Passive Integrated Transponder (PIT) Tracking versus Snorkeling: Quantification of Fright Bias and Comparison of Techniques in Habitat Use Studies

Abstract

AbstractQuantitative assessment of day and night fright bias (i.e., flight response) of Atlantic Salmon Salmo salar parr during passive integrated transponder (PIT) tracking surveys was carried out during summer (water temperature, 18–22°C) and autumn (water temperature, <3°C). In addition, PIT‐tracking and snorkeling survey methods were compared to assess whether the two methods result in similar habitat use data for Atlantic Salmon parr at the same study site. During summer fright bias surveys, 0–15% of parr displayed a flight response to PIT‐tracking techniques in the riffle–run–pool habitat types commonly used by Atlantic Salmon parr; 24–25% displayed a flight response in relatively unused, shallow, calm water habitats. No flight responses were observed in autumn surveys with colder water temperatures in any habitat type. Larger numbers of salmon parr were observed using PIT tracking regardless of stream discharge. Furthermore, significant differences in habitat use frequency curves between these two methods were observed due largely to higher Atlantic Salmon parr abundances being detected by PIT tracking in shallow water depths at lower discharges and the ability to detect inactive salmon parr hiding within the substrate. PIT tracking was found to be a valid method for habitat assessment and provides more reliable habitat use data than traditional snorkeling methods in small streams.