Efficiency of fishways and impact of dams on the migration of grayling and brown trout in the Glomma river system, south‐eastern Norway

Abstract

This study was carried out to assess the efficiency of eight fishways constructed in connection with hydroelectric dams in the Glomma river system in south-eastern Norway. The fishways were of the pool and weir type, except for one which was of the counter current (Denil) type, and had a discharge of 0.5-1.0 m3/s. During 1985-8 3077 grayling and 2995 brown trout were captured in traps in the fishways, measured and floy-tagged before being released in the river upstream of the fishways. The number of fish captured in two of the fishways were compared with estimated fish stocks in the areas around the fishways. Migrations began in May or June when the water temperature was > 5-6°C. Spawning migration of grayling occurred in May. During May more than 200 grayling may enter a single fishway within a week. In other fishways grayling occur only sporadically before late June or early July, when they migrate upstream to feed. Brown trout migrate during late spring, summer and autumn. The spawning migration takes place more or less during the whole summer, but mostly in late July and August. Immature brown trout also pass through the fishways, with a peak in October in three fishways. This migration is probably an ascending emigration from recruitment areas located downstream of these fishways. The efficiency of these fishways appears low, as the number of fish ascending was less than 2% of the estimated stock within the stretches where 90% of the recaptures occurred. The discharge in the fishway relative to the total discharge seemed to be of great importance, and to achieve efficient fishways they should be constructed for higher discharges, compared with river discharge, than the fishways in this area. The longest migration of grayling was 100 km, whereas the longest migration of brown trout was 122 km. The fish seemed to exploit shorter river stretches in areas influenced by several dams/fishways than fish in an area influenced by only one dam. KEY WORDS Migration timing Distances Purpose Trends

Evaluation of nature-like fishways for re-establishing connectivity in fragmented salmonid populations in the River Emån

“…The high passage efficiency we observed indicates that the fishways at Finsjö are not particularly physically demanding for strong swimming species such as brown trout, especially when considering that brown trout successfully ascended the fishways at temperatures <2 C while maintaining a high mean rate of ascent (only decreasing slightly with temperature). Many fishways are physically demanding, and fish, being poikilothermic, generally do not attempt to pass fishways at temperatures below 5-6 C (Gowans et al, 1999;Jensen and Aass, 1995;Laine et al, 1998;Linlokken, 1993;Thorstad et al, 2003). Furthermore, the mean rate of ascent for brown trout in the Finsjö fishways (c. 180-190 m h À1 ) is higher than reported from other studies (Aarestrup et al, 2003;Gowans et al, 1999).…”

“…The fish either returned downstream or remained between the two fishways, where there was no spawning habitat available. Problems associated with poor attraction efficiencies for Atlantic salmon and brown trout have been related to insufficient attraction flows (Aarestrup et al, 2003;Arnekleiv and Kraabøl, 1996;Jensen and Aass, 1995;Laine et al, 2002;Linlokken, 1993;Rivinoja et al, 2001;Thorstad et al, 2003), and to inappropriate design or location of the entrances of the fishways (Gowans et al, 1999;Laine et al, 1998Laine et al, , 2002. For our study, we cannot be certain why the attraction is low.…”

“…Evaluations have been performed for other types of fishways and for many different species (Bunt et al, 2001;Gowans et al, 1999Gowans et al, , 2003Linlokken, 1993;Lucas et al, 1999), but only a handful have looked at naturelike fishways (Aarestrup et al, 2003;Jungwirth, 1996;Schmutz et al, 1998). Most have been focused strictly on the efficiency of fishways, whereas few have looked at the overall effect of re-establishing connectivity, e.g.…”

Ichthyological Evaluation of Fish Passes Constructed in Lithuania

“…It has been established that the efficiency of fish passes depends upon their type, migrating fish species, environmental conditions and other factors (Katopodis & Rajaratnam 1983). Up till now, the data on the efficiency of fish passes presented in scientific publications have been very scarce (Web 1990;Travade & Larinier 1992;Linokken 1993;Aprahamian et al 1996). The aim of this paper is to overview the fish passes constructed at the dams on Lithuanian rivers and to estimate their efficiency on the basis of research carried out in the period 19981999.…”

Restoring Ecological Connectivity in Rivers to Improve Conditions for Anadromous Brown Trout (Salmo trutta)

“…These passage efficiencies are high in comparison with other studies (Jungwirth 1996, Schmutz et al 1998, Aarestrup et al 2003) not only for brown trout but also for non-salmonid species (Calles & Greenberg 2007). This suggests that the passageways at Finsjö are not particularly physically demanding for trout, especially when considering that trout successfully ascended the passageways at water temperatures as low as 2 • C, and fish, being poikilothermic, generally do not attempt to pass passageways at temperatures below 5-6 • C (Linlokken 1993, Jensen & Aass 1995, Laine et al 1998, Gowans et al 1999, Thorstad et al 2003.…”