The first line says it all
"There will be virtually nothing left to fish from the seas by the middle of the century if current trends continue, according to a major scientific study. "
Anyone ever read 'How to lie with statistics' by By Darrell Huff?
Near the end he explains that if you know how something is changing over some short time period, you can make the situation seem much more extreme by projecting the trend into the future. There may be no particular reason to believe that the trend will continue, but in the meantime, you have got your headline.