Opening the season in the sign of cormorants

I do not understand why the cormorant birds are protected species in Croatia? It is not autochthonous species, and the number of cormorants that destroys fish of our rivers, lakes and the sea is increasing each year. They have no natural enemies, and every year, causing terrible damage to fish stocks. After years of destroying fish stocks in Međimurje channel, this year the damage is done to Gacka river. Precisely because of the damage done by cormorants killing innocent Gacka trout, this year the season is not open to the best manner. Caught and seen very few fish and I hope in next few weeks when it warms up, much more fish will be seen. But the problem of the cormorant birds will stay, and our lakes, especially rivers will be sadly empty without fish, if the law will ignore this issue.