Abstract
Repeat spawners constitute an important component of Atlantic salmon populations, but survival of post-spawning individuals (kelts) are often compromised by anthropogenic structures such as hydropower plants (HPPs). Potential effects of HPPs include migration delays and associated increased energy depletion, which potentially results in increased overall mortality. We combined a detailed 3D hydraulic model with high-resolution 3D tracking of tagged kelts (length 73–104 cm) to obtain estimates of kelt movement through water. These estimates were then used in an energetics model to estimate hourly energy expenditure while negotiating the HPP area. Hourly kelt energy expenditure varied between 0.8 and 10.1 kJ × h−1 and was dependent on kelt length. Degree of additional energy depletion can amount to several percent of remaining energy content (our study indicates 4–5 percentage points) potentially leading to reduced post-spawning survival. In turn, this can nullify the iteroparous breeding strategy and jeopardize long-term stability and persistence of Atlantic salmon populations inhabiting HPP rivers.
Highlights
In Atlantic salmon (Salmo salar) populations, repeat spawners may make up a variable, but significant proportion of the total spawning fish biomass and egg deposition [1,2,3]
River connectivity is fragmented by several hydropower plants (HPPs), fish have particular difficulties negotiating the lowermost intake where water is directed to the Svorkmo HPP
Our study documents that kelt energy reserves are depleted as kelts spend time negotiating anthropogenic structures
Summary
In Atlantic salmon (Salmo salar) populations, repeat spawners may make up a variable, but significant proportion of the total spawning fish biomass and egg deposition [1,2,3]. Modeling studies have shown that repeat spawners may have an important buffering and stabilizing effect on Atlantic salmon populations [6] and that kelt (i.e., post-spawning salmon) survival can be a significant factor for long-term population persistence [7]. Post-spawning, Atlantic salmon kelts can resume some feeding whilst in-river [9], but given the size of available prey items relative to kelt size in most salmon rivers, their ability to restore their energy reserves before returning to sea is very low. Unobstructed river connectivity from spawning areas to the ocean is crucial for survival of the individual kelt and potentially for long-term persistence of local populations as increased mortality can compromise the bet-hedging breeding strategy leaving the population vulnerable to seasons with reproductive failure
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