Hydroacoustic surveys reveal the distribution of mid-water fish around two artificial reef designs in temperate Australia

Abstract

Artificial reef designs have evolved rapidly over the past two decades, but further work is needed to inform how specific design features affect reef function. In south-eastern Australia, most artificial reefs consist of either a field of concrete modules, or large steel structures which are deployed to enhance recreational fisheries. To evaluate how these two designs might influence the densities and distribution of fish, hydroacoustic surveys were completed across multiple concrete module and steel reefs located in the temperate inshore environment of New South Wales, Australia. There were no differences in the densities of fish between the two reef types, however there was an interactive effect between reef design and distance-from-structure. Fish associated with steel reefs at greater distances from the structure, with this effect occurring throughout the water column. Steel reefs had higher relief and may therefore provide more structure to support mid-water fish at greater distances up in the water column. Assemblages were dominated by small pelagic species that likely benefit from such high relief structure. In contrast, the concrete module reef fields provide numerous structures for mid-water fish to congregate, which may therefore reduce competition for space and the need to disperse large distances from the reef. At both reef types, fish densities were greatest in the direction of prevailing currents, which may reflect foraging behaviour by small zooplanktivores which were the most abundant type of species observed. Regardless of the area occupied by artificial reefs or the type of material, the inclusion of high vertical relief structures appears an important design feature in establishing mid-water fish assemblages.