Contribution of a bioenergetics model to investigate the growth and survival of European seabass in the Bay of Biscay – English Channel area

The European seabass (Dicentrarchus labrax) is a species of particular ecological and economic importance. Stock assessments have recently revealed the worrying state of the “Northern stock”, probably due to overfishing and a series of poor recruitments. The extent to which these poor recruitments are due to environmental variability is difficult to assess, as the processes driving the seabass life cycle are poorly known. Here we investigate how food availability and temperature may affect the growth and survival of wild seabass at the individual scale. To this end, we developed a bioenergetics model based on the Dynamic Energy Budget (DEB) theory. We applied it to seabass population of the Northeast Atlantic region (Bay of Biscay – English Channel area) throughout their entire life cycle. We calibrated the model using a combination of age-related length and weight datasets: two were from aquaculture experiments (larvae and juveniles raised at 15 and 20°C) and one from a wild population (juveniles and adults collected during surveys or fish market sampling). By calibrating the scaled functional response that rules the ingestion of food and using average temperature conditions experienced by wild seabass (obtained from tagged individuals), the model was able to reproduce the duration of the different stages, the growth of the individuals, the number of batches and their survival to starvation. We also captured one of the major differences encountered in the life traits of the species: farmed fish mature earlier than wild fish (3 to 4 years old vs. 6 years old on average for females, respectively) probably due to better feeding conditions and higher temperature. We explored the growth and survival of larvae and juveniles by exposing the individuals to varying temperatures and food levels (including total starvation). We show that early life stages of seabass have a strong capacity to deal with food deprivation: the model estimated that first feeding larvae could survive 17 days at 15°C. We also tested individual variability by adjusting the specific maximum assimilation rate and found that larvae and juveniles with higher assimilation capacity better survived low food levels at a higher temperature. We discuss our results in the context of the recent years of poor recruitment faced by European seabass.