Download List of species and areas for stocking measures 3.2

Annex 2 - List of species and areas
for stocking measures
Background
The potential for stocking of fish in the Baltic Sea Region (BSR) as a means of maintaining or improving
natural fish stocks is one of the issues being addressed in AQUAFIMA. Stocking can be used either as
reestablishing the wild stocks which have been declined through overfishing or as establishing species
that are of special commercial interest.
For a number of species like salmon, trout and white fish the stocks have been in the decline. The
possibility of producing fish for stocking certain areas of the Baltic Sea including adjacent rivers or
Bodden waters have been evaluated as one of the means of reestablishing the natural stocks such as
white fish, sea trout and salmon or re-stocking, for example sturgeon in the BSR. The commercial fish
stocks have been suffering due to technical and technological innovations, together with the expansion
of the fishing fleets. Despite years of fisheries management, several of the fish and shellfish stocks
have yet to show signs of recovery. Important fish stocks are at the verge of collapse, not only because
of over-exploitation, but also because of the degradation or loss of spawning and nursery grounds. This
prevents their natural replenishment. The maximum sustainable output of many marine habitats is far
from being achieved. The traditional management measures (catch and effort regulations or technical
measures to improve gear selection) are not enough. There is a need for alternative recovery plans for
fish stocks in the BSR. Insufficient natural recruitment may be overcome by releasing hatchery reared
juveniles in the wild. This is referred to as stocking or re-stocking depending on its purpose.
Several countries have experience with the production of fish for release in the sea. The most common
species for release is salmon and other salmonids (like sea trout, white fish), which are of commercial
interest (e.g. small-scale fisheries and recreational fisheries) and have been produced from national
stocks and released to river beds.
Recommended species
Based on evaluation of former experience with stocking and restocking presented, AQUAFIMA has
decided to evaluate salmon, trout, white fish and sturgeon as potential species for re-stocking in the
Baltic Sea or Bodden waters. In addition other species like pike, pikeperch, vimba vimba, turbot and eel
were evaluated, but not enough data for evaluation were available to base a selection or
recommendation on.
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Salmon (Salmo salar)
Salmon is the most common and well known species for
aquaculture and is a good candidate for stocking. Salmon
has their early life stage in fresh water before it enters the
sea as smolts. The time it will spend in fresh water depends
on a number of factors like nutrition, time of year,
temperature and the internal changes has to prepare the fish
for transition to salt water. In farmed fish the normal life
cycle of salmon is 18 months in the fresh water stage before
it can be transferred to the sea in the spring. Salmon start
their migratory phase to the sea which last for one to three years, a phase that is very different from the
rivers. The survival rate depends on the availability of food, but is also affected by diseases and
predators in addition to commercial fisheries. In order to continue their propagation it has to return to
the rivers and spawn. The survival varies from one year to another, but the overall survival between egg
and spawner is considered to be less than 0.05%. In the wild salmon can take several years to reach 3
– 5 kg, whereas in cultured salmon will reach harvesting size o f 3 – 4 kg in
12 – 18 months.
Rearing of salmon for restocking has been done in Denmark, Russia,
Poland, Lithuania, Latvia and Estonia to varying degree. Since fish
released into the river does not need to be smoltified, juveniles can be
released to rivers throughout the year. The reported sizes of fish released
vary between 0.5 – 25 gram. The larger fish is expected to halve larger
survival rates and more likely to survive in the wild. Releasing small salmon
into the river will, however, depend on time of year and temperature of the
water, presence of predators and availability of food. There might therefore
be different strategies for restocking which are dependent of the production
facility, but also the environmental conditions at the sites of release.
Fig. 1: Checking salmon for
smoltification
Trout (Oncorhynchus mykiss L or Salmo trutta)
There are two species of trout are be suitable for stocking.
Sea trout or brown trout (Salmo trutta) is a natural species in
the Northern Europe. It is found both as freshwater stocks
that spend their whole life cycle in the lakes and rivers and
the migratory stocks which spends part of their life cycle in
the sea in its adult stage. Growth depends on availability of
feed, but in the lakes fish preys on insects and fish larvae
whereas in the sea their normal feed is local fish species. In areas with good availability of feed, they
grow fast and will reach 2 kg in 2 years. Growth is normally slower in lakes than the sea. In addition to
commercial fisheries, the trout is important for anglers in sport fishing. Overfishing has reduced stocks
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and millions of fry has been produced for restocking. In Germany alone, has an annual production of
6.5 million for release since 1992.
The rainbow trout, Oncorynchus mykiss, has been introduced
to Europe from North America as a suitable candidate for
aquaculture. In aquaculture it spans in freshwater and
transferred to the sea. In the wild it may remain in the lakes for
their entire life cycle. Since being introduced all over the world
since the mid 1800 it has become endemic to most areas and
juveniles are produced for stocking purposed, primarily for
sport fishing. When released at catch size (0.5 – 2.0 kg), as is
currently common practice, they do not usually grow much anymore. Rainbow trout released in flowing
water tend to be caught near the release site. When released in lakes or the sea, they make lengthy
migrations. For example, catch-size rainbow trout released in the Gulf of Finland in 1994 were
eventually caught in the Southern Baltic Sea.
White fish (Coregonus lavaretus L.)
White fish is a common freshwater fish, widespread from central
and northwest Europe to Siberia. It is normally found in lakes,
rivers and sometimes brackish water. In Finland the white fish is
one of the most common species for stocking of lakes and has
been reared for over 100 years. Natural white fish stocks have
decreased in many areas because of deteriorating reproduction
conditions. The breeding grounds of river-spawning stocks have
been dredged, and migrations have been blocked by powerplant dams. Regulation of the water level may be fatal to lake
spawning stocks. Most vulnerable to regulation are stocks that spawn in shallow water. Mature fish
usually spawn in lakes in the fall, but some stocks in the sea will migrate to the rivers for spawning.
According to “Game and Fisheries Research Institute” in Finland, easy rearing and stocking obligations,
the management of whitefish waters and stocks now consists almost entirely of releases. About 30
million newly hatched or one-summer-old white fish are released annually. Many economically valuable
white fish stocks are dependent on releases. In the Northern Gulf of Bothnia, fishing is oriented too
much towards young, immature migrating white fish. The need for fishing regulation is strongest for the
bottom-net fishery aimed at anadromous white fish. An increase in the mesh size for sea trout (Salmo
trutta) and pikeperch (Sander lucioperca) fishing would also benefit white fish stocks. Over large areas
of the Gulf of Bothnia, the smallest allowable mesh size is already 50 mm. Of Finland's six white fish
forms, the anadromous white fish and the plankton white fish are classified as vulnerable (VU) and the
lake white fish as near threatened (NT).
Rearing of white fish juveniles is considered to be fairly easy as hatched larvae can be fed artificial feed
and has good survival rate. It seems a good candidate for hatchery production in commercial scale and
can benefit from the same rearing systems as salmon and trout. The challenge in German breeding
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programs is to establish an artificial breeding population to obtain a
good egg supply for rearing of juveniles. An experimental white fish
breeding plant in Kaliningrad produces juveniles for release in the
Curonian lagoon. This is a normal breeding area for white fish that
migrate to the lagoon from October to December and then later returns
to the Baltic Sea. Stocking of juveniles are being done in an attempt to
replace the depleting natural stocks.
Sturgeon (Acipencer oxyrinchus)
The American sturgeon, A. oxyrinchus, migrated to the Baltic
Sea and replaced the European sturgeon (A. sturgio). The
population has gradually been depleted in the 20th century due
to pollution and industry which has driven them from their natural
spawning grounds. The species still exist in North America and a
number of broodstocks have been imported from Canada in an
attempt to reintroduction sturgeon into rivers in Germany, Russia
and Poland. Sturgeon spends most of their lives in the sea and
will migrate to the rivers to spawn. In Germany, breeding
programs has successfully produced 300.000 juveniles in 2010
and 2011 for restocking purposes. A similar program will start in Kaliningrad is Russia in 2014 and in
Poland a national breeding facility has a population of sturgeon broodstock brought in from Saint John
River in Brunswick, Canada. Restocking the rivers might be the start of a new population of sturgeon,
but it takes almost 7 years before reaching maturation. Broodstock will spawn in captivity using
hormone injection (LHRAa) and eggs and sperm stripped, but have also been seen to spawn naturally.
The eggs hatches after three days and larvae are fed rotifers and later Artemia as live feed. The long
term plan is to import more broodstock from Canada or alternatively strip eggs and sperm and import
the fertilized eggs to Germany for start feeding.
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Table 1: Commercial hatcheries in the Baltic Sea Region with an annual production of > 100.000 juveniles.
Producer
Country, location
Species
Voklhovsky Fish breeding plant
Russia, Kaliningrad
Nevsky Fish Breeding Plant
Russia, St. Petersburg
White fish
Salmon
Lugzsky Fish breeding plant
Narvsky Fish breeding plant
Kalingrad fish breeding plant
Russia, St. Petersburg
Russia, St. Petersburg
Russia, Kaliningrad
Private fish breeding plant
Russia, Kaliningrad
Bornholm lakseklekkeri, Nexö
Denmark
Association Fish and Environment
Experimental research station
National Park Unteres Odertal
Germany, MecklenburgVorpommern
Germany, MecklenburgVorpommern
Salmon
Salmon
Salmon
Pike
Pikeperch
Salmon
100.000
100.000
100.000
3 mill
0,5 mill
300.000/400.000g
annually (fry)
Sturgeon
< 100.000
Salmon
800.000 annually
(average length:
4cm)
600.000 annually
(average length:
4cm)
Approx. 200.000
annually (average
length: 3cm)
2 mill since 2000
Trout
1,1 mill larvae
Germany, MecklenburgVorpommern
White fish
Limited liability company BIMES,
Frauenmark
Germany, MecklenburgVorpommern
White fish
Hatchery Tassilo Jäger-Kleinicke,
Kiel
Germany Schleswig Holstein
White fish
Põlula Fish Farming Centre (state
owned)
Õngu Fish Farm
Estonia,
Härjnurme and Ongu
Six state owned hatcheries ,
10 – 15 private hatcheries
Lithuania, Rivers, lakes,
Curonian lagoon
Latvia, Riga bay
100.000
Sea trout
Association Fish and Environment
State hatcheries “Bior”
Annual
production
2,8 mill
White fish,
salmon,
trout,
Salmon
Trout
9 mill white fish
since 2000
15 mill larvae
Methods for stocking
There are several considerations to make when releasing fish to rivers or the sea. The individuals
reared for stocking should be of high quality in order to be able to compete in the wild. Stocking of fish
should be done when conditions are favorable and feed abundant, normally in the spring when plankton
blooms and fish larvae will provide feed for the fish. Temperatures should be within optimal range for
the species. In cold temperatures the metabolism will be slower and less feed is needed, but at
subnormal temperatures the fish will lose their appetite and mortalities will occur. Similarly, if the
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temperatures are too high, it increases the risk of diseases. Handling stress is reduced in cooler water
but will cause delayed, high mortality in warm water.
Before releasing fish to the sea it is essential to evaluate the suitability of the fish. Young larvae have
low survival opportunity in the wild and larvae reared in captivity will be even less likely to survive. The
two main reasons are predation from larger fish and availability of feed to grow. Small larvae do not
swim long distances and will need to have the feed available where they are. Experience from
Norwegian release of cod juveniles rather than larvae showed a recapture of nearly 20%.
Other factors like the ability of the released fish to adapt to wild conditions are important. Cultured
individuals are often less well adapted to natural habitats than wild fish and therefore less likely to
survive.
Culture process
Broodstock obtained from
wild or cultured fish
Release for stocking
Moving mature fish to spawn
in depleted areas
Sustainability
Success depends on
fertilization success and
availability of feed . Extremely
low survival rate of offspring
Natural spawning or stripping
and fertilizing of eggs
Fertilized eggs
Demersal eggs in rivers more
successful than pelagic eggs.
High risk of predation and
starvation. Very low survival
rate
Incubation of eggs for
hatching
Release of newly hatched
larvae in areas with a plenty
of live feed
High risk of predation and
starvation.
Very low survival rate
Start feeding of larvae until
larvae fully able to catch prey
Ongrowing of larvae to
juveniles on formulated feed
Release of fully developed
larvae
Release of juveniles of
varying size
Risk of predation and
starvation.
Low survival rate
Time of release can be
selected.
Fish able to chase prey.
Low to medium survival rate
Fig.2: Methods for stocking
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This publication was prepared within the framework of the INTERREG IV B project AQUAFIMA
www.aquafima.eu
The content of this publication is the sole responsibility of the authors and can in no way be taken to
reflect the views of the European Union.
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