Trophic ecology of the mid-slope demersal fish community off southern Tasmania, Australia

Abstract

The demersal fish community on the mid-slope off southern Tasmania in south-eastern Australia is dominated by orange roughy Hoplostethus atlanticus (Trachichthyidae), several species of oreosomatids, macrourids, squalids, alepocephalids and a synaphobranchid eel. Cluster analysis based on diet dissimilarities of proportional prey weight identified five major trophic guilds: pyrosome-feeders, crustacean feeders, piscivores, benthopelagic omnivores and benthic-invertebrate feeders. Overall, the fish fed predominantly on pelagic or benthopelagic prey, consistent with other trophic studies in the Australasian region and the Northern Hemisphere. H. atlanticus, warty dory Allocyttus verrucosus, and the macrourid Coryphaenoides serrulatus were benthopelagic omnivores that ate mesopelagic fishes, crustaceans and squid. The first two species ate more mesopelagic fishes as their sizes increased. The squalids were predominantly piscivorous but might also scavenge. Macrourids were benthic-invertebrate feeders, pelagic crustacean feeders or benthopelagic omnivores. The alepocephalids and the smooth oreo Pseudocyttus maculatus were pyrosome-feeders. No seasonal variation in diet was found for any species. Ecological indices varied within each guild. Benthopelagic omnivores and piscivores had the largest diet breadth, evenness and diversity. Trophic levels ranged from 3.0 for pyrosome-feeders to 4.9 for piscivores and the overall average for the community was 3.7.