Impacts of gravel jetting on the composition of fish spawning substrates: Implications for river restoration and fisheries management

Abstract

Fine sediments can impact river biota, with egg and larval stages of lithophilic fish particularly sensitive to deposition of sand-and clay-sized particles ('fines') in spawning gravels. Mitigation and restoration methods include jetting to cleanse gravels of fines. Despite wide application, impacts of jetting on gravel composition and quality have rarely been quantified. Here, gravel jetting impacts on sediment composition in the River Great Ouse (UK), were tested during an in-situ experiment completed at riffle (55.6 ± 13.4 m 2) and patch (0.3 m 2) scales to determine its magnitude and persistence on surface and subsurface substrate conditions. Before-after (riffle) and control-impact (patch) designs were used, with bedload sediment traps installed downstream of experimental patches to investigate the sediments mobilised during jetting. At the riffle scale, surface grain size was significantly altered; fines were removed resulting in coarser and better-sorted sediments. Similar patterns were detected at the patch scale, although sediment sorting was not significantly altered. Despite reduced fine sediment content of subsurface gravels at the riffle scale, the overall grain size composition was not significantly altered. At the patch scale, no subsurface improvements were detected. Temporally, at the riffle scale, no changes in surface or subsurface sediments lasted more than 12 months; patch scale changes generally persisted for less than 3 months. Thus, whilst gravel jetting could improve spawning gravel quality for surface spawning fishes, including European barbel Barbus barbus, its effects are short-term. However, because subsurface sediments are not affected by gravel jetting, the benefits are limited for redd-building fishes, such as salmonids. Consequently, reducing fine sediment delivery to rivers, such as by changes in agricultural practices, would be more sustainable for managing excessive river sedimentation.

Influences of angler subsidies on the trophic ecology of European barbel Barbus barbus

“…Moreover, these large fish are no longer present due to natural mortality and have not been replaced by either natural recruitment or other stocked fish (Bašić & Britton 2016). This recruitment failure is likely to be due to poor spawning habitat (Bašić et al 2017;. Consequently, in the last decade, angling effort for B. barbus, including the use of marine fishmeal, has declined sharply in the river due to the perception by anglers of decreased angling quality (Post & Parkinson, 2012).…”

Direct observations of the effect of fine sediment deposition on the vertical movement of Gammarus pulex (Amphipoda: Gammaridae) during substratum drying

“…Such management strategies should include measures to reduce fine sediment inputs into streams using sediment detention ponds/ wetlands and planting riparian vegetation to stabilise river banks (Verstraeten & Poesen, 2000;Hughes, 2016). Where high river flows are insufficient in flushing fine sediment from streambeds, management techniques such as gravel jetting (Bašić et al, 2017), replenishing depleted coarser grained sediments (Merz & Ochikubo Chan, 2005;McManamay et al, 2010) and the use of instream structures to enhance hydraulic efficiency to transport fine sediments (Palm et al, 2007;Michel et al, 2014) should be considered.…”

Substrate composition determines emergence success and development of European nase larvae (Chondrostoma nasus L.)

“…Restoration can include long-term measures, such as re-establishing dynamic flow processes in lateral and longitudinal direction and thereby sediment dynamics (Auerswald & Geist, 2018) as well as reduction of fine sediment infiltration in rivers due to erosion by land use (Davies, Biggs, Williams, & Thompson, 2009;Knott, Mueller, Pander, & Geist, 2018) and short-term restoration measures, such as gravel cleaning (e.g. Bašić, Britton, Rice, & Pledger, 2017;Shackle, Hughes, & Lewis, 1999) and gravel introduction (e.g. Pander et al, 2015;Pulg et al, 2013).…”