Assessing the freshwater distribution of yellow eel

In the global context of the decline in wild species, modeling the distribution of populations is a crucial aspect of ecological management. This can be a major challenge, especially for species, such as the European eel, that have complex life cycles, exhibit cryptic behavior, or migrate over long distances. A review of the literature suggests that eel size data could be used to assess and analyze freshwater distribution of eel. We argue that analyses based on small yellow eels (≤ 300 mm) along the longitudinal course of rivers could provide a valuable tool for population monitoring. We propose a standardized catchment recruitment index and a colonization index based on the probability of occurrence (presence/absence data) using logistic models for different size classes. The model developed here provides a convenient guide for assessing yellow eel stages in freshwater areas, and should have concrete applications for management of the species

Patterns in fish assemblages in the Loire floodplain: the role of hydrological connectivity and implications for conservation

Hydrological connectivity is known to determine biodiversity patterns across large river floodplains, but it is often greatly altered by human activities. Indicators and predictors of the response of river alteration or restoration are therefore needed. Recent papers suggested that fish environmental guilds – based on species flow preferences – could be used as a tool to assess ecological status of rivers. In the Loire floodplain, we described fish assemblages across the floodplain at the onset of the dry season and we determined whether observed spatial patterns could be related to environmental variables, especially connectivity. Based on specific composition of 46 electrofished waterbodies, a hierarchical typology of the Loire floodplain assemblages was built using self-organizing maps. Each assemblage of the typology was characterized by a set of species using the indicator value method. These species sets and the composition of the assemblages revealed a gradient of flow preferences in the different assemblages identified. A stepwise discriminant analysis showed that the most important variable determining assemblage composition was the hydrological connectivity. Finally, the conclusion was made that a high connectivity level is needed to conserve native fish diversity in the Loire floodplain, notably because the number of protected and native species increased with connectivity, and because the number of exotic species increased with isolation

Genetic compatibility exceeds possible ‘good genes’ effects of sexual selection in lake char

Mating is rarely random in nature, but the effects of mate choice on offspring performance are still poorly understood. We sampled in total 47 wild lake char (Salvelinus umbla) during two breeding seasons and used their gametes to investigate the genetic consequences of different mating scenarios. In a first study, 1,464 embryos that resulted from sperm competition trials were raised singly in either a stress- or non-stress environment. Offspring growth turned out to be strongly reduced with increased genetic relatedness between the parents while male coloration (that reveal aspects of male health) was no significant predictor of offspring performance. In a second experiment one year later, block-wise full-factorial in vitro breeding was used to produce 3,094 embryos that were raised singly after sublethal exposures to a pathogen or water only. Offspring growth was again strongly reduced with increased genetic relatedness between the parents while male coloration was no significant predictor of offspring performance. We conclude that the genetic benefits of mate choice would be strongest if females avoided genetic similarity, while male breeding colors seem more relevant in intra-sexual selection

Warming winters threaten peripheral Arctic charr populations of Europe

As the global climate warms, the fate of lacustrine fish is of huge concern, especially given their sensitivity as ectotherms to changes in water temperature. The Arctic charr (Salvelinus alpinus L.) is a salmonid with a Holarctic distribution, with peripheral populations persisting at temperate latitudes, where it is found only in sufficiently cold, deep lakes. Thus, warmer temperatures in these habitats particularly during early life stages could have catastrophic consequences on population dynamics. Here, we combined lake temperature observations, a 1-D hydrodynamic model, and a multi-decadal climate reanalysis to show coherence in warming winter water temperatures in four European charr lakes near the southernmost limit of the species’ distribution. Current maximum and mean winter temperatures are on average ~ 1 °C warmer compared to early the 1980s, and temperatures of 8.5 °C, adverse for high charr egg survival, have frequently been exceeded in recent winters. Simulations of winter lake temperatures toward century-end showed that these warming trends will continue, with further increases of 3–4 °C projected. An additional 324 total accumulated degree-days during winter is projected on average across lakes, which could impair egg quality and viability. We suggest that the perpetuating winter warming trends shown here will imperil the future status of these lakes as charr refugia and generally do not augur well for the fate of coldwater-adapted lake fish in a warming climate

Assessment of yellow european eels populations trends: toward the establishment of a common methodology?

