Analysis of fish consumption of harbour seals in north western Iceland assessed by DNA metabarcoding. Iceland Harbour Seal Diet

Understanding ecological relationships between humans and marine predators is crucial for the implementation of sustainable management practices. Comprehensive estimation of pinniped diet is essential for assessing interaction with fisheries and often have an important conservational value. Due to uncertainty regarding accuracy of methods traditionally used to estimate harbour seal (Phoca vitulina) diet it is necessary to improve analysis methods. We investigated the diet of harbour seals hauling out in an estuary area in north western Iceland between June and September of 2010 and 2011 by DNA analysis of prey in faeces using DNA metabarcoding. The results were compared to previously published results from morphological analysis. Our results showed that species consumed were at large in agreement with species availability in the area; mainly sand eels (Ammodytes sp.), flatfishes (Pleuronectidae), gadoids (Gadidae), herring (Clupea harengus) and capelin (Mallotus villosus). The results from molecular and morphological analysis were similar in regards of important prey species, but species diversity was lower in the morphological analysis and 37.5% of the samples included prey items that were unidentifiable in the morphological analysis. Notably, despite Atlantic salmon (Salmo salar), brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) availability in the study area, neither of the methods found evidence of salmonids in the harbour seal diet. Recently, a severe decline has been observed in the Icelandic harbour seal population. Since the main reason for culling harbour seals in Iceland is to reduce predation on salmonids, findings presented in this paper have essential conservation implications and suggest that culling need to be reassessed.