Prior to giving birