Sea lice and salmon population dynamics: migration, domestication, and conservation

Background/Question/Methods

The migratory lifecycles of Pacific salmon limit the opportunities for parasite transmission among host generations to brief periods of sympatry between adults and juvenile hosts. For a marine ectoparasitic copepod, the salmon louse, the transmission period occurs several months after the ocean migration of juvenile salmon begins. Some coastal ecosystems have experienced rapid growth of sea-cage salmon aquaculture, with millions of domesticated salmon hosts now situated on the migration routes of wild fish. This change in host population structure has important implications for parasite transmission dynamics and the productivity and conservation of wild salmon populations.

Results/Conclusions

Sea-cage salmon aquaculture changes transmission dynamics of sea lice in two important ways: (1) it amplifies the abundance of parasites in coastal marine ecosystems; and (2) it changes the phenology of transmission such that juvenile hosts become exposed to parasites longer and earlier in the salmon lifecycle. Infection alters the behavior of juvenile salmon as well as their survival resulting in a decrease in the productivity of wild stocks, as well as a risk of extirpation. Effective control of parasites on farmed salmon populations has become an important component of biodiversity conservation in salmon ecosystems where aquaculture operations exist or are proposed.