Addition of spawning gravel—a means to restore spawning habitat of atlantic salmon (Salmo salar L.), and Anadromous and resident brown trout (Salmo trutta L.) in regulated rivers

Abstract

In regulated rivers, canalization and reduced water discharge may lead to loss or impairment of salmonid spawning areas, and thereby negative effects on stock recruitment. We discuss the possibility of mitigating such effects through establishing new spawning areas by addition of gravel. We monitored the occurrence of nests in seven gravel deposition sites in five different Norwegian rivers. The total area covered by each of the depositions spanned from 25 m 2 to 300 m 2 . The areas were examined for nests during a 2-5 year period following the addition of gravel, that is, a total of 27 spawning periods. The fish were found to spawn at all localities and years with the exception of two occasions when gravel was lost during floods. Spawning success measured as egg survival was generally high (>80%). These results show that the additions met the criteria for successful spawning. Nests of Atlantic salmon were found to be aggregated in the area with the highest water current. However, successful nests were also found in areas with added gravel where the water current was much reduced. This unusual selection of spawning site most likely reflects the lack of other, more favourable spawning areas. The results therefore suggest that gravel additions can be successful even if the only available areas are suboptimal with respect to water flow and water depth. Three of the seven localities were unsuitable as the gravel was partly or totally displaced downstream during floods. At two of these localities, nests were probably lost because the floods occurred after the spawning season. This shows that large floods can be a major drawback. Monitoring of the spawning success and displacement of gravel is therefore essential to evaluate the method. Subsequently, stable areas, favoured by the spawners, can be expanded by supplementary addition of gravel. In sum, the results show that the careful addition of gravel areas can be used to provide suitable spawning locations for salmonids in regulated rivers.

Fine sediment reduces vertical migrations of Gammarus pulex (Crustacea: Amphipoda) in response to surface water loss

“…If vertical connectivity is maintained during and after a disturbance event, subsequent community recovery and related provision of ecosystem services such as organic matter processing may be enhanced (Navel et al, 2010). River restoration by manipulation of riverbed sediments may have multiple ecological benefits, for example the addition of gravel may create fish spawning grounds as well as increasing the use of sedimentary refuges during instream disturbances (Barlaup et al, 2008). However, the success of such restoration schemes may be limited if activities are confined to the channel.…”

Riverine Ecosystem Management

“…Excessively large grains (large cobble) or armor layers prevent salmonids from redd building (Kondolf 2000), while, on the other hand, high percentages of small grains (fine gravel, sand, silt, clay) do not allow successful reproduction due to reduced permeability and, consequently, insufficient supply of water and oxygen (Sear and DeVries 2008). Besides fines, washout of spawning gravel as well as reduced gravel supply from upstream sources can limit spawning habitats (Barlaup et al 2008).…”

“…Wheaton et al (2004) highlight the use of artificial gravel placement as one possible measure to restore or enhance hydro-morphologically suitable spawning habitat conditions for salmonids. For example, in Western Norway, the restoration of anthropogenically impacted (partially destroyed) spawning habitats of Atlantic salmon (Salmo salar) was mainly achieved by artificial gravel dumping (e.g., Barlaup et al 2008) and the restoration of fluvial processes (Fjeldstad et al 2012). Other restoration techniques include hydraulic structure placement (e.g., single boulders or groins), mainly to create suitable water depths and flow velocities combined with specific sediment sorting, or an "artificial enhancement" of existing spawning gravels by periodic turnovers of spawning substrate to reduce the amounts of aggregated fine sediments at spawning grounds.…”

The effectiveness of spawning habitat creation or enhancement for substrate spawning temperate fish: a systematic review protocol

“…These structures not only provide favourable habitat for juveniles [5,7], but can also recruit and store gravel [8] which is of particular benefit to substrate spawners. For example in salmonids, enhanced gravel beds provide suitable spawning habitat [9,10] and have resulted in higher survival rates to swim-up stage [11].…”