Study Into Freshwater Fish Migration

The Environment Agency is working with Lincoln University on the project which aims to record fish movements and habitat use on the lower River Witham. Information gathered will be used to help develop habitat improvement schemes.

Chris Gardner, of the Environment Agency’s Data Analysis and Reporting (Fisheries) team, is leading the study.

He said: “The course of the lower River Witham has changed many times over its 2,000-year history. Its current course - without meanders and a free-flooding floodplain - dates from 1830 and can be quite inhospitable for fish.

“One of the biggest pressures is the lack of a natural floodplain. When the river rises, high banks prevent the river escaping into fields and fish have difficulty finding shelter away from the heavy flow in the main channel. For this reason, the river’s side channels are particularly precious as it is thought these are used by the river’s fish population. This study aims to gain evidence to be used to maintain and enhance this important habitat.”

The Witham Bream Project began in 2006 when seven native bream were caught and tagged with acoustic transmitters. Over the last three-and-a-half years, more than 80 large adult bream, weighing between 4lb and 7lb, have been tagged. The survey is taking place on a 40km stretch of river between Bardney Lock, near Lincoln, and the Witham’s tidal limit at Boston. Data will continue to be collected until November 2010.

The tags, which emit ultrasonic ‘pings’, can last up to 20 months. They transmit signals to 27 fixed receivers along the length of the river and in some of the side channels and can monitor fish movements 24 hours a day, seven days a week.

Receivers log the date, time and tag number when activated by a passing fish. Data is downloaded every couple of months and enables movements of individual fish to be monitored. So far, more than 3-million fish detections have been recorded and it has been found that the tagged bream regularly travel more than 20km in just a few days.
Dr Paul Eady, Reader in Behavioural Ecology at the department of Biological Sciences, University of Lincoln, and Dr Charles Deeming, the university’s Senior Lecturer in Conservation Biology, are working with Mr Gardner on the project.

Dr Eady said: “This is truly groundbreaking research into the secret lives of lowland river fish. Apart from the practicalities of tagging and monitoring the fish, one of the main challenges has been the analysis and interpretation of over 3-million pieces of data. However, from this data, we have uncovered some fascinating insights into the behaviour and ecology of bream in the river Witham which can be used to inform the management of this important lowland river habitat”.

The study has also identified that most activity happens in spring and that the fish congregate en-masse in certain areas of the river over winter.

Mr Gardner said: “The results of the work demonstrate the mobility of freshwater fish and the importance of shallow side-channels that provide valuable spawning habitat. It also highlights how fish use deeper side-channels as essential refuge during winter floods.”