Heuch & Mo (2001) have devised a model for the production of salmon lice in Norway from Vest-Agder up to Troms. The model operates with threshold values: (1) the level of lice in 1986-1987 (before disconcerting effects on sea trout were observed) and (2) a level that implies a doubling of estimated natural infestation pressure. The thresholds imply a production of salmon louse eggs of between 50 billion and 5.2 billion.

The number of louse eggs produced by wild salmonids was estimated at 2.6 billion. With a limit in accordance with the current salmon lice regulation (0.5 lice per fish), the number of eggs produced from farmed fish is estimated at 29 billion in 2000.As a result of a continued increase in the number of farmed fish in the sea, Heuch and Mo operated with an increase in louse production from fish farms in 2005 to 46 billion eggs. Given the current escape situation, the contribution from escaped farmed fish is on the order of 15 billion eggs. Salmon louse production from escaped farmed fish is thus six times higher than the total production from wild salmonids. (Heuch, P.A. et al., 2001)

[picture1right]In 2000, the official threshold was supposed to have been 0.6 lice per farmed fish, assuming a threshold of 50 million eggs. If all fish farmers had followed the official order that year, total louse production would be close to 50 billion eggs. In order not to exceed the limit for a doubling of the natural infestation pressure, with the production in 1999, we would have had to lower the limit of lice per fish to 0.05 (Heuch, P.A. et al., 2001).