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Olson, R. J., Young, J. W., Menard, F., Potier, M., Allain, V., Goni, N., et al. (2016). Bioenergetics, Trophic Ecology, and Niche Separation of Tunas. In B. E. Curry (Ed.), (pp. 199–344). Advances in Marine Biology, Vol 74, 74. San Diego: Elsevier Academic Press Inc.
Résumé: Tunas are highly specialized predators that have evolved numerous adaptations for a lifestyle that requires large amounts of energy consumption. Here we review our understanding of the bioenergetics and feeding dynamics of tunas on a global scale, with an emphasis on yellowfin, bigeye, skipjack, albacore, and Atlantic bluefin tunas. Food consumption balances bioenergetics expenditures for respiration, growth (including gonad production), specific dynamic action, egestion, and excretion. Tunas feed across the micronekton and some large zooplankton. Some tunas appear to time their life history to take advantage of ephemeral aggregations of crustacean, fish, and molluscan prey. Ontogenetic and spatial diet differences are substantial, and significant interdecadal changes in prey composition have been observed. Diet shifts from larger to smaller prey taxa highlight ecosystem-wide changes in prey availability and diversity and provide implications for changing bioenergetics requirements into the future. Where tunas overlap, we show evidence of niche separation between them; resources are divided largely by differences in diet percentages and size ranges of prey taxa. The lack of long-term data limits the ability to predict impacts of climate change on tuna feeding behaviour. We note the need for systematic collection of feeding data as part of routine monitoring of these species, and we highlight the advantages of using biochemical techniques for broad-scale analyses of trophic relations. We support the continued development of ecosystem models, which all too often lack the regional-specific trophic data needed to adequately investigate climate and fishing impacts.
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Amandé, M., Ariz, J., Chassot, E., Molina, A. D. de, Gaertner, D., Murua, H., et al. (2010). Bycatch of the European purse seine tuna fishery in the Atlantic Ocean for the 2003-2007 period. Aquatic Living Resources, 23(4), 353–362.
Résumé: Bycatch of several groups of species and their characteristics are presented for the period 2003 to 2007 for the European purse seine tuna fishery operating in the Atlantic Ocean. Data were collected through French and Spanish observer programmes and represented a total of 27 trips corresponding to 2.9% coverage. Bycatch is defined as non-targeted species and small or damaged target species. Bycatch species composition, main species length, sex ratio and the fate of the most common species are presented first. Stratified ratios relative to landings of major commercial tunas were then used to estimate the total bycatch; these ratios were considered the most appropriate variable for extrapolation. Stratification was based on the fishing mode (free school vs. floating object), season (quarters) and spatial areas. The annual average bycatch was estimated at about 6400 t, corresponding to a mean annual value of 80.8 t per 1000 t of tuna landed or 7.5% of the total catch. Tunas represent 83% (67.2 t/1000 t) of the total bycatch, followed by other bony fishes (10%, 7.8 t/1000 t), billfishes (5%, 4.0 t/1000 t), sharks (1%, 0.9 t/1000 t) and rays (1%, 0.9 t/1000 t). Based on estimates of the annual bycatch, 16% was kept on board and sold in local markets.
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Bonnin, L., Lett, C., Dagorn, L., Filmalter, J. D., Forget, F., Verley, P., et al. (2020). Can drifting objects drive the movements of a vulnerable pelagic shark? Aquat. Conserv.-Mar. Freshw. Ecosyst., .
Résumé: Juvenile silky sharks (Carcharhinus falciformis)regularly associate with floating objects yet the reasons driving this behaviour remain uncertain. Understanding the proportion of time that silky sharks spend associated with floating objects is essential for assessing the impacts of the extensive use of fish aggregating devices (FADs) in the tropical tuna purse-seine fisheries, including increased probability of incidental capture and the potential of an ecological trap. Previous studies provided insight into the amount of time that silky sharks spent at an individual FAD but were unable to assess neither the time spent between two associations nor the proportion of time spent associated/unassociated. The percentage of time that juvenile silky sharks spend unassociated with floating objects was estimated through the analysis of horizontal movements of 26 silky sharks monitored with pop-up archival tags. Under the assumption that a high association rate with drifting FADs would align the trajectories of tracked sharks with ocean surface currents, a novel methodology is proposed, based on the comparison of shark trajectories with simulated trajectories of passively drifting particles derived using a Lagrangian model. Results revealed that silky shark trajectories were divergent from surface currents, and thus unassociated with FADs, for at least 30% of their time. The potential of the methodology and the results are discussed in the context of increasing FAD densities in the Indian Ocean.
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Escalle, L., Gaertner, D., Chavance, P., Murua, H., Simier, M., Jose Pascual-Alayon, P., et al. (2019). Catch and bycatch captured by tropical tuna purse-seine fishery in whale and whale shark associated sets: comparison with free school and FAD sets. Biodivers. Conserv., 28(2), 467–499.
Résumé: In an ecosystem approach to fisheries management (EAFM) framework of the tuna purse-seine fishery, the assessment of target species, but also that of bycatch species, is essential. In the Atlantic and Indian oceans, purse-seine nets are sometimes set around tuna schools associated with whale sharks and baleen whales, although less frequently than around free-swimming tuna schools or those associated with fish aggregating devices (FAD). However, knowledge on the targeted catch and bycatch in these megafauna associated fishing sets is still relatively limited. Therefore, the aims of this study were to assess species and size composition of the target tuna species, as well as the diversity of bycatch species in whale and whale shark associated sets. Whale associated sets were found to be very similar to free school sets in terms of tuna catch (large yellowfin tuna), bycatch occurrence (presence in half the sets) and species assemblage (alpha and beta diversity). Whale shark associated sets were intermediate between FAD and free school sets, with tuna catch (skipjack and juvenile yellowfin) closer to FAD than to free school sets. However, the presence of large yellowfin, the bycatch composition (with almost no finfish, abundantly captured in FAD sets) and the species assemblage showed similarity with free school sets. This study highlights the need for an EAFM in the tuna purse-seine fishery by providing knowledge on pelagic multi-specific catches and bycatches.
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Nikolic, N., Lauretta, M., Patucca, A., & Morandeau, G. (2018). Characterization and standardization of the Atlantic albacore French pelagic trawl fishery. Aquat. Living Resour., 31, 31.
Résumé: We compiled and analysed logbook data from the French trawl albacore fishery covering the period 1991-2015. The dataset comprised catch and effort data for the French fleet operating in the Bay of Biscay and Celtic Sea, as well as spatiotemporal and gear characteristics. Generalized linear modelling was used to model spatial, seasonal, environmental, and gear covariates of fleet CPUE rates. A long-term index of relative abundance is provided that can be integrated into the stock assessment of North Atlantic albacore. The analysis revealed higher albacore CPUE associated with relatively low sea surface temperature and distinct seasonal effects. The derived abundance trend for the French trawl fishery agreed with the estimated time series of stock abundance from recent assessments.
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