Original: Other areas seem to support fairly healthy populations of some of the over 48 different species of tuna -- for example , the central and western Pacific skipjack tuna , Katsuwonus pelamis -- but there is mounting evidence that overexploitation threatens tuna populations worldwide .
Simplified: Other populations seem to support fairly healthy fisheries ( for example , the central and western Pacific skipjack tuna ) , but there is mounting evidence that overfishing threatens tuna fisheries world-wide .