Connectivity is a two‐way street—the need for a holistic approach to fish passage problems in regulated rivers

Abstract

We evaluated the effects of a rehabilitation project, whose goal was to re-establish longitudinal connectivity for anadromous trout in the regulated river Emån. We used a holistic approach, by tagging and following both upstream-migrating spawners (N ¼ 348) and downstream-migrating smolts (N ¼ 80) and kelts as they passed two hydroelectric plants (HEP 2-3) with naturelike fishways.When migrating upstream, 84-88% of the spawners stopped, primarily at spawning grounds, before reaching HEP2. The proportion of stoppers was lower (56%) for fish that had been to the fishways in previous years, indicating that the recolonization rate is likely to increase over time. Of the spawners that approached the fishway at HEP2, 77% rapidly located the fishway situated next to the tail-race, resulting in an attraction efficiency of 81% and a passage efficiency of 95%. The time required to locate the fishway inside the former channel at HEP3 was substantial, but the attraction efficiency (89%) and passage efficiency (97%) were nevertheless high.The kelts swam downstream mainly in spring, using spill gates and the fishways, to swim past HEP2 and 3 and continue downstream to the Baltic Sea. Iteroparity was confirmed by the fact that 20% of the spawners were tagged in previous years. Smolt loss was about 30% for both HEPs, with a higher turbine-induced loss 30% for fish passing through Francis runners than a Kaplan runner. Fifteen per cent of the tagged smolt reached the sea and none of these fish had swum through the Francis runners.It will probably take many years before longitudinal connectivity is fully re-established in the river Emån, due to substantial losses of both upstream-migrating spawners (35% loss) and downstream-migrating smolts (50%) and kelts. In addition, smolt production in areas upstream of HEP3 is far below carrying capacity. Thus, additional measures that not only facilitate movement of upstream spawners, but also reduce mortality and injuries of downstream migrants are urgently needed to create a self-sustaining fish population.

Spatiotemporal patterns of mountain whitefish (Prosopium williamsoni) in response to a restoration of longitudinal connectivity

“…Management of riverine connectivity for fish has largely focused on maintaining upriver spawning migrations of anadromous species (Baxter, 2002;Calles & Greenberg, 2009). Our results, in conjunction with other studies (Baxter, 2002;Benjamin et al, 2014;Radinger & Wolter, 2014), highlight the importance of longitudinal connectivity for mobile nondiadromous fish by allowing them to migrate for purposes other than reproduction.…”

“…Our results, in conjunction with other studies (Baxter, 2002;Benjamin et al, 2014;Radinger & Wolter, 2014), highlight the importance of longitudinal connectivity for mobile nondiadromous fish by allowing them to migrate for purposes other than reproduction. sediment flux), when assessing the effects of natural and artificial obstructions on the longitudinal connectivity of river ecosystems (Calles & Greenberg, 2009;van Leeuwen, Dokk, Haugen, Kiffney, & Museth, 2017;Moore, 2015). sediment flux), when assessing the effects of natural and artificial obstructions on the longitudinal connectivity of river ecosystems (Calles & Greenberg, 2009;van Leeuwen, Dokk, Haugen, Kiffney, & Museth, 2017;Moore, 2015).…”

“…& Layman, 2011), culverts (MacPherson, Sullivan, Foote, & Stevens, 2012) and dams (Couto & Olden, 2018) can constrain both upstream and downstream movement of riverine fish (Calles & Greenberg, 2009). How riverine fish respond to artificial barriers depends on a variety of factors such as location and permeability of the barrier, and fish life history traits especially size and mobility (Cooney & Kwak, 2013).…”

Movements of dead fish in rivers

“…Besides a delay in migration, turbines and other installations at power stations may cause injury and mortality in downstream migrating fish [e.g., [12][13][14]. Telemetry is a useful tool to monitor the behavior of fish during passage of hydropower stations and other sites impacted by anthropogenic activities.…”

Development of a National Fish Passage Database for Canada (CanFishPass): Rationale, Approach, Utility, and Potential Applicability to Other Regions

“…Fishways function as a means of passage around barriers for fish migrating both upstream and downstream (Clay, 1995). These facilities, may also partially restore habitat and river connectivity to fragmented ecosystems (Calles and Greenberg, 2009). There are documented accounts of fishways built in France approximately three hundred years ago, with the first science-based design developed in 220…”