Conservation versus harvest of wild Atlantic salmon. The cost of sea lice induced mortality

- The paper presents a bioeconomic stage structured model for wild Atlantic Salmon harvest.
- The problem of sea lice induced mortality is analyzed.
- Even under quite severe sea lice induced mortality, we find a quite aggressive harvest pattern to be optimal.
- We find that the welfare and economic losses in a typical Norwegian salmon river may be in the range of 15-25%.
- At high sea lice induced mortality levels, the welfare improvements of selective harvest are substantial.

Increased sea lice densities in the farmed salmon sector have recently led to the growing concerns in Canada, Chile and Norway as the main producer countries. The sea lice incur problems within the farmed fish industry itself as well as in wild stocks. We present a bioeconomic model for wild Atlantic salmon (Salmo salar) and explore to what extent the harvest and social benefit of wild salmon fishing in Norway are affected by sea lice-induced mortality. An age-structured population model is required to analyze the losses because the salmon post-smolts are the most vulnerable to attack by sea lice, while the harvest value is related to the three age classes of mature spawning fish. Losses are analyzed by determining the reduced harvesting value as well as the non-consumptive (conservation) value of the wild salmon stock pertinent to various sea lice-induced mortality levels. Our findings indicate that welfare and economic losses in a typical Norwegian salmon river may range from 15 to 25%. In addition, at low sea lice levels, the welfare improvement associated with selective harvest is quite modest, and is even lower when non-consumptive values are deemed important. On the other hand, when sea lice-induced mortality levels are very high, the welfare improvements of selective harvest are substantial.