The near shore migration behaviour of post-smolt sea trout potentially impacts their life history choices. Parameters that may be affected by migration choices of post-smolts are growth rate, fecundity and timing of first spawning migration.
|Vemco VR2W receiver|
We chose to use V6 tags made by Vemco, the world’s leading manufacture developer of acoustic technology for fish tracking. The V6 tag is 6 mm in diameter, 16 mm long, weighs 1 gr and has a detection range of approximately 200 metres.
On the 26th of March 10 Vemco WR2W receivers were deployed throughout Poole Harbour. The receivers (listening stations) were deployed strategically to record movement both into and out of Poole Harbour as well as potential feeding areas (see Map 1 below for location of the receivers in Poole Harbour).
|Map 1: Location of WR2W receivers in Poole Harbour, the area shaded red represents|
approximate detection range of the receivers. Click image to enlarge.
|Map 2: Location of East Burton eel rack (yellow dot) and WR2W receivers|
in the River Frome (red dots). Click image to enlarge.
Capture and tagging of trout smolts
We acquired 50 V6 tags for the 2014 smolt run and another 50 tags for the 2015 smolt run.
Trapping trout smolts on the Eel Rack at East Burton
The eel rack at East Burton has been restored and is now an excellent tool for GWCT to intercept down-stream migrating fish in a fish friendly manner. Click here to see a video clip of an eel rack in operation on the River Test.
The capture and tagging at the eel rack commenced on the 28th of March and was carried out at night time as this is the time when the majority of smolts migrate. The trout smolts were captured, anaesthetised, measured, weighed, scales taken, PIT and acoustic tag inserted, moved to a recovery tank and released when fully recovered (see pictures below for tagging process).
The last of the 2014 tags were deployed on the 23rd of April.
|Trout smolt on measure board with acoustic and PIT tags|
|Insertion of acoustic tag|
Tracking of tagged trout smolts
By 21st of Aril 70% of the tagged trout had been recorded entering the tidal section of the river. The battery life of the acoustic tags is 105 days from the day they are deployed. This battery life of the acoustic tags will give us an excellent window into the migration behaviour of the tagged post-smolts in the near shore area.
However, as the battery in the acoustic tags will run out before their first spawning migration we also fitted the smolts with PIT tags. The PIT tags will enable us to record returning adults on our PIT readers at East Stoke and Bindon Mill.
GWCT Fisheries Research
To find out more about the GWCT's fisheries work please click here and to find out more about our trout research please click here.