Trophic niche changes during settlement in the Argentine hake Merluccius hubbsi reveal the importance of pelagic food post metamorphosis

Among those factors that determine the success of a fish cohort, trophic interactions play a key role, especially during the larval and juvenile stages. The Argentine hake Merluccius hubbsi is the most abundant demersal fish in the southwestern Atlantic and also one of the main commercial resources for Argentina. By employing C and N stable isotope analysis, we evaluated M. hubbsi changes in trophic niche and trophic position throughout their early life from early larvae to juveniles 2+ (8-330 mm total length, TL) during their drift from the spawning to the nursery ground. We analyzed 121 individuals and 7 possible resources in different sectors as fish move from the spawning to the nursery ground in the coastal region of northern Argentine Patagonia. Our results show that Argentine hakes occupy different trophic niches during their ontogenetic development. While larval stages (8-34 mm TL) feed almost exclusively on copepods, larger juveniles showed shrimps as their main prey. Individuals between 35 and 89 mm TL showed the most generalist diet, with a mix of both pelagic and epibenthic prey. Therefore, our results indicate that the change from a planktonic to a demersal habitat (settlement), which is of paramount importance in the early life history of hakes, is a gradual process.