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BCBC2019-05: Determining the diet of New Zealand king shag using DNA metabarcoding (PDF, 1,500 K)

Summary

The New Zealand king shag (Leucocarbo carunculatus) is a nationally endangered endemic seabird that is confined to the coastal margins of the outer Marlborough Sounds, in the South Island of New Zealand. There is concern that anthropogenic activities, such as marine farming and fishing, may impact the feeding in this species. However, the diet of the New Zealand king shag is poorly described. Therefore, the aim of this study was to develop and apply DNA metabarcoding methods to attempt to determine the composition of the diet of New Zealand king shag based on analyses of regurgitated pellets of indigestible food material and/or faecal samples.

185 pellets were collected from seven king shag colonies, 183 of the pellets were of sufficient quality for further analyses. The DNA metabarcoding revealed a total of more than 300 species present in the pellets, of which 32 species were fish. Fish occurred in 181 (99%) of samples indicating their importance in the diet. Lefteyed flounder species were the dominant species found in pellets, with witch (Arnoglossus scapha) most commonly found (present in 122 samples), followed by crested flounder (Lophonectes gallus; 79 samples). There were some differences in the composition of fish species in the pellets among the seven colonies, and between male and female king shags, with bird gender also being determined by DNA methods.

In addition to fish, a variety of crustacean (crabs and shrimps), as well as octopus, were identified as a small component of species present in the pellets. These may have represented prey species, or possible secondary prey species, i.e., species from the digestive tract of fish that were then consumed by king shag. Many non-dietary items were detected from the DNA metabarcoding, including parasitic species, such as parasitic worms from the gut and feather mites.

Overall, the results suggest king shags are opportunistic generalists that include a wide diversity of fish species in their diet, with benthic fish species, especially flatfish, most commonly targeted. Consequently, the diet of the New Zealand king shag is strongly linked to the waters surrounding their colonies with localised differences in diet apparent from this study, that most likely represents localised differences in prey availability. The study confirms the effectiveness of DNA metabarcoding methods for assessing the composition of the diet in New Zealand king shag, and potentially other seabirds of conservation interest.