Postrelease exploration and stress tolerance of landlocked and anadromous Atlantic salmon and their hybrids

Abstract

Threatened fish populations worldwide are relying on stock supplementation by hatchery‐reared fish. Although stocking with non‐native fish may lead to hybridization, thereby disrupting local adaptations, it could also improve the adaptive potential of small populations by increasing variability in essential behavioral traits. In this study, we crossbred the critically endangered Finnish landlocked salmon with a geographically close Baltic anadromous salmon population to compare boldness‐related behavioral traits among the crossing groups. We studied postrelease exploration in seminatural streams and tested stress tolerance of the fish, as reflected by their response during swimming trials and commencement of feeding after the trials. In the stress tolerance experiments, we compared fish with different rearing backgrounds to gain insight into environmentally induced variability in stress tolerance. When compared with the anadromous salmon, the landlocked salmon showed more active postrelease exploration and higher stress tolerance. The hybrids displayed intermediate behaviors compared with the purebred salmon, indicating heritability of these traits. The landlocked salmon showed less variable exploration than the hybrids with anadromous salmon as the maternal strain, but we did not find rearing‐dependent responses in stress tolerance. In summary, our findings suggest that hybridization could help in reversing likely domestication‐related negative behavioral traits in the landlocked salmon.

Selection among critically endangered landlocked salmon (Salmo salar m. sebago) families in survival and growth traits across early life stages and in different environments

“…However, the possible fixation of behavioral features reported by Eronen et al. (2023) might impose considerably stronger selection and G × E under natural conditions where the fish are susceptible to predation.…”

“…A recent study by Eronen et al. (2023) showed that Saimaa salmon juveniles exhibited, on average, more explorative behavior in a novel environment and were more stress‐tolerant than conspecifics from a genetically more diverse anadromous strain. The authors concluded that the observed behavioral differences between the strains may be related, at least in part, to higher level of domestication of the Saimaa salmon.…”

“…The relatively high genetic association for growth between our study environments could be partly due to predatorfree conditions that consistently favored the most active and bold genotypes. However, the possible fixation of behavioral features reported by Eronen et al (2023) might impose considerably stronger selection and G × E under natural conditions where the fish are susceptible to predation.…”

“…Low genetic diversity in Saimaa salmon is also linked to impaired foraging success and incidence of early developmental malformations (Primmer et al., 2003; Tiira et al., 2006). Moreover, a long hatchery history may have contributed to the apparent signs of domestication in behavioral traits related to exploration (boldness) and stress tolerance (Eronen et al., 2023). These factors may compromise the ability of the strain to tolerate and/or adapt to environmental changes and thus its return to the wild, despite recent habitat restoration efforts (Hatanpää et al., 2021; Leinonen et al., 2021).…”