DNA metabarcoding reveals species-specific selectivity and spatio-seasonal variability in the diet of preflexion larvae of European hake (Merluccius merluccius) in the Atlantic

The diet of preflexion European hake larvae (Merluccius merluccius) in the North-Eastern Atlantic was assessed by means of miniCOI metabarcoding in its fishery´s Northern and Southern stocks, encompassing the main spawning period (March and June surveys). As previously reported for other species of hake species larvae worldwide, copepods of the genera Clausocalanus, Paracalanus, Pseudocalanus and Ctenocalanus represented the bulk of prey, with copepod DNA corresponding to 74 % of the gut contents in average. A high positive selection for the species Clausocalanus pergens and Ctenocalanus vanus corresponded to March and June surveys, respectively. As also reported elsewhere for other species of hake larvae, neither the 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, in average, 16 % of prey DNA in the fours surveys analyzed, is unprecedented. Interestingly, when copepod prey was less abundant, in June, European hake larvae enhanced its piscivore behaviour with fish DNA encompassing 31 % of gut contents. 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.