An Al Jazeera investigation has prompted authorities in Sierra Leone to take action against illegal fishing off the country's coast.

The problem has been particularly acute in West African waters for decades, where fish is a vital and often the only protein source for millions of people.

There was a big jump in the number of South Korean and other foreign trawlers fishing in the country's exclusion zone last year.

But after Al Jazeera launched a probe to try and identify and expose the vessels in October 2010, the network returned to Sierre Leone to discover that authorities have made it more difficult to fish illegally.

Juliana Ruhfus reports from the coast of Sierre Leone.