Non-lethal method to obtain stomach samples from a large marine predator and the use of DNA analysis to improve dietary information

Dietary information of apex predators is crucial to understanding community dynamics and ecosystem processes. However, as dietary studies traditionally involve lethal sampling, obtaining this essential information can have repercussions on predator populations and the structure and functioning of marine ecosystems. With stronger emphasis being placed on conservation of species that are vulnerable to overexploitation, the need for non-destructive methods of sampling is imperative, as is the requirement to maximize the information obtained from each sample. Stomach flushing (gastric lavage) and DNA analysis of stomach contents methods were tested on the broadnose sevengill shark Notorynchus cepedianus Peron 1807. Acoustic tracking and recaptures of sharks implied high survivorship post-fishing and stomach flushing. From 85 prey items collected, 36 (43%) could be identified to species level using morphological analysis. After DNA analysis, a further 35 items were identified to species level, doubling the information obtained from these stomachs. The number of N. cepedianus that were confirmed to have eaten gummy sharks Mustelus antarcticus Gunther 1870 also doubled after DNA analysis. Without DNA analysis (of stomach contents) the importance of M. antarcticus in the diets of N. cepedianus would have been substantially underestimated. In addition, the non-lethal approach provides an opportunity to obtain meaningful information from non-harvested, endangered or rare species or sampling of species within protected areas.