Papers by Jean-marc Fromentin
The overexploitation of East Atlantic and Mediterranean bluefin tuna (ABFTE) stock has been consi... more The overexploitation of East Atlantic and Mediterranean bluefin tuna (ABFTE) stock has been considered as an archetype of overfishing and general mismanagement of national and international fisheries bodies. The crisis highlighted, among other things, the fact that uncertainties that are inherent to any scientific advice can be used in lobbying to attempt to discredit science-based management. It also showed how interactions between science and management can change through time according to public awareness and opinion. This long and highly publicized crisis finally came to an end, in 2009, when ICCAT, under the pressure of NGOs and public opinion, fully endorsed the scientific advice within a rebuilding plan. Nowadays, the ABFTE stock is recovering, even more quickly than expected, although uncertainties involved in current scientific advice do not allow the precise quantification of the level of this recovery. Despite this, the case of the ABFTE stock clearly demonstrates that th...
Barents Sea 2050 - uncertain future ahead
Evaluation of the performance and robustness of VPA-based stock assessment and MSY-based manageme... more Evaluation of the performance and robustness of VPA-based stock assessment and MSY-based management strategy to process error: The Atlantic bluefin
Egestion: the process by which undigested food is eliminated by an organism in the form of faeces... more Egestion: the process by which undigested food is eliminated by an organism in the form of faeces. End-to-end model: model of marine ecosystems with representation of the dynamic effects of both the physical environment and human activities on living organisms, ranging from the lowest trophic levels (phytoplankton and zooplankton) to the highest trophic levels (fish, birds and mammals). ENSO: the El Niño Southern Oscillation is a global event arising from an oscillation in the surface pressure (atmospheric mass) between the south-eastern tropical Pacific and the Australian-Indonesian regions. When the waters of the eastern Pacific are abnormally warm (an El Niño event), sea-level pressure drops in the eastern Pacific and rises in the west. The reduction in the pressure gradient is accompanied by a weakening of the low-latitude easterly in a given year and thereby becoming available to the fisheries.at developing realistic and robust models at different levels of organisation and a...
The 2001 size composition of Atlantic bluefin tuna catches of the French purse seiners has been e... more The 2001 size composition of Atlantic bluefin tuna catches of the French purse seiners has been estimated from the EU log-books and appears roughly in agreement with those estimated from the local seafood traders between 1982 and 1998. However, the accuracy of the 2001 size composition remains uncertain because of a lack of a standard protocol and of sampling on catch coming from heterogeneous and/or multiple shoals. Regarding the spatial and temporal dynamic of the French fishery, an observer program should be implemented to correct and validate the size frequencies of these catches.
ICES Journal of Marine Science, 2021
In the Gulf of Lions, small pelagic fish have shown reduced body size and body condition after 20... more In the Gulf of Lions, small pelagic fish have shown reduced body size and body condition after 2007 that would result from changes in zooplankton community. We therefore examined zooplankton density, body size, and taxonomic composition at the closest long-term monitoring station (1995–2019): the coastal Point-B. To cover a broader spectrum of zooplankton community, samples obtained from two nets, the WP2 (200 µm mesh size) and the Regent (690 µm), were analysed with the imaging Zooscan method. One important result was the high stability through time of the zooplankton community. No long-term monotonous trends in density, size, and taxonomic composition were detected. Interannual variations in zooplankton size and density were not significantly correlated to any environmental variable, suggesting the possible importance of biotic interactions. Still, an increase in temperature was followed by a sharp decrease of zooplankton density in 2015, after which only gelatinous groups recover...
Fisheries Oceanography, 2015
Pop-up archival tags (PAT) provide summary and high-resolution time series data at predefined tem... more Pop-up archival tags (PAT) provide summary and high-resolution time series data at predefined temporal intervals. The limited battery capabilities of PATs often restrict the transmission success and thus temporal coverage of both data products. While summary data are usually less affected by this problem, as a result of its lower size, it might be less informative. We here investigate the accuracy and feasibility of using temperature at depth summary data provided by PATs to describe encountered oceanographic conditions. Interpolated temperature at depth summary data was found to provide accurate estimates of three major thermal water column structure indicators: thermocline depth, stratification and ocean heat content. Such indicators are useful for the interpretation of the tagged animal's horizontal and vertical behaviour. The accuracy of these indicators was found to be particularly sensitive to the number of data points available in the first 100 m, which in turn depends on the vertical behaviour of the tagged animal. Based on our results, we recommend the use of temperature at depth summary data as opposed to temperature time series data for PAT studies; doing so during the tag programming will help to maximize the amount of transmitted time series data for other key data types such as light levels and depth.
