Snorkelmerd: Produksjonseffektivitet, adferd og velferd. Sluttrapport FHF-prosjekt 900884

• Published in: Rapport fra Havforskningen 2016
• Main Authors: Oppedal, Frode, Dempster, Tim, Stien, Lars Helge
• Format: Report
• Language: Norwegian

English: The snorkel cage creates a mismatch between the salmon lice infestative larvae stage and the salmon, thus minimizing infestations. The snorkel cages comprise a roof of net to keep the fish down, but with a tarpaulin dressed passage to the surface. Through this the salmon have access to surface air and can refill the swim bladder while still avoiding surface waters where lice larvae are most abundant. The idea was initiated in one of the Norwegian Research Council Centre’s for Research-based Innovation, CREATE, and further development of the principle has been supported by The Norwegian Seafood Research Fund since 2013. Egersund Net AS has been responsible for the design and manufacture of snorkels. Bremnes Seashore AS was the first to use commercial snorkels. In medium-scale experiments sea lice infestation was reduced by 84 to 66% through the summer in spring-transferred smolts, but growth was declined as a result of underfeeding. In a follow-up study with low stocking density and medium-sized fish, minimal growth differences were noted, but slightly increased snout wear and only partly swim bladder re-filling. With a brackish layer as deep as the snorkel depth there was no mitigating effects on infestations. Next trial on slaughter-sized fish, commercial stocking density, medium-scale cages and 4 m deep snorkels in coastal waters showed recurring reduction in sea lice infestation ranging 24-65%. Concurrently, production efficiency, behaviour and welfare were adequately maintained. "Proof of concept" was thus proven for medium-scale cages. The final trial displayed clearly that lice reduction increased with deeper swim depth of the fish (snorkel depth) and were virtually zero when the salmon had to swim deeper than 12 m in winter. At commercial scale, 50% lower lice levels were noted at a snorkel site compared to a neighbouring site during autumn 2014. In 2015, 100-65% less lice was counted in snorkel compared to normal cages within the same site. In snorkel cages, treatments against amoebic gill disease were avoided by introducing a fresh water layer in the top of the snorkel. There have been some challenges with deployment, management and maintenance of the water quality of the snorkels. There is still room for optimization of design, use, and handling at large scale. However, most normal operations in large-scale snorkels may be performed (e.g. net changing, chemical lice treatment, sampling). Use of commercial snorkels needs further developed