Recommendations for monitoring freshwater fishes in river restoration plans: A wasted opportunity for assessing impact

Abstract

1. Many human activities in and on rivers cause the loss of freshwater biodiversity, especially fish, which now are one of the most endangered vertebrate groups. River fragmentation caused by the construction of dams is one of the main threats to fish species. In Spain, which has the highest number of dams per square kilometre in the world, more than half of all fish species are threatened by these constructions. The government has initiated the National Strategy for River Restoration, a plan to restore rivers and preserve their inhabitants, which includes the removal of dams.2. An information search and query was conducted to determine if fish monitoring was performed before and after dam removal, and the result was negative. Therefore, an assessment of the effects of dam removal on fish communities at a large spatial scale was not possible.Instead, an analysis was carried out to measure the effects of dam removal on river connectivity using a geometric network.3. The analysis of river connectivity improvement showed that 66% of removed dams had one or more dams less than 5 km away. The removal of dams increased the connected river length by an average of 6.4 km per dam removed, with the range varying between 1.04 km and 9.48 km, depending on the river basin. 4. These results show that, although monitoring programmes are strongly recommended after restoration actions, they are not usually performed. This is a wasted opportunity to gather large datasets to understand better the effects of human actions on fish communities and on rivers.5. River connectivity results may reflect a demolition strategy based more on economic and social opportunism rather than on ecological considerations. It is strongly recommended that dam removal plans should be based on ecological selection methods to achieve greater river improvements with less investment.

Stocking impact, population structure and conservation of wild brown trout populations in inner Galicia (NW Spain), an unstable hydrologic region

“…Although the area studied here is located in the Atlantic region, its climate is defined as Mediterranean subtype Csb, similar to that present in the Mediterranean drainages with the most unstable environmental conditions for the species (Vera et al, ). Moreover, even though the studied region is within the anadromy range of S. trutta (Bouza et al, ), an important human‐mediated hydrological perturbation occurs (Rodeles, Galicia, & Miranda, ), which increases population isolation. In this regard, significant correlations between genetic introgression and environmental variables were found in the present study.…”

Structural microhabitat use by endemic cyprinids in a Mediterranean‐type river: Implications for restoration practices

“…Depth, velocity and substratum were also key variables for barbel and nase, particularly the latter, which displayed shifts to fasterflowing positions with coarser substrata during the spring. Implementation of all these measures should be followed by long-term monitoring programmes (Rodeles, Galicia, & Miranda, 2017) so that large datasets can be assembled to understand better the effects of restoration practices on native cyprinid fish assemblages of Mediterranean rivers. These substrata (particularly larger pebbles and boulders) should ideally be placed below the water surface to prevent the rehabilitated section turning into a feeding area for fish-eating birds, such as herons (Cowx & Welcomme, 1998).…”

“…These substrata (particularly larger pebbles and boulders) should ideally be placed below the water surface to prevent the rehabilitated section turning into a feeding area for fish-eating birds, such as herons (Cowx & Welcomme, 1998). Implementation of all these measures should be followed by long-term monitoring programmes (Rodeles, Galicia, & Miranda, 2017) so that large datasets can be assembled to understand better the effects of restoration practices on native cyprinid fish assemblages of Mediterranean rivers.…”

Editorial: Measuring river restoration success: Are we missing the boat?

“…David and Hamer () demonstrated the rapid gains that can be achieved by relieving single fish passage barriers to open up large areas of upstream forested stream habitat for colonization by migratory species using a novel application of mussel spat ropes, although the effectiveness of this method was dependent on fish species' climbing ability (see also David, Tonkin, Taipeti, & Hokianga, ). At a larger scale, dam removal restores connectivity and sediment processes leading to beneficial biodiversity outcomes if sediment legacies can be addressed so that sensitive downstream ecosystems and species are protected (Catalano, Bozek, & Pellett, ; Doyle et al, ), although the extent of upstream benefits may be limited by multiple dams (Rodeles, Galicia, & Miranda, ). Notwithstanding the caveats discussed, such restoration projects that relieve single stressors typically demonstrate clear and rapid positive ecological responses.…”