Biology subjects

Nevoux, M.

Publications and source records attributed to Nevoux, M..

5 recordsLinked to original sources

bioRxiv2026

Smolt migration in relation to latitude, season and migratory distance

Downstream migration and sea entry are periods of high mortality for sea trout smolts and migration timing is a critical aspect of survival. We aimed to investigate migration timing of PIT-tagged sea trout smolts across a latitudinal gradient in five freshwater systems across Europe: Norway, Sweden, Denmark, France and Portugal. In two systems, smolt migration was further examined to assess a) differences in sex, body size and condition between autumn and spring migrants; b) the influence of spatial origin within the stream; and c) relationships between individual body size and migration date. Tagged smolts were not detected migrating in the Portuguese watershed. Spring migration timing differed significantly between watersheds in Norway, Sweden, Denmark and France. Generally, there was a trend of earlier migration at lower latitudes. Autumn vs spring migration was examined in Gudso-Denmark. Autumn migrants were larger in both length and mass, with no differences were found in sex ratios or body condition. In terms of spatial origin, fish originating from an upstream site were more likely to migrate in the autumn compared to the spring and vice versa. Size dependent migration was found in the Swedish system, Haga [a]-Sweden, with larger individuals migrating earlier in the spring than smaller individuals. Outward-migrating smolts were also more likely to originate from a downstream site than an upstream site. Overall, these results show both large-scale geographic and fine-scale individual influences on migration timing. Given that climate change may have large impacts on migration patterns in sea trout, understanding variability in migratory patterns across a latitudinal gradient is an important tool for predicting responses to environmental changes.

ecology↗

bioRxiv2023

Changes in length-at-first return of a sea trout (Salmo trutta) population in northern France

The resilience of sea trout populations is increasingly concerning, with evidence of major demographic changes in some populations. Based on trapping data and related scale collection, we analysed long-term changes in body length of a sea trout population in the Bresle River, France. From 1984-2022, the length of first-time returning individuals decreased by 1.73 mm.year-1 (SD = 0.08), which resulted in the loss of c. 12.3% of mean body length. This decrease results from a decrease in the age at first return, with a gradual loss of the oldest individuals and an increase in the proportion of the youngest. Timing of the return migration advanced drastically, although shorter sea sojourn had little influence on body length. We found little evidence of a decrease in length-at-age, to the exception of the oldest age class, suggesting that growth conditions at sea might not have deteriorated greatly during the study period.

ecology↗

bioRxiv2023

Fast, safe and high-throughput Real-Time PCR protocol for molecular sex identification in Salmo salar, applicable to historic scale collections

Conservation and management of wild species needs a detailed understanding of their population structure and dynamics. For instance, there are increasing evidence for sex-specific life history trajectories, even in species with limited morphological sexual dimorphism. In these species, identifying the sex of individuals in some or all life stages is a methodological challenge, which requires the development of new tools. Building on recent findings in molecular biology, we developed a new protocol for sex identification in Atlantic salmon (Salmo salar), aiming at the following criteria: accurate sex identification, fast diagnostic, applicable to large sample size, applicable to degraded DNA extracted from e.g. fish scales, and safe for the operator by limiting health and safety hazard. The protocol relies on multiplex Real-Time PCR using a set of specific primers. We tested its accuracy on a test set of 90 DNA samples from individuals of known morphological sex, and demonstrated its applicability on a large DNA sample from 384 individuals of unknown sex.

molecular biology↗

bioRxiv2022

Where does the rainbow end? A case study of self-sustaining rainbow trout Oncorhynchus mykiss populations in tropical rivers

The great physiological, behavioral and morphological plasticity of salmonids contributed to the success of their introduction into a wide range of habitats. However, rainbow trout (Oncorhynchus mykiss) is the only salmonid species to live in the tropics. Like for any cold-water species, water temperature is assumed to be a major constraint to the presence and expansion of rainbow trout. In this study, we collected detailed records of the introduction history of rainbow trout at 35 sites across the island over 80 years, and we document the presence of self-sustainable trout at each site. We explored the linear relationship between water temperature and elevation.

ecology↗

bioRxiv2018

Assessing precocious maturation in salmon using ultrasound imaging

AO_SCPLOWBSTRACTC_SCPLOWSalmonids are characterized by a large diversity of life histories, but their study is often limited by the imperfect observation of the true state of an individual in the wild. Challenged by the need to reduce uncertainty of empirical data, recent development in medical imaging techniques offered new opportunities to assess precocious maturation in Atlantic salmon parr. Traditional phenotypic (external) examination and ultrasound (internal) examination were compared and recommendations on fish handling and ultrasound image interpretation are provided. By allowing to see the unseen, portable ultrasound imaging offers great opportunities for ecological studies in the wild, such as the assessment of individual sexual maturation.

ecology↗