Contributor – Céline Artero, Game and Wildlife Conservation Trust (UK)
Migration routes of sea trout kelts in the Tamar and Frome estuaries (UK) & Bresle estuary (France) are relatively unknown. The SAMARCH (SAlmonid MAnagement Round the CHannel) project uses acoustic technology alongside our G5 Standard Data Storage Tag to better understand the kelts’ use of these transitional and coastal waters. It is hoped that the data retrieved from the tags will help to inform authorities of the salmonids’ behavioural pattern and thus reduce the risk to them.
The tags are housed inside a flotation collar (Fig. 1) and inserted into the body cavity alongside an acoustic tag, which provides rough location information. If the location of the fish is known, electrofishing is used as the recapture method. Alternatively, if the tag naturally releases from the kelt (when the fish dies), it would float and wash up onto shore, either on a beach (if the fish died at sea) or by the river’s edge if the fish was returning to its natal river. The bright orange colouring of the flotation collars makes them easier to spot by members of the public, who could read the return information on the label, encapsulated within the float.
Fig 1. A G5 Standard DST with collar float attachment, next to a sea trout kelt
Returned tags are then re-connected to a PC and data is downloaded from them. Temperature and pressure data recorded by the G5 DSTs will be analysed using the Hidden Markov Model to reconstruct the sea trout kelts’ migration path and swimming behaviour.
A benefit of using archival loggers in this study (in addition to acoustic tags) is that they can provide additional information on mortality rates during the migration. Acoustic technology alone can provide location information as the tags pass through detection gates deployed downstream. Whilst you can infer mortality from non-detection between downstream gates; there are distinct patterns in archival tag data which represents a mortality event, such as sudden raised temperatures (through predation) or depth readings nearing zero (tag separated from the fish and floating to the surface, again perhaps through predation). In this case, by logging temperature and pressure at a 2-minute rate, Céline and her team can capture mortality information whilst also ensuring the longest possible logging duration.
Deployment of the tags started in the winter of 2018-19, where 116 individuals were tagged. The project – running until the end of 2021 – plans to tag a further 150 individuals during winter 2019-20.
Other organisations associated with the project:
Environment Agency
Agrocampus Ouest
Office Français de la Biodiversité
Institut National de la Recherche Agronomique
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