Distribution and community structure of midwater fishes in relation to the subtropical convergence off eastern Tasmania, Australia

Abstract

Midwater fishes were sampled at night to a depth of 400 m in oceanic waters east of Tasmania, Australia, in May/June of 1992, 1993 and 1994. We examined whether there were differences in the distribution and density of these fishes in relation to the subtropical convergence (STC) separating East Australia Current (EAC) water from subantarctic water (SAW) to the south. A total of 23999 fishes from 107 taxa and 43 families were identified. Four new records were identified from the study area. Myctophids and stomiatoids were the main fish taxa captured. We found no evidence of increased density of the combined fish catch in any particular area. However, differences between areas in the density of individual species were noted, although no species was confined to any one area. Ceratoscopelus warmingi, Lobianchia dofleini and Vinciguerria spp. were most abundant in the EAC, whereas Lampichthys procerus was most abundant in the SAW. Only Diaphus danae was found in significantly higher numbers in the STC. Multivariate analysis revealed that community structure in the EAC was significantly different from that of the SAW but not from the STC. Further, when separated by depth, the shallow EAC group was significantly different in all group comparisons bar that with the shallow STC. Our data indicated that the thin EAC layer above 200 m could be distinguished by its fauna from the SAW. However, we could not detect a separate community in the STC. We conclude, therefore, that the STC is not an area of increased micronekton abundance, nor does it contain a distinct community, during the Australian autumn/winter.