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Auteur |
Travassos Tolotti, M.; Filmalter, J.D.; Bach, P.; Travassos, P.; Seret, B.; Dagorn, L. |
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Titre |
Banning is not enough: The complexities of oceanic shark management by tuna regional fisheries management organizations |
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Article scientifique |
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Année |
2015 |
Publication |
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Revue Abrégée |
Global Ecology and Conservation |
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Volume |
4 |
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1-7 |
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Mots-Clés |
Bycatch; conservation; Fin trade; Pelagic shark; Tuna fisheries |
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Résumé  |
Recently, declining populations of several pelagic shark species have led to global conservation concerns surrounding this group. As a result, a series of species-specific banning measures have been implemented by Regional Fishery Management Organizations (RFMOs) in charge of tuna fisheries, which include retention bans, finning bans and trading bans. There are both positive and negative aspects to most management measures, but generally, the positive aspects outweigh the negatives, ensuring the measure is beneficial to the resource and its users in the long term. Banning measures are a good first step towards the conservation of pelagic shark species, especially since they improve conservation awareness among fishers, managers and the public. Measures that impose total bans, however, can lead to negative impacts that may jeopardize the populations they were intended to protect. The majority of pelagic shark catches are incidental and most sharks die before they reach the vessel or after they are released. The legislation set out by RFMOs only prevents retention but not the actual capture or the mortality that may occur as a result. Managers should be fully aware that the development and implementation of mitigation measures are critical for a more effective conservation strategy. |
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2351-9894 |
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MARBEC @ isabelle.vidal-ayouba @ |
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1498 |
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Auteur |
Van Beveren, E.; Fromentin, J.-M.; Bonhommeau, S.; Nieblas, A.-E.; Metral, L.; Brisset, B.; Jusup, M.; Bauer, R.K.; Brosset, P.; Saraux, C. |
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Titre |
Predator-prey interactions in the face of management regulations: changes in Mediterranean small pelagic species are not due to increased tuna predation |
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Article scientifique |
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Année |
2017 |
Publication |
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Revue Abrégée |
Can. J. Fish. Aquat. Sci. |
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Volume |
74 |
Numéro |
9 |
Pages |
1422-1430 |
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Mots-Clés |
anchovy engraulis-encrasicolus; atlantic bluefin tuna; Energy density; fish condition; fisheries; food-consumption; Proximate composition; sea; thunnus-thynnus; Yellowfin tuna |
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Résumé |
Recently, the abundance of young Atlantic bluefin tuna (Thunnus thynnus) tripled in the northwestern Mediterranean following effective management measures. We investigated whether its predation on sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) could explain their concurrent size and biomass decline, which caused a fishery crisis. Combining the observed diet composition of bluefin tuna, their modelled daily energy requirements, their population size, and the abundance of prey species in the area, we calculated the proportion of the prey populations that were consumed by bluefin tuna annually over 2011-2013. To assess whether tuna could alter the size structure of the three small pelagic fish populations (anchovy, sardine, and sprat (Sprattus sprattus)), the size distributions of the consumed prey species were compared with those of the wild populations. We estimated that the annual consumption of small pelagic fish by bluefin tuna is less than 2% of the abundance of these populations. Furthermore, size selectivity patterns were not observed. We thus concluded that tuna predation is unlikely to be the main cause of major changes in the small pelagic fish populations from this area. |
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0706-652x |
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MARBEC @ alain.herve @ |
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2195 |
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Auteur |
Lefevre, S.; Mckenzie, D.J.; Nilsson, G.E. |
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Models projecting the fate of fish populations under climate change need to be based on valid physiological mechanisms |
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Article scientifique |
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Année |
2017 |
Publication |
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Revue Abrégée |
Glob. Change Biol. |
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Volume |
23 |
Numéro |
9 |
Pages |
3449-3459 |
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Mots-Clés |
aerobic scope; coryphaena-hippurus; energy-demand teleosts; gadus-morhua l; gill surface area; growth; makaira-nigricans; marlin tetrapturus-albidus; metabolism; metabolism-size relationship; oxygen consumption; oxygen-consumption; ram ventilation; Respiration; scaling; swimming performance; tuna katsuwonus-pelamis |
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Résumé |
