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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

Estimates of tag reporting rates are necessary in order to estimate tag-recovery rates and interpret tagging data in terms of movement rates, exploitation rates and abundance. We describe a Bayesian framework for the estimation of reporting rates for multiple fleets using coincidental tagging and catch data disaggregated by fish size, species, location and time. The method was applied to the data of the Indian Ocean Tuna Tagging Programme (2006–2011) and tag seeding experiment of the Indian Ocean Tuna Commission (2004–2009). Reporting rates were estimated for 13 Indian Ocean tuna fleets. These estimates varied widely from 94% for the European Union purse seine fleet to less than 1% for fishing operations of non-longline/non-purse seine fleets in the Eastern Indian Ocean. Generally, reporting rates were high compared with estimates for tuna fisheries in other Oceans.

Indices of CPUE are presented for skipjack tuna (Katsuwonus pelamis) for the Indian Ocean over the period 1980-2013. The analysis was initiated under the framework of the E.U. research project CECOFAD, whose objectives are to enhance our understanding of fishing effort units and improve the accuracy of purse-seine CPUE estimates. Skipjack stock assessments mainly depend on abundance indices derived from purse-seine fleets, thus standardisation of purse seiner CPUEs for this species is a priority. We follow a CPUE definition framework where three different types of CPUE are calculated to describe trends in number of schools, school detectability and catchability and school size. CPUE standardization is typically achieved with the development of GLM models; these estimates are often biased because the range of the fishing area changes from one year to the next. We compare CPUE trends derived from conventional GLMs with trends based on GLMMs, where the spatial explanatory variables are treated as a random effect. According to a definition, a variable is random when it constitutes only a part of the entire population: spatial variables can be considered random since each year fishing vessels sample only a part of the historically fished area. Exploratory analyses revealed issues of heterogeneity and autocorrelation, supporting the use of mixed models and the shift towards a Bayesian approach to CPUE standardization modeling. Our analysis uses fishing sets targeting free swimming tuna schools for the French purse seiners operating in the western Indian Ocean. Future work will address the problem of accounting for the major changes in purse seine fishing strategies and the implementation of new technology on board (mainly the use of FAD technology) under a Bayesian framework.

This paper discusses the skipjack movements observed in the Indian Ocean based on an analysis of fishery data of the 13.128 selected recoveries of tagged skipjack. Its goal is to evaluate the potential geographical heterogeneity of the skipjack population fished in the Indian Ocean. Significant latitudinal & longitudinal movements have been frequently observed; the geographical range of skipjack movements appears to be wide in scale, showing an average distance over 1000 miles between tagging & recovery positions. These distances are showing an increasing trend with time at liberty, and reaching average distances of 1400 miles after 2 years. Recovery data are also showing that skipjack movements are often very fast, for instance reaching average distances over 800 miles after only 1 month at liberty in the Tanzania tagging. Distances covered are the lowest for skipjack tagged in the Maldives and in Seychelles islands and much larger in the Tanzania and Seychelles tagging. these differences are discussed. Because of these fast and extensive movements of skipjack, it can be concluded that its population is highly mobile in the Indian Ocean, but that the mixing rates of individual skipjack that are fished in remote parts of the Indian Ocean are probably low or very low. Based on these results, it is proposed that skipjack indicators and future skipjack stock assessment should be stratified on at least 4 areas, and estimating the mixing rates of skipjack tunas fished in each of these areas.

15 pages, 11 figures, 4 tables, 2 annex, 3 tables supporting information http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0085670, Background: The expansion of fishing activities has intensively transformed marine ecosystems worldwide. However, available time series do not frequently cover historical periods. Methodology: Fishers’ perceptions were used to complement data and characterise changes in fishing activity and exploited ecosystems in the Spanish Mediterranean Sea and Gulf of Cadiz. Fishers’ interviews were conducted in 27 fishing harbours of the area, and included 64 fishers from ages between 20 to > 70 years old to capture the experiences and memories of various generations. Results are discussed in comparison with available independent information using stock assessments and international convention lists. Principal Findings: According to fishers, fishing activity substantially evolved in the area with time, expanding towards deeper grounds and towards areas more distant from the coast. The maximum amount of catch ever caught and the weight of the largest species ever captured inversely declined with time. Fishers (70%) cited specific fishing grounds where depletion occurred. They documented ecological changes of marine biodiversity during the last half of the century: 94% reported the decline of commercially important fish and invertebrates and 61% listed species that could have been extirpated, with frequent mentions to cartilaginous fish. Declines and extirpations were in line with available quantitative evaluations from stock assessments and international conventions, and were likely linked to fishing impacts. Conversely, half of interviewed fishers claimed that several species had proliferated, such as cephalopods, jellyfish, and small-sized fish. These changes were likely related to trophic cascades due to fishing and due to climate change effects. The species composition of depletions, local extinctions and proliferations showed differences by region suggesting that regional dynamics are important when analysing biodiversity changes. Conclusions/Significance: Using fishers’ perceptions, fishing and ecological changes in the study area were documented. The recovery of local ecological knowledge provides valuable information complementing quantitative monitoring and evaluation surveys, MC was supported by the Marie Curie EC CIG grant to BIOWEB and the Spanish Research Program Ramon y Cajal. GG was funded through the EC program Science in Society EC. FP7 (ref # 266544-GAP2)

