The impact of a small-scale riverine obstacle on the upstream migration of Atlantic Salmon

Hydrobiologia, Sep 2017

The behaviour of returning Salmo salar (Linnaeus, 1758) approaching, and attempting to pass low-head weirs remains relatively unknown. A radio telemetry array was created at a low-head weir to enable the behaviour of S. salar (n = 120) to be observed as they approached and attempted to pass the barrier. The majority of fish successfully passed the barrier on their first or second attempt, some individuals required 11 attempts prior to successful passage occurring. Mean delay at the barrier per fish was 47.8 h (±SD 132.0 h), range 15 min to 31 days. Passage success on a fish’s initial attempt was significantly predicted by the amount of searching a fish undertook, fork length, and fat content. Fish were more likely to have a successful first passage attempt if it was smaller with a low fat content and exerted a greater effort in searching for a passage channel. Small-scale barriers cause delays and increased energy expenditure in migrating fish. Barriers may be creating an anthropogenic selection pressure for traits which enable passage success. The impact of a delay at a barrier and increased energy expenditure on reproduction and gonad development remains unknown but is likely to be negatively impacted by instream anthropogenic structures.

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The impact of a small-scale riverine obstacle on the upstream migration of Atlantic Salmon

Hydrobiologia The impact of a small-scale riverine obstacle on the upstream migration of Atlantic Salmon M. Newton 0 1 . J. A. Dodd . J. Barry . P. Boylan . C. E. Adams 0 1 0 P. Boylan Loughs Agency , 22 Victoria Road, Derry BT47 2AB, Northern Ireland , UK 1 M. Newton (&) J. A. Dodd J. Barry C. E. Adams Scottish Centre for Ecology & the Natural Environment, IBAHCM, University of Glasgow , Rowardennan, Glasgow G63 0AW , UK The behaviour of returning Salmo salar (Linnaeus, 1758) approaching, and attempting to pass low-head weirs remains relatively unknown. A radio telemetry array was created at a low-head weir to enable the behaviour of S. salar (n = 120) to be observed as they approached and attempted to pass the barrier. The majority of fish successfully passed the barrier on their first or second attempt, some individuals required 11 attempts prior to successful passage occurring. Mean delay at the barrier per fish was 47.8 h (±SD 132.0 h), range 15 min to 31 days. Passage success on a fish's initial attempt was significantly predicted by the amount of searching a fish undertook, fork length, and fat content. Fish were more likely to have a successful first passage attempt if it was smaller with a low fat content and exerted a greater effort in searching for a passage channel. Small-scale barriers cause delays and increased energy expenditure in migrating fish. Barriers may be creating an anthropogenic selection pressure for Handling editor: Michael Power traits which enable passage success. The impact of a delay at a barrier and increased energy expenditure on reproduction and gonad development remains unknown but is likely to be negatively impacted by instream anthropogenic structures. Upstream migration; Behaviour; Telemetry; Fish passage; Anthropogenic selection Introduction The loss and fragmentation of habitat truncate movement, reduce connectivity, and often precede the decline and extirpation of a species (Ceballos & Ehrlich, 2002; Baguette et al., 2013) . In rivers, habitat connectivity is primarily longitudinal and in general confined to the river corridor. A single impoundment thus has the potential to isolate adjacent habitats completely for many species (Jager et al., 2001; Cote et al., 2009; Branco et al., 2012) . In-river structures, both natural and artificial such as waterfalls and weirs can have major impacts on species that have multiple, life stage dependent, aquatic habitat requirements. Highly mobile anadromous and catadromous fish, which have a complex life-cycle, are among some of the species most affected. The Atlantic salmon (Salmo salar Linnaeus, 1758) is one species shown to be highly vulnerable to river corridor fragmentation (Baras et al., 1994; Lucas & Frear, 1997; Jager et al., 2001; O’Hanley & Tomberlin, 2005; Kemp et al., 2008) . The impacts of large-scale obstacles ([5 m hydraulic head height), particularly their effect on fish migrations, are well documented (Gowans et al., 2003; Antonio et al., 2007; Meixler et al., 2009; Branco et al., 2012) . Considerable effort has been made to mitigate the effects of river obstacles through the development of fish passes, which aim to facilitate the upstream and downstream migration of individuals around or through obstacles (Larinier, 1998; Guiny et al., 2005; Bunt et al., 2012) . The efficiency of such structures is however often questioned; flow conditions such as water velocity and depth within the pass itself are not always conducive to upstream passage of fish (Thorstad et al., 2008; Noonan et al., 2012; Cooke & Hinch, 2013) . For example, the addition of fish screens at the 86-m-high Pitlochry Dam (Scotland) increased the proportion of fish ascending the dam from 45% of fish which attempted (Webb, 1990) up to 100% by guiding fish away from the turbine entrances (Gowans et al., 1999) . Fish pass facilities are generally built at large, high head impoundments. Low-head obstacles (defined here as \5 m hydraulic head height), in general, lack such passage structures, relying on the fish’s own ability to successfully ascend them. In Europe, there is a legislative framework requiring EU member states to ensure fish passage and are outlined within the EU Water Framework Directive (Directive 2000/60/EC), and EU Eel legislation (EC No. 1100/2007). It is estimated that within England and Wales there are some 25,000 in-river obstructions, of which 3,000 are significant and require mitigation in order to meet the ecological objectives set out in these directives (Environment Agency, 2009) . There is a paucity of knowledge on the effects of low-head obstacles; it is likely that they may also present serious deleterious impacts for fish populations through habitat fragmentation (Lucas & Frear, 1997; Ovidio & Philippart, 2002; O’Connor et al., 2006) . Determining the likelihood of fish passage at riverine obstacles is highly complex due to variable swimming and leaping capabilities of fish of different sizes and sp (...truncated)


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M. Newton, J. A. Dodd, J. Barry, P. Boylan, C. E. Adams. The impact of a small-scale riverine obstacle on the upstream migration of Atlantic Salmon, Hydrobiologia, 2018, pp. 251-264, Volume 806, Issue 1, DOI: 10.1007/s10750-017-3364-3