Some recent modelling papers projecting smaller fish sizes and catches in a warmer future are based on erroneous assumptions regarding (i) the scaling of gills with body mass and (ii) the energetic cost of 'maintenance'. Assumption (i) posits that insurmountable geometric constraints prevent respiratory surface areas from growing as fast as body volume. It is argued that these constraints explain allometric scaling of energy metabolism, whereby larger fishes have relatively lower mass-specific metabolic rates. Assumption (ii) concludes that when fishes reach a certain size, basal oxygen demands will not be met, because of assumption (i). We here demonstrate unequivocally, by applying accepted physiological principles with reference to the existing literature, that these assumptions are not valid. Gills are folded surfaces, where the scaling of surface area to volume is not constrained by spherical geometry. The gill surface area can, in fact, increase linearly in proportion to gill volume and body mass. We cite the large body of evidence demonstrating that respiratory surface areas in fishes reflect metabolic needs, not vice versa, which explains the large interspecific variation in scaling of gill surface areas. Finally, we point out that future studies basing their predictions on models should incorporate factors for scaling of metabolic rate and for temperature effects on metabolism, which agree with measured values, and should account for interspecific variation in scaling and temperature effects. It is possible that some fishes will become smaller in the future, but to make reliable predictions the underlying mechanisms need to be identified and sought elsewhere than in geometric constraints on gill surface area. Furthermore, to ensure that useful information is conveyed to the public and policymakers about the possible effects of climate change, it is necessary to improve communication and congruity between fish physiologists and fisheries scientists. |
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1354-1013 |
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Numéro d'Appel |
MARBEC @ alain.herve @ |
collection |
2169 |
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Auteur |
Sardenne, F.; Chassot, E.; Fouche, E.; Menard, F.; Lucas, V.; Bodin, N. |
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Titre |
Are condition factors powerful proxies of energy content in wild tropical tunas? |
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Article scientifique |
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Année |
2016 |
Publication |
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Revue Abrégée |
Ecol. Indic. |
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Volume |
71 |
Numéro |
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Pages |
467-476 |
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Mots-Clés |
body condition; cod gadus-morhua; condition indexes; ecosystem; Energy variability; fish; Fish health; katsuwonus-pelamis; Large pelagic species; Proximate composition; thunnus-albacares; western indian-ocean; Yellowfin tuna |
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Résumé |
The “condition” is used as an indicator of fish health and is generally equated with the quantity of energy reserves. Biometric condition factors have been widely used and preferred over costly and time-consuming biochemical condition. Here, we investigated the relevance of four common condition factors based on biometric measurements (Le Cren's index, girth -length index, gonado-somatic index and hepato-somatic index) and of size- and weight -based empirical models to describe the physiological condition of tropical tunas. Biometric condition factors of bigeye (Thunnus obesus), skipjack (Katsuwonus pelamis) and yellowfin (Thunnus albacares) tunas sampled throughout 2013 in the western Indian Ocean region were assessed against benchmark biochemical indices (lipid content, protein content, triacylglycerol:sterol ratio and energy density) estimated in tissues with different physiological functions, i.e. red muscle, white muscle, liver, and gonads. Our findings suggest that tropical tunas do not store lipids in white muscle and that protein content is less variable than lipid content, which largely varies with ontogeny and the seasons according to tissue and species. This variability induced inconsistency between biometric factors, including the empirically adjusted ones, and biochemical indices, with the exception of the gonado-somatic index that fitted well to the composition of the gonads in the three species, and especially in females. (C) 2016 Elsevier Ltd. All rights reserved. |
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1470-160x |
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Numéro d'Appel |
MARBEC @ alain.herve @ |
collection |
1697 |
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Auteur |
Mullon, C.; Guillotreau, P.; Galbraith, E.D.; Fortilus, J.; Chaboud, C.; Bopp, L.; Aumont, O.; Kaplan, D. |
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Titre |
Exploring future scenarios for the global supply chain of tuna |
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Article scientifique |
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Année |
2017 |
Publication |
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Revue Abrégée |
Deep Sea Research Part II: Topical Studies in Oceanography |
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Volume |
140 |
Numéro |
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251-267 |
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Mots-Clés |
climate change; Global supply chain; marine protected area; Scenarios; Tuna |
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Résumé |
The abundance of tuna, an important top predator that ranges throughout tropical and subtropical oceans, is now largely determined by fishing activity. Fishing activity, in turn, is determined by the interaction of fish availability, fishing capacity, fishing costs and global markets for tuna products. In the face of overfishing, the continued sustainable supply of tuna is likely to require improved global governance, that would benefit from modeling frameworks capable of integrating market forces with the availability of fish in order to consider alternative future projections. Here we describe such a modeling framework, in which we develop several simple, contrasting scenarios for the development of the tuna supply chain in order to illustrate the utility of the approach for global evaluation of management strategies for tuna and other complex, stock-structured fisheries. The model includes multiple national and multi-national fishing fleets, canneries and fresh/frozen markets, and connects these to global consumers using a network of flows. The model is calibrated using recent data on fish catch, cannery and fresh/frozen production, and consumption. Scenarios explore the control on future outcomes in the global tuna fishery by representing, in a simple way, the effects of (1) climate change, (2) changes in the global demand for tuna, and (3) changes in the access to fishing grounds (marine reserves). The results emphasize the potential importance of increasing demand in provoking a global collapse, and suggest that controlling tuna production by limiting technical efficiency is a potential countermeasure. Finally we discuss the outcomes in terms of potential extensions of the scenario approach allowed by this global network model of the tuna supply chain. |
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ISSN |
0967-0645 |
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MARBEC @ isabelle.vidal-ayouba @ |
collection |
2098 |
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