The rich marine life off Tanzania's coast is coming under threat because of blast fishing - a technique using explosives that some fishermen use to maximise their catch.

''Blast fishing destroys the fish habitats under water where fish reproduce and that has had a big impact, especially on us who use ring nets to fish," a 32-year-old fisherman says.

"The number of fish has drastically reduced we are not able to catch many fish like before," he said as prepared his wooden boat to go fishing in the calm and beautiful waters of the Indian Ocean.

Small fishing vessels like his dot the coastline that hugs Tanzania for thousands of kilometres.