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

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Abstract:

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 age1. Age1.25 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 age1.25 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.

Nous avons réalisé une série de simulations à l’aide d’un modèle numérique doté de paramètres validés et réalistes dans les régions portugaises du sud et du sud-ouest pour tenter de comprendre les patrons de dispersion des larves chez le homard de Norvège (Nephrops norvegicus). Nous avons introduit les larves dans le modèle comme des particules lagrangiennes possédant différents scénarios comportementaux relatifs à leur capacité de migration verticale. Le taux de croissance est dépendant de la température et les larves ont pu être suivies individuellement. Le terme final des simulations est la position des larves au moment où elles peuvent vivre indépendamment à l’âge 1. Nous avons aussi examiné l’âge 1,25 pour simuler la possibilité de délais dans l’établissement dus à la pénurie de substrats appropriés. Les résultats montrent que la majorité des larves atteignent l’âge 1 près du lieu d’éclosion le long de la plate-forme sud; on peut cependant observer un faible échange de larves entre les côtes sud et ouest, particulièrement dans les scénarios comportementaux dans lesquels les larves demeurent en eaux relativement peu profondes. Les scénarios dans lesquels les larves font des migrations verticales diurnes et retardent leur établissement jusqu’à l’âge 1,25 montrent une tendance vers un déplacement vers l’ouest à cause des interactions avec le courant sous-marin de la Méditerranée. Nous estimons l’auto-recrutement du stock de l’Algarve à 0,2 % à 0,5 %, ce qui soulève des inquiétudes sur la possibilité de limitation du recrutement dans ce stock.

Document Type: Research Article

Publication date: 2008-10-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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