The management of sea lice is a major challenge for salmon farmers in Scotland, as it is in most salmon farming regions. Although farmed salmon are clear of sea lice when they are put into marine farms, they are subsequently affected by the parasites which are attracted to both wild and farmed salmon. However, with a large number of salmon in each farm it is important that the sea lice are kept to a minimum. There are a number of different methods used to control sea lice, including management measures, medicines, functional feeds, breeding programmes, passive control measures, physical removal methods and biological controls.
Salmon farmers use farmed and wild caught lumpfish and wrasseas a biological control. They cohabit with the salmon and pick the sea lice off. Programmes for farming both lumpfish and Ballan wrasse have been running for a number of years and these will be continually developed with the aim of farming all the industry’s requirement for cleaner fish in the future. Significant investments have been made to develop appropriate hatchery and nursery facilities for these new farmed species.
While the farming of cleaner fish is in development, there is a need for continued use of wrasse caught in the wild. These are live caught by experienced fishermen around the west coast of Scotland and the Western Isles using wrasse traps. This fishery does not have a quota system, but fishermen must have a static gear licence and are required to report their catch, similar to other commercial fisheries.
Over the last 6 months, Marine Scotland, the SSPO, fish farming companies and fishermen have worked to introduce a range of voluntary measures with the aim of ensuring the sustainability of this important fishery. These include minimum and maximum landing sizes, a closed season, effort control and research to better understand the stocks.
Demonstrating the sustainability of the wild wrasse stock is important and the salmon farming industry continues to seek to better understand both how it uses these fish as a biological control and the population structure of this fishery.