Fish tracking network

Acoustic telemetry is the method used to track Pollack movement within Pollack FISP. This technology relies on two main parts:

1- an acoustic transmitter tag which is attached to or implanted within an animal. This tag will emit a unique code every 2 minutes for a period of up to 3 years.

2- A receiver network. A network of sensors which detect passing fish when within a range of 200-300m (depending on the water conditions and background noise). Each receiver will log when it has detected a fish. This data is then stored on the sensor and each unit must be serviced every 4-6 months, to reduce biofouling, change the battery and download the data.

As part of various project University of Plymouth manage one of the largest receiver network in Europe (Figure 1), providing fish tracking coverage over approximately 500km of south UK coastline. University of Plymouth also sign up to the https://www.europeantrackingnetwork.org/en. This free service allows the project to track tagged Pollack movement across any registered receiver within Europe.

Pollack tagging

To date 95 pollack have been acoustically tagged by University of Plymouth under projects FISH INTEL and Pollack FISP. The mean length for tagged fish is 55.08 cm (fork length) +/- 1.1cm (Figure 2). Several methods were used to treat barotrauma and maximise survival rates after the fish were released following tracking tag implantation. The most successful method included: minimising time at the surface (max 5 minutes), then returning the fish to the depth it was caught using a release cage/descending device. The majority of fish tagged using the deep water release method were done from March 2023, with methods continuing to be refined on each following trip. This includes a total of 71 fish. The mean length for tagged fish using the deep water release method is 56.32 cm (fork length) +/- 1.16cm.

Fish were captured across several reef and wreck sites off Plymouth (Figure 4) in 2022-2023. Fish were captured in a range of depths (10 - 50m) and all showed symptoms of barotrauma.

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Pollack tracking

To date, a total of 171,898 detections have been recorded from 43 fish. This highly exciting data is the first attempts to track Pollack, which up till now have not had much research largely due to the baratrauma issues mentioned earlier. These detections are shown as an “abacus plot” in Figure 3. Each row represents the detection history of each fish with time shown on the y axis. The points are then colour coded by the receiver that detected each fish. The movements of these fish are then shown on a map in Figure 4. Data to date suggests that while fish do move occasionally they generally stay local to the reef or wreck site where they were caught. Fish tagging will continue for the project duration, allowing us to measure behavioural changes in Pollack distributions over the next 2 years.