Evaluating the effects of secondary predation when using DNA metabarcoding for diet assessment in large pelagic fishes

Our lack of knowledge of oceanic predatory fish complicates the task of sustainably managing them and as such, many are data deficient, threatened or even endangered. One particularly poorly understood area is the preferred diet, or trophic ecology, of these fish. This poor understanding increases the likelihood of overfishing or depleting the food predatory fish depend on. DNA metabarcoding, which uses genetic sequencing to identify the prey in the stomach of fish, has become a popular technique for researching trophic ecology. However, recent research shows that DNA metabarcoding may not only pick up the predators’ diet, but also the diet of the prey, termed secondary predation or the Russian doll effect. This study will undertake stomach content analysis of a range of game fish caught at fishing tournaments to investigate their trophic ecology. Metabarcoding will be undertaken on both the game fish stomach and on any prey found with intact stomachs to better understand the poorly understood Russian doll effect. This research will not only fill management-hindering knowledge gaps surrounding game fish, but also improve our understanding of the Russian doll effect and its drivers, improving the accuracy of future metabarcoding studies.