Displaying items by tag: survey

Over the past month, fisheries staff from the Environment Agency have been out surveying the fish populations on the rivers Ancholme, Witham, Welland and Nene.

The team has been using an acoustic fish finder which is the freshwater equivalent of the equipment trawlers use at sea. A pulse of sound is fired out from a transducer, and from the strength and direction of the echo received, the location and number of fish can be found.

Using this type of equipment means large areas of river can be surveyed in a few hours, compared to the usual netting method that only covers 100 metres and can take most of the day.

In the past, the areas the acoustic boat has surveyed has been dictated by the need for a suitable slipway nearby for the boat to enter the water, however a smaller boat has now been fitted with the equipment for the first time this year and is able to reach areas of water that were not possible to survey before.

Ecological Appraisal team leader, Chris Reeds, said: ‘The information gathered from the acoustic survey is invaluable in identifying areas of river that fish use for shelter and feeding, as well as giving a good idea of fish distribution over many miles of river. Monitoring fish populations also gives us an idea of the state of the rivers and how healthy they are’.

The acoustic survey is carried out at night as fish move about far more under the cover of darkness and can be detected more easily.

‘It is still necessary to net some fish to find out more about the age and species of fish in our rivers, but for monitoring fish population numbers, acoustic methods take some beating,’ said Chris.

The acoustic survey begins in spring and runs through to the summer routine survey, and then the autumn acoustic survey. All the data is processed during the winter to find out the population numbers and health of fish in rivers.

Source: The Environment Agency