Farmed stocks of Atlantic salmon in Ireland are inspected on 14 occasions throughout the year to monitor sea lice levels as part of a national programme. Sea lice are a naturally occurring parasite found on marine fish, including salmonids. They are small ecto-parasitic copepod crustaceans and there are approximately 559 species. The objectives of the National Sea Lice Monitoring Programme are: *To provide an objective measurement of infestation levels on farms. * To investigate the nature of infestations. * To provide management information to drive the implementation of control and management strategies. * To facilitate further development and refinement of this strategy. The sea lice control and management strategy has five principal components: * Separation of generations. * Annual fallowing of sites. * Early harvest of two-sea-winter fish. * Targeted treatment regimes, including synchronous treatments. * Agreed husbandry practices.