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Ce document présente une méthode objective visant à identifier et à évaluer les regroupements des bancs de thons autour des monts sous-marins. La méthode associe la sélection statistique des monts sous-marins actifs sur la base d'une analyse du temps de pêche de la flottille et du schéma de points spatiaux. Le document analyse brièvement les caractéristiques des prises de thonidés pour cinq monts sous-marins sélectionnés par cette méthode dans l'océan Atlantique au titre de la période 1999-2010 pour les flottilles de senneurs et de canneurs français et espagnols. Les prises par km2 sont plus élevées à proximité des monts sous-marins pour les deux flottilles. La composition spécifique change et la proportion des thons obèses augmente dans les captures alors que celle des albacores et des listaos se réduit. Les distributions des fréquences des tailles montrent que les spécimens plus petits sont plus fréquents à proximité des monts sous-marins. Toutefois, ces schémas peuvent varier en fonction des monts sous-marins considérés.

In the lack of direct estimate of tuna abundance, the French tropical tuna fleet of purse-seiners provides a way to monitor the tuna stocks particularly through the calculation of Catch per Unit of Effort (CPUE). The objective of this study was to analyze the individual track of purse seiners with the aim to identify which part of the searching behaviour should be used to perform the fishing effort. In this context, Vessel Monitoring Systems (VMS) data are useful to analyse the different fishing activities of a purse seiner at a small scale (i.e.. stop, track and cruise), generally embedded into the concept of fishing effort. A state-space model (run in a Bayesian framework) was applied to speeds and turning angles from Vessel Monitoring Systems (VMS) data, to identify the different “states” of the fishing behaviour of a purse seiner over a fishing trip. Then a threshold was fitted to distinguish the activities “fishing” and “stop” without fishing (from the “still” state), “tracking” (from “meander”), and “cruising” (from “straight”). On a subset of VMS data corresponding to observers' data, some differences of fishing efforts between fishing on free-swimming schools and schools associated with FAD (Fish Aggregating Devices) are highlighted.

The document describes the fishing activities of the French purse seiners targeting tropical tunas, i.e. Thunnus albacares, Katsuwonus pelamis, and Thunnus obesus in the Indian Ocean during 1991-2009. The catch time series of the fleet over the period 2001-2009 has been updated following a change in the spatial stratification used in the multispecies sampling and a few modifications in data processing. Information is provided on fishing effort (fishing days, searching days, and fishing sets), catch, catch rates, and mean weights for the major tropical tuna species. Two major fishing modes are considered for the fishery: log-associated and free swimming schools.

Working Group ICCAT July 2008; Florianopolis, Brasil; The PROCEAN (PRoduction Catch / Effort ANalysis) model is a multi-fleet biomass dynamic model developed in a Bayesian framework to conduct stock assessments based on catch and effort time series data. PROCEAN was applied to the eastern component of the Atlantic skipjack (Katsuwonus pelamis) to assess the current status of the stock and provide reference points to fishery managers. Data included 8 time series of catch and effort data spanning from 1969 to 2006 and mostly standardised based on generalized linear modelling techniques. Informative priors and constraints for some parameters were used to allow the model to converge. Model fits were generally good but indicated increasing trends in the residuals for some fishing fleets. Results suggested that the eastern Atlantic skipjack stock would be underexploited, with a biomass in 2006 equal to 1.8 times the biomass at the maximum sustainable yield (MSY) and a fishing mortality in 2006 equal to 30% of the fishing mortality at MSY (FMSY). A sensitivity analysis performed to account for uncertainty in some input parameters showed that FMSY estimates were robust to parameter changes while MSY estimates were sensitive to the prior distribution for MSY. Based on the different model runs, the MSY was estimated to be comprised between 152,000 and 185,000 t. The use of random walks on catchability was useful for tracking changes in catchability and associated increasing fishing power for some baitboat fishing fleets targeting skipjack.

This document presents a standardized index update of adult yellowfin (>30 kg) of tropical purse seine fleets in the Atlantic Ocean from 1980 to 2006. The data used were taken from spear fishing logbooks and detailed information of the fleet. The standardization has been carried out by generalized linear models (GLM) using the delta model. The standardized indices are obtained from the GLM model estimations: one is calculated from the least squares means (LSMeans) and another from the annual averages of the adjusted values. The variability of the latter is lower. Therefore, in this case, it is a more adequate index to be used in assessment models. The year, country, category, age of vessel and catches of skipjack tuna, which is the other target species of these fleets, were considered as explanatory variables.