Some Aspects of the Ecology of Stomiatoid Fishes in the Pacific Ocean near Hawaii

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 rIlrity 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, migration 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 frequently collected species, little is known of their ecology-especially in comparison to knowledge of the myctophids, another important group of me~opelagic 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 Sternoptychidae and the gonostomatid genus Cyclothone are being investigated by other workers, and the systematics of three genera of the Melanostomiatidae 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, migralHawaii Institute of Marine Biology and Department of Oceanography, University of Hawaii, Honolulu, HI 96822. ~1anll"cripl iH:l:cptl'd !\ugu,t 1\}7_~. FISHFI{Y IIlIl I FI IN: VOL. n NO. ~. 1~74 tions, and seasonal changes in size composition. The habits ofthis diverse group are compared with those of other mesopelagic fishes.