Wednesday, 14 May 2014

Trout Life History Project - An Update

Acoustic tracking of trout smolts

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 WR2W receiver
Vemco VR2W receiver
Acoustic tags were chosen to study post-smolt migration behaviour in the near shore environment. Unlike radio tags and PIT tags, acoustic tags actively transmit signals that can be heard effectively in the marine environment.

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
Map 1: Location of WR2W receivers in Poole Harbour, the area shaded red represents
approximate detection range of the receivers. Click image to enlarge.
In addition to the receivers monitoring movement in the harbour, receivers were deployed in the River Frome at Bindon Mill, East Stoke, and at the tidal limit by the bypass around Wareham (see Map 2 below for position of in-river receivers). These in-river receivers were deployed to monitor post tagging in-river loss rate and freshwater migration speed.

Map 2
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
Trapping trout smolts on the Eel Rack at East Burton
Tagging of the trout smolts is done at the eel rack at East Burton, 8 km up-stream of East Stoke. The eel rack at East Burton represents a piece of cultural history as it was made many decades ago to trap down-stream migrating silver eels for commercial purposes.

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

Trout post-surgery

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.

1 comment:

  1. Thank you - interesting and I have forwarded it to The Deveron Biologist.
    The next report will be more interesting - hoping that responders will have information to release. Is it expected that the Smolts will remain in Poole Harbour or will they go to sea to Feeding Grounds? Perhaps you are waiting to discover. R.F. McConnell