Abstract
Genetic homogenization has been recognized as
a serious threat in an increasing number of
species, including many salmonid fishes. We
assessed the rate and impact of immigration from
the main hatchery stocks of Atlantic salmon in
the Gulf of Bothnia into one of the largest wild
salmon populations in the Baltic Sea, the River
Vindelälven, within a temporal framework of 18
years (from 1985-2003). We provide genetic
evidence based on mtDNA and microsatellite
markers, using mixed-stock analysis, that a
large proportion (66%) of fin-damaged spawners
(n=181) caught in the Ume/Vindelälven during
1997-2003 originated from the hatcheries in the
Rivers Angermanälven, Luleälven and Ljusnan. The
maximum-likelihood estimate of immigration rate
from these hatcheries into the wild Vindelälven
population was 0.068 (95% CI 0.021-0.128) over
the studied time period (1985-2003) and reached
up to a quarter (m=0.249, 95% CI 0.106-0.419) of
the total population during 1993-2000. This
resulted in significant (P<0.01) genetic
homogenization trend between the wild
Vindelälven population and hatchery stocks of
the Angermanälven and Luleälven. Our results
demonstrate extensive straying from
geographically distant hatchery releases into
wild salmon population and emphasize the genetic
risks associated with current large-scale
stocking practices in the Baltic Sea.