In this communication we propose a new way to assess yellow eel populations trands in developing a "catchment colonization index" based on the survey of small eels

A literature review of helminth parasites in the sea lamprey Petromyzon marinus (Petromyzontidaeà, with a field-study in postmetamorphics from French rivers and coastal waters

International audienc

A literature review of helminth parasites in the sea lamprey Petromyzon marinus (Petromyzontidaeà, with a field-study in postmetamorphics from French rivers and coastal waters

International audienc

Higher temperature exacerbates the impact of sediments on embryo performances in a salmonid

In a warming climate, higher temperatures are likely to modulate positively or negatively the effect of other environmental factors on biota, although such interactions are poorly documented. Here, we explore under controlled conditions the combined effects of two common stressors in freshwater ecosystems, higher temperature and sediment load, on the embryonic development of arctic charr (Salvelinus alpinus L.). In the warm treatment, embryos had a lower survival, a longer incubation period and a smaller body size with a bigger yolk sac volume. Our data show a significant interaction between temperature and sediment load with temperature increasing dramatically the negative effects of sediment load on fitness-related traits. In the climate change context, these findings highlight the importance of taking into account different thermal scenarios when examining the effect of environmental or anthropogenic stressors

Egg sqize versus number of offspring trade-off: Female age rather than size matters in a domesticated arctic charr population

International audienceUnderstanding how organisms adjust reproductive allocation trade-offs between offspring size versus number (OSN trade-off) is a central question in evolutionary biology. In organisms with indeterminate growth, changes in OSN according to maternal size or age have been reported in numerous taxa. The relative contribution of age and size remains largely unclear, as they are often highly correlated. In this study, we investigated how females adjust the offspring size versus number trade-off and analyzed the relative contribution of female age and size in a domesticated population of Arctic charr Salvelinus alpinus (Linnaeus, 1758) that exhibit large variation in size within five age classes. Our results show that the reproductive output (i.e. as measured by the clutch mass), was strongly correlated to female mass and age suggesting that the proportion of resources allocated to reproduction do not vary along lifetime. Egg mass and fecundity (egg number) increased with female mass overall. However, within an age class, larger females had higher fecundity but egg mass was poorly related to female mass. At the population level, a positive relationship was observed between fecundity and egg mass but within each class age the relation was negative revealing a OSN trade-off. Overall, our results show that, in our model Arctic charr population, allocation trade-off to reproduction and the way females allocate to egg mass and fecundity is largely determined by their age rather than mass

Petromyzon marinus (Petromyzontidae), an unusual host for helminth parasites in Western Europe

International audienceThe sea lamprey Petromyzon marinus, which is among the most phylogenetically ancient vertebrates, is a hematophagous ectoparasite that feeds on vertebrates and is considered vulnerable in Europe but is a pest in the North American Great Lakes. We conducted a literature review of helminth parasites of P. marinus and investigated postmetamorphic lampreys sampled in rivers and northeast Atlantic coastal waters (western France) during spawning migration. Based on the literature review, 16 helminth taxa have been recorded in P. marinus, among them 14 in North America but only 2 in Europe, with no species in common between these areas. Specific parasites are lacking, and helminth parasites recorded in P. marinus are mostly opportunistic and are trophically transmitted to fish hosts with both extremely low prevalence and mean intensity. Thus, P. marinus seems an unusual host that is probably infected through accidental ingestion of parasites by microphagous larvae (ammocoetes) and/or hematophagous postmetamorphs. Our field study supports this hypothesis, since only a single third-stage larva of Anisakis simplex sensu stricto was found in 2 postmetamorphic P. marinus among the 115 individuals dissected. This opportunistic, trophically transmitted, and cosmopolitan nematode species has never been recorded in North American sea lampreys and only once in Galician rivers (southern Europe). Infestation pathways of P. marinus by A. simplex are proposed vis-à-vis the feeding strategy of postmetamorphs and fish host species which potentially harbor anisakid larvae in their musculature. More generally, the complexity of biotic interactions is discussed considering P. marinus both as a host for helminth parasites and as a parasite for hosts such as fish and mammals, which are also potential predators of sea lamprey