Euphausiids in the Coral and Tasman Seas during May 1972, I. Horizontal and Vertical Distribution

Abstract

Thirty-three species belonging to seven genera of euphausiids were collected at two stations, 20º S.,153º E. and 33º 40'S.,153º E., during May 1972 off the east Australian coast. In all, 33 hauls at the northern station and 21 at the southern station were made with a mouth-opening-losing Tucker trawl at various depths between the surface and 400 m. The hauls were grouped into four time periods: dawn (0401-1000 h), noon (1001-1600 h), dusk (1601-2000 h) and midnight (2001-0400 h). The mean number of euphausiids of all species was 20.78 per 1000 m³ at 33º 40's. and 18.34 per 1000 m³ at 20%. Night-time abundances were greater than day-time abundances at both stations. Twenty-five species were found at the northern station and 29 species at the southern station. Four species, Thysanopoda astylata, T. obtusifrons, T. monacantha, and Nernatoscelis atlantica, were found only at the northern station and eight species, Thysanopoda acutifrons, T. orientalis, Pseudeuphausia latifrons, Euphausia recurva, E. pseudogibba, E. similis variety armata, E. spinifera, and Nematoscelis megalops were found only at the southern station. Euphausia similis is reported from 20º CS..153º E. for the first time. The abundance of 14 species was large enough to allow examination of their diel migration patterns. Only one, Stylocheiron abbreviatum; did not show evidence of a diurnal migration pattern. Thysanoesa gregaria exhibited a probable reversed-migration pattern.