2021 |
Rouyer, T., et al. "The environment drives Atlantic bluefin tuna availability in the Gulf of Lions." Fish Oceanogr (2021): fog.12532.
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2020 |
Hachim, M., et al. "Oxygen uptake, heart rate and activities of locomotor muscles during a critical swimming speed protocol in the gilthead sea bream Sparus aurata." J. Fish Biol. (2020).
Résumé: Oxygen uptake, heart rate and contraction frequencies of slow oxidative (SO) and fast glycolytic (FG) muscle were measured simultaneously in gilthead seabream Sparus aurata submitted to stepwise increases in current speed in a swimming respirometer. Variation in oxygen uptake was closely related to variation in heart rate, over initial steps these rose in concert with an increase in contraction frequency of SO muscle. There was an asymptote in oxygen uptake and heart rate at high speeds that reflected a transition from exclusive use of aerobic SO muscle to a combination of SO and anaerobic FG muscle, and which preceded fatigue.
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Rouyer, T., et al. "Tagging Atlantic bluefin tuna from a Mediterranean spawning ground using a purse seiner." Fish Res.. 226 (2020): 105522.
Résumé: Atlantic bluefin tuna, Thunnus thynnus, is as an emblematic and commercially valuable large pelagic species. In the past ten years, the purse seine fishery in the Mediterranean represents more than 50 % of the catch. Nowadays, purse seines target large fish and operate during the spawning season in the spawning grounds. Electronic tagging has shed a considerable amount of light on the ecology and behaviour of bluefin tuna over the past twenty years. However, such technique has rarely been applied on large bluefin tunas caught by the Mediterranean purse seine fishery despite its major importance. The logistical constraints related to this specific fishery, combined with the timing of migration of the fish and the requirements related to the handling of big fish have made adequate tagging from purse seines complex. Here we detail such an operation, designed to bridge the knowledge gap on the migratory behaviour of tunas targeted by the purse seine fishery. Three large bluefin tunas from the same school were tagged during the fishing operation of a French purse seine, resulting in a different migration pattern than previous deployments. The fish were tagged onboard in less than 2 min and efficiently, avoiding any subsequent mortality. These results contrast with those from tagging operations carried out in the Northwest Mediterranean, which underlies the importance of tagging operations from purse seines to obtain unbiased description of the movements of the eastern Atlantic bluefin tuna stock in the context of its management.
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2019 |
Rouyer, T., et al. "Tagging Atlantic bluefin tuna from a farming cage: An attempt to reduce handling times for large scale deployments." Fisheries Research. 211 (2019): 27–31.
Résumé: Our knowledge on the biology and ecology of marine species have improved greatly through the use of archival tags by enabling the collection on information from individual in the wild. This is specifically true for large pelagic species such as the Atlantic Bluefin tuna (ABFT, Thunnus thynnus) where, for the first time, it has been possible to confirm through fisheries-independent data, migration patterns, reproductive and feeding behaviours and habitat use. However, large-scale tagging experiments that would enable researchers to tackle group behaviour are difficult to set up. On the one hand, the impact of the actual tagging operation should be as minimal as possible to avoid any change in behaviour of the fish which could influence tag data analyses. On the other hand, large scale tagging experiments require handling a large number of animals in a relatively short period of time. In the present manuscript, a methodology for tagging several large ABFT with satellite tags was tested with ABFT caught from a cage of a Maltese farm. The total time of the operation, from the moment fish were caught by handline to release back to the sea lasted an average of 10 min for the 3 fish tagged. The handling of the fish on the deck lasted less than 2 min. This methodology proved successful at tagging several large (158–182 cm) fishes in a very short time, while ensuring the best conditions for the fish during tagging and subsequent release. This procedure requires substantial logistical preparation and an experienced crew team but, by reducing the time required for the operation, opens up the possibility of large scale tagging activities of large fish held in cages or caught by purse seiners.
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Sardenne, F., et al. "Effects of extraction method and storage of dry tissue on marine lipids and fatty acids." Analytica Chimica Acta. 1051 (2019): 82–93.
