What is “fallback”?: metrics needed to assess telemetry tag effects on anadromous fish behavior

Abstract

Telemetry has allowed researchers to document the upstream migrations of anadromous fish in freshwater. In many anadromous alosine telemetry studies, researchers use downstream movements (''fallback'') as a behavioral field bioassay for adverse tag effects. However, these downstream movements have not been uniformly reported or interpreted. We quantified movement trajectories of radio-tagged anadromous alewives (Alosa pseudoharengus) in the Ipswich River, Massachusetts (USA) and tested blood chemistry of tagged and untagged fish held 24 h. A diverse repertoire of movements was observed, which could be quantified using (a) direction of initial movements, (b) timing, and (c) characteristics of bouts of coupled upstream and downstream movements (e.g., direction, distance, duration, and speed). Because downstream movements of individual fish were almost always made in combination with upstream movements, these should be examined together. Several of the movement patterns described here could fall under the traditional definition of ''fallback'' but were not necessarily aberrant. Because superficially similar movements could have quite different interpretations, post-tagging trajectories need more precise definitions. The set of metrics we propose here will help quantify tag effects in the field, and provide the basis for a conceptual framework that helps define the complicated behaviors seen in telemetry studies on alewives and other fish in the field.

Spawning dynamics of American shad (Alosa sapidissima) in the St. Lawrence River, Canada–USA

“…6. In the case of migrating alewife radio tagged and tracked in the Ipswich River (Massachusetts, USA), bouts of downstream movements following periods of upstream migration were relatively common (Frank et al 2009). Upstream (FSL-FOIN, n = 26, P = 0.016), midstream (N12, n = 50, P < 0.001; S13, n = 50, P < 0.001; S17, n = 52, P < 0.001) and downstream (N18, n = 52, P = 0.002; S20, n = 49, P = 0.025; N21, n = 81, P = 0.014).…”

Thermal exposure of adult Chinook salmon in the Willamette River basin

“…Additional among-individual differences were attributable to passage times in the main stem Willamette, with some fish requiring several weeks to reach tributaries. Some appeared to delay migration near Willamette Falls, but it is unknown whether the delay was an artifact of fish capture and handling (e.g., Frank et al, 2009;Caudill et al, 2014), a response to environmental conditions, or due to some combination of factors. Regardless, behavioral differences among fish and differences in recapture timing had a much greater influence on total DDs than the date that salmon were collected at Willamette Falls.…”

Poor oxic conditions in a large estuary reduce connectivity from marine to freshwater habitats of a diadromous fish

“…Moreover, short term downstream movements associated with upstream movements were almost systematically observed, whether just after the release or after a long time. Although it can be surprising for an anadromous fish, it may represent the normal diversity of movements and they cannot be a priori excluded from the dataset (Frank et al, 2009). Rare patterns aside (i.e., individual patterns related to unknown methodological problems such as tag loss, catching/tagging induced mortality or technical dysfunctions in the acoustic system), we do not have evidence that fish behav- iour was strongly modified although this cannot be totally ruled out.…”

“…The first step often displayed bouts of adjacent upstream and downstream movements. Such short term downstream movements were not necessarily an adverse reaction to tagging and may represent the normal diversity of movements (Frank et al, 2009). Consequently, they cannot be a priori excluded from the dataset.…”