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.

Thursday, 8 May 2014

2013 Salmon research report now available online

Our 2013 salmon research report has been published and is now available to download as a PDF.

The abstract from the report is below:

2013 was the 41st year of the salmon counter’s operation at East Stoke. It was an extremely good year for the juvenile phases of salmon with high numbers of every life stage being recorded. For the adults it was very poor. Parr numbers in the river in September 2012 were very good: the third highest since 2002 and the number of autumn migrant parr that went past East Stoke was high: the second highest we have recorded. The spring monitoring of smolts was excellent and, at over 13,000, was over twice the number recorded in 2012.

On the adult count, equipment failure meant that some data that we normally collect on salmon movement was lost. For this reason we have added an efficiency estimate to the collected data to give an estimated nett upstream count of 343 fish.

This is the lowest number ever recorded on the counter. Adult numbers calculated from PIT tag returns give an estimate very similar to this (383) so we are confident that the numbers were low. This low number of adults is also in agreement with our prediction last year about low numbers of grilse returning this year.

The collaboration with the Poole Harbour netsman continues with only one sea trout caught, tagged and released in 2013.

Our research (with Cefas) on the effect of using rotary screw traps to assess salmon smolt numbers was completed and results will be analysed and written up as soon as possible. The research on the medium and long-term effect of Archimedes screw turbines on salmon smolts and eels also got underway using the facility at Bindon Abbey.

Our current Passive Integrated Transponder (PIT) tag detection equipment is getting very fragile and the manufacturer is no longer supplying new equipment. After reviewing available options we have found sponsorship and funding to replace the readers with new ‘state of the art’ equipment. The new detectors will be better able to withstand the high river flows we have recently experienced and installation should take place this summer.

Mean annual discharge (up to December) was above average, however, the mean monthly discharge in January 2014 was the highest ever recorded for that month.

Finally we are continuing to work with our French colleagues at INRA in Rennes, France, on the Monitoring for Migratory Fish (MorFish) project which will compare data to give us a better understanding of the changes in our populations of migratory fish.

Professor Nick Sotherton
Director of Research, Advisory & Education

Download GWCT 2013 Salmon research report >