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Summary
This report encompasses the first component of a project to deduce diet of king shags from analysis of prey remains from 225 regurgitated pellets collected in Marlborough Sounds during 2019 and 2020. The other component of this research involved Determining the diet of New Zealand king shag using DNA metabarcoding.
This study represents the second published investigation of king shag diet from analysis of prey remains in pellets. We increased the biodiversity of prey from the first study in 1991–1992 with 10 taxa (two crustaceans and eight fishes) from 22 pellets at one site to this study with 26 taxa (two crustaceans, two cephalopods and 22 fishes) from 215 pellets at seven sites. The basic understanding of foraging and diet remains unchanged – king shags target bottom-dwelling fishes and flatfishes, particularly witch (Arnoglossus scapha), predominate.
Frequencies of occurrence deduced from prey remains analysis and DNA analysis provide a simple qualitative assessment of king shag diet through the presence/absence of taxa in pellets. In future a more thorough analysis of the prey remains in these pellets would quantify diet as an average daily biomass for each prey species. The equivalent in DNA analysis is more qualitative: relative read abundance, an assessment of the strength of DNA signatures, generates estimates for proportion of total biomass. Comparisons between results from these two analyses could facilitate calculation of indices to transform relative read abundances into real masses.
The key issue for future projects on king shag diet is to decide on the purpose and desired outcome of research and then select the appropriate methods and analyses before samples are collected.