Decadal changes in water temperature and ecological time-series in Lake Geneva, Europe - detecting relationships with the subtropical Atlantic climate variability

We investigated connections between subtropical Atlantic climate variability, atmospheric conditions in the European Alpine region (45 to 47° N and 5 to 8° E) and the interannual variability of the thermal conditions in the largest body of freshwater in Western Europe (Lake Geneva). The long-term water temperature was related to climate variability by means of a multivariate regression model. Results revealed atmospheric connections that have been elusive so far, and showed that over the period from 1959 to 2000, summer thermal conditions in Lake Geneva appear tightly linked to the long-term variability of the subtropical Atlantic climate. The multivariate model revealed high skills and tight correlations, which suggest the possibility of assessing future thermal changes in Lake Geneva from the Atlantic climate variability. The implications of such climatic forcing on the functioning of the pelagic ecosystem in Lake Geneva were illustrated by analysing the long-term changes in abundance of the summer-dominant carnivorous cladocerans Bythotrephes longimanus and Leptodora kindtii during the period 1974 to 2000. Again, the multivariate model revealed high skills and excellent correlations between the interannual changes in abundance of these species and the variability of summer climate. Our approach provides a general understanding of the interrelations between large- and regional-scale climates, local environmental conditions and the ecological responses in Lake Geneva during summer, and is therefore applicable to other retrospective studies

Seasonal and interannual variability of cladoceran communities in two peri-alpine lakes: uncoupled response to the 2003 heat wave

Seasonal and interannual dynamics of cladoceran species were analyzed during the period 1995–2003 in two deep peri-alpine lakes morphologically different but subjected to similar regional climatic forcing. The seasonal succession of cladoceran species was characterized and the impact of extreme climatic events on the annual pattern of species succession was assessed. Using a multivariate method, we show that the cladoceran species display marked seasonality patterns that differed in the two lakes. The differences observed between the lakes were driven by their trophic state, the plankton species composition and the abundance of predators. We show that the sensitivity of the annual pattern of species succession to extreme weather changes, illustrated by the 2003 heat wave, differs markedly in these two lakes. In Lake Annecy, the annual pattern of cladoceran succession observed in 2003 is not different from the one usually observed. In contrast, in Lake Geneva, the annual pattern recorded in 2003 is unusual and characterized by the maintenance of herbivorous cladocera during summer. These findings underline the need to consider the morphology of lakes and trophic state in the assessment of ecological responses to global warming. Our results contribute to the debate about the predictability of the impacts of climate change on aquatic ecosystems, and their extrapolation from one site to another

La truite commune (Salmo trutta L.) dans le Redon, un petit affluent du lac Léman : caractéristiques des géniteurs de truite de lac (1983-1988) et premières données sur l'impact des relâchers d'alevins nourris

L'étude précise les caractéristiques (âge, croissance) des géniteurs de truite de lac échantillonnés cinq années consécutives sur le Redon, un petit affluent (10 km) du lac Léman (58.240 ha). Les jeunes géniteurs de 2 ou 3 ans représentent 73 % des mâles contre seulement 33 % des femelles. L'examen des écailles montre l'existence de 1 (type 1 : 56 %), 2 (type 2 : 43%) ou 3 ans (type 3 :1 %) de croissance initiale lente "type rivière". La longueur totale rétromesurée à 1 an est significativement plus élevée (129 mm) pour les géniteurs de type 1 que celle (100 mm) des géniteurs de type 2. Un lot de 6.000 alevins, nourris en pisciculture jusqu'à 4 cm, issus de géniteurs de truite de lac et marqués, a été déversé en août 1983 dans la partie aval du Redon. Les géniteurs de truites de lac issus de ce petit lot représentaient une part importante (46 % des femelles et 22 % des mâles) de la cohorte d'adultes correspondante remontant frayer dans le Redon

Impacts of climate warming on the long-term dynamics of key fish species in 24 European lakes

Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10-100 years) fish data series from 24 European lakes (area: 0.04-5,648 km(2); mean depth: 1-177 m; a north-south gradient from Sweden to Spain). Along with an annual temperature increase of about 0.15-0.3A degrees C per decade profound changes have occurred in either fish assemblage composition, body size and/or age structure during recent decades and a shift towards higher dominance of eurythermal species. These shifts have occurred despite a reduction in nutrient loading in many of the lakes that should have benefited the larger-sized individuals and the fish species typically inhabiting cold-water, low-nutrient lakes. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal brown trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch has apparently been stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore, Italy. Where introduced, roach seems to take advantage of the higher temperature after years of low population densities. Eurythermal species such as common bream, pike-perch and/or shad are apparently on the increase in several of the lakes. The response of fish to the warming has been surprisingly strong and fast in recent decades, making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems

Effects of climate and land-use changes on fish catches across lakes at a global scale

Globally, our knowledge on lake fisheries is still limited despite their importance to food security and livelihoods. Here we show that fish catches can respond either positively or negatively to climate and land-use changes, by analyzing time-series data (1970–2014) for 31 lakes across five continents. We find that effects of a climate or land-use driver (e.g., air temperature) on lake environment could be relatively consistent in directions, but consequential changes in a lake-environmental factor (e.g., water temperature) could result in either increases or decreases in fish catch in a given lake. A subsequent correlation analysis indicates that reductions in fish catch was less likely to occur in response to potential climate and land-use changes if a lake is located in a region with greater access to clean water. This finding suggests that adequate investments for water-quality protection and water-use efficiency can provide additional benefits to lake fisheries and food security

Tissus durs et âge individuel des vertébrés

La variabilité des mesures scalimétriques chez les corégones du lac d'Annecy a été étudiée pour comparer les composantes inter- et intra-poisson. La variabilité entre écailles d'un même poisson s'avère nettement plus faible que la variabilité entre poissons. Toutefois, il est judicieux d'effectuer des mesures sur 3 à 4 écailles par poisson. On met ainsi en évidence des différences de la taille à 1 an à l'intérieur d'une même cohorte entre les poissons qui entrent jeunes dans la pêcherie et ceux qui y entrent plus tardivement. Il serait possible, en tenant compte de ce phénomène, d'avoir une estimation de la pression de pêche importante sur cette espèce à Annecy. (Résumé d'auteur

Revue des méthodes d'estimation de l'effectif d'une population par pêches successives avec retrait. Programme d'estimation d'effectif par la méthode de Carle et Sturb

Les méthodes traditionnelles de LESLIE, de DE LURY sont rappelées. La méthode de ZIPPIN est présentée avec la possibilité de réaliser les calculs par ordinateur sans recours aux estimations graphiques. La méthode de CARLE et STRUB étant plus robuste, un programme de calcul sur microordinateur est proposé en annexe

La population de gardons (Rutilus rutilus (L.)) du Lac Léman en 1983-85. Structure en âge, déterminisme du recrutement, analyse de la croissance

La distribution en tailles des gardons du Lac Léman, entre 1983 et 1985 est nettement bimodale avec absence de poissons de taille comprise entre 17 et 20 cm de longueur totale. On explique, en partie, l'absence de certaines cohortes par des conditions climatiques défavorables (coups de vent avec brassage des eaux entraînant une mortalité massive des oeufs et alevins). La croissance relative annuelle à partir de la deuxième année de vie du gardon est corrélée à la somme des degrés-jours pour des températures supérieures à 15°C au mois de septembre.L'automne chaud permet une prolongation de la période annuelle de croissance