Does ice matter? Site fidelity and movements by Atlantic salmon (Salmo salar L.) parr during winter in a substrate enhanced river reach

Abstract

In-stream habitat enhancement is a common remedial action in rivers where degradation/lack of suitable fish habitat can be diagnosed. However, post-project monitoring to assess the response of the biota to modification is rare particularly during winter. We conducted in situ monitoring during the winters of [2004][2005][2006] in the regulated Dalåa River, central Norway, in order to determine if winter habitat requirements of Atlantic salmon (Salmo salar L.) parr were realized in an enhanced (substrate and mesohabitat modification) reach. In total, 140 parr were marked with passive integrated transponder (PIT) tags and the fish were followed by carrying out active tracking surveys under variable ice conditions throughout the winter. Highest emigration (44%) occurred before ice formation started. Emigration was reduced after ice formed and was largely offset by parr re-entering the enhanced area. Dispersal into the non-enhanced, small substrate control area was observed only when the study reach was ice covered, and no parr were subsequently encountered in the control section after ice had melted. In the enhanced area, declining water temperature and surface ice conditions did not affect the spatial distribution of the resident salmon parr at the studied scale. Areas with 'solid' anchor ice precluded access for salmon parr whilst areas with 'patchy' anchor were used throughout the winter. Our results indicate that surface ice creates conditions that allow salmon parr to use stream habitats that otherwise provide only a limited amount of in-stream cover. Ice processes should be taken into consideration when habitat enhancement projects are carried out and subsequently assessed for effectiveness.

Effects of Changes in Arctic Lake and River Ice

“…Through the modifications of ice regimes, climate change will have a profound influence on the behavior and biological response of stream biota (Huusko et al 2007) and, therefore, will play a central role in their growth, survival and reproduction. Surface ice creates shelter habitats for fish in areas that are too exposed for use during open-water periods Linnansaari et al 2009). A reduction in such ice shelter will, therefore, lead to a loss of suitable winter habitat during the period when the water temperature has not yet reached the level to cause changes in fish habitat use.…”

“…Energy deficiency is important to winter survival, and a change in ice cover can reduce their ability to survive winter (Finstad et al 2004b). Movement of salmonids to overwintering habitats mostly occurs prior to ice formation in rivers; however, local movements between habitats also occur after ice formation (Jakober et al 1998;Linnansaari et al 2009). Extensive anchor ice precludes access, whereas patchy anchor ice and ice-covered areas appear to be preferred (Linnansaari et al 2009).…”

“…Movement of salmonids to overwintering habitats mostly occurs prior to ice formation in rivers; however, local movements between habitats also occur after ice formation (Jakober et al 1998;Linnansaari et al 2009). Extensive anchor ice precludes access, whereas patchy anchor ice and ice-covered areas appear to be preferred (Linnansaari et al 2009). Accordingly, reduced ice cover or duration on river systems is likely to result in a tradeoff between increased habitat (or access to such) with that habitat being less preferred due to lack of surface ice cover.…”

Stress responses of juvenile brown trout under winter conditions in a laboratory stream

“…Access to shelter in low embedded bottom substrates with stream wood is a key habitat factor for overwintering juvenile salmonids (Finstad et al, 2007;Stickler et al, 2008;Linnansaari et al, 2009), and in its absence, surface ice may provide overhead cover (Linnansaari et al, 2009;Watz et al, 2016). This study showed that, when denied access to winter shelter, juvenile brown trout display a stress response, mainly by increasing their ventilation frequency.…”

An Assessment of Ice Effects on Indices for Hydrological Alteration in Flow Regimes

“…If ice is a case in climate change studies, the combination of changes in temperature and the current indexes of ice-induced flow changes could be used to assess future ice effects. Linnansaari et al [44] showed that ice had an effect on how Atlantic salmon utilized an artificial habitat in a regulated river, and unpublished data from the same river shows significant icedriven modification to the water level and thereby the function of the habitat in the same river. The Figure 8.…”