New research from Norway's Institute for Nature Research (NINA) and the Norwegian University of Science and Technology (NTNU) indicates that sea lice larvae may be more abundant at greater depths than near the surface, challenging a key industry strategy for lice prevention.
The aquaculture industry has invested heavily in submersible cages, which are lowered to avoid lice infestations believed to occur near the surface.
However, a study in the Hardangerfjord found that there may be a higher density of lice larvae at twelve and eighteen metres deep than at two and six metres.
The findings were made using new passive lice traps that can sample water at multiple depths simultaneously, with the samples then analysed using DNA methods.
Frode Fossøy, a senior researcher at NINA, noted that a current limitation is that the genetic analyses cannot yet distinguish between infective and non-infective larval stages. NTNU is working to combine this with machine learning and video analysis to solve this.
Researchers emphasized that the findings do not mean submersible cages are ineffective, but that a more holistic approach is needed, suggesting that lice distribution should be investigated at a location before deployment. They also added that the findings are also relevant for closed and semi-closed facilities that draw water from deeper layers.