Abstract
Environmental fluctuations exert strong control on behavior, survival, and fitness of stream biota. Technical improvements increasingly allow for tracking the response of large numbers of individuals to environmental fluctuations, for instance, by remote detection of animals equipped with PIT (passive integrated transponder) tags. PIT tags were implanted into 393 juvenile and adult brown trout Salmo trutta L. and European sculpin Cottus gobio L. in a boreal stream subjected to considerable ice formation. With weekly trackings over 6 months, we quantified apparent survival and detection probability in relation to biological, environmental, and methodological factors. Individuals with a higher physical condition in autumn showed a higher apparent survival; this pattern was consistent across all species and age classes. Detection probability decreased with increasing thickness of the surface ice layer; this effect was most pronounced for juvenile trout and benthic‐living sculpin, both tagged with smaller‐sized tags. Detection probability was reduced in structurally complex habitats. Our study demonstrates that apparent survival and particularly detection probability may show pronounced spatiotemporal variation. In order to compare results from different sampling occasions and sites, a good knowledge of the study site and of the regulating factors is crucial.
Highlights
River ecosystems are highly dynamic, with environmental conditions undergoing more frequent and more rapid spatiotemporal fluctuations than in terrestrial, marine, or lentic habitats (Power 2001)
Our results show that detection probability decreased with growing ice volume and was smallest in structurally complex reaches
One-fourth of all adult trout, but less than 10% of the juvenile trout and sculpin were transients
Summary
River ecosystems are highly dynamic, with environmental conditions undergoing more frequent and more rapid spatiotemporal fluctuations than in terrestrial, marine, or lentic habitats (Power 2001). Environmental fluctuations shape riverine habitats and exert strong control on behavior, survival, and fitness of stream biota (Resh et al 1988). In high-latitude and high-altitude rivers, environmental fluctuations follow a pronounced seasonal pattern. Winter is generally regarded as a bottleneck for stream biota (Heggenes et al 1993), that is, as a period of increased susceptibility and mortality (Power et al 1993). The winter season has been understudied, among others due to methodological difficulties under harsh environmental conditions (Huusko et al 2007; Weber et al 2013)
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