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Soulier, F., et al. "Very Low Resource Digital Implementation of Bioimpedance Analysis." Sensors. 19.15 (2019): 3381.
Résumé: Bioimpedance spectroscopy consists of measuring the complex impedance of biological tissues over a large frequency domain. This method is particularly convenient for physiological studies or health monitoring systems. For a wide range of applications, devices need to be portable, wearable or even implantable. Next generation of bioimpedance sensing systems thus require to be implemented with power and resource savings in mind. Impedance measurement methods are divided into two main categories. Some are based on “single-tone” signals while the others use “multi-tone” signals. The firsts benefit from a very simple analysis that may consist of synchronous demodulation. However, due to necessary frequency sweep, the total measurement may take a long time. On the other hand, generating a multi-frequency signal allows the seconds to cover the whole frequency range simultaneously. This is at the cost of a more complex analysis algorithm. This makes both approaches hardly suitable for embedded applications. In this paper, we propose an intermediate approach that combines the speed of multi-tone systems with a low-resource analysis algorithm. This results in a minimal implementation using only adders and synchronous ADC. For optimal performances, this small footprint digital processing can be synthesized and embedded on a mixed-mode integrated circuit together with the analog front-end. Moreover, the proposed implementation is easily scalable to fit an arbitrary frequency range. We also show that the resulting impact on noise sensitivity can be mitigated.
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2018 |
David-Grignot, S., et al. "On-chip Generation of Sine-wave Summing Digital Signals: an Analytic Study Considering Implementation Constraints." J. Electron. Test.-Theory Appl.. 34.3 (2018): 281–290.
Résumé: In the context of biosensor as much as Built-In-Self Test (BIST), on-chip sine-wave signal generation is a recurring research topic. Considering the implementation constraints, it implies a trade-off between the amount of resources and the signal quality. An attractive solution consists in combining several digital signals to build this analog sine-wave. The objective of this paper is to give an analytic study of various potential digital-based solutions. Thanks to this study, we prove that the technique consisting in setting the phase shifts and various amplitude values of the square-wave signals is the most efficient approach. This study allows the selection of the optimal square-wave signal parameters to cancel low-order harmonics of the generated signal. We proposed a solution for specification-oriented definition of the architecture.
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Pierre, M., et al. "Assessing causal links in fish stock–recruitment relationships." ICES J Mar Sci. 75.3 (2018): 903–911.
Résumé: Abstract. Understanding whether recruitment fluctuations in fish stock arise from stochastic forcing (e.g. environmental variations) rather than deterministic
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2016 |
Van Beveren, E., et al. "The fisheries history of small pelagics in the Northern Mediterranean." ICES J. Mar. Sci.. 73.6 (2016): 1474–1484.
Résumé: Since 2007, the biomass of sardine and anchovy in the NW Mediterranean has remained persistently low, whereas the biomass of the commercially low-valued sprat has exploded. Also, simultaneous decreases in condition, size, and/or age of these populations were observed. Altogether, this resulted in a drop in landings of small pelagics. To understand the amplitude of these events and to provide a baseline scenario against which current changes can be compared, we compiled exceptionally long landing series (1865-2013) of sardine, anchovy, and mackerel for different subregions of the southern French coast. We characterized the fluctuations of these landings and compared these with environmental drivers (sea surface temperature, Rhone river discharge, North Atlantic Oscillation, Western Mediterranean Oscillation-WeMO, and Atlantic Multidecadal Oscillation-AMO), using different time-series analyses. We also collated historical data to infer qualitative changes in fishing effort over time. A fishing effort related increase in landings was observed around 1962 for all three species, although current sardine landings have dropped below levels observed before this period. Sardine and anchovy landings were, respectively, positively and negatively related to the AMO index and anchovy landings were also positively related to the WeMO. We finished by discussing the potential role of the environmental variables and fishing on long-term fishery landings trends.
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2014 |
CASINI, M., et al. "Density-Dependence in Space and Time: Opposite Synchronous Variations in Population Distribution and Body Condition in the Baltic Sea Sprat (Sprattus sprattus) over Three Decades." Plos One. 9.4 (2014).
