Colonization of a temperate river by mobile fish following habitat reconnection

Abstract

Mobile species are particularly affected by artificial barriers requiring large investments to restore connectivity. However, few large-scale, long-term studies have investigated the ecological outcomes of restoring connectivity for these species. Our study, spanning 15-20 years, quantified response trajectories, which represent temporal trends following disturbance, of three native salmonids colonizing 20 km of protected habitat following restoration of fish passage at Landsburg Dam, Cedar River, WA, in 2003. Built in 1901, the dam blocked the upriver movement of native anadromous coho and Chinook salmon and nonanadromous mountain whitefish for 102 years. Restoration effectiveness was also assessed by comparing temporal trends in freshwater productivity of juvenile coho and Chinook salmon in the Cedar River after restoration to a nearby undammed subbasin. We also compared summer densities of juvenile coho and Chinook salmon, and mountain whitefish above the dam measured a decade after restoration to undammed reference systems. Anadromous salmon and nonanadromous mountain whitefish populations increased linearly or nonlinearly following restoration. The positive, asymptotic response represented by adult Chinook salmon counts indicates a slowing in population recovery rate, plateauing a decade after restoration. In contrast, annual abundance of adult coho salmon increased at a constant rate, indicating additional capacity 15 years post-restoration. Salmonid compositional diversity, driven largely by juvenile coho salmon, also increased nonlinearly, plateauing in a decade. We observed substantial spatial variation in the temporal response, as juvenile coho salmon and mountain whitefish population expansion slowed linearly with upstream distance from the restoration site. There was evidence that some of the annual variation in salmonid biomass in summer was a result of discharge variability in winter and spring, with biomass declining as flow variability increased. Species reintroduction and establishment had no discernible effect on stream-rearing salmonids living above

Adfluvial migration and passage of Steelhead before and after dam removal at a major Great Lakes tributary

“…Those that have, primarily described changes in the river community using perhaps more basic metrics such as community composition, species richness, abundance or density (e.g., Catalano et al, 2007;Stanley et al, 2007;Maloney et al, 2008;Burroughs et al, 2010;Kornis et al, 2015;Magilligan et al, 2016;Poulos and Chernoff, 2017;Bubb et al, 2021). Furthermore, such studies often used methods that have provided information regarding only a snap-shot in time and/or space such as electrofishing, hydroacoustics, snorkeling or eDNA (e.g., Dorobek et al, 2015;Hogg et al, 2015;Duda et al, 2020;Scherelis et al, 2020;Huang et al, 2023;Jones et al, 2023;Kiffney et al, 2023;Whittum et al, 2023) and were often narrowly-scoped temporally, spatially or both (Bellmore et al, 2017;Foley et al, 2017;Whittum et al, 2023). These methods may not fully reflect fish responses, and do not reveal any direct information about fish movement and timing.…”