A us federal judge has blocked scientists from carrying out trials of newly developed sonar on migrating grey whales. The Woods Hole Oceanographic Institution and Scientific Solutions Inc. had planned the tests off the coast of central California during the whales' southward movement, but environmentalists protested.

The us government argues that the research "is intended to benefit whales". Pressure groups, however, allege that the sonar could disorient whales and separate calves from their mothers. The National Marine Fisheries Service had approved the experiments last year. Scientists say the sonar could be deployed to keep vessels from ramming whales.

The Channel Islands Animal Protection Association contends that such systems "harass" marine mammals as they are susceptible to sonar interference. The whales rely on sound for communication, feeding, mating and migration.The intense low-frequency sonar transmissions are on the same frequency used for communication by many large whales.