A pregnant porbeagle shark that was being tracked off the coast of Bermuda has disappeared, and scientists believe they have identified the primary suspects in the case – a great white shark or a shortfin mako. This event represents the first recorded case of shark-on-shark violence with species of this size, which has surprised and alarmed researchers. The loss of the reproductive female porbeagle and all her developing babies could have major impacts on the already suffering porbeagle shark population, which is endangered and critically endangered in various regions due to overfishing and habitat degradation.
Porbeagle sharks are large creatures that can reach lengths of up to 12 feet and weigh as much as 500 pounds. They have a slow reproductive cycle, with females not reproducing until around 13 years of age and giving birth to an average of four pups every one or two years. Due to their slow reproductive rate, porbeagle populations are vulnerable to threats like overfishing and habitat degradation, leading to their classification as endangered and critically endangered by the IUCN. The pregnant porbeagle involved in this study was tagged off Cape Cod and tracked for 158 days before suddenly disappearing due to a larger predator, likely a great white shark.
After equipping the pregnant porbeagle with two satellite tags, researchers tracked its movements until March 24, 2021, when the data showed a sudden and drastic change indicating that the shark had been consumed by a larger predator. The continued transmission of data from the pop-off satellite archival tag suggested that the predator had consumed the porbeagle and then excreted the tag after a few days. The two potential predators large enough to predate on a mature porbeagle were the great white shark and the shortfin mako shark, with the data pointing to the great white as the more likely culprit based on its behavior patterns.
The unexpected discovery of a pregnant porbeagle being preyed upon by a large predator highlights the complexity of predator interactions in the marine ecosystem. Large sharks are commonly perceived as apex predators, but technological advancements are enabling researchers to uncover more about their interactions with each other. The study emphasizes the need for continued research on predator interactions to understand how often large sharks prey on each other and the potential cascading impacts on the ecosystem. This discovery sheds light on the intriguing behavior of large sharks and the importance of ongoing studies in marine science to protect vulnerable species like the porbeagle.
