Environmental threats and conservation implications for Atlantic salmon and brown trout during their critical freshwater phases of spawning, egg development and juvenile emergence

Abstract

Atlantic salmon Salmo salar L. and brown trout Salmo trutta fario L. are species of high socio‐economic and ecological value. Declining populations make them target species of fisheries management. This paper reviews the direct effects of deficient longitudinal connectivity, changes in discharge, high water temperatures, oxygen depletion, changes in water chemistry and increasing loads of fine sediment on the critical life stages of spawning, egg incubation and emergence. It further provides an overview about the basic autecological requirements of Atlantic salmon and brown trout and summarises important thresholds of physico‐chemical tolerances. This collection of information provides important baselines for assessing historical, ongoing and new threats relevant for the management of both species in fresh waters. Critical early‐life stages of both species are almost identical, creating synergies in conservation and restoration. Seaward‐migrating forms are exposed to further stressors, but improving starting conditions can also greatly improve their resilience.

Contribution of a groundwater-influenced hinterland drainage system to the restoration of salmonid spawning grounds at the upper river Danube

“…The larval mortality of the brown trout, on the other hand, was much higher in the HDS with almost 100% of dead larvae in the HESTs. The differences in egg versus larval mortality in the HDS can be explained by the higher oxygen requirement of larvae compared to the eggs in general (Serigstad, 1987;Smialek et al, 2021). In addition, with a potentially limited transport of metabolites due to the clogging, the larval stages were prevented to develop further.…”

“…Recently published results using the HEST, assessing the effects of hydropeaking on spawning grounds, suggest a slightly lower susceptibility of eggs to low oxygen concentrations, with sharply increasing egg mortality when oxygen levels fall under 10 mg L −1 (Pander et al, 2022b, also reviewed for salmonids in Smialek et al, 2021). Nevertheless, lower larval survival can also be attributed to a successive decrease of oxygen availability over the exposure time of the brown trout that happened simultaneously in all spawning grounds.…”

In situ management options to improve crucian carp (Carassius carassius, L.) and brown trout (Salmo trutta, L.) population status in Central Europe: A case study from the Czech Republic

“…It partially suggests that the crucian carp and brown trout populations are very prone to changing environmental conditions, and one extremely dry or cold year could potentially decimate them if the migration between the habitats is impossible or if there is no source population to supplement the sink population (Tarkan et al, 2011; Závorka et al, 2015). If we want to create a wild population of the crucian carp and the brown trout that is self‐sustainable, we must create suitable habitats, connect local populations, and allow for migration and replenishment (Hilderbrand & Kershner, 2000; Smialek et al, 2021).…”

Carryover effects of environmental stressors influence the life performance of brown trout

“…Sedimentation is a common stressor within natural salmon redds; it reduces the circulation of water in the gravel bed and hence oxygen availability, or physically prevents the fry from emerging from the gravel bed. The direct effects of suspended and deposited fine sediment on the early life stages of salmonids are relatively well known (most recently reviewed by Smialek et al, 2021). However, evidence for the deleterious carryover effects of embryonic oxygen depletion or a simplified habitat caused by sedimentation is scarce.…”