Can tiny, cultured cod larvae save the critically endangered Baltic cod?
A research project is in full swing to investigate whether it is possible.
Since the beginning of June, approximately 600,000 cod larvae per week have been released into a bay in Stockholm’s southern archipelago – but the researchers will not get answers until next year.
Six buckets of tiny cod larvae are carried out onto the jetty and loaded aboard the fishing boat Vegas.
They are bred in pools at a research station on Gotland and have been transported by transport truck with the Gotland ferry to the mainland. Soon they will be released into the open sea for the first time.
The researchers’ hope is that the larvae will survive the release, develop into fry and next year have grown into small fish. In that case, they may have found an artificial method for many more cod to be able to spawn where cod spawning can still function, that is in the Bornholm Deep and Arcona Basin.
– The big dream is that these little ones will become sexually mature and grow up and be able to reproduce themselves naturally in the Baltic Sea, says Johanna Fröjd, project manager for the cod project run by the Baltic Waters foundation.
Critical where the larvae are dragged
There is a lot that has to be right for the little larvae to have a chance to survive when they are released. The water where they are released must not be too warm, it must be sufficiently salty and there must be the right kind of plankton to eat.
The larvae are only five days old and scientists do not yet know if they will survive.
– We will try to rake up the larvae that we have put out earlier in the season, and also try to do a trial fishing in the autumn to see when they have gotten a little bigger, says Johanna Fröjd.
The eggs die
Overfishing and the oxygen-free bottoms of the Baltic Sea are two important reasons why the cod stock is in such poor condition. Cods lay their eggs floating slightly above the seabed, but the low salinity of the Baltic Sea causes the eggs to fall to the bottom instead, where there is not enough oxygen.
The eggs die too much even in the few places where reproduction is possible.
If the research project is successful, fry can be planted out where the cod still manage to reproduce. But more measures are still needed, according to Johanna Fröjd, such as reduced fishing quotas and proper efforts against the eutrophication that causes oxygen-free bottoms.
– In the deep places in the water, there is no oxygen in two of the three places where the cod have spawned. So now only Bornholmsdjupet works.