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<\/div>The pregnant porbeagle shark after being tagged by researchers<\/p>\n
Jon Dodd<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
A pregnant porbeagle shark may have been eaten by a great white shark near Bermuda, in the first recorded incident of its kind.<\/p>\n
In October 2020, Brooke Anderson<\/a>, then at Arizona State University, and her colleagues tagged a pregnant porbeagle shark (Lamna nasus)<\/em> south-east of Cape Cod in Massachusetts as part of research into pregnant shark migration.<\/p>\n The researchers used pop-off tags, which continuously measure the depth and temperature of the shark. When the tag detaches from the shark and floats to the surface, the stored data is pinged back to shore.<\/p>\n Five months after the pregnant shark was tagged, the tag resurfaced south-west of Bermuda and the researchers received data on its recent movements.<\/p>\n The shark had spent five months cruising through waters at a depth of 600 to 800 metres during the day and 100 to 200 metres at night, with water temperatures varying from 6.4 to 23.5\u00b0C (43.5 to 74.3\u00b0F), according to the tracker.<\/p>\n But from 24 March 2021, something changed. The ambient temperature around the pregnant shark remained between 16.4\u00b0C and 24.7\u00b0C (61.5\u00b0F and 76.5\u00b0F), despite it swimming at a similar depth to before. As well as the change in temperature, there was a shift in diving patterns.<\/p>\n <\/p>\n It suggests the tag \u2013 and the attached shark \u2013 was eaten, says Anderson, who now works at North Carolina Division of Marine Fisheries. \u201cAll our evidence points to the same conclusion,\u201d she says. \u201cIt\u2019s clear that our porbeagle shark was eaten by another shark.\u201d<\/p>\n A great white shark (Carcharodon carcharias<\/em>) is the most likely culprit, the team concluded, as it is the only predator in the area large enough to mount such an attack. The diving patterns and body temperature of a great white also match the data collected by the tag.<\/p>\n \u201cThis was a big female shark that got eaten,\u201d says team member James Sulikowski<\/a> at Oregon State University. \u201cSo something probably larger than it had to have attacked it.\u201d<\/p>\n Anderson says the attack was most likely opportunistic. \u201cThe predation occurred about 300 meters deep in the open ocean where there may be sporadic pulses of prey available for predators,\u201d she says. \u201cIn this scenario, if you can pull it off, a large pregnant porbeagle shark would be a lot of bang for your buck in terms of a meal.\u201d<\/p>\n Porbeagle sharks, which are endangered, are found in the Atlantic Ocean, the South Pacific Ocean and the Mediterranean Sea. They grow up to 3.7 metres long, can weigh up to 230 kilograms and live for up to 65 years.<\/p>\n Female porbeagle sharks don\u2019t start breeding until they are about 13 years old, and give birth to around four pups every one or two years, with a gestation period of 8 to 9 months.<\/p>\n Shark-on-shark predation is relatively common, says Sulikowski, but it is rare for a shark to target another large shark in deep water. This is the first documented case of a porbeagle being eaten by another shark.<\/p>\n If it is happening more widely, it could be a worry for conservationists, says Anderson. \u201cIn one instant, the population not only lost one of these important reproductive females, but also all of her babies,\u201d she says. \u201cWhile predation is a natural event, this discovery highlights the need to continue studying predation of porbeagle sharks and to determine how often it really occurs.\u201d<\/p>\n