Tracking anadromous fish over successive freshwater migrations reveals the influence of tagging effect, previous success, and abiotic factors on upstream passage over barriers

Abstract

Predicting and mitigating the impact of anthropogenic barriers on migratory fish requires an understanding of the individual and environmental factors that influence barrier passage. Here, the upstream spawning migrations of iteroparous twaite shad Alosa fallax were investigated over three successive spawning migrations in a highly fragmented river basin using passive acoustic telemetry (n=184). More fish approached and passed barriers in the lower river reaches than further upstream, with the median cumulative weir passage time (IQR) of 4.6 (1.8 - 9.2) days representing 18% of their time in river. Returning fish in their second year had significantly higher weir passage rates than in their tagging year, with passage rates also positively influenced by previous passage success. Higher water temperature and river level also had positive impacts on passage rates. Lower weir passage rates by newly tagged individuals suggests that reliance on within-year passage estimates in telemetry-based barrier impact assessments could result in conservative results, while higher passage rates of previously successful versus unsuccessful individuals suggests a conserved motivation and/or inherent ability to pass barriers.

Tagger effects in aquatic telemetry: Short‐term and delayed effects of surgery in Atlantic Salmon smolts

“…For example, Davies et al. (2023) found that Twaite Shad Alosa fallax that were tagged a year prior had better weir passage performance than those that were tagged in the year of the performance trial. Similarly, Daniels et al.…”

“…Although few studies have paired laboratory observations of tagger effects with field evaluations, a growing body of work continues to reveal lingering effects of tagging procedures in the wild. For example, Davies et al (2023) found that Twaite Shad Alosa fallax that were tagged a year prior had better weir passage performance than those that were tagged in the year of the performance trial. Similarly, Daniels et al (2021) documented improved performance (survival and migration speed) for fish that were tagged 75 days prior to release relative to those that were tagged 24 h prior to release.…”

“…Although direct observation in a laboratory can provide advantages over field-based studies (control over conditions, fish densities, ease of monitoring outcomes), it is not always clear how these results translate to fish performance in the wild (Peake et al 1997). The adverse effects of tagging procedures or tag burdens can be exacerbated by predators, challenging environmental conditions, stressful sampling methods, or stochastic events that are not present in the laboratory (Chapman et al 2020;Davies et al 2023). Some laboratory studies report little disruption to the survival, growth, or swimming performance of salmonids when appropriately sized transmitters are used (Brown et al 1999;Ammann et al 2013); however, it is unclear whether the results would be similar had fish performance been assessed in the wild under challenging conditions.…”

“…2020; Davies et al. 2023). Some laboratory studies report little disruption to the survival, growth, or swimming performance of salmonids when appropriately sized transmitters are used (Brown et al.…”

Bidirectional connectivity in fishways: A mitigation for impacts on fish migration of small hydropower facilities

“…An analysis of bidirectional connectivity should consider factors such as the number of fish and seasonality during the monitoring period. Short monitoring periods and the use of a low number of fish can influence results owing to the seasonal changes in river discharge (García‐Vega, Sanz‐Ronda & Fuentes‐Pérez, 2017; García‐Vega et al, 2021), the partial migration behaviour of some species (Alexandre et al, 2016; Branco et al, 2017; Bravo‐Córdoba et al, 2018a), the handling and tagging effect (Thiem et al, 2011; Radinger et al, 2019; Davies et al, 2023) or other factors such as fish mortality during the monitoring period. For instance, 27 barbel started providing data 1 year after their tagging.…”