SNH staff induction and a modification to the electrofishing equipment

On Tuesday we were asked to deliver a short session for some new SNH staff who are participating in a staff induction week looking at various issues in the area. Our task was to provide an overview of local fish and fisheries. This year and last we held the session at the Allt Ruadh, a small Feshie tributary. The demo site on the Allt Ruadh is located 130km by river from the sea but it usually supports a population of salmon. We started with a chat about the importance of salmon to the local area, moving on to the lifecycles and management etc.

An electrofishing demo followed and we were able to show them an assortment of fry and two years classes of salmon parr. It is still early in the year for electrofishing, primarily because the fry are still small making certain identification difficult, especially this far up the catchment where the water temperatures are considerably colder than lower down the river. I didn’t look closely at the fish but Steve, who is very reliable on these matters, thought the fry were trout and all the parr salmon. When Grant Morrison (Delfur ghillie) and myself counted redds on the Allt Ruadh last year we didn’t find any salmon redds as far upstream at the electrofishing demo site, although there were trout redds. It is not unusual to find parr further upstream than fry, they often migrate up looking for vacant territory.

SNH staff induction fisheries session by the Allt Ruadh

SNH staff induction fisheries session by the Allt Ruadh

With its catchment in the Cairngorms the conductivity of the Ruadh was low, about 15microsiemens/cm. In that type of low conductivity water electrofishing can be difficult as relatively pure water doesn’t conduct electricity very well. In these circumstances the gear used can be adjusted, either by altering adjustable outputs on the machine such as the voltage or pulse width or by changing the hardwear. The key is to increase the voltage gradient between the anode (the ring) and the cathode; one way of doing that is to reduce the size of the ring and/or increase the size of the cathode.

There is a lot of low conductivity water in the Spey catchment so we needed a range of ring sizes for different conditions, e.g. for adult v’s juvenile fish surveys. To that end we asked the local blacksmith in Knockando to make two more rings, one at 150mm (6″) diameter and one at 450mm (18″) diameter just in case we need to do specific adult surveys. Our standard ring size is 12″.  Like all proper local blacksmiths Jolyon can turn his hand to anything made of metal so after the SNH team departed we tested the 6″ ring in the Allt Ruadh.

The 6" electrofishing anode in use in the Allt Ruadh.

The 6″ electrofishing anode in use in the Allt Ruadh.

No formal comparisons were made but we did appear to catch, or at least turn over more fry (many went straight through the mesh on the banner net), using the smaller ring. In theory that is what you would expect as the more concentrated electrical field produced by the smaller ring should be more effective on fry, which are subject to lower electrical gradient over their short body length.

Introducing any modification to the equipment can introduce unaccounted variables when conducting surveys which are designed to be repeatable. The small ring will probably only be used in a few locations but we will try and calibrate its effectiveness in comparison to the standard ring so that results are comparable. The small ring was intended specifically for the upper Avon, which we will be surveying in detail this summer. The wide shallow riffles present there will provide good opportunities for comparing one equipment set up with another. In Ayrshire there was one area with low conductivity water draining the granite rocks of the Galloway Hills. After a days surveying there I often left feeling frustrated that we hadn’t properly assessed the fish population as we could see them when electrofishing but not stun them sufficiently well to catch them. I believe we should use the most appropriate set up for those circumstances and I hope that carrying a range of ring sizes will allow us to survey these very low conductivity areas more effectively.

My main aim during the SNH staff induction day was to stress the economic importance of salmon to the local area. SNH’s main role is biodiversity conservation and I’m sure sustainable development. Different organisations will of course have different priorities but if we succeeded in instilling the huge economic importance of this local natural resource in some of the new SNH staff then it was an afternoon well spent.


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