BSEP116B Biodiversity in the Baltic Sea - Helcom

Box 3.5.1. Sturgeon re-introduction programme
Until the 19th century, sturgeons were widely distributed
in the Baltic Sea and its southern tributaries. Their decline
became obvious already in the 18th century and was caused
by overfishing, as well as the increasing pollution and regulation
of rivers. As a result, the species was considered missing
or extinct throughout the range states and the last sturgeon
in the Baltic Sea was caught in Estonia in 1996 (Paaver 1997).
Attempts to remediate the sturgeon population in the Baltic
Sea started under the auspices of HELCOM in 1996. While
focusing on Acipenser sturio in the first years, genetic and
morphological evidence revealed that the sturgeon present
in the Baltic until the 20th century resulted from colonization
by the American Atlantic sturgeon (Acipenser oxyrinchus)
approximately 1 200 years before present (Ludwig et al.
2002). These findings resulted in a shift to remediation of the
Atlantic sturgeon. The remediation attempts were facilitated
by shipments of early life stages of fish both for building up a
broodstock as well as for experimental release. Furthermore,
transfer of adult fish for broodstock development has taken
place since 2006. In both cases, the fish originated from the
natural population of the St. John River, which is genetically
closely related to the historic sturgeon that used to occupy
the Baltic Sea.
All marked sturgeons regardless of size released in the
upriver sections had a tendency to migrate downstream
immediately, entering coastal waters. Pronounced individual
differences were observed with regard to migration speed,
both in telemetry studies as well as in fisheries reports.
The presence of the first sturgeon in the Gulf of Gdańsk as
well as in the Pomeranian Bay was noted only 10 days after
the release, with maximum distances of 400 km covered
during this time span. According to the information from
the fishery, sturgeons spent two or more weeks at the river
mouth foraging intensively. This resulted in rapid growth,
providing clear evidence for the abundance of available
food resources (Kolman & Kapusta 2008). Atlantic sturgeon,
similar to a majority of other sturgeons, is a typical
benthic species feeding mainly on a variety of invertebrate
species. Because it used to be the only fish species with this
feeding characteristic in the Baltic Sea, there is little probability
of competition for food resources with other fish
species following its re-introduction.
The results of the Polish-German project suggest that there
is a significant chance for a successful re-introduction if
natural reproduction and limitation of by-catch can be
ensured.
Along with broodstock rearing, research on the behaviour
of juveniles in their natural habitat has been carried out in
experimental release programmes since 2006. For these
purposes, mainly the Drawa (Odra River tributary) and the
Drwęca (Vistula River tributary) rivers have been utilized. In
the past, these rivers included sturgeon reproduction sites
and habitat for early life stages and these ecological conditions
have been maintained until today.
Under the bilateral Polish-German cooperation, more than
7 000 individuals of Atlantic sturgeon were released into
the Odra and the Vistula tributaries in 2007, while in 2008
more than 35 000 sturgeons were stocked. The sizes varied
from 1.5 cm to 70 cm in an attempt to identify their respective
suitability for release. Released fish were equipped with
Floy or Carlin tags. An additional 150 fish were marked with
transmitters to determine their migration routes.
Sturgeon release, Odra River 2006
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