Effects of a Warm-Core Eddy on Fish Distributions in the Tasman Sea of East Australia

Abstract

Distributions of fishes were determined in and near a warm-core eddy off the east coast of Australia from 28 November to 13 December, 1978. Samples were collected with a midwater trawl (n = 39) in the upper 500 m of the water column during day and night. 88 % of the 14602 fish caught belonged to the family Myctophidae. Few fish (< 4 % of total) were caught during day. At night the structure of the fish community within the eddy was recognizably distinct from that in surrounding water masses. Most fish distributions correlated well with thermal structure. Common species were categorized as eddy species (n = 5), outside eddyicold-water species ( n = S ) , warm-water species ( n = l ) , cold-water species (n = 8) and widespread species (n = 7) based on nocturnal d~stributions. Eddy species were largely restricted to warm water w ~t h i n the eddy, w h ~l s t warm-water species were also abundant near surface outside the eddy. Outside eddylcold-water species \yere caught almost exclusively outside the eddy or at the eddy edge. 2 of these species were concentrated in the cold water o u t s ~d e the eddy. For most cold-water species, the extent of the upward vclt~cal migration at night did not appear to penetrate into the warmer surface layers. Widespread species included 4 of the 5 most abundant species caught (60 % of total catch) and occurred inside and outside the eddy and at the eddy edge. Individuals of 4 species caught inslde and outside the eddy d~ffered in sizc, and individuals of 2 specles differed in d i ~t .