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Juvenile fish surveys

Recording details of anaesthetised juvenile salmon and trout

Recording details of anaesthetised juvenile salmon and trout

Sorting a kick sample of invertebrate larvae by the Grudie River near Loch Maree

Sorting a kick sample of invertebrate larvae by the Grudie River near Loch Maree

During the period July to October, WRFT field teams make the most of every opportunity to survey the rivers and streams of the area for juvenile fish. Up to 16 river systems are surveyed each year. A primary objective is to assess the distribution of juvenile salmon, and thereafter to find out about fish abundance. If healthy populations of juvenile salmon are not found where expected, further investigations may be required to investigate problems. Trout, eels, minnows, sticklebacks, lampreys, and sometimes even small flounders, are also recorded where present during electro-fishing surveys.

Surveys are carried out using trained staff using specially designed electro-fishing equipment. Electro-fishing is a standard survey method that has been developed over many years across Europe and America for investigating fish populations. Fish are temporarily immobilized to enable capture. Following measurement and examination, all fish are returned to the water after a period of recovery. Occasionally a small sample of fish is retained for disease testing. Through marking studies at Tournaig and elsewhere, we, and other fishery scientists, have been able to demonstrate that juvenile salmon caught by electro-fishing survive, grow, and migrate to sea in much the same way as other fish.

Field teams often work alongside fishery proprietors or estate staff. Sometimes there are opportunities for volunteers to help carry equipment. Where possible, problems and possible solutions are discussed on site. Results are presented in river reports along with suggestions or recommendations for actions to address issues of concern to fisheries.

Field workers are trained to follow SFCC (Scottish Fisheries Co-ordination Centre) electro-fishing protocol. This is to ensure safety and consistency of data with that collected by electro-fishing teams working in other parts of Scotland. Data is collected primarily for local fisheries management purposes. Our juvenile fish data has also been used by SEPA, SNH and other government agencies for assessing fish populations on a larger scale. Private companies (including hydro-power developers) sometimes approach the Trust for fisheries information relating to the potential impacts of proposed developments.

Please contact the WRFT biologist if you would like to join a field team for a day. All surveys are weather and river-conditions dependent. A good level of fitness is required and protection from ticks, clegs and midges. Other wildlife is usually encountered, from invertebrate larvae in the stream bed to eagles overhead.

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