Population and Stock Hypotheses for North Atlantic Bluefin Tuna
A standard yield per recruit (YPR) analysis is used to analyse the effects of minimum size regula... more A standard yield per recruit (YPR) analysis is used to analyse the effects of minimum size regulations and time area closures on bluefin tuna from the eastern stock (east Atlantic and Mediterranean). Analyses were based on a fishing mortality vector computed over the period 1990-1994 for which data were more reliable and VPA (performed during the 2002 stock assessment) showed a relatively good convergence. This fishing mortality vector was modified according to some combinations of minimum size regulations and time area closures. It is concluded that: (i) PSmed is the main contributor to catch at age in the range of ages 1-13; (ii) The minimum size regulations considered would increase the YPR more than the time area closures, but these would enhance SPR more than minimum size regulations; (iii) Closing the Mediterranean has a bigger impact on both YPR and SPR than closing the east Atlantic, given that the majority of the catch occurs there; (iv) under some scenarios, some fleets could increase their long term YPR over 100%. On the other hand, some fleets would reduce their short term yield to near 30% with respect their equilibrium yield before implementing the measures discussed in this document. * *Following the initial submission of this document, the 2006 Bluefin Tuna Species Group carried out computations based on the approach presented here, but using improved datasets. Thus, the conclusions derived from the assessment may differ somewhat from those presented here. Nevertheless, the authors decided to publish this paper in order to make a detailed description of the method used permanently available.
IMPLICATIONS OF ENVIRONMENTAL VARIABILITY FOR THE STOCK ASSESSMENT OF NORTH EAST ATLANTIC ALBACORE (Thunnus alalunga)
Reference points are important elements of fisheries management and the supporting scientific adv... more Reference points are important elements of fisheries management and the supporting scientific advisory frameworks. However, fish stocks can fluctuate extensively over a large range of spatial and temporal scales independent of human exploitation and there has been a classical tendency to assume a dichotomy, i.e., that changes in fish populations are primarily attributable either to exploitation or to environmental variability. Therefore we look at variability in surplus production and examine the relative impacts of the environment and exploitation on the productivity of North Atlantic albacore (Thunnus alalunga). The analysis revealed that variations were driven by environmental effects. It was also found that substantial variations in time-series of biomass and catch could be expected even under a constant F equal to F MSY .
Past studies have indicated that numbers-at-age 1 of albacore may be correlated with the winter N... more Past studies have indicated that numbers-at-age 1 of albacore may be correlated with the winter NAO index in the previous year. Two main hypotheses have been stressed to explain such observation, i.e. an impact of the NAO on the recruitment or on migration patterns and consequently in the availability and catchability of specific age classes to the surface fishery. The objective of the present paper is to test whether such processes can be distinguished using VPA outputs. We first computed simple cross-correlations between the NAO at various lags, catches-at-age, Numbers-atage and Fat age estimated in the last assessment. Since results were inconclusive, simulations were undertaken. The results showed that the probability of detecting spurious correlations between a given environmental variable, such as the NAO, and VPA outputs appears to be strongly related to the level of errors due to the observation process and modelling assumptions made within the assessment procedure. We concluded that correlations based solely on VPA outputs should be interpreted with great care. las asunciones realizadas en la evaluación. Concluimos que las correlaciones basadas solamente en outputs del VPA deben ser interpretadas con suma precaución.
The Relative Value-of-Information for Model Based and Empirical Management Procedures: A Mediterranean Bluefin Example
ABSTRACT The relative value-of-information for model based and empirical Management Procedures is... more ABSTRACT The relative value-of-information for model based and empirical Management Procedures is compared for Mediterranean bluefin tuna using Management Strategy Evaluation. This is done by conditioning an Operating Model on alternative hypotheses about population and fishery dynamics. Data, fisheries and fisheries independent are sampled from the Operating Model to evaluate different harvest control rules as part of a Management Procedure. This allows scenarios and data sets to be simulated that reflect uncertainty about our knowledge of biology, ecology and our ability to observe and control the fisheries. The different Management Procedures are evaluated with respect to their ability to meet multiple management objectives. This is done by considering the trade-offs between the objectives for different choices (e.g. to invest in fisheries independent surveys, tagging studies to estimate natural mortality) and the robustness of the MPs, e.g. to environmental variability. This allows the relative benefits of improving knowledge on population and fishery dynamics to be evaluated.
