What is the added value of including fleet dynamics processes in fisheries models? Auteur(s) : Marchal, Paul De Oliveira, Jose A. A. Lorance, Pascal Baulier, Loic Pawlowski, Lionel Éditeur(s) : Canadian Science Publishing, Nrc Research Press Résumé : We develop a spatially and seasonally explicit bioeconomic model with three fleet dynamics processes built in endogenously. The model has been applied to the large French trawlers harvesting a medium-depth demersal stock, North Sea saithe (i.e., pollock, Pollachius virens), and a mix of deepwater species over a 10-year period (1999-2008), and the predictions have been contrasted with observations. The best overall fit was achieved where effort allocation was determined to be 80% by traditions and 20% by economic opportunism and where harvest efficiency increased by 8% a year. With this fleet dynamics parameterization, annual trends in fishing effort and profit were well reproduced by the model over the whole time period. Time series of the observed fishing effort by metier were generally well fitted by the model over the period 1999-2003, but less so over 2004-2008. The model also reasonably reproduced the catches by species over most of the time series, except for black scabbardfish (Aphanopus carbo). Nous développons un modèle bio-économique spatial et saisonnier dans lequel trois processus caractérisant la dynamique des flottilles sont décrits de manière explicite. Ce modèle a été appliqué aux grands chalutiers français exploitant le lieu noir de mer du Nord (Pollachius virens) et une variété d'espèces profondes au cours d'une période de 10 ans (1999–2008), et les prévisions ont été contrastées avec les observations. Le meilleur ajustement est obtenu lorsque l'allocation de l'effort de pêche est déterminée a` hauteur de 80% par les traditions et 20% par l'opportunisme économique, et lorsque l'augmentation de l'efficacité de pêche est d'environ 8% par an. En paramétrant ainsi le module de dynamique des flottilles, les tendances annuelles de l'effort de pêche et du profit sont bien reproduites par le modèle sur l'ensemble de la période. Les variations temporelles de l'effort de pêche par métier sont généralement bien prises en compte sur la période 1999–2003, mais non sur la période 2004–2008. Le modèle ajuste les captures raisonnablement sur la plus grande partie de la période d'étude, pour toutes les espèces sauf le sabre noir (Aphanopus carbo). Canadian Journal Of Fisheries And Aquatic Sciences (0706-652X) (Canadian Science Publishing, Nrc Research Press), 2013-07 , Vol. 70 , N. 7 , P. 992-1010 Droits : 2013 NRC Research Press http://archimer.ifremer.fr/doc/00151/26227/24329.pdf DOI:10.1139/cjfas-2012-0326 http://archimer.ifremer.fr/doc/00151/26227/ | Partager |
Genetic connectivity of the reef fish Lutjanus kasmira at the scale of the western Indian Ocean Auteur(s) : Muths, Delphine Gouws, G. Mwale, M. Tessier, Emmanuel Bourjea, Jerome Éditeur(s) : Canadian Science Publishing, Nrc Research Press Résumé : Examining the genetic structure of species allows an estimate of the level of evolutionary connectivity between localities; this information is important for marine biodiversity protection, in particular, for the delineation of marine protected areas. In this context, a total of 601 Lutjanus kasmira (Forsskal, 1775) were sampled in 16 localities of the western Indian Ocean and analyzed with both mitochondrial cytochrome b sequencing and eight microsatellite loci genotyping. Both genetic markers indicate that differentiation was not significant even between samples separated by more than 4000 km. This absence of genetic differentiation among samples was favored by ecological plasticity of the species and is now ensured by resultant high levels of dispersal. Nevertheless, some significant genetic structure was detected for the areas of Mauritius and Moroni, as well as within populations in all localities, which will have to be explained by additional studies on local processes. Canadian Journal Of Fisheries And Aquatic Sciences (0706-652X) (Canadian Science Publishing, Nrc Research Press), 2012-05 , Vol. 69 , N. 5 , P. 842-853 Droits : 2012 Published by NRC Research Press http://archimer.ifremer.fr/doc/00079/19044/16647.pdf DOI:10.1139/F2012-012 http://archimer.ifremer.fr/doc/00079/19044/ | Partager |