Restored river habitat provides a natural spawning area for a critically endangered landlocked Atlantic salmon population

Abstract

Supplementing endangered fish populations with captive bred individuals is a common practice in conservation management. The aim of supplementary releases from hatchery broodstocks is to maintain the viability of populations by maintaining their genetic diversity. Landlocked Lake Saimaa salmon (Salmo salar m. sebago) has been critically endangered for the past half-century. As a result of anthropogenic disturbance, especially construction of hydroelectric power plants, the Lake Saimaa salmon has become completely dependent on hatchery broodstock. Recently, habitat restoration has been done in one of the former spawning rivers with the aim of creating a new natural spawning ground for the critically endangered population. Hatchery fish releases have also been revised so that in addition to juveniles, adult fish from the hatchery and from the wild have been released into the restored river. We assessed here if a restored river stretch can be used as a natural spawning ground and juvenile production area with the aim of improving genetic diversity of the critically endangered Lake Saimaa salmon. By constructing a pedigree of the released adults, and juveniles sampled from the restored river, we found that the majority of the released adults had produced offspring in the river. We also found that wild-caught spawners that were released into the restored river had much higher reproductive success than hatchery-reared parents that were released into the restored river at the same time. We found no significant differences in genetic diversity between the parent and offspring generations. Meanwhile, relatedness among different groups of adults and juveniles varied a lot. For example, while the hatchery-reared females were on average half-siblings, wild-caught females showed no significant relatedness. This highlights the importance of using pedigree information in planning the conservation and management of endangered populations, especially when artificial propagation is involved.

Fitness effects of assisted gene flow in an endangered salmonid population

“…Ultimately, however, the success of assisted gene flow depends on overcoming the factors that led to the decline of the population. In the case of the Saimaa LS, habitat restoration efforts are in progress and the first results suggest that natural reproduction can be successfully restored (Hatanpää et al, 2021; Leinonen et al, 2020).…”

“…Given the ongoing disruption of natural reproduction, persistence of the population relies heavily on assisted breeding (Hutchings et al, 2019). For this, mature individuals are wild‐caught every year from the population, and their gametes are used to produce offspring for stocking (Leinonen et al, 2020). This practice allows targeted assistance of gene flow.…”

River Damming Impacts on Fish Habitat and Associated Conservation Measures

“…Overall, artificial breeding and release of target fish species is an important measure to recover endangered fish species, maintain genetic diversity, support population expansion, and further preserve the ecosystem integrity of dammed rivers (Le Luyer et al., 2017; Leinonen et al., 2020). However, monitoring data shows that the number of juvenile Chinese sturgeon in the estuary of the Yangtze River has not shown a visible increase (Wei et al., 2004), as there are only small‐scale natural breeding activities in the spawning grounds below the Gezhouba Dam (P. Zhuang et al., 2016).…”

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

“…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). Thus far, there have been few experimental studies on possible early‐environment‐dependent selection patterns for salmonid genotypes (Crespel et al., 2013; Vasemägi et al., 2016).…”