Influence of personality traits on the response of a modelled population of stream-dwelling rainbow trout (Oncorhynchus mykiss) to microplastics consumption

Microplastics in freshwater habitats are consumed by fish, including stream-dwelling salmonids, which can alter food consumption or negatively affect swimming and foraging behaviour. As population-level effects are largely unknown, a population of stream-dwelling rainbow trout ( Oncorhynchus mykiss ) was simulated using the agent-based model ‘inSTREAM 7’ to model population-level effects (biomass) of behavioural changes caused by microplastics consumption. Individual fish were assigned all possible combinations of two personality traits (dominance, boldness/shyness) and consumed microplastics while foraging; and their microplastics consumption, body length and abundance were tracked for three different life stages (fry, juvenile, adult) for a period of 10 years. Three scenarios were explored: a low-impact scenario with microplastics causing decreased food consumption, a medium-impact scenario which added lower swimming speed and a high-impact scenario with additional reductions of foraging efficiency. Each scenario was tested for microplastics concentrations of 0%, 1% (i.e. current levels) and 3% (i.e. future levels) of drift food. Overall, microplastics consumption did not strongly affect trout abundance. Dominant adult trout consumed disproportionally more microplastics than all other fish, especially at higher microplastic concentrations. Personality traits influenced the response of the trout to microplastics ingestion: dominant and bold adults were smaller when food consumption was reduced; shy and subordinate adults were smaller when swimming speed was lowered; and all dominant adults, regardless of boldness, were smaller when foraging efficiency was impeded, with dominant and bold fry also less abundant in this scenario. However, effects on fish body length were only found at microplastic concentrations of 3%, indicating these outcomes can be prevented, as current levels of microplastics pollution are below this concentration. Nevertheless, microplastics ingestion may become an additional stressor that interacts with the myriad of mostly anthropogenic stressors that already affect wild salmonid populations.