Pacific Institute for the Mathematical Sciences - PIMS

The continuing decline of ocean fisheries and rise of global fish
consumption has driven aquaculture growth by 10% annually over the last
decade. The association of fish farms with disease emergence in
sympatric wild fish stocks remains one of the most controversial and
unresolved threats aquaculture poses to coastal ecosystems and
fisheries. I will present a comprehensive analysis of the spread and
impact of farm-origin parasites on the survival of wild fish
populations. The methods mathematically couple extensive data sets of
native parasitic sea lice (Lepeophtheirus salmonis) transmission and
pathogenicity on migratory wild juvenile pink (Oncorhynchus gorbuscha)
and chum (Oncorhynchus keta) salmon.

Farm-origin lice induced 9–95% mortality in several sympatric wild
juvenile pink and chum salmon populations. The epizootics arise through
a mechanism that is new to our understanding of emerging infectious
diseases: fish farms undermine a functional role of host migration in
protecting juvenile hosts from parasites associated with adult hosts.
Although the migratory life cycles of Pacific salmon naturally separate
adults from juveniles, fish farms provide L. salmonis novel access to
juvenile hosts, in this case raising infection rates for at least the
first 2.5 months of the salmon’s marine life (80 km of the migration
route). Spatial segregation between juveniles and adults is common
among temperate marine fishes, and as aquaculture continues its rapid
growth, this disease mechanism may challenge the sustainability of
coastal ecosystems and economies.

PIMS-MITACS Mathematical Biology Seminar Series 2006

Marty Krkosek is a PhD Candidate, Biological Sciences, University of Alberta.