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Fish acoustic receiver network

As part of the Belgian LifeWatch observatory, a permanent acoustic receiver network for fish tracking is established in the Belgian Part of the North Sea and the Western Scheldt estuary. Using acoustic telemetry distribution, movements and habitat use of tagged migratory fish can be tracked. Tags or transmitters are surgically implanted in the belly of individual fish; and acoustic receivers are installed on buoys, ship wrecks and river banks. When a fish swims in the vicinity of an acoustic receiver, the information of the unique ID-code of the transmitter is stored on the receiver together with an exact timing of the event. When signals are simultaneously received by multiple receivers, an exact positioning of the tagged individuals can be derived from the raw data.

 

 
 
Left: location of acoustic receivers in the Western Scheldt estuary and the Belgian coastal area - Top right: acoustic receivers (©VLIZ) - Bottom right: mooring of the acoustic receivers on buoys (©Jan Reubens)

In the framework of LifeWatch the permanent acoustic receiver network will be maintained as a research infrastructure that allows studies on migration patterns of several migratory fish species. For marine, coastal and estuarine systems, Atlantic cod (Gadus morhua Linnaeus, 1758), will be the model species, while in Belgian rivers European eel (Anguilla anguilla (Linnaeus, 1758)) is representative for catadromous downstream migration. In a later phase, other species, such as European sea bass (Dicentrarchus labrax (Linnaeus, 1758)), twaite shad (Alosa fallax (Lacepède, 1803)), river lamprey (Lampetra fluviatilis (Linnaeus, 1758)) and sea trout (Salmo trutta Linnaeus, 1758) can be investigated.

Setting up the fish acoustic receiver network is a cooperation between the Flanders Marine Institute (VLIZ), the Research Institute for Nature and Forest (INBO), and the Ghent University - Marine Biology Research Group (UGent-MARBIOL).

Currently (situation end 2015), a total of 103 individuals are tagged, and a total of 83 receivers are installed in the Belgian tidal areas: 20 in the Belgian Part of the North Sea, 39 in the Western Scheldt estuary (Westerschelde) (outer belt: 12, middle belt: 21, inner belt: 6), and 24 in the Sea Scheldt (Zeeschelde) from Antwerp to Ghent.

NOTE: The LifeWatch Acoustic Fish Tracking Network is part of the Belgian fish tracking network, which spans a larger area, includes more acoustic receivers and tags, and tracks additional fish species. This overarching fish tracking network, which was initiated by the INBO in 2012, is currently tracking over 300 fishes from 10 different species with 160 active receivers.

 

Atlantic cod

Atlantic cod (Gadus morhua Linnaeus, 1758) is a species with high commercial value. However, as fishing pressure has been very high for decades, population levels dropped in the 80s and have ever since been at very low levels. Although fishing pressure is strongly reduced nowadays, the population in the North Sea has not yet recovered. Information on ecology, migration routes and habitat preferences is crucial to support and give advice on efficient, long-term management plans for the recovery of Atlantic cod. This telemetry study in the framework of LifeWatch will help to gather the information needed.

So far 59 individual cods were tagged. In 2016, 30 extra individuals will be tagged. Some data visualizations can be seen here.

 

    

Left: fish tag (©Jan Reubens) - Middle: tagging of a cod (©Karl Vanginderdeuren) - Right: tagging of a cod (©Jan Reubens)

European eel

In order to stop the decline of the endangered European eel (Anguilla anguilla (Linnaeus, 1758)), all European countries are obliged to set up an eel management plan and support this with scientific data. Particularly downstream eel migration, when maturing eels migrate from their freshwater habitat to the open ocean, is thought to be a critical phase in the eel's life cycle. On their way to the ocean, eels have to face several challenges such as sluices and pumping stations. We need to understand how these barriers affect the chances of eels to reach the sea, to reveal whether constructions such as fish passages indeed have a positive impact and to create innovative solutions to facilitate migration. Therefore it's crucial to understand the behavior, habitat use and migration patterns of the eel. The INBO initiated an acoustic telemetry network in 2012 and the LifeWatch fish tracking network will build on that expertise.

So far 40 eels have been tagged in the LifeWatch network. In 2016, 30 extra individuals will be tagged.

 

    

Left: measurement of an eel before tag implantation (©INBO) - Middle: tagging of an eel (©Pieterjan Verhelst) - Right: installment of an acoustic receiver (©INBO)

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