Strong, mandatory measures to prevent the escape of fish from aquaculture facilities might also help prevent the spread of disease. Farmed salmon pose disease threats and have the potential to pose genetic threats. Farmed salmon are more susceptible to disease because they live in contained areas in relatively high density. Diseases in farmed populations can spread when a fish escapes. Because some aquaculture facilities are located near salmon migratory paths, there is also the potential for disease to spread to free-swimming fish as they migrate past the salmon farm.
Cultured salmon pose a genetic threat if they escape and reproduce with fish in the river.
A particular threat is farmed salmon raised from European populations. Some people have called for additional reviews of the science behind the proposed listing. Most of the scientific work that led to the proposal to list has already been peer reviewed. The services have no objection in principle to another peer review, but the ESA requires timely action when a species may be threatened or endangered. The few fish that returned to spawn last year left on their ocean migrations before the Maine plan was in effect.