Dietary studies on common commercial and ecologically important fishes from the 1980s & 1990s form the basis of ecosystem models currently in use in southern Australia. These models are increasingly relied upon to provide guidance for fisheries management, particularly as ecosystem-based management ideals are embraced. Therefore it’s vitally important that the dietary data underpinning these models are kept current and accurate.
Oceanographic conditions off eastern Australia are highly variable but now there are indications that oceanographic regimes might shift permanently as a result of climate change. Moreover, there is evidence that species distributions are changing, so we asked whether the diets of several fishes from the early studies have changed to an extent that we need to re-parametrise our models? We sampled ten commercially-caught species from the southeastern Australian shelf to determine their current diets and compare them mid-1990s diets. We used traditional stomach content analysis (visual) but we also established base-line data-sets for DNA meta-barcoding analyses of the stomach contents and for analyses of bulk and compound-specific amino acid stable isotopes, and fatty acids of the fish tissue samples.
Diet compositions of some of the species had changed but for others the results were unclear, complicated by a high incidence of un-identifiable prey or by small sample sizes. DNA analyses increased prey identification in many cases, particularly where contents were unidentifiable, and identified new trophic links but not quantitatively. The biochemical markers provided insights into longer-term nutritional status, trophic positions and basal food web sources but were limited by small sample sizes. Potentially these newer techniques add greater depth of ecological understanding to ecosystem models and may eventually help to overcome the financial constraints of long-term sampling programs but visual stomach content analyses still remain invaluable to the trophic biologists and ecosystem modellers.