No Nets, No Shocks, No Problem: Assessing Replicability and Disturbance Effects in Fish Monitoring Using Remote Video Cameras in Low Order Streams

Conventional fish population sampling methods such as electrofishing and netting, pose risks to fish and are often restricted to small, shallow headwater streams—especially where endangered species may be present. Additionally, non-capture surveying (e.g., snorkelling) can disturb fish and make observation more challenging. This study evaluates the effectiveness and reproducibility of remote underwater video (RUV) surveys in a shallow (<0.5 m deep), freshwater stream. Additionally, fish response to disturbances (e.g., shadows, noise, surface disruptions) were characterized. Fish abundance was estimated by maxN (maximum number of individuals observed in a single frame) and used multiple cameras placed in the same habitat (pool). Findings indicated a high consistency in maxN when fish numbers were low (<5 individuals), with increasing variability at higher numbers (>15 individuals). This suggests that single camera setups can reliably detect minimum abundance. Fish responses to four disturbances (e.g., shadows, noise, surface disruptions, mink) were noted throughout. Typically, these responses were short-lived, with fish returning to pre-disturbance maxN values within minutes, with the most significant response to researcher-induced disturbance occurring immediately after RUV deployment. Overall, RUVs proved effective for passive, non-capture fish monitoring in shallow, sensitive habitats, producing replicable data with minimal impact caused by researcher disturbance. This technique can be added to our toolboxes for studying small-bodied fishes in challenging environments.