In 2012 the River Ythan Trust undertook the first comprehensive habitat survey of the River Ythan. The Trust commissioned the River Don Trust to carry out 300 km (187 miles) of habitat survey, the remaining 100 km (63 miles) was carried out by volunteers from the Trust. Each waterway was surveyed down to a width of 500 mm (20 inches).
The information discovered and recorded during this survey provides all the habitat data regarding the Ythan and its tributaries. The data has been used to make significant improvements to the habitat and fishery.
The survey was primarily concerned about the quality of the habitat within the river and tributaries to support salmon. The survey recorded potential spawning sites, salmon fry habitat and salmon parr habitat.
Juvenile salmon, both fry and parr, require shallow fast riffles to develop before migrating to the sea as smolts. Suitable habitat for juvenile salmon was found to be scarce, mainly due to historical modifications of the waterways over the last several centuries.
All waterways in the Ythan catchment have to some degree or another been affected by historical straightening. This reduces the quality of habitat for both salmon and trout, especially salmon.
Canalisation is very difficult to rectify and would involve resolving various legal issues and incurring potentially high costs.
The survey also recorded trout habitat information. Fortunately, trout are less sensitive to the conditions in the beds of the river and tributaries and can survive provided the water quality is good and were found almost everywhere in the Ythan catchment.
Trout do not have the same need for fast shallow riffles as juvenile salmon, provided there is enough gravel present for spawning, they can reproduce. Trout are more content to occupy slower water including glides and pools. In many cases the habitat was found to be poor, however trout were still seen in the smallest of waterbodies.
Both salmon and trout, including the anadromous (fish born in freshwater who spend most of their lives in saltwater and return to freshwater to spawn) trout and sea trout, need to be able to swim upstream to reach their spawning gravels and useful habitat for juvenile salmon and trout.
The habitat survey discovered that obstacles and part obstacles were widespread and numerous. The survey found 362 obstacles throughout the catchment.
The survey recorded relatively few manmade obstacles, some were found on the Bronie Burn, Kelly/Keithfield Burn and the Fordoun Burn. However, the survey did find livestock watering stations in the catchment area.
The survey found that some diffuse pollution, mainly silt, in the Ythan catchment is from livestock in unfenced fields alongside the waterways. However most diffuse pollution is from silt and livestock faeces at livestock watering stations due to livestock poaching and/or entering the waterways.
Animal faeces damage the water quality and silt clogs up gravels fish use for spawning. Excessive amounts of silt increase the amount of macrophytes (aquatic weeds emanating from the beds of streams) thereby reducing the amount good habitat available for juvenile salmonids. In addition, many livestock watering stations cause obstacles to fish migration.
The survey found 373 livestock watering stations, one for every 600 metres of waterway. These stations did not comply the Scottish Environment Protection Agency (SEPA) General Binding Rules to prevent silt and faeces entering the water.
Tunnel vegetation from bankside trees can damage the habitat for fish. However this is not a large problem on the Ythan catchment. The survey identified and recorded some 8.7 km (5.4 miles) of tunnel vegetation mainly on the Ythan main stem, Auchmacoy Burn, Bronie Burn, Kelly/Keithfield/Raxton Burns, Stonehouse Burn and the Fordoun/Red/Black Burns.
By 2012 when the survey was carried out there was more interest in the number and location of invasive non – native plants, especially Giant Hogweed, Japanese Knotweed and Himalayan Balsam.
Giant Hogweed was found to be the most common and widespread of the invasive non-native plants. It was present in over 80 km (50 Miles) of waterway banks. Japanese Knotweed was much less common, only 6 or 7 locations - Himalayan Balsam was found only on the lower reaches of the Foveran Burn.
The only aquatic invasive non-native plant the survey found was Canadian Pondweed which exists in a number of lakes and ponds in the catchment from just above Fyvie downstream. Several of these lakes and ponds suffer considerably from Canadian Pondweed choking out all other plants.
The plant also existed in the margins of some slow pools in the Ythan from Methlick downstream to Ellon but does not seriously affect the flow of the river.
Another aquatic plant (not an invasive non – native species) that causes a problem is Water Crowfoot (Ranunculus) which is a translocated species and is present in the Ebrie Burn and from there, in the Ythan downstream to the top of the tide in Ellon. Some years, dense stands overwhelm the riverbed, accumulating silt and possibly impacting salmon and trout spawning beds.
The Ythan District Salmon Fishery Board is a member of Fisheries Management Scotland.
The River Ythan Trust is a registered charity
Scottish Charitable Incorporated Organisation (SCIO) number SCO 41269