In the middle of the Pacific Ocean, Gonzalo Mucientes has discovered an invisible line in the sea that separates male mako sharks from females. The line runs from north to south with the Pitcairn Islands to its west and Easter Island to its east. On the western side, a fisherman that snags a mako will most probably have caught a male. Travel 10 degrees of longitude east and odds are they’d catch a female. This is a shark that takes segregation of the sexes to new heights.
Mucientes and colleagues from Spain, Portugal and the UK spent four months aboard a Spanish longline fishing vessel. Amid more typical catches, the boat often snagged shortfin makos and blue sharks. When they did, the researchers meticulously noted the boat’s position, and analysed the shark carcasses on board.
Their results showed a clear “line in the sea”. All in all, the fishermen captured 264 male makos, mostly towards the west of the line and 132 females predominantly in the east. Makos are found all over the world, but this study shows that at a more regional level, their populations are structured to an astonishing degree.
This segregation is even more surprising when you consider that makos are the world’s fastest sharks. They can clock speeds of up to 45 miles per hour, about eight times as fast as Michael Phelps at his peak. They really shouldn’t have any problems in covering vast tracts of water.