potential interactions between species are considered relative to the degree of similarity of depth 

 ranges or size-depth patterns. 



Stomiatoids are a dominant and diverse group of 

 mesopelagic fishes. Most previous work on the 

 group has been of a systematic or zoogeographic 

 nature, and only recently have the systematics of 

 some families come into order. With the exception 

 of a few works such as Kawaguchi and Marumo 

 (1967) and Krueger and Bond (1972), ecologically 

 pertinent information such as depth ranges, mi- 

 gration habits, etc., has been appended to other 

 studies and is usually based on so few specimens or 

 inappropriate sampling programs that it is of 

 dubious value. Consequently, even for the fre- 

 quently collected species, little is known of their 

 ecology — especially in comparison to knowledge of 

 the myctophids, another important group of 

 mesopelagic fishes. 



This paper considers data on 47 species of 

 stomiatoids collected by a mid-water trawling 

 survey in the central North Pacific near the 

 Hawaiian Islands. (Specimens of the Sternop- 

 tychidae and the gonostomatid genus Cyclothone 

 are being investigated by other workers, and the 

 systematics of three genera of the Melanos- 

 tomiatidae are so confused at present that these 

 genera cannot be considered in detail here.) For 

 many species, sufficient numbers were collected to 

 present reliable estimates of depth ranges, migra- 



'Hawaii Institute of Marine Biology and Department of 

 Oceanography, University of Hawaii, Honolulu, HI 96822. 



tions, and seasonal changes in size composition. 

 The habits of this diverse group are compared with 

 those of other mesopelagic fishes. 



METHODS 



All specimens considered here were collected 

 near the island of Oahu, Hawaii (lat. 22°20-30'N, 

 long. 158°20-30'W). Details of the sampling pro- 

 gram are given in Clarke ( 1973), and will be only 

 summarized here. Four series of samples were col- 

 lected with a 10 foot Isaacs-Kidd mid-water trawl 

 (IK). These were taken at approximately quar- 

 terly intervals (September 1970, December 1970, 

 March 1971, and June 1971) and attempted to 

 cover the upper 1,000 m of the water column both 

 day and night for each season. Useful information 

 was also derived from a series of samples collected 

 with a 6-foot IK in the upper 400 m at night and 

 between 400 and 1,000 m during the day in June 

 1970, from a series of samples with a 10-foot IK in 

 the upper 190 m at night during periods of new 

 and full moon in September-October 1971, and 

 from preliminary samples taken in September- 

 November 1969. Also included are data from a 

 series of tows made by the Southwest Fisheries 

 Center Honolulu Laboratory, National Marine 

 Fisheries Service (NMFS), NOAA in conjunction 

 with the March 1971 IK series; these sampled the 



Manuscript accepted August 1973. 



FISHERY BULLETIN: VOL. 72. NO. 2. 1974. 



337 



