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

Abstract

Carryover effects of environmental stressors occur when experiences of the environment in earlier life stages or seasons influence the performance of individuals later in life. These can be especially critical for species that have diverse developmental transition periods in their life cycle, such as salmonid fish. Sublethal changes in metabolism, size, or growth experienced in early life stages may have a long‐lasting effect on the subsequent life performance of these species, but very few studies have formally tested these changes in relation to environmental stressors. Here, we investigated whether different types of fine sediment result in carryover effects that change the life performance of migratory brown trout. First, we manipulated the early habitat conditions of brown trout through the life stages from egg to fry by incubating them in varying substrate treatments (i.e., gravel without added sediment, gravel with added fine sand, and gravel with added organic matter). Exposure to fine sediment during early development had serious effects on the metabolism, size, escape responses, timing of emergence, and potential survival of early life stages. These carryover effects were persistent and remained present over the critical life shift from relying on parentally provided resources as immobile eggs to independent exogenous feeding as parr. Second, fish were relocated as parr to either their original or different treatment environments and their metabolism, size, and growth were reanalyzed. The effects of environmental stress were observed later in their life cycle when fry from the gravel treatment were relocated to sand or organic‐rich treatments. These were found to be significantly smaller in size and had a higher metabolic rate than fry maintained in their original treatment environment. Together, our study experimentally demonstrated that the carryover effects of environmental stressors experienced in early stages may influence the fitness outcomes of migratory fish later in life. We suggest that sublethal environmental stressors should be better considered in restoration schemes and management strategies to reverse the current trend of declining salmonid populations.

Spatial and life history variation in a trait-based species vulnerability and impact model

“…While overall vulnerability scores were similar, by dividing the green sea turtle life history into four stages, we identified higher vulnerabilities to specific stressors (e.g., inorganic pollution and marine heat waves) during earlier rather than later life stages. Mitigation of stressor impacts in early life stages is critical to avoid potentially harmful carry-over effects, which occur when an individual’s previous environmental experiences affects their current performance [ 28 , 67 ]. Carry-over effects may have negative effects, such as long-term sublethal effects that reduce resilience to future stressors.…”

“…Carry-over effects may have negative effects, such as long-term sublethal effects that reduce resilience to future stressors. However, carry-over effects may also have positive effects, whereby individuals become more resilient to future stressors resulting in enhanced survival and reproductive output [ 28 , 67 ]. Carry-over effects may occur from as early as the egg stage in turtles [ 28 ].…”

“…However, carry-over effects may also have positive effects, whereby individuals become more resilient to future stressors resulting in enhanced survival and reproductive output [28,67]. Carry-over effects may occur from as early as the egg stage in turtles [28]. For example, warming incubation temperatures of sea turtle eggs can impact individual behaviour, physiology, morphology, and performance, and may have long-term impacts on sex ratios resulting in reduced species or population fitness [68][69][70].…”

“…For instance, carry-over effects from a stressor at one life stage may result in higher vulnerability at a subsequent stage, which is not captured in an aggregated trait value set [24][25][26][27]. One study found even minor differences in early life stage habitat conditions, such as coarseness of sedimentation in nursery areas, can result in reduced metabolic rate and size of a species later in life, thereby altering a species vulnerability to stressors in later life stages [28]. Thus, identifying stressors that threaten individual life stages, instead of a species as a whole, could lead to more effective conservation actions [29,30].…”

Effects of pre‐winter cortisol exposure on condition, diet, and morphology of wild juvenile brown trout (Salmo trutta)

“…Many juvenile fish are particularly susceptible to overwinter mortality, with fish size and energetic condition influencing survival (Cunjak, 1996; Gosselin et al, 2021; Hurst, 2007; Shuter et al, 2012). However, fewer studies have investigated effects of stressors on those individuals that survive the event (i.e., sublethal impacts; e.g., Louhi et al, 2023; Saboret & Ingram, 2019).…”