Unravelling the effects of water temperature and density dependence on the spatial variation of brown trout (Salmo trutta) body size

Abstract

This study looks at the relative influence of water temperature and density dependence on the spatial variation in body size of 126 brown trout (Salmo trutta) cohorts from 12 Iberian rivers over a 12-year period. Mean cohort mass and length of age groups 0+ to 2+ varied significantly among sampling sites because of the concurrent effect of water temperature and density dependence. Density in suitable habitat had a limiting role that influenced potential maximum growth of cohorts, and water temperature differentiated these cohorts in two groups of sites with high and low potential maximum growth. Water temperature had a positive cumulative effect on body size of all age classes. However, body size of age-0 trout was nonlinearly influenced by short-term exposure to extreme water temperature. Thus, extremely high temperatures became a limiting factor and had deleterious effects on growth. There were intracohort and intercohort effects of density dependence throughout the life span, which were mainly due to the density in the available suitable habitat of trout of the same age or older. The present study supports the hypothesis that both density-dependent and density-independent processes are crucial for the understanding of population dynamics and that their relative importance varies across scales of space and time.Résumé : L'étude s'intéresse à l'influence relative de la température de l'eau et de la dépendance de la densité sur les variations spatiales de la taille du corps pour 126 cohortes de truite brune (Salmo trutta) de 12 rivières ibériennes, sur une pé-riode de 12 ans. La masse des cohortes et la longueur moyenne des groupes d'âge de 0+ an et 2+ ans variaient de manière significative selon le site de prélèvement, en raison des effets concomitants de la température de l'eau et de la dépendance de la densité. La densité dans les habitats convenables, jouait un rôle limitant qui influait sur la croissance maximum potentielle des cohortes, alors que la température de l'eau différenciait ces cohortes selon deux groupes de localités, qui présen-taient des croissances maximums potentielles élevée et faible, respectivement. La température de l'eau avait un effet cumulatif positif sur la taille du corps pour toutes les classes d'âges. Toutefois, l'exposition de courte durée à des températu-res d'eau extrêmes avait un effet non linéaire sur la taille du corps des truites de 0 an. Les températures extrêmement éle-vées devenaient ainsi un facteur limitant et avaient des effets néfastes sur la croissance. Des effets intracohorte et intercohorte de la dépendance de la densité étaient présents tout au long de la durée de vie, ces effets étant principalement dus à la densité dans l'habitat convenable disponible de truites du même âge ou plus vieilles. L'étude appuie l'hypothèse voulant que des processus dépendants et indépendants de la densité soient nécessaires pour expliquer la dynamique des populations et que l'importance relative de ces deux types de processus varie en fonction de l'échelle spatiale et temporelle.[Tra...

Density dependence and its impact on individual growth rates in an age‐structured stream salmonid population

“…Oppositely, Kvingedal and Einum (2011) found that subyearling brown trout densities in Norway were associated with depressed size-at-age for both subyearling and yearling fish, and that yearling density did not cause depressed sizes in either age class. Parra et al (2012) reported on density-dependent effects both within and among cohorts of brown trout in northern Spain, and notably that the size of overyearling fish was negatively associated with densities of younger cohorts. This finding could owe to marginally better rearing conditions for younger fish in habitats suitable for several age classes, and that the energetic cost of fending off subyearling competitors could depress growth rates in older fish in these habitats (Parra et al 2012).…”

“…Parra et al (2012) reported on density-dependent effects both within and among cohorts of brown trout in northern Spain, and notably that the size of overyearling fish was negatively associated with densities of younger cohorts. This finding could owe to marginally better rearing conditions for younger fish in habitats suitable for several age classes, and that the energetic cost of fending off subyearling competitors could depress growth rates in older fish in these habitats (Parra et al 2012).…”

“…The interacting effects of density and temperature have been studied in several recent works (Crozier et al 2010, Parra et al 2012, Baerum et al 2013, and reveal complex constraints on individual growth and size-at-age. Whereas we did not find any conclusive effects of temperature and density interactions on juvenile steelhead growth rates, Crozier et al (2010) found that the negative effects of density on individual Chinook salmon (O. tshawytscha) size were exacerbated at high temperatures, and that growth correlated positively to temperature at relatively low densities.…”

“…However, with the potentially strong influence of density on individual growth rates, and the consequences for life history expression and fitness, it is important to understand the extent to which density dependence is manifested at the individual level (Sogard 1997, DeAngelis and Mooij 2005, Kaspersson et al 2013. These effects can be particularly important in age-structured populations, in which the presence of one cohort can alter the behavior of another (Rosenfeld andBoss 2001, Kaspersson andHö jesjö 2009), and in populations experiencing abiotic conditions which can exacerbate the effects of competition (Crozier et al 2010, Parra et al 2012). Here we study the effects of population density on individual growth rates in juvenile age classes of steelhead (Oncorhynchus mykiss) in a population listed as threatened under the Endangered Species Act (NMFS 2010).…”

Summer Season Water Temperature Modeling under the Climate Change: Case Study for Fourchue River, Quebec, Canada

“…In addition, it is especially important to cold water fishes such as salmonids [9][10][11][12][13][14]. Water temperature increases that could potentially be induced because of climate change could be a critical issue of aquatic species [15][16][17][18][19].…”