Annual fish surveys are underway

Our annual electrofishing surveys are underway across the Teign catchment, making this the tenth year of these surveys on the river. Each year about 40 sites in the Teign catchment, including major tributaries such as the River Bovey and Kate Brook, are surveyed for salmon and trout fry (juvenile fish).

TACA (Teign Angling and Conservation Association) have been conducting annual fry surveys since 2012, and have increased the number of sites surveyed annually from 20 to 40 since the start of this project. The aim is to monitor changes principally in the salmon but also the trout population, and thereby their breeding success as an overall indication of the health of the entire Teign river system.

It is important to stress that despite the name, electrofishing when done correctly does not harm the fish. The E-Fish electrofishing equipment is carried in a backpack, powered by a battery, with the voltage in the water determined by the local water temperature and conductivity at each location and the species of fish required to be collected. A cathode is trailed in the water and the anode is a circular hoop on a rod that can be directed at specific areas beneath the water surface. Once the current is applied to the anode, the fish within a short distance are lured in. The electrical current causes forced swimming – harmless involuntary muscular convulsion – and the fish are scooped up in a net and gathered in a large bucket.

Electrofishing in progress, photo © Mike Rego

The water temperature is critical; electrofishing surveys cannot be conducted at water temperatures of greater than 18°C, as due to lower levels of oxygen in the water the fish can easily become distressed.

Once electrofishing has been carried out for a total of five minutes, the collected fish are taken to the riverside, air pumps are inserted into the bucket to oxygenate the water, and each fish is then measured by hand before they are transferred to another aerated bucket for release back into the river as quickly as possible.

The results this year so far have been very encouraging, with exceptionally good results at some locations. There are several possible reasons for this. Once we have completed all the surveys and collated all of the data, we will publish the results on the website.

Our thanks to project partners Westcountry Rivers Trust for their expertise on leading these surveys, and to National Lottery Heritage Fund which has allowed us to expand the number of sites and continue this work.