A modelling study of Norway lobster (Nephrops norvegicus) larval dispersal in southern Portugal: predictions of larval wastage and self-recruitment in the Algarve stock

A set of simulations using a validated and realistic parameterization of a numerical model was conducted for the south and southwest Portuguese regions as an attempt to understand larval dispersal patterns in the Norway lobster (Nephrops norvegicus). Larvae were introduced in the model as Lagrangian particles with five different behavioural scenarios concerning their ability to migrate vertically. Growth rate was temperature dependent and the larvae were tracked individually. The end point of the simulations was the position of the larvae when they reached competency at age 1. Age 1.25 was also considered to simulate a possible delay in settling due to lack of an appropriate substrate. The results showed that the majority of the larvae reached age 1 near the hatching area along the southern shelf, while low exchange of larvae between the south and the west coasts was observed, especially for behavioural scenarios where larvae remained in relatively shallow waters. Scenarios where larvae performed diurnal vertical migration and delayed settlement until age 1.25 indicated a tendency for westward motion because of interactions with the Mediterranean undercurrent. Self-recruitment to the Algarve stock was estimated at 0.2% to 0.5%, raising the concern that this stock may be experiencing recruitment limitation.