Catch me if you can: How to recapture lumpfish using light as an attractant

Abstract

The use of lumpfish in salmon farming allows the removal of sea lice all year round, without the use of chemicals or mechanical treatments. In Norway alone, around 31 million lumpfish are currently put into sea pens whereas no efficient method to re-catch these fish once they no longer are efficient salmon lice grazers (from 300 g) exists. At present, collecting lumpfish in sea-cages is a labour- and time-consuming process and, if these fish are to be harvested, an efficient method for collecting lumpfish is urgently needed. In this study, we tested coloured light as an attractant to lure lumpfish into passive traps (pods). Three small-scale pilot experiments both demonstrated the highest re-capture rate when a blue light-source was used, whereas red and yellow light gave the lowest re-capture rate. A subsequent large-scale trial failed to demonstrate significant re-catch of lumpfish. It is concluded that although blue light clearly attracted lumpfish in laboratory trials, further studies are needed in order to exploit this attribute commercially.