Aggressive fish is spreading rapidly in the Baltic Sea – Swedish Radio

An aggressive and anti-social behavior is one reason why the round goby rapidly now spreading along the coast of Gotland.

The round goby has taken to the Baltic Sea from the Black Sea and the Caspian Sea, with the help of ships’ ballast water. The alien fish may include out-compete the flounder.

– The individuals who spreads first has a different behavior than those who stay. When it thinks it’s getting crowded when they go on. And they are more risk averse, more active and stays rather for themselves than in a group. They are anti-social, so to say.

Magnus Thorlacius, Umeå University, added in December presented her thesis on how the fish is spreading in the Baltic Sea. He has studied the round goby in Visby harbor. And it is therefore up to individuals who do not like when it gets too many fish in the same place, which spreads first, shows his research. It is therefore urgent, once discovered the fish in a new location – in all if you want to try to prevent it from spreading further.

– It takes as little as three to five years before they begin to spread in large quantities. So action must be taken any time within three years.

Another factor that may contribute to the spread are fish behavior winter. Then pull it up out in deeper water, and at night the larvae swim up to the surface, feeding on plankton.

– And then they can be spread by currents in the water or end up in ballast water on ships, says Magnus Thorlacius.

1990 found round goby for the first time in the Baltic Sea, then in Poland. 2010 appeared it up in Visby, and since then it has been found in several ports on the island. The Visby harbor is the now numerous and 2014 found Magnus Thorlacius plenty of round goby along the beaches outside the harbor, north and south.

While some predatory fish could serve to round goby establishes itself – by goby becomes food for them – so see others like it will be the losers. The blenny and especially flounder risk being driven out by the aggressive fish who like staying in the same places and live on the same feed as the flounder.

– It will probably have a negative impact on flounder and eelpout and others less, like fish.

Magnus Thorlacius considers it unlikely that it is possible to stop the round goby from spreading in the Baltic Sea.

– But by fishing them intensively, in the beginning, so you could slow down the spread.

Johan Hellstrom
johan.hellstrom@sverigesradio.se
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