Résumé: Spatio-temporal density-dependent processes are crucial regulatory factors for natural populations. However, there is a lack of studies addressing spatial density-dependence in fish growth. A previous investigation has suggested spatio-temporal density-dependence in body condition of Baltic sprat. Here, we used different techniques, such as centre of gravity, distance, and homogeneity indices, to better characterize the spatial and temporal variations in sprat density and body condition in the Baltic Proper. Our results evidenced a negative spatio-temporal co-variation between the centres of gravity of density and maximum condition. In the 1980s-early 1990s both centres were located in the middle of the Baltic Proper. From the mid 1990s the centres progressively separated in space, as the sprat population moved towards the north-eastern Baltic Proper, and the centre of maximum condition towards the south-western areas. Moreover, at low abundances, sprat density and condition were homogeneously distributed in space, whereas at high abundances both density and condition showed pronounced geographical gradients. The ecological processes potentially explaining the observed patterns were discussed in the light of the Ideal Free Distribution theory. We provide evidence that the shift in the spatial distribution of cod, the main predator of sprat, has been the main factor triggering the overall spatial changes in sprat density, and thus condition, during the past thirty years. The spatial indices shown here, synthesizing the spatio-temporal patterns of fish distribution, can support the implementation of the EU Marine Strategy Framework Directive.
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ROUYER, T., et al. "Combined effects of exploitation and temperature on fish stocks in the Northeast Atlantic." Ices Journal Of Marine Science. 71.7 (2014): 1554–1562.
Résumé: Fish stock fluctuations are affected by two potentially confounding forces: the removal of individuals by fisheries and climatic variations affecting the productivity of fish populations. Disentangling the relative importance of these forces has thus been a question of primary importance for fisheries management and conservation. Through the analysis of long-term time-series for 27 fish stocks from the Northeast Atlantic, the present study shows that the sign and intensity of the effect of temperature on biomass are dependent on the geographical location: the stocks located at the southernmost and northernmost latitudes of our study displayed stronger associations with temperature than the stocks located in the middle range of latitudes. As a consequence, the investigation of the combined effects of exploitation and the environment revealed that the stocks at the northern/southern boundaries of the spatial extent of the species were more prone to combined effects. The interplay between geographic location, climate and exploitation thus plays a significant role in fish stock productivity, which is generally ignored during assessment, thus affecting management procedures.
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2013 |
Durant, J. M., et al. "Population growth across heterogeneous environments: effects of harvesting and age structure." Mar Ecol Prog Ser. 480 (2013): 277–287.
Résumé: ABSTRACT: Population growth is affected by several factors such as climate, species interaction and harvesting pressure. However, additional complexity can arise if fishing increases the sensitivity to environmental variability. To predict the effects of fisheries and climate on marine populations, there is a need for improved understanding of how they affect key ecological processes such as population growth. In this study, we used a comparative approach investigating commercially fished species across different ecosystems: the Norwegian Sea-Barents Sea (Northeast Arctic cod), the North Sea (North Sea cod), the Atlantic Ocean (European hake), the Mediterranean Sea (European hake), and the Gulf of Alaska and Bering Sea (walleye pollock). Our objective was to compare the effects of commercial fisheries, age structure and environmental variability on population growth rate. We show that although all stocks experienced a decline in abundance, only 3 of them showed a concomitant decreasing trend in generation time (South Atlantic hake, North Atlantic hake and Northeast Arctic cod), suggesting a fishing-induced erosion in their age structure. Intra-specific analysis shows that changes in generation time triggered an increase in the relative contribution of recruitment to population growth. Furthermore, the contribution from recruitment to population growth changes due to large-scale climate indices or regional-scale environmental covariates, such as sea temperature. This study illustrates how and where the interaction between large-scale ecological patterns and regional/short-scale processes are important for designing management regulations.
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Hjermann, D., et al. "Spatial analysis of North Sea cod recruitment: concurrent effects of changes in spawning stock biomass, temperature and herring abundance." Mar Ecol Prog Ser. 480 (2013): 263–275.
Résumé: ABSTRACT: The decline of the North Sea cod Gadus morhua has been attributed to both overfishing and ocean warming. However, another hypothesis is that overfishing of piscivorous cod has caused an increased abundance of formerly predatory-controlled pelagic fish including herring Clupea harengus, which in turn has suppressed the recruitment of cod through predation on the early life stages of cod. Here we analyze 40 yr of trawl survey data in order to explore how the abundance of young herring affects cod recruitment, and how cod biomass affects the abundance of herring. In both cases we also take into account the effects of spawner biomass (of cod and herring, respectively) and sea temperature. We take a novel, explicitly spatial, approach by analyzing these effects on a local (185 × 167 km) scale. Our results indicate large spatial variability in ecological mechanisms. In the German Bight, high cod recruitment is associated with low herring abundance, low temperatures and high overall cod spawner biomass. This area used to contain a large portion of the cod recruits, and there is a strong correlation between the fraction of cod recruits found in this area and overall recruitment. In this area, herring recruitment is also negatively associated with the abundance of large cod. Thus, for this part of the North Sea, our findings are consistent with a reversal of dominance between cod and herring; however, herring may affect the cod by competition rather than by predation.
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Lindegren, M., et al. "Climate, fishing, and fluctuations of sardine and anchovy in the California Current." Proceedings of the National Academy of Sciences (2013).
Résumé: Since the days of Elton, population cycles have challenged ecologists and resource managers. Although the underlying mechanisms remain debated, theory holds that both density-dependent and density-independent processes shape the dynamics. One striking example is the large-scale fluctuations of sardine and anchovy observed across the major upwelling areas of the world. Despite a long history of research, the causes of these fluctuations remain unresolved and heavily debated, with significant implications for fisheries management. We here model the underlying causes of these fluctuations, using the California Current Ecosystem as a case study, and show that the dynamics, accurately reproduced since A.D. 1661 onward, are explained by interacting density-dependent processes (i.e., through species-specific life-history traits) and climate forcing. Furthermore, we demonstrate how fishing modifies the dynamics and show that the sardine collapse of the 1950s was largely unavoidable given poor recruitment conditions. Our approach provides unique insight into the origin of sardine–anchovy fluctuations and a knowledge base for sustainable fisheries management in the California Current Ecosystem and beyond.
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Ottersen, G., et al. "Temporal shifts in recruitment dynamics of North Atlantic fish stocks: effects of spawning stock and temperature." Mar Ecol Prog Ser. 480 (2013): 205–225.
Résumé: ABSTRACT: Effects of variation in spawning stock and sea temperature on long-term temporal patterns in recruitment dynamics of 38 commercially harvested fish stocks in the northern North Atlantic were studied. Different statistical models were explored within a Ricker stock-recruitment framework. This includes, in order of complexity, adding a linear temperature term, a nonlinear (smooth) temperature effect, and non-stationarities (trends in intercept or in temperature effect) and finally allowing for a stepwise change (a threshold). The different models were compared in a uniform approach using Akaike’s information criterion corrected for small sample size as the model selection criterion. The relationship between recruitment, spawning stock biomass and temperature varied over time. The most frequent alteration in the non-stationary linear models was, for 14 stocks, in the intercept in recruitment success, suggesting a change in pre-recruit mortality over time. Threshold models performed better than the best linear or nonlinear stationary models for 27 of the stocks, suggesting that abrupt changes (maybe even regime shifts) are common. For half of the stocks studied, the temperature effect was statistically significant when added to the model of the relationship between recruitment success and spawning stock biomass. This includes all 6 of the herring stocks studied, with a positive effect for cold-water stocks and negative effect for stocks in the more temperate southern areas. For the 4 plaice stocks analysed, all located towards the centre of the overall distribution range of plaice, a tendency toward recruitment being favoured by lower temperatures was found.
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2012 |
Hidalgo, M., et al. "Context-dependent interplays between truncated demographies and climate variation shape the population growth rate of a harvested species." Ecography. 35.7 (2012): 637–649.
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Rouyer, T., et al. "Does increasing mortality change the response of fish populations to environmental fluctuations?" Ecology Letters. 15.7 (2012): 658–665.
Résumé: Ecology Letters (2012) 15: 658–665 Abstract
Fluctuations of fish populations abundances are shaped by the interplay between population dynamics and the stochastic forcing of the environment. Age-structured populations behave as a filter of the environment. This filter is characterised by the species-specific life cycle and life-history traits. An increased mortality of mature individuals alters these characteristics and may therefore induce changes in the variability of populations. The response of a generic age-structured model was analysed to investigate the expected changes in the fluctuations of fish populations in response to decreased adult survival. These expectations were then tested on an extensive dataset. In accordance with theory, the analyses revealed that decreased adult survival and mean age of spawners were linked to an increase in the relative importance of short-term fluctuations. It suggests that intensive exploitation can lead to a change in the variability of fish populations, an issue of central interest from both conservation and management perspectives.
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2011 |
Hidalgo, M., et al. "Synergistic effects of fishing-induced demographic changes and climate variation on fish population dynamics." Mar Ecol Prog Ser. 426 (2011): 1–12.
Résumé: ABSTRACT: The synergistic effects of fishing, climate and internal dynamics on population fluctuations are poorly understood due to the complexity of these interactions. In this paper, we combine time series analysis and simulations to investigate the long-term dynamics of an overexploited population in the Mediterranean Sea, and its link with both fishing-induced demographic changes and hydroclimatic variability. We show that the cyclicity of the catch per unit of effort (CPUE) of European hake Merluccius merluccius (EH) vanished in the 1980s, while the correlation between the CPUE and a local environmental index increased. Using simulations, we then show that the cyclicity observed in the EH biomass before the 1980s can have an internal origin, while that its disappearance could be due to the fishing-induced erosion of the age structure. Our results suggest that fishing can trigger a switch from internally generated to externally forced population fluctuations, the latter being characterised by an increasing dependency of the population on recruitment and ultimately on environmental variability. Hydroclimatic modifications occurring in the Mediterranean in the early 1980s could have enhanced these changes by leading to a mismatch between early life stages of EH and favorable environmental conditions. Our conclusions underline the key effect of the interaction between exploitation and climate on the dynamics of EH and its important consequences for management and conservation.
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Rouyer, T., et al. "Shifting dynamic forces in fish stock fluctuations triggered by age truncation?" Global Change Biology. 17.10 (2011): 3046–3057.
Résumé: Accumulating evidence shows that environmental fluctuations and exploitation jointly affect marine fish populations, and understanding their interaction is a key issue for fisheries ecology. In particular, it has been proposed that age truncation induced by fisheries exploitation may increase the population's sensitivity to climate. In this study, we use unique long-term abundance data for the Northeast Arctic stock of cod (Gadus morhua) and the Norwegian Spring-Spawning stock of herring (Clupea harengus), which we analyze using techniques based on age-structured population matrices. After identifying time periods with different age distributions in the spawning stock, we use linear models to quantify the relative effect of exploitation and temperature on the population growth rates. For the two populations, age truncation was found to be associated with an increasing importance of temperature and a relatively decreasing importance of exploitation, while the population growth rate became increasingly sensitive to recruitment variations. The results suggested that the removal of older age classes reduced the buffering capacity of the population, thereby making the population growth rate more dependent on recruitment than adult survival and increasing the effect of environmental fluctuations. Age structure appeared as a key characteristic that can affect the response of fish stocks to climate variations and its consequences may be of key importance for conservation and management.
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2010 |
Ari, T. B., et al. "Interannual Variability of Human Plague Occurrence in the Western United States Explained by Tropical and North Pacific Ocean Climate Variability." Am J Trop Med Hyg. 83.3 (2010): 624–632.
Résumé: Abstract.
Plague is a vector-borne, highly virulent zoonotic disease caused by the bacterium Yersinia pestis. It persists in nature through transmission between its hosts (wild rodents) and vectors (fleas). During epizootics, the disease expands and spills over to other host species such as humans living in or close to affected areas. Here, we investigate the effect of large-scale climate variability on the dynamics of human plague in the western United States using a 56-year time series of plague reports (1950–2005). We found that El Niño Southern Oscillation and Pacific Decadal Oscillation in combination affect the dynamics of human plague over the western United States. The underlying mechanism could involve changes in precipitation and temperatures that impact both hosts and vectors. It is suggested that snow also may play a key role, possibly through its effects on summer soil moisture, which is known to be instrumental for flea survival and development and sustained growth of vegetation for rodents.
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Corbineau, A., et al. "Patterns of variations in large pelagic fish: A comparative approach between the Indian and the Atlantic Oceans." Progress In Oceanography. 86.1-2 (2010): 276–282.
Résumé: Catch data of large pelagic fish such as tuna, swordfish and billfish are highly variable ranging from short to long term. Based on fisheries data, these time series are noisy and reflect mixed information on exploitation (targeting, strategy, fishing power), population dynamics (recruitment, growth, mortality, migration, etc.), and environmental forcing (local conditions or dominant climate patterns). In this work, we investigated patterns of variation of large pelagic fish (i.e. yellowfin tuna, bigeye tuna, swordfish and blue marlin) in Japanese longliners catch data from 1960 to 2004. We performed wavelet analyses on the yearly time series of each fish species in each biogeographic province of the tropical Indian and Atlantic Oceans. In addition, we carried out cross-wavelet analyses between these biological time series and a large-scale climatic index, i.e. the Southern Oscillation Index (Sol). Results showed that the biogeographic province was the most important factor structuring the patterns of variability of Japanese catch time series. Relationships between the SOI and the fish catches in the Indian and Atlantic Oceans also pointed out the role of climatic variability for structuring patterns of variation of catch time series. This work finally confirmed that Japanese longline CPUE data poorly reflect the underlying population dynamics of tunas. (C) 2010 Elsevier Ltd. All rights reserved.
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Llope, M., et al. "Overfishing of top predators eroded the resilience of the Black Sea system regardless of the climate and anthropogenic conditions." Global Change Biology. 17.3 (2010): 1251–1265.
Résumé: It is well known that human activities, such as harvesting, have had major direct effects on marine ecosystems. However, it is far less acknowledged that human activities in the surroundings might have important effects on marine systems. There is growing evidence suggesting that major reorganization (i.e., a regime shift) is a common feature in the temporal evolution of a marine system. Here we show, and quantify, the interaction of human activities (nutrient upload) with a favourable climate (run-off) and its contribution to the eutrophication of the Black Sea in the 1980s. Based on virtual analysis of the bottom-up (eutrophication) vs. top-down (trophic cascades) effects, we found that an earlier onset of eutrophication could have counteracted the restructuring of the trophic regulation at the base of the food web that resulted from the depletion of top predators in the 1970s. These enhanced bottom-up effects would, however, not propagate upwards in the food web beyond the zooplankton level. Our simulations identified the removal of apex predators as a key element in terms of loss of resilience that inevitably leads to a reorganization. Once the food web has been truncated, the type and magnitude of interventions on the group replacing the apex predator as the new upper trophic level have no effect in preventing the trophic cascade. By characterizing the tipping point at which increased bottom-up forcing exactly counteracts the top-down cascading effects, our results emphasize the importance of a comprehensive analysis that take into account all structuring forces at play (including those beyond the marine system) at a given time.
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Rouyer, T., J. - M. FROMENTIN, and N. C. STENSETH. "Environmental noise affects the fluctuations of Atlantic large pelagics." Progress In Oceanography. 86.1-2 (2010): 267–275.
Résumé: 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. (C) 2010 Elsevier Ltd. All rights reserved.
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2008 |
Chassot, E., et al. "Investigating trophic-level variability in Celtic Sea fish predators." Journal of Fish Biology. 73.4 (2008): 763–781.
Résumé: The trophic level (TL) mean and variance, and the degree of omnivory for five Celtic Sea fish predators were estimated using a database of stomach content records characterized by a high level of taxonomic resolution. The predators occupied a high position in the food web, i.e. 4·75 for Atlantic cod Gadus morhua, 4·44 for haddock Melanogrammus aeglefinus, 4·88 for European hake Merluccius merluccius, 5·00 for megrim Lepidorhombus whiffiagonis and 5·27 for whiting Merlangius merlangus. The level of taxonomic resolution of the prey did not greatly affect mean TL predator values; an effect on variance was evident, low resolution masking intra-population variability in TL. Generalized additive models (GAM) were used to explain the variability of predator TL caused by environmental variables (International Council for the Exploration of the Sea, ICES, division and season) and predator characteristics (total length, LT). Significant year, location season and interaction effects were found for some species and with LT at the scale of ICES subdivision. The species-specific variability of TL could be due to spatio-temporal variations in prey availability and in predator selectivity following ontogenetic changes. Omnivorous fish TL was less affected by spatio-temporal variations. In addition, results showed that the omnivory index and TL variability provide dissimilar information on predator feeding strategy. Combining information on TL variability and omnivory allowed between within-individual and between-individual components contributing to trophic niche width to be separated and the type of generalization of fish predators to be identified.
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Corbineau, A., et al. "Time series analysis of tuna and swordfish catches and climate variability in the Indian Ocean (1968-2003)." Aquat. Living Resour.. 21.3 (2008): 277–285.
Résumé: Aquatic Living Resources, Fisheries Science, Aquaculture, Aquatic Biology and Ecology
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Rouyer, T., et al. "Complex interplays among population dynamics, environmental forcing, and exploitation in fisheries." Pnas. 105.14 (2008): 5420–5425.
Résumé: The patterns of variations in fisheries time series are known to result from a complex combination of species and fisheries dynamics all coupled with environmental forcing (including climate, trophic interactions, etc.). Disentangling the relative effects of these factors has been a major goal of fisheries science for both conceptual and management reasons. By examining the variability of 169 tuna and billfish time series of catch and catch per unit effort (CPUE) throughout the Atlantic as well as their linkage to the North Atlantic Oscillation (NAO), we find that the importance of these factors differed according to the spatial scale. At the scale of the entire Atlantic the patterns of variations are primarily spatially structured, whereas at a more regional scale the patterns of variations were primarily related to the fishing gear. Furthermore, the NAO appeared to also structure the patterns of variations of tuna time series, especially over the North Atlantic. We conclude that the patterns of variations in fisheries time series of tuna and billfish only poorly reflect the underlying dynamics of these fish populations; they appear to be shaped by several successive embedded processes, each interacting with each other. Our results emphasize the necessity for scientific data when investigating the population dynamics of large pelagic fishes, because CPUE fluctuations are not directly attributable to change in species' abundance.
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Rouyer, T., et al. "Analysing multiple time series and extending significance testing in wavelet analysis." Mar Ecol Prog Ser. 359 (2008): 11–23.
Résumé: ABSTRACT: In nature, non-stationarity is rather typical, but the number of statistical tools allowing for non-stationarity remains rather limited. Wavelet analysis is such a tool allowing for non-stationarity but the lack of an appropriate test for statistical inference as well as the difficulty to deal with multiple time series are 2 important shortcomings that limits its use in ecology. We present 2 approaches to deal with these shortcomings. First, we used 1/ƒβ models to test cycles in the wavelet spectrum against a null hypothesis that takes into account the highly autocorrelated nature of ecological time series. To illustrate the approach, we investigated the fluctuations in bluefin tuna trap catches with a set of different null models. The 1/ƒβ models approach proved to be the most consistent to discriminate significant cycles. Second, we used the maximum covariance analysis to compare, in a quantitative way, the time–frequency patterns (i.e. the wavelet spectra) of numerous time series. This approach built cluster trees that grouped the wavelet spectra according to their time–frequency patterns. Controlled signals and time series of sea surface temperature (SST) in the Mediterranean Sea were used to test the ability and power of this approach. The results were satisfactory and clusters on the SST time series displayed a hierarchical division of the Mediterranean into a few homogeneous areas that are known to display different hydrological and oceanic patterns. We discuss the limits and potentialities of these methods to study the associations between ecological and environmental fluctuations.
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Stenseth, N. C., and T. Rouyer. "Ecology: Destabilized fish stocks." Nature. 452.7189 (2008): 825–826.
Résumé: Fishing of natural populations increases the variability of fish abundance. A unique data set from the southern California Current has allowed an evaluation of three hypotheses for why that should be so.
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