‘Snorkel’ sea lice barrier technology reduces sea lice loads on harvest-sized Atlantic salmon with minimal welfare impacts

Abstract

The infestation of farmed Atlantic salmon (Salmo salar) by ectoparasitic sea lice (Lepeophtheirus salmonis) presents a need for new approaches to parasite control. One option is the use of ‘snorkel’ sea lice barrier technology, which restricts salmon from accessing the surface except via a vertical chamber impermeable to sea lice larvae. This prevents the salmon from swimming at the depths where infective sea lice are most abundant. Before snorkels can be implemented in commercial sea-cages, knowledge is required about their effects on salmon welfare and growth. Here, we installed snorkels of 4m depth into three 12×12×12m3 cages, and recorded the lice infestation of stocked fish along with their growth, behaviour, and snout and fin condition over a 12-week period. Three standard sea-cages were utilised for comparison, and all six cages were stocked with ~3500 salmon (2.3±0.6kg). After 3, 6, 9, and 12weeks, fish in snorkel cages had 65, 24, 43, and 56% lower lice levels than in standard cages, respectively. Salmon in both snorkel and standard cages grew similarly well and we detected little or no adverse effects on fish mortality or welfare. The results indicate that snorkel sea-cage barrier technology provides a promising new tool in parasite management in salmon aquaculture. Statement of relevanceThe ectoparasitic sea louse (L. salmonis) is the key obstacle for further expansion of industrial on-growing of salmon in sea-cages in Norway and Scotland. There is therefore high demand from both the industry and the governments for new environmental friendly technologies that reduce the sea louse problem. Here we demonstrate that snorkel sea cages can be used to control lice loads under the problematic autumn months for high valued slaughter ready salmon without significant adverse effects on fish welfare and fish growth. This study is therefore highly relevant for the Aquaculture journal.