Diet of European hake (Merluccius merluccius) preflexion larvae in the Atlantic through DNA metabarcoding: eating fish from the very beginning

Abstract

The diet of preflexion European hake larvae (Merluccius merluccius) in the North-Eastern Atlantic was assessed through miniCOI metabarcoding in its fishery's Northern and Southern stocks. As previously reported for the larvae of other hake species worldwide, copepods of the genera Clausocalanus, Paracalanus, Pseudocalanus and Ctenocalanus represented the bulk of prey, with copepod DNA corresponding to 75\% of the gut contents on average. By combining the high taxonomic resolution of metabarcoding with a parallel sampling of the food field, prey selection could be determined at the species level. The highest positive selection was reported for the copepod species Clausocalanus pergens and Ctenocalanus vanus. Neither the larval size (2-4 vs. 4-6 mm SL) nor the time of capture (Day vs. Night) affected dietary composition. However, the herein-reported importance of fish prey, only second to copepods and comprising, on average, 14\% of prey DNA in the four surveys analyzed, is unprecedented. Moreover, our data suggest that European hake larvae enhanced their piscivore behaviour when copepod prey was less abundant. The present work reinforces the utility of DNA-based diet assessment to disclose previously neglected, but albeit potentially important, mortality sources when modelling fishery resources.