Individual differences in dominance-related traits drive dispersal and settlement in hatchery-reared juvenile brown trout

Abstract

Effective management of exploited populations is based on an understanding of population dynamics and evolutionary processes. In spatially structured populations, dispersal is a central process that ultimately can affect population growth and viability. It can be influenced by environmental conditions, individual phenotypes, and stochastic factors. However, we have a limited knowledge of the relative contribution of these components and its interactions, and which traits can be used as reliable predictors of the dispersal ability. Here, we conducted a longitudinal field experiment aimed to identify traits which can be used as proxy for dispersal in juvenile brown trout (Salmo trutta L.). We measured body size and standard metabolic rates, and estimated body shapes for 212 hatchery-reared juvenile fish that were marked with individual codes and released in a small coastal stream in northwest Spain. We registered fish positions and distances to the releasing point after 19, 41, 60 and 158 days in the stream. We detected a high autocorrelation of dispersal distances, demonstrating that most individuals settle down relatively soon and then hold stable positions over the study period. Body size and fish shape were reliable predictors of dispersal, with bigger and more robust-set individuals being more likely to settle closer to the release site than smaller and more elongated fish. In addition, the analysis of spacing and spatial patterns indicated that the dispersal of introduced fish could affect the distribution of resident conspecifics. All together, these results suggest that stocking programs aimed to the enhancement of overexploited populations at fine spatial scales can be optimized by adjusting the size and shape of the introduced fish to specific management targets and environmental conditions.

Comparing dominance relationships and movement of native marble trout (Salmo marmoratus) and introduced rainbow trout (Oncorhynchus mykiss)

“…Thus, it seems like the dominant and aggressive behaviour of rainbow trout seen in the laboratory before release might have influenced marble trout's subsequent behaviour in the river, by marble trout leaving the areas occupied by rainbow trout and moving to locations further away from the release site. Potential differences in habitat preference between rainbow trout and marble trout might have also contributed to their different behaviour after release, and further studies of the specific habitat preferences by marble trout are needed.After release, only a small fraction of fish (15%) moved upstream, consistent with previous research(Sánchez-González & Nicieza, 2021). Throughout the study, individuals of the two species occupied different locations, because the rainbow trout remained in pools and marble trout spread more out, which is a behaviour that may contribute to reduce competitive encounters between the species in the river environment.…”

“…Because settlement often requires the newcomers to overcome the aggressive superiority of several residents to remain there (Jenkins Jr., 1969), bigger and more robust‐set individuals are more likely to settle closer to the release site than smaller and more elongated fish (Sánchez‐González & Nicieza, 2021) and the costs of searching for the best territory may overweight the benefits of obtaining an optimal territory (Cutts et al ., 1999), the dominant fish are expected to settle faster and closer to the release site. This was found in this study for rainbow trout, despite the fact that all fish were released simultaneously.…”

“…gated fish(Sánchez-González & Nicieza, 2021) and the costs of searching for the best territory may overweight the benefits of obtaining an optimal territory(Cutts et al, 1999), the dominant fish are expected to settle faster and closer to the release site. This was found in this study for rainbow trout, despite the fact that all fish were released simultaneously.…”

What’s the effectiveness of stocking actions in small creeks? The role of water discharge behind hatchery trout downstream movement

“…Therefore, trout may struggle to find any suitable cover on creek margins or in deep pools during high-water events. As stated before, spatial competition with established wild trout could also limit the number of available covers for post-release hatchery trout, through a prior-resident effect ( Deverill, Adams & Bean, 1999 ; Sánchez-González & Nicieza, 2021 ).…”

Fish morphology and passage through velocity barriers. Experience with northern straight-mouth nase (Pseudochondrostoma duriense Coelho, 1985) in an open channel flume

“…4,5,Table 2,and Online Resource). This pattern could be explained by the fact that deep-bodied shapes are related to burst swimming, territorial and hierarchical behaviour, and dominance (Monet et al, 2006;Rouleau et al, 2009;Sa ´nchez-Gonza ´lez & Nicieza, 2021). In consequence, overdeveloped dorsal muscular mass, robust bodies, and caudal peduncles attain faster burst velocities (Cadrin, 2000;Pakkasmaa & Piironen, 2001), which, apparently, profit from a lower flow velocity, where burst swimming mode, short but explosive, could be more advantageous.…”