Global aquaculture adds to world fish supplies, but the method has the potential to damage ocean and coastal resources. Of particular concern to the Atlantic salmon industry, “biological pollution” (or the escape of farmed Atlantic salmon into the wild) can negatively affect the stocks of wild and farmed fish.
In the United States, both states of Washington and Maine maintain salmon farms. Reported regulation data from Washington state shows that about 600,000 farmed salmon escaped between 1996 to 1999. It is theorized that many of these salmon were taken by recreational fishermen and commercial fishermen in Puget Sound and beyond. However, there were a few reported cases of farmed salmon recovered as far as the Alaskan Peninsula (15, 18).
When farmed salmon escape from ocean pens, they may threaten wild salmon and other fish in the following ways (7):
- Colonization of salmonid habitat
- Competition with native species for forage
- Predation on indigenous species
- Vectors for the introduction of diseases and parasites
Hybridization is of particular interest. If a farm escaped Atlantic salmon were to hybridize with wild species, an alteration of the genetic makeup of wild Atlantic salmon populations may be seen. In the table below, Gross (1998) summarizes the observed and suspected genetic differences between farmed and wild Atlantic salmon. It is hypothesized that the genetic differences in wild salmon populations reflect a “fit” for their environments. Thus, a change in genetic makeup may contribute to a decline in wild Atlantic salmon (12, 16).
In general, the genetic effects of accidentally or intentionally released farmed Atlantic salmon on wild populations may be unpredictable, variable, and potentially negative (17).