Farm Salmon Thrive, Wild Salmon Sicken

Salmon aquaculture grew into a 2.7-million-tonne global industry, making salmon affordable, widely available, and generating enormous economic value for coastal communities. Norway alone produces 1.1 million tonnes annually. But open net-pen salmon farms become amplification reservoirs for sea lice and bacterial pathogens. Wild juvenile salmon migrating past farms encounter lethal parasite loads that would not exist without farm-density amplification. In western Norway, estimated post-smolt mortality from sea lice exceeds 30% in several areas, with ~50,000 wild adult Atlantic salmon lost annually — approximately 10% of the national population. In Chile, the dominant pathogen *Piscirickettsia salmonis* (causing SRS) accounts for 83.3% of farmed salmon mortality and drives antibiotic use 300–500× higher per tonne than Norway. The industry's success created the pathogen reservoir that now threatens both farmed and wild stocks.

Wild Atlantic salmon populations are declining across their range. Three pathogen types spill over from farmed Atlantic salmon to wild Pacific salmon in British Columbia: piscine orthoreovirus, *Tenacibaculum* spp., and sea lice. Chile uses ~660 g/tonne of antibiotics (98.6% florfenicol) versus Norway's ~0.02–0.39 g/tonne — a biological asymmetry caused by Chile's dominant pathogen evading adaptive immune responses, making the Norwegian vaccine-based model non-transferable. Chemical sea lice treatments pollute surrounding waters and are toxic to non-target crustaceans. The salmon aquaculture industry is in a sustainability crisis where the scale of production creates the pathogen load that undermines both wild populations and farm profitability.

Norway's "traffic light" system regulates production growth based on wild salmon lice impact (green/yellow/red zones), but doesn't reduce existing production. Closed containment and land-based recirculating aquaculture systems (RAS) are technically viable but 2–5× more expensive, making them uncompetitive for commodity salmon. Lice skirts, cleaner fish (wrasse/lumpfish), and laser delousing reduce parasite loads but don't eliminate them. Vaccine development for *P. salmonis* has had limited success because the bacterium is a facultative intracellular pathogen that evades adaptive immune responses. Canada (BC) announced a transition away from open net-pen farms by 2025, but implementation has been delayed and contested by the industry. Sea lice are developing resistance to chemical treatments, following the pesticide treadmill pattern.

Economically viable closed-containment aquaculture that eliminates the environmental interface with wild stocks. Novel vaccine platforms for intracellular pathogens like *P. salmonis*. Integrated spatial planning that separates farm locations from wild salmon migration corridors. Selective breeding programs that increase disease resistance without compromising growth performance.

A team could design a low-cost environmental DNA (eDNA) monitoring system to detect sea lice and pathogen concentrations in the water column near salmon farms and along wild salmon migration routes, providing spatial data currently missing from most management systems. Alternatively, a team could develop an economic model comparing long-term profitability of open net-pen versus closed-containment systems when wild stock depletion externalities and antibiotic resistance costs are internalized. Aquatic ecology, bioengineering, and fisheries economics skills apply.