Six species of prawns (four penaeid and two carid) provide most of the catch of a trawl fishery on the continental slope of north-western Australia. The occurrence and volume of prey in the stomach contents of demersally trawled animals (315–485 m) were examined and related to
diel changes in the commercial catch rates of each species. The prey included midwater (siphonophores, chaetognaths, heteropods and pteropods) and benthic forms (sponges, polychaetes, other gastropods, bivalves and echinoderms). The dominant prey were decapod crustaceans (7.9–67.2% by
volume) and fish (0.5–33.0%), most of which could not be identified as midwater or demersal in origin; significant quantities of foraminiferans (1.8–15%) and squid (0.5–6.5%) were also eaten. The penaeids Aristeus virilis, Haliporoides sibogae and Plesiopenaeus
edwardsianus ate mainly benthic or demersal animals. The catch rates of these prawns were 1.4–2.0 times greater during the day than at night, with the lower night-time catches probably resulting from some nocturnal swimming above the bottom. The penaeid Aristaeomorpha foliacea
and the carid Heterocarpus sibogae ate both midwater and demersal animals, while the carid Heterocarpus woodmasoni ate mainly midwater animals. The catch rates of these prawns were 2.6–16.5 times higher during the day than at night, which suggests that a large proportion
of them migrate into the water column at night, possibly to feed.
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