A continuum of life history tactics in a brown trout (Salmo trutta) population

Abstract

Life history tactics of the brown trout (Salmo trutta) population of the Oir River (Normandy, France) were studied using passive integrated transponder (PIT) tagging data of five consecutive cohorts (5900 individuals) monitored between 1995 and 2002. Results demonstrate that (i) life history traits vary among cohorts, chiefly caused by environmental variability, (ii) juvenile growth, particularly second-year growth, plays an important role in the determination of the growing environment and trout exhibit variable migratory behaviour (from remaining in the natal brook to migrating in the sea) related to their juvenile growth rate, and (iii) the description of life history tactics (including juvenile growth, fine-scale migratory behaviour, and reproduction) can be clarified. Tactics are expressed along a continuum in time (age to reproduce) and space (distance of migration). Flexible life history tactics varying with juvenile growth is consistent with previous studies, but the use of empiric data on growth and migration from PIT tagging allows refining the description of life history tactics, taking into account their continuous distribution in time and space.Les tactiques d'histoire de vie de la population de truite commune (Salmo trutta) de l'Oir (Normandie, France) ont été étudiées par le marquage individuel à l'aide de « PIT tag » de cinq cohortes consécutives (5 900 individus) suivies de 1995 à 2002. Les résultats confirment et démontrent que (i) les traits d'histoire de vie varient entre les cohortes et que cette variabilité peut être reliée principalement aux fluctuations des conditions environnementales, (ii) la croissance juvénile, plus particulièrement celle de la seconde année de vie, est un facteur important dans la détermination de la zone de croissance et les truites possèdent des comportements migratoires variables, allant de la résidence stricte au ruisseau natal jusqu'à la migration en mer, que l'on peut relier à leur taux de croissance juvénile et (iii) la description des tactiques d'histoire de vie (en incluant la croissance juvénile, le comportement migratoire à fine échelle et la reproduction) peut être affinée, les tactiques se distribuant le long d'un continuum temporel (age de reproduction) et spatial (distance de migration). La flexibilité des tactiques d'histoire de vie et leurs liens avec la croissance juvéniles sont confirmés dans cette étude. Cependant l'utilisation de données empiriques sur la croissance et la migration issues du marquage individuel par PIT tag a permis d'améliorer la description des tactiques en prenant en compte leur distribution continue dans le temps et l'espace

Marine migrations in anadromous brown trout (Salmo trutta). Fjord residency as a possible alternative in the continuum of migration to the open sea

“…The underlying causes of the present partial migrations are not elucidated by this experiment. However, in the context of a conditional strategy, it is possible that factors related to the energetic status (Forseth et al, 1999), growth and/or metabolic rate (Cucherousset et al, 2005), energy allocation (Jonsson and Jonsson 1998), and inherited components (Giger et al, 2006) might affect the individual's decision to 19/28 migrated. We suggest further studies on the initial marine behaviour of sea trout incorporating measurements on the above mentioned factors to potentially identify proximate causes for the observed behaviour.…”

“…Overall, the diversification of migratory behavioural traits in the fjord (FR and SM) may lead to increased evolutionary fitness of the sea trout population in the river Villestrup, as indicated by Cucherousset et al, 2005. For instance, the migratory tactic could provide a selective advantage in fluctuating environments, especially when extremely changeable conditions appear.…”

“…Partial migration is a phenomenon where a population is composed of both migratory and resident individuals (Chapman et al, 2012, Hendry et al, 2004, Jonsson and Jonsson 1993. Partial migration in fishes is seen as an adaptive response to a changeable 3/28 environment, and the ultimate goal is to increase individual fitness and population persistence (Cucherousset et al, 2005).…”

Sur quelles connaissances se baser pour évaluer l’état de santé des populations de truite commune (Salmo trutta) ?

“…Le rapport des sexes dans la population est le plus souvent considéré comme équilibré (0,5) dans les premiers stades de vie. Mais ce rapport des sexes peut varier ensuite en fonction de la stratégie d'histoire de vie des individus qui est sexe dépendant (Cucherousset et al, 2005). Les migrations de reproduction pour l'accès aux zones de frayères ont lieu généralement de fin septembre à fin janvier (Ovidio et al, 1998).…”

Fish scale δ15N and δ13C values provide biogeochemical tags of fish comparable in performance to element concentrations in scales and otoliths

“…Here, we examine the relative performance of stable isotopes in scales and element concentrations in both scales and otoliths of an anadromous salmonid, Salmo trutta. The species is phenotypically plastic, and after a period of juvenile growth in freshwater can either remain in freshwater during its entire lifespan or utilise a combination of freshwater, estuarine and marine habitats (Cucherousset et al, 2005). S. trutta is an excellent candidate for studies on biogeochemical tags, due to the continuum of life history strategies that it exhibits, which can involve migration/movement over considerable distances (Ovidio et al, 1998).…”