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Fish INTEL update: find out what our tagged fish are up to

3 minute read

It's been a busy few months for our Fish INTEL team, with 16 bass, 29 bluefin tuna and 30-35 crawfish now tagged. Here's how the project is progressing and what our researchers are hoping to learn.

Our Fish INTEL public launch event went live at 0930-1130 on Tuesday 30 November 2021.


What is the Fish INTEL project?

Fish INTEL is a major EU-funded project to learn more about fish behavior within UK, French and Belgian seas.

The project involves tagging fish with innovative acoustic tracking devices and monitoring how they use different ecosystems such as estuaries, mussel farms, shipwrecks, reefs and windfarms.

By tracking fish movements and studying their habitats, we hope to build a comprehensive picture that will inform commercial fishing policies and help marine life to thrive.

The project will focus on the following commercially important species:

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Bass in Belgium

A total of 16 bass have now been tagged around Belgian offshore windfarms. Scientists will be watching to see if the bass remain close to the windfarms, using the area for shelter and feeding.

A recent scientific paper from University of Plymouth FISH INTEL scientist Tom Stamp and colleagues has shown that juvenile fish spend most of their early lives within 20 km of the estuary where they are tagged.

Even though fish can move considerable distances (one individual moved between south Devon and southern Wales), 81% return to, or stay near their original capture sites.

This shows how important protection of estuaries is to the fish.


Bass aggregating off ‘the longships’ Cornwall

Credit: Thomas Stamp, University of Plymouth

Bluefin tuna in Cornwall

There has been great success in catching bluefin tuna this summer and 29 fish have been tagged off Cornwall.

Calm seas have led to sightings of these pelagic fish feeding at the surface (on pilchard or sprat).

Professional anglers are employed by the project to ‘troll’ fishing lines with squid-like lures. Once the tuna strike these plastic bait, they are hauled into the vessel as quickly and gently as possible.

University of Exeter and Cefas scientists then tag the fish with acoustic tags, which transmit an acoustic signal every 30 to 120 seconds for up to five years.

These signals can be detected by listening stations to be deployed by Fish INTEL scientists and by existing listening stations along the migratory routes of this species.

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A large bluefin being tagged by University of Exeter scientists

Credit: Lucy Hawkes, University of Exeter

Bluefin tuna can be enormous, regularly growing to over 200 kg. Working with them is a skilled job and any project members handling these animals must have a government licence to ensure the animals are kept in good condition while being tagged.

Crawfish off the Isles of Scilly

Some 30-35 crawfish have been tagged in waters off the Isles of Scilly. About half of them were collected by freedivers, and the other half by using a trammel net (made up of layers of netting). The crawfish have all been tagged and replaced into waters within 1.5 km of the acoustic listening device, which will monitor their location.

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Crawfish with acoustic tag on it

Credit: Thomas Stamp, University of Plymouth

What's happening with pollock?

Pollock are to be caught and tagged this winter in UK and northern French waters.

It's thought that the fish gather around offshore artificial structures (such as wrecks and windfarms) before spawning, then move back inshore for spring.

Anglers working with us on the project target the pollock in these locations. It's essential that they bring the animals up slowly from the deep waters so their swim-bladders can adjust to the pressure change.

France Energie Marine are placing acoustic receivers in and around new French windfarms from December to February and working with partners IFREMER and University of Brest to record movements of key fish species within these structures.

Technical update: keeping our equipment clean

Acoustic receivers (“listening stations”), which record the movement of tagged fish, should be serviced every four months to remove algal growth, to resecure the moorings and to download the data.

Receivers are attached to heavy mooring blocks on the seabed and can be released from their mooring by Fish INTEL scientists, using a remote control mechanism.

The receivers are then brought to the surface using a lobster-pot hauler or capstan whey they are serviced and returned to their original GPS position.

The distances between listening devices vary depending on the mobility of the species being observed. For crawfish, the distance between arrays is 250m. For bass it is usually slightly greater. For bluefin tuna, listening devices are spread much more widely (about 10 km apart) as the fish move much greater distances.

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Receiver being deployed in Belgian windfarm

Credit: VLIZ