The management and conservation of large pelagic fish commonly rely on fisheries data and thus crucially depend on our understanding of the fish response to the fishing gear. Stock assessment of both tropical and temperate tuna strongly leans on the catch statistics derived from pelagic longline fisheries. However, the role of the spatial distribution of catches of tuna and bycatch species over the gear, which can affect the estimated tuna abundance, is still neglected. In this study, we analyzed data obtained from 147 instrumented pelagic longline sets equipped with hook timers and temperature depth recorders to characterize the distribution of hooking contacts and success at a fine temporal and spatial scale. Scientific surveys were carried out in the Central–South Pacific Ocean (French Polynesia), targeting tropical (Thunnus albacares, Thunnus obesus) and temperate (Thunnus alalunga) tuna. Data analysis based on spatial point processes and stochastic modeling demonstrate the presence of spatio-temporal clusters for both hooking contacts and hooking success. The comparative analysis of the observed spatio-temporal patterns for different oceanographic zones revealed the persistent structure of the clusters, suggesting that they are neither related to local environmental conditions nor to the spatial distribution of prey species.

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.

An acoustic survey was carried out in the bay of Biscay from May 3rd to June 1st on board the French research vessel Thalassa. The objective of PELGAS05 survey was to study the abundance and distribution of pelagic fish in the Bay of Biscay. The target species were mainly anchovy and sardine and were considered in a multi-specific context. The results have to be used during ICES working groups in charge of the assessment of sardine, anchovy, mackerel and horse mackerel and in the frame of the Ifremer fisheries ecology program "resources variability"., Une campagne acoustique a été organisée dans le golfe de Gascogne du 3 mi au 1er juin 2005, à bord du navire océanographique français, Thalassa. L'objectif de cette campagne Pelgas 06 était d'étudier l'abondance et la distribution des poissons pélagiques dans le golfe de Gascogne. Les deux espèces cibles étaient principalement l'anchois et la sardine. Les résultats ont été utilisés lors des groupes de travail en charge de l'estimation des stocks de sardine, anchois, maquereau et chinchard et dans le cadre du programme d'écologie des pêcheries de l'Ifremer, "ressources variability".

Survey data from 2000 to 2004 were used to analyse whether sardine show a preferential distribution in relation to bottom depth and/or latitude. For this analysis, four strata were considered; North or South of latitude 46°N (separating VIIIa and VIIIb) and bottom depths deeper or shallower than 110m. Sardine length distributions are plotted as the proportion of small (< 18.5 cm) or big (larger than 18.5 cm) fish on the samples over the years. This division was chosen to take into account the bimodal structure of sardine length distributions (usually with a "valley" at 18.5 cm fish length). Small fish (mainly 1 year old) are generally found close to the coast and preferentially in the southern part. The year 2003 is different to the others but this year was totally atypical for all species and sardine was rather absent of the Bay of Biscay at the time of the survey.

The schooling behaviour of sardine Sardinops sagax in False Bay on the south coast of South Africa was studied in October 1995 using high-resolution sonar and a hull-mounted, echo-integration unit. School formation and disintegration were studied, and school shape, packing density, swimming behaviour and inter- and intra-school event rates were quantified. Mean fish density was 29.5 fish m-3 (SD 46 fish m-3), but it varied between schools by a factor of about 100 (from 2 to 233 fish m-3). Tracked schools moved at average speeds of 0.67–1.59 m s-3. Schools changed shape on average every 2.08 minutes, and underwent either splits or merges with other schools on average every 5 minutes. Relationships between the geometric dimensions and biomass of the schools were established.Afr. J. mar. Sci. 25: 185–193

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.

Lack of reliable data on the fisheries of northern Cote d’Ivore reservoirs is a major limi-tation for management of the fish stocks. As individual reservoirs cannot be studied due tothe high costs and lack of trained investigators, empirical and production models have tobe used to evaluate exploitation rates and fisheries potential. Daily yield (DY, in kg fishingday 1 year ) and total catch (TC, in kgyear 1 ) appear to be better descriptors than annual yield (in kg ha 1 year ). TC is related to variables linked to nutrient availability(watershed area, conductivity and Morphoedaphic Index). DY is related to fish speciesrichness and to reservoir area, indicating that fish population structure could be a key tounderstanding the patterns observed. Correlation between fish population structure andyield was significant. It was hypothesised that overall catch, TC, is related to nutrient avail-ability, but that catch per unit effort is related to the presence of given species in the reser-voirs, and particularly to the presence of bottom feeding species.Keywords: fish population structure, fisheries, reservoirs, yield models.

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.