THE MID-SLOPE DEMERSAL FISH COMMUNITY OFF SOUTHEASTERN AUSTRALIA

The mid-slope (800-1200 m) demersal fish community off southeastern Au stralia was sampled at 376 random, depth-stratified trawl stations. Th e mean density of demersal species was 4.82 g m-2. Thirty-seven famili es and 111 species of demersal fish were represented in the catch. The density of mid-slope fishes off southeastern Australia was comparable to that observed in the Northern Hemisphere. However, landings and ac oustic and egg surveys of orange roughy (Hoplostethus atlanticus) indi cate that densities of that species alone are an order of magnitude hi gher than the total fish density indicated by trawl surveys. Water-col umn productivity over the mid-slope region appears insufficient to sup port the higher range of density estimates, implying a significant flu x of energy into the region either from offshore or downslope. The dom inant mid-slope demersal fishes appear to comprise an identifiable com munity within a biogeographic province that extends at least from the Great Australian Bight to the Chatham Rise (New Zealand), a distance o f approximately 5000 km. Distinct assemblages of demersal fish were fo und at upper (500 m) and mid-slope (800-1200 m) depths off southeast A ustralia. The mid-slope community could be sub-divided into assemblage s by depth (shallow. intermediate and deep) and area (east and west Ta smania), which were statistically robust although with considerable ov erlap of species composition. There was no overlap in species composit ion of the southeast Australian mid-slope demersal fish community with fish communities at similar latitudes and depths in the North Pacific , but there were affinities with those in the North Atlantic. These bi ogeographic patterns, which appear consistent with oceanic circulation at intermediate depths, provide strong evidence that negates the rece nt hypothesis that deepwater fish communities cannot be defined over b road areas and are only random assemblages (HAEDRICH and MERRETT, 1990 , Progress in Oceanography, 24, 239-250).