Marine Policy, 2014
Atlantic bluefin tuna (ABFT) has always displayed spectacular changes in its spatial distribution... more Atlantic bluefin tuna (ABFT) has always displayed spectacular changes in its spatial distribution, but the underlying mechanism of such variations still remains obscure. This study focuses on this challenging issue by scrutinizing the intriguing 'Brazilian episode' during which a large quantity of ABFT (a temperate species) was caught during the 1960s in the equatorial Atlantic. To investigate this event, we applied a niche model to an extensive data set of catch and environmental variables from 1960 to 2009. ABFT exhibited a remarkably large ecological niche, which matches well with our current knowledge of ABFT. Our results also depicted a high probability of ABFT occurrence in the South Atlantic and, more interestingly, favorable environmental conditions in the western equatorial Atlantic during the 1960s, but not later. ABFT could thus have migrated from their northern spawning grounds to the South Atlantic during the 1960s through the western equatorial Atlantic, playing the role of an 'ecological bridge'. We argue that the rarity of ABFT in the southern Atlantic during the last four decades would result from the interaction of several processes, particularly oceanographic conditions, migratory behavior, density-dependence, exploitation levels and population structure. Examination of the catch data further indicated that the fish caught in the equatorial Atlantic were from the western stock and we concluded that the lack of rebuilding of this stock could result from a regime shift due to the combination of oceanographic changes in the equatorial Atlantic and overfishing in the North Atlantic in the 1960s and 1970s.
Nature, 2002
There is now ample evidence of the ecological impacts of recent climate change, from polar terres... more There is now ample evidence of the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The responses of both¯ora and fauna span an array of ecosystems and organizational hierarchies, from the species to the community levels. Despite continued uncertainty as to community and ecosystem trajectories under global change, our review exposes a coherent pattern of ecological change across systems. Although we are only at an early stage in the projected trends of global warming, ecological responses to recent climate change are already clearly visible.
Progress in Oceanography, 2010
Environmental variables affect many processes of fish biology and their fluctuations are thought ... more Environmental variables affect many processes of fish biology and their fluctuations are thought to be one of the main factors in variability of fish stocks. Recent work has shown that the variability of the environment in the frequency domain (i.e., the environmental noise) can interact with endogenous processes (e.g., density dependence) and affect fluctuations of animal populations. In this study, we investigate whether fluctuations of large pelagics' time series are affected by environmental noise and whether life-history traits of species modulate this response. By analysing several environmental variables and a large dataset of tuna and billfish catch per unit effort (CPUE) time series from the Atlantic, we show that in environments dominated by long-term fluctuations (i.e., red noise) CPUE time series were less variable and displayed smoother fluctuations. Furthermore, larger, slower-growing and later-maturing species were found to be more sensitive to changes of environmental noise than species with a shorter turnover rate. Our results suggest that environmental noise interacts with fish biology; understanding how it is integrated into biological processes might provide important insights to understand the responses of fish stocks dynamics to exploitation and environmental changes.
Cycles and trends in cod populations
Proceedings of the National Academy of Sciences, 1999
Year-to-year fluctuations in fish stocks are usually attributed to variability in recruitment, co... more Year-to-year fluctuations in fish stocks are usually attributed to variability in recruitment, competition, predation, and changes in catchability. Trends in abundance, in contrast, are usually ascribed to human exploitation and large-scale environmental changes. In this study, we demonstrate, through statistical modeling of survey data (1921-1994) of cod from the Norwegian Skagerrak coast, that both short- and long-term variability may arise from the same set of age-structured interactions. Asymmetric competition and cannibalism between cohorts generate alternating years of high and low abundance. Intercohort interactions also resonate the recruitment variability so that long-term trends are induced. The coupling of age-structure and variable recruitment should, therefore, be considered when explaining both the short- and long-term fluctuations displayed by the coastal cod populations. Resonant effects may occur in many marine populations that exhibit this combination of traits.
PLoS ONE, 2012
The intrinsic population growth rate (r) of the surplus production function used in the biomass d... more The intrinsic population growth rate (r) of the surplus production function used in the biomass dynamic model and the steepness (h) of the stock-recruitment relationship used in age-structured population dynamics models are two key parameters in fish stock assessment. There is generally insufficient information in the data to estimate these parameters that thus have to be constrained. We developed methods to directly estimate the probability distributions of r and h for the Atlantic bluefin tuna (Thunnus thynnus, Scombridae), using all available biological and ecological information. We examined the existing literature to define appropriate probability distributions of key life history parameters associated with intrinsic growth rate and steepness, paying particular attention to the natural mortality for early life history stages. The estimated probability distribution of the population intrinsic growth rate was weakly informative, with an estimated mean r = 0.77 (60.53) and an interquartile range of (0.34, 1.12). The estimated distribution of h was more informative, but also strongly asymmetric with an estimated mean h = 0.89 (60.20) and a median of 0.99. We note that these two key demographic parameters strongly depend on the distribution of early life history mortality rate (M 0 ), which is known to exhibit high yearto-year variations. This variability results in a widely spread distribution of M 0 that affects the distribution of the intrinsic population growth rate and further makes the spawning stock biomass an inadequate proxy to predict recruitment levels.
Uploads
Papers by Jean-marc Fromentin