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Auteur Robert, M.; Dagorn, L.; Filmalter, J.D.; Deneubourg, J.L.; Itano, D.; Holland, K.
Titre Intra-individual behavioral variability displayed by tuna at fish aggregating devices (FADs) Type Article scientifique
Année 2013 Publication (up) Revue Abrégée Mar Ecol Prog Ser
Volume 484 Numéro Pages 239-247
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Résumé ABSTRACT: Fishers have exploited the associative behavior displayed by several pelagic fish species with floating objects for decades, through the use of man-made fish aggregating devices (FADs), which facilitate the capture of such species. However, our understanding of this associative behavior and its adaptive value is poor and the scientific community is ill-equipped to provide fishery managers with science-based recommendations on the impacts of FADs on ecosystems. In an array of 13 anchored FADs around Oahu, Hawaii, USA, 72 yellowfin tuna Thunnus albacares were equipped with internal acoustic tags, which facilitated the continuous monitored of their presence and absence around each FAD using automated acoustic receivers. Data were analyzed using survival curves with the objective of determining the behavioral dynamics of fish joining and leaving the FADs. Residence times at FADs were characterized by 4 behavioral modes: briefly passing near a FAD (average 13.1 min), short association (average 2.9 d), and 2 long association behaviors (13.8 and 23.2 d, respectively). Statistical analyses suggest that different behavioral modes were likely dependent upon local conditions around the FAD at a given time (environmental factors or social interactions). We observed 2 behavioral modes for absence times from FADs: short (2.8 d) and long (infinite). More importantly, individuals exhibited behavioral variability, switching between short and long residence times at FADs. This suggests that large pelagic fish can display a range of behavioral responses while in an array of FADs, challenging the common hypothesis of a single behavioral pattern, which could ultimately lead to an ecological trap. Survival curves were best fitted with exponential models, suggesting that underlying behavioral processes were time independent.
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Numéro d'Appel LL @ pixluser @ collection 262
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Auteur Ottersen, G.; Stige, L.C.; Durant, J.M.; Chan, K.S.; Rouyer, T.A.; Drinkwater, K.F.; Stenseth, N.C.
Titre Temporal shifts in recruitment dynamics of North Atlantic fish stocks: effects of spawning stock and temperature Type Article scientifique
Année 2013 Publication (up) Revue Abrégée Mar Ecol Prog Ser
Volume 480 Numéro Pages 205-225
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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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Numéro d'Appel LL @ pixluser @ collection 293
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Auteur Hjermann, D.; Fisher, J.A.D.; Rouyer, T.; Frank, K.T.; Stenseth, N.C.
Titre Spatial analysis of North Sea cod recruitment: concurrent effects of changes in spawning stock biomass, temperature and herring abundance Type Article scientifique
Année 2013 Publication (up) Revue Abrégée Mar Ecol Prog Ser
Volume 480 Numéro Pages 263-275
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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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Numéro d'Appel LL @ pixluser @ collection 294
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Auteur Durant, J.M.; Hidalgo, M.; Rouyer, T.; Hjermann, D.; Ciannelli, L.; Eikeset, A.M.; Yaragina, N.; Stenseth, N.C.
Titre Population growth across heterogeneous environments: effects of harvesting and age structure Type Article scientifique
Année 2013 Publication (up) Revue Abrégée Mar Ecol Prog Ser
Volume 480 Numéro Pages 277-287
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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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Numéro d'Appel LL @ pixluser @ collection 295
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Auteur Duarte, L.; Rossi, F.; Docal, C.; Viejo, R.M.
Titre Effects of alga Fucus serratus decline on benthic assemblages and trophic linkages at its retreating southern range edge Type Article scientifique
Année 2015 Publication (up) Revue Abrégée Mar Ecol Prog Ser
Volume 527 Numéro Pages 87-103
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Résumé ABSTRACT: Canopy-forming seaweeds are important coastal ecosystem engineers that sustain diverse multi-trophic assemblages. Their losses, with the subsequent reduction in habitat complexity, have been documented across many parts of the world and are often attributed to climate change and other anthropogenic factors. The general aim of the present study was to understand the repercussions of the decline of the canopy-forming alga Fucus serratus L. at its retreating southern range edge in the diversity and food-web linkages of intertidal assemblages. Few studies have attempted to document changes in benthic food webs following canopy loss. We examined the differences among southern locations situated at different distances from the range margin: those at the very edge, where F. serratus experienced a dramatic decline during recent years (marginal locations), and those where F. serratus is still dominant (central locations). Comparisons were made among locations situated at the same latitude and sharing a recent history of F. serratus dominance. Trophic relationships were analyzed using natural abundances of carbon and nitrogen stable isotopes. We report clear changes in the structure of benthic assemblages and lower trophic positioning of some consumers, suggesting an overall shrinkage of the food web length at the contracting range edge of F. serratus, which will transfer to higher trophic levels. Under present and future climatic scenarios, shifts in the distribution of coastal ecosystem engineers could entail a reorganization of local natural assemblages and food webs. More attention should be given to measure how much these shifts can modify the whole coastal food webs and their functioning.
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Numéro d'Appel MARBEC @ alain.herve @ collection 1340
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