New DIDSON technology captures eels on film
ZSL has teamed up with the Environment Agency to trial a new acoustic imaging device, aimed at monitoring yellow/silver eel migration from a Thames tributary. A 2011 pilot study aimed to test whether a DIDSON – Dual-Frequency Identification Sonar could be used to improve understanding of yellow/silver eel behaviour and movement during their downstream migration phase. Following success in this short trial ZSL now intends to embark on a larger research study in 2012, extending the time over which monitoring is carried out.
The European Commission has responded to a decline in European eel populations by setting a target which encourages all member nations to implement measures to improve the number of yellow/silver eels migrating downstream in their Rivers. It is thought that by helping to increase the number of spawning eels reaching the Sargasso, future populations will increase. This project hopes to address issues in our current ability to assess changes in downstream migrations.
Counting migrating mature eels is shrouded with difficulties, due to their cryptic nature, endangered classification and nocturnal life style. In this trial a DIDSON, a high resolution acoustic imaging device, originally used in underwater naval surveillance, was used to detect the unique anguillid swimming motion. By positioning the device in front of a swinging weir in a Thames tributary the radiating beam allowed almost complete coverage of the channel and detection of any migrating eels, as well as recording any interactions they have with the weir.
Despite the short time frame of the trial the footage and subsequent analysis lent some interesting results, including an idea of numbers of migrating eels, their lengths (and consequently and idea of sex ratios) and also the environmental conditions associated with their migratory behaviour.
This pilot study has highlighted the potential of using DIDSON to monitor yellow/silver eel migration in the future and the opportunities new technology such as this hold for increasing our understanding of these elusive animals. Over the winter of 2012/3 ZSL hope to temporally expand the project to cover more of the migratory season, to elucidate the efficacy and potential for expanding the project spatially in the future. Watch this space for more on this pioneering initiative.