Now there is a literature review on the Atlantic Salmon Federation that is fighting to get fish farms out of the water on Canada's Atlantic coast: http://www.asf.ca/effects-of-sea-lice-on-sea-trout.html.
This is the abstract and PDF link:
Effects of salmon lice Lepeophtheirus salmonis on wild sea trout Salmo trutta—a literature review
This review focuses on impacts of sea lice on sea trout, but also has mention that sea lice can lead to an average of 12 - 29% fewer salmon spawners.
The article can be downloaded on this page, and from the website below.
ABSTRACT: Salmon farming increases the abundance of salmon lice, which are ectoparasites of salmonids in the sea. Here we review the current knowledge on the effects of salmon lice on wild sea trout. Salmon lice feed on host mucus, skin and muscle, and infestation may induce osmoregulatory dysfunction, physiological stress, anaemia, reduced feeding and growth, increased susceptibility to secondary infections, reduced disease resistance and ultimately mortality of individual sea trout. Wild sea trout in farm-free areas generally show low lice levels. In farm-intensive areas, lice levels on wild sea trout are typically higher, and more variable than in farm-free areas. Lice on wild sea trout are found at elevated levels particularly within 30 km of the nearest farms but can also extend to further ranges. Salmon lice in intensively farmed areas have negatively impacted wild sea trout populations by reducing growth and increasing marine mortality. Quantification of these impacts remains a challenge, although population-level effects have been quantified in Atlantic salmon by comparing the survival of chemically protected fish with control groups, which are relevant also for sea trout. Mortality attributable to salmon lice can lead to an average of 12-29% fewer salmon spawners. Reduced growth and increased mortality will reduce the benefits of marine migration for sea trout, and may also result in selection against anadromy in areas with high lice levels. Salmon lice-induced effects on sea trout populations may also extend to altered genetic composition and reduced diversity, and possibly to the local loss of sea trout, and establishment of exclusively freshwater resident populations.- See more at: http://www.asf.ca/effects-of-sea-lice-on-sea-trout.html#sthash.aqQ2gj5G.dpuf
And in Norway, there are severe penalties for having too many lice on farmed fish: http://www.undercurrentnews.com/reports/?utm_source=Undercurrent+News+Alerts&utm_campaign=b26baf019f-Salmon_roundup_Sep_04_2015&utm_medium=email&utm_term=0_feb55e2e23-b26baf019f-92426209.
In Canada, the exact opposite situation. Just look at recent posts on fishfarmnews.blogspot.com how the laws has been weakened and new aquaculture regs allow fish farms to use chemicals far in excess of the past.