Depth influences fish welfare when tagged

Electronic tags are tools used all over the world for studying aquatic animal behaviour. However, tags can have negative welfare outcomes and can also cause behavioural manipulation. While conducting different experiment, Dr Daniel Wright from the Institute of Marine Research discovered negative tagging effects on fish held in depth-modified cages. Fish were kept in unmodified cages and depth-modified cages which forced fish below or into a narrow seawater or freshwater filled snorkel. While all tagged individuals survived in the unmodified cages, survival was reduced to 62% in depth-modified cages. Further, survivors in depth-modified cages spent less time above 4 m compared to those in unmodified cages, and dying individuals tended to position in progressively shallower water. Overall, they found that the internal tag weight and volume affected buoyancy regulation, survival, and behaviour of tagged fish. Dr Wright recommends that future tagging studies on aquatic animals should carefully consider the buoyancy-related consequences of internal tags as well as the inclusion of data from dying tagged animals when estimating normal depth behaviours.

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