Since the mid-20th century, catches of salmon and sea trout in Scotland have been declining, an indication of population declines. The decline has been attributed to a fall in marine survival rates. The increase in salmon farming in Scotland over the latter part of the century, and the landing of wild salmonids infested with sea lice, has led to claims that increased parasitism on wild fish, caused by salmon farms, is a contributory factor to the decline. It is claimed that farms inflate the sea lice populations of species Lepeophtheirus salmonis and Caligus elongatus, leading to increased infection pressure and mortality of wild fish.