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International audience; Quantitative applications of mobile multibeam sonar in aquatic ecology and fisheries require accurate and efficient in-tank calibration methodologies. Calibration factors for a Simrad SM20 multibeam sonar are experimentally extracted thereby enabling sonar estimation of target strength and volume backscattering strength. Measured and modeled sonar characteristics are systematically compared and show good overall correlation. Due to the limited angular span of the sonar head array, well quantified sonar operation is restricted to an equatorial angular sector of only 80° (vs. rated 120°) in 'imaging' mode. In 'echo-sounder' mode, the 'high' power transmit setting appears to introduce artifacts. A routine in-tank measurement procedure is described which for given multibeam sonar minimizes the time required for quality multibeam calibration

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.

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.

Conventional “spaghetti” tags have been used for a long time in Tropical Atlantic Ocean and have been collected by ICCAT secretary with the collaboration of scientists and fishermen. Despite, careful examination of the information provided at release and at recapture some errors may persist into the ICCAT tagging data base. The aim of this short note is to highlight some types of errors existing in the tagging data bases for tropical tunas and to suggest potential clues for corrections.

In this document, different scenarios of uncertainties in a multispecies fishery are presented. Uncertainties have been considered in the estimation of the species composition of the tropical tuna catch as well as in the total catch. Although three species (yellofin, skipjack and bigeye) are involved in the tropical tuna fishery, only uncertainties in the bigeye vs skipjack have been taken into account, in order to simplify the analysis. Regarding the total catch, bigeye has been considered as the species with higher uncertainty due to the IUU catch component. Analyses have been focused in evaluating the sensitivity of the current assessment methods to these uncertainties. Taking into account that the two sources of uncertainty affect the age structure of the catch as well as the total catch, surplus production methods have been applied in the assessment.

Atlantic bigeye is a highly migratory species widely distributed through the whole Atlantic. Recent assessments conducted by the ICCAT SCRS are highly uncertain due to the large uncertainties in biological parameters, such as M, as well as in fishery statistics (e.g., IUU fleets, juvenile catch) or abundance indexes. Similar uncertainties can be found in the Indian or Pacific stocks. The development of an operational model has been recommended by different regional fishery organizations as a good approach to investigate the sensitivity of the assessment results to the uncertainties in the different inputs. This document presents an operational model for the Atlantic bigeye as part of a simulation framework that will allow the performance of management strategies based on current and improved biological knowledge and management procedures to be evaluated.

Molecular markers allow insights into the population biology and ecology of deep-sea organisms, which are usually hardly accessible to direct observation and poorly known. Such a study was undertaken here for the deep-sea fish Beryx splendens , a species of growing interest to fisheries. B. splendens populations were sampled on seamounts and continental margins in the southwestern Pacific (New Caledonia, New Zealand, southeastern Australia) and in the northeastern Atlantic. Two hundred and fifty individuals were characterised by their single-strand DNA conformation (SSCP) of a ∼ 360-base-pair (bp) fragment of the mitochondrial cytochrome b gene, amplified by the polymerase chain reaction (PCR). Two major SSCP haplotypes were observed in New Caledonia, a and w , whose frequencies were negatively correlated along a north-to-south cline. All SSCP haplotypes in the total sample were sequenced on 273 bp. The phylogenetic tree of B. splendens haplotype sequences, rooted by two B. decadactylus sequences, showed that a and w belong to distinct mitochondrial clades, A and W, which are separated by ∼ 4–6 % nucleotide divergence. Thirty individuals from New Caledonia were characterised by their DNA fingerprint from arbitrary-primed PCR. The distribution of individual-pairwise similarity indices was strongly bimodal. The larger similarity values all corresponded to comparisons within a clade (A or W) while the lower values were all between clades. Therefore, there was a strict association between the mitochondrial type and the DNA (presumably, nuclear DNA) fingerprint of an individual. Altogether, these results point to the existence of two biological species (sp. A and sp. W) within the current taxon B. splendens . No within-species differentiation was detected at the regional scale (New Caledonia). A remarkable result is that the three cytochrome b haplotypes of northeastern Atlantic B. cf. splendens sp. A were also the three commonest in the southwestern Pacific populations of this species. Such a level of homogeneity in the distribution of haplotypes suggests there is, or recently has been, gene flow at the inter-oceanic scale.