Mediterranean Bluefin Research Articles

Age and growth of Atlantic bluefin tuna,Thunnus thynnus(Osteichthyes: Thunnidae), in the Mediterranean Sea

Summary The objective of the study was to describe the biometry of Mediterranean bluefin tuna, Thunnus thynnus, the biology of which is not yet well understood. A total of 504 specimens was collected from 1998 to 2005 in the central part of the Mediterranean basin. They were sexed and measured; fork lengths (FL) ranged from 51.0 to 255.0 cm while body weights (W) ranged from 2.6 to 247.0 kg. The first spiniform ray (spine) of the first dorsal fin was removed and cross-sectioned near the condyle base in order to count annuli for age estimation. The regression coefficient (b) of the female FL–W relationship was significantly higher than that of the male, and both sexes displayed a negatively allometric growth (b < 3); male regression equation: ln W = )2.942 + 2.730 ln FL; female regression equation: ln W = )3.660 + 2.878 ln FL. Based on counts of the translucent zones in the sections of the first ray of the first dorsal fin, estimated ages ranged from 1 to 15 years for males and 1 to 14 years for females. The correlation between the spine ray (R) and FL fit the allometric model best; the R–FL regression equations of the two sexes did not differ significantly and the overall equation was: ln FL = 3.721 + 0.851 ln R. Due to the R–FL allometric correlation, estimates of fork lengths at previous ages, FLi, were back-calculated with a body proportional hypothesis. Von Bertalanffy growth equations were derived from both observed and back-calculated FLs-at-age, which did not differ significantly. Moreover, no significant difference was found between the growth equations of the two sexes; the overall equation was FLt = 373.08 [1)e )0.07(t + 1.76) ]. Weight-at-age values were derived from the von Bertalanffy predicted FLs-atage by the FL–W correlation equations for males and females. The paper represents the first comprehensive study on the biometry, including age and growth, of bluefin tuna captured in the Mediterranean Sea.

Pan‐steatitis in farmed northern bluefin tuna, Thunnus thynnus (L.), in the eastern Adriatic

Clinical, gross and histopathological investigations were carried out into large-scale mortalities on eastern Mediterranean bluefin tuna, Thunnus thynnus (L.), farms. Fish showed only nervous signs and darkened colour. At post-mortem the liver was bronze coloured and the pyloric area waxy in consistency. There was no evidence of any other gross pathology. Histopathology showed severe hepatic necrosis and lipidosis. Peri-pancreatic lipoid tissue was heavily infiltrated with an inflammatory round cell infiltrate. Fish on all three farms had been fed on a North African pilchard diet rather than traditional local or Baltic species. Once the diet was modified, losses ceased. A diagnosis of pan-steatitis as seen in other farmed fish species, as well as in terrestrial animals, on particular fish-based diets was made, although the actual factor within the diet which induced the inflammatory effect is not known.

Feeding habits and trophic levels of bluefin tuna Thunnus thynnus of different size classes in the Mediterranean Sea

Summary Possible changes in diet and trophic levels in relation to size of Mediterranean bluefin tuna, Thunnus thynnus, were investigated using labelled carbon (δ13C) and nitrogen (δ15N) stable isotopes. Samples were obtained from two locations in the southern Tyrrhenian Sea (Western Mediterranean Sea) in May and October 2004. The δ13C and δ15N analyses revealed at least three significant isotopic groups [small juveniles (0.7–2.2 kg), sub-adults (15–50 kg) and adults (70 to 225 kg)]. δ13C was negatively dependent on weight, while δ15N was positively dependent on weight [TW = 8.2 (±0.16) + 0.03 (± 0.0) *δ15N (n = 49; r = 0.91; P < 0.001)]. Different prey contribution to the diet was highlighted for each class. The diet of juveniles comprised zooplankton, small pelagic fish and some coastal fish; sub-adults relied on medium pelagic fish, shrimps and cephalopods, and adults relied mainly on cephalopods and larger fish. The trophic level (TL) of tunas belonging to each size class was closely correlated to weight, starting from ca 3.0 TL for Group I and reaching 4.4–4.8 TL for the giants. Bluefin tuna, from small juveniles to giants, showed a shift in feeding preferences due to different use of habitats and food items as a function of the life stage.

First data on growth and nucleic acid and protein content of field-captured Mediterranean bluefin (&lt;em&gt;Thunnus thynnus&lt;/em&gt;) and albacore (&lt;em&gt;Thunnus alalunga&lt;/em&gt;) tuna larvae: a comparative study

The waters surrounding the Balearic archipelago are considered to be prime spawning habitats of the bluefin tuna (Thunnus thynnus) and other tuna species such as albacore (T. alalunga) in the Mediterranean. During the 2003 bluefin and albacore spawning season, a tuna larval survey (TUNIBAL 0703) was carried out to assess the distribution of bluefin larvae in relation to hydrographic mesoscale features. Tuna larvae were collected by means of surface plankton tows with a bongo gear with a quadrangular mouth measuring 1 m diagonally. The otolith microstructure of 157 and 71 field-captured larvae of Mediterranean bluefin and albacore, respectively, were analyzed to estimate the daily growth pattern. Furthermore, biochemical analysis to estimate DNA, RNA and protein content was done on another batch of 114 bluefin and 132 albacore larvae. The size range included pre-flexion to post-flexion larvae, from 2.8 to 8.6 mm in body length. bluefin and albacore larvae grew linearly in standard length (0.35 and 0.33 mm/day, respectively) and potentially with respect to dry weight. No significant differences between species were observed in the size-weight relationship, or in the allometric relationship of body size and weight to otolith radius. However, the relationship of DNA and RNA to body size and weight showed a significant difference between species. Bluefin tuna larvae showed a greater nucleic acid content than albacore larvae. Protein content showed no significant differences with respect to body length.

Recurrent and density-dependent patterns in long-term fluctuations of Atlantic bluefin tuna trap catches

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 319:237-249 (2006) - doi:10.3354/meps319237 Recurrent and density-dependent patterns in long-term fluctuations of Atlantic bluefin tuna trap catches F. Royer1,2,*, J. M. Fromentin1 1IFREMER, Centre de Recherche Halieutique Méditerranéen et Tropical, avenue Jean Monnet, BP 171, 34203 Sète cedex, France 2Present address: Large Pelagics Research Lab, University of New Hampshire, Durham, New Hampshire 03824, USA *Email: francois.royer@unh.edu ABSTRACT: We present a methodology for the non-linear analysis of long-term ecological time series. Using a time-delay embedding procedure, we investigated the complexity of 1-dimensional signals and compared their structure to their stochastic counterparts. Recurrence-based statistics and surrogate testing were used for this purpose. The method was first tested on elementary models for illustrative purposes and its potentialities and limits reviewed. We then investigated the time structure of 6 Mediterranean bluefin tuna trap catches known to display long-term fluctuations. These time series showed significantly more determinism than linear stochastic processes, displaying more recurring patterns/states than stochastic surrogates. The short term structure of these series also showed a direct and delayed negative feedback in their rate of increase. These results were homogeneous over all studied time series. An interaction between climate forcing and the life history traits of bluefin tuna was postulated to explain the first result, while the density-dependent pattern may be explained either by density-dependence processes during early stages, or by non-successive (non-yearly) spawning events in the Mediterranean. KEY WORDS: Thunnus thynnus · Recurrence · Density-dependence · Surrogate testing · Embedding Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 319. Online publication date: August 18, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Stochastic Bio-Economic Model of Northern Atlantic and Mediterranean Bluefin Tuna

The purpose of this paper is to study the implications of introducing a stochastic stock in a multi-gear and age structured bio-economic model for the Northern Atlantic Bluefin tuna. In order to account for variations on the recruitment, uncertainty is introduced on a bilinear recruitment function, and it is represented by an exponential random error term leading the stock to be, on average, higher than in the deterministic case. Both the bionomic equilibrium and the optimal management of this species are examined. In the latter, two alternative instruments are studied: the constant total allowable catch and the constant effort and the purpose is to maximize the expected total net present value. The conclusions enhance that the results do not differ significantly from those in the deterministic model, that is, the fishing effort should be the policy instrument to adopt, both in the East and the West Atlantic. Despite the previous reasoning, the shock on recruitment should be taken into account, as certain realizations of the random variable may lead to different results. In particular, for low Bluefin tuna stock levels, it is optimal to regulate the caches instead of the fishing effort, to ensure the stock recovery.

Environmental sociology: from analysis to action

Acknowledgments Preface Introduction: Environmental Problems Require Social Solutions, Deborah McCarthy and Leslie King Imagining Nature 1.Nature's Looking Glass, Hillary Angelo and Colin Jerolmack Political Economy 2.Why Ecological Revolution?, John Bellamy Foster 3.The Tragedy of the Commodity: The Overexploitation of the Mediterranean Bluefin Tuna Fishery, Stefano B. Longo and Rebecca Clausen 4.Ecological Modernization at Work? Environmental Policy Reform in Sweden at the Turn of the Century, Benjamin Vail 5.A Tale of Contrasting Trends: Three Measures of the Ecological Footprint in China, India, Japan, and the United States, 1961-2003, Richard York, Eugene A. Rosa and Thomas Dietz Environmental Inequalities 6.Breaking the Food Chains: An Investigation of Food Justice Activism, Alison Hope Alkon and Kari Marie Norgaard 7.Turning Public Issues into Private Troubles: Lead Contamination, Domestic Labor, and the Exploitation of Women, Lois Bryson, Kathleen McPhillips, and Kathryn Robinson 8.Addressing Urban Transportation Equity in the United States, Robert D. Bullard Social Construction of the Environment, Identity, Emotions and Community 9.Wild Horses and the Political Ecology of Nature Restoration in the Missouri Ozarks, J. Sanford Rikoon 10. People Want to Protect Themselves a Little Bit: Emotions, Denial, and Social Movement Nonparticipation, Kari Marie Norgaard 11.Community Economic Identity: The Coal Industry and Ideology Construction in West Virginia, Shannon Elizabeth Bell and Richard York Perspectives on Disaster 12.Silent Spill: The Organization of an Industrial Crisis, Thomas D. Beamish 13.The BP Disaster as an Exxon Valdez Rerun, Liesel Ashley Ritchie, Duane A. Gill, J. Steven Picou Globalization 14.The Unfair Trade-off: Globalization and the Export of Ecological Hazards, Daniel Faber 15.Driving South: The Globalization of Auto Consumption and Its Social Organization of Space, Peter Freund and George Martin Science, Risk and Knowledge 16.Risk Society and Contested Illness: The Case of Nuclear Weapons Workers, Sherry Cable, Thomas E. Shriver, and Tamara L. Mix 17.The Knowledge-Shaping Process: Elite Mobilization and Environmental Policy, Eric Bonds 18.Hurricane Katrina, Contamination, and the Unintended Organization of Ignorance, Scott Frickel and M. Bess Vincent 19.Media Framing of Body Burdens: Precautionary Consumption and the Individualization of Risk, Norah MacKendrick Social and Environmental Change - Ideas and Actions 20.Individualization: Plant a Tree, Buy a Bike, Save the World?, Michael Maniates 21.Cleaning the Closet: Toward a New Fashion Ethic, Juliet Schor 22.Poitics by Other Greens: The Importance of Transnational Environmental Justice Movement Networks, David Naguib Pellow 23.On the Trail of Courageous Behavior, Myron Glazer and Penina Glazer

Atlantic bluefin tuna: population dynamics, ecology, fisheries and management

AbstractBoth old and new information on the biology and ecology of Atlantic bluefin tuna have confronted scientists with research challenges: research needs to be connected to current stock‐assessment and management issues. We review recent studies on habitat, migrations and population structure, stressing the importance of electronic tagging results in the modification of our perception of bluefin tuna population dynamics and behaviour. Additionally, we question, from both scientific and management perspectives, the usefulness of the classical stock concept and suggest other approaches, such as Clark's contingent and metapopulation theories. Current biological information confirms that a substantial amount of uncertainty still exists in the understanding of reproduction and growth. In particular, we focus on intriguing issues such as the difference in age‐at‐maturity between West Atlantic and Mediterranean bluefin tuna. Our description of Atlantic bluefin tuna fisheries places today's fishing patterns within the two millennium history of exploitation of this species: we discuss trap fisheries that existed between the 17th and the early 20th centuries; Atlantic fisheries during the 1950s and 1960s; and the consequences of the recent development of the sushi–sashimi market. Finally, we evaluate stock status and management issues since the early 1970s. While important uncertainties remain, when the fisheries history is confronted with evidence from biological and stock‐assessment studies, results indicate that Atlantic bluefin tuna has been undergoing heavy overfishing for a decade. We conclude that the current exploitation of bluefin tuna has many biological and economic traits that have led several fish stocks to extreme depletion in the past.

The East Atlantic and Mediterranean bluefin tuna stock management: uncertainties and alternatives

Although the Atlantic bluefin tuna has been studied for more than a century, the assessment of the East stock is characterised by a large amount of uncertainty. In 2000, this situation became so critical that quantitative stock assessment has been postponed. The first part of the present study aims to list the main difficulties that have led to the current situation and tries to discern between subjective and objective uncertainty. The former, which is due to an incomplete knowledge of the system and which has increased in the past few years, is mainly due to a decreasing quality of the catch and effort data, that has followed the establishment of a TAC. The latter source of uncertainty, which results from the underlying variability in stochastic processes, mainly relates, for this species, to spatial and temporal changes in stock size, growth and migration. The second part of this study presents the results of simulation modelling, which could be, in the meantime, an useful tool for short-term management of the East Atlantic and Mediterranean BFT stock.

Inter-laboratory comparison of Atlantic and Mediterranean bluefin tuna otolith microconstituents

Elemental analysis of juvenile (age 0+ and 1 year) Atlantic bluefin tuna Thunnus thynnus otoliths by isotope dilution and conventional inductively coupled plasma mass spectrometry (ID ICP-MS and ICP-MS) indicated that the concentrations of certain elements varied among putative nursery grounds in the Atlantic Ocean. Further, trace element fingerprints of age-1 tuna from each nursery–the western Atlantic and Mediterranean Sea–were distinct and varied sufficiently to distinguish individuals from different regions with moderate confidence. Overall correct classification rates for a simulated test set of age-1 tuna were 68% (using ICP-MS) and 81% (using ID ICP-MS), despite a small sample size (9 Mediterranean vs. 19 western Atlantic tunas). Although ID ICP-MS was the more accurate of the two ICP-MS technologies, inter-laboratory precision was moderately high (3–18%) for individual elemental concentrations (Li, Na, Mg, K, Ca, Mn, Sr, and Ba), and multi-variate elemental fingerprints were similarly ordinated between laboratories (r=0.75). Age-0 tuna samples were too small to permit statistical classification tests, but showed similar levels of elemental concentrations between laboratories. Our results indicate that it should be possible to assign nursery ground origin to adult bluefin tuna based on the elemental composition of their extracted otolith core.

Long-term fluctuations in the eastern Atlantic and Mediterranean bluefin tuna population

Long-term time-series of bluefin tuna catches from ancestral Mediterranean and Atlantic trap fisheries are presented and analysed. The trap is a passive gear, little modified for centuries, that catches bluefin tuna Thunnus thynnus during their annual spawning migration. These features, together with preliminary analyses, lead us to suggest that long-term fluctuations in trap catches could reflect those in true abundance if they vary in the same manner all around the western Mediterranean and adjacent Atlantic. To test this hypothesis, we investigated 54 time-series more than 20 years long (the longest ones spanning four centuries) of trap catches along the western Mediterranean coasts of Italy, Sicily, Sardinia, Tunisia, Spain, and Morocco, and the adjacent Atlantic coasts of Spain, Portugal, and Morocco. Trends and cycles were identified using Eigen Vector Filtering and spectral analysis, and the synchrony between short- and long-term fluctuations in trap catches was studied with the modified correlogram of Koenig and Knops. The magnitude of fluctuations in trap catches is large, periods of great abundance being up to seven times bigger than those when abundance was low. More interesting was the occurrence of 100-year-long periodic fluctuations as well as 20-year cycles. These medium- to long-term fluctuations, representing more than 50% of the total variability in the time-series, were synchronous all around the western Mediterranean and adjacent North Atlantic. In contrast, short-term variability was synchronous at a local scale only. It is argued that long-term fluctuations in trap catches could be considered as a proxy for those of true abundance, and a synthetic time-series has been computed to depict them. Biological and ecological processes that could cause such long-term fluctuations are also discussed.