A report released by the United Nations Environment Programme predicted that the fish populations in the world will decline drastically in the next 40 years due to the factors including overfishing, rises in sea surface temperatures, and marine pollution, local media reported on Thursday.

It warns that larger species such as tuna will almost disappear, leaving fisheries dependent on smaller species measuring around 20 centimeters, the public broadcaster NHK reported.

The release of the report on marine ecosystems coincided with an ongoing international conference on biodiversity in the central Japanese city of Nagoya.

Representatives from all corners of the world gathered in the central Japanese city of Nagoya on Monday for the 10th meeting of the Conference of the Parties to the Convention on Biological Diversity, known as COP10.

If the marine environment continues to deteriorate at the current rate, multi-million dollar services including fisheries and tourism could be adversely affected, UNEP officials were quoted as saying. They called for urgent countermeasures.

According to a separate UN report released at the meeting on Wednesday, the world will suffer an annual economic loss of some 4.5 trillion U.S. dollars if no measures are taken to protect ecosystems and maintain biological diversity.