HOHHOT - Seven people have been nabbed for poisoning 233 swans in north China's Inner Mongolia autonomous region, local authorities said on Friday.

The police spent nine days searching for the suspects and had caught them in Beijing and Tianjin municipalities as well as the provinces of Jilin and Hebei as of Thursday, according to the information office of Zhenglan Banner in Xilingol League.

The swans were found dead in a lake in Zhenglan Banner where migrating swans had stopped in late October. Tests revealed that they were poisoned with carbofuran, a type of pesticide, which was detected on the dead birds.

Further investigation is under way.