abdallah: i've been a fisherman for 38 years. a lot has changed in that time.enty years ago we used to catch loads of prawns. but in recent years, there have been repeated events that have reduced our catch. the latest problem was the blue crab, they wiped out everything. >> the first blue crabs were spotted here at the end of 2014. it's a species that was previously unknown in tunisia. their numbers increased rapidly, and within eight months the crabs had become a real menace. they would cut the fishing nets, eat the fish and devour anything else they could find. they became such a problem, that the fishermen nicknamed them "daesh," after the notorious militant group islamic state. the blue crab is native to the indopacific region. they came here via the red sea and the suez canal, like most of the roughly one thousand non-native species that have reached the mediterranean. because of climate change, the waters here are now also warm enough to support tropical species. mohamed nejmeddine bradai has spent decades udying the migratory patterns in the mediterrane