Utility of direct observational methods for assessing competitive interactions between non‐native and native freshwater fishes

Biological invasions are a major threat to global freshwater biodiversity. Competition is a frequent negative interaction between non‐native and native species, and this process is commonly quantified using indirect methods (e.g. dietary overlap, comparison of habitat use/selection). However, direct observation can provide crucial information on these biotic interactions. This paper reviews studies that used direct observational methods to quantify interactions between non‐native and native freshwater fishes. Although laboratory and field studies using direct observations are not common, both have been used to demonstrate impacts by non‐native species on native species. These effects include: (1) altered habitat selection and foraging behaviour and (2) disruption of reproductive behaviour. Direct observational techniques have great potential for quantifying the impacts of non‐natives on native freshwater fishes and can detect negative behavioural impacts that would be missed using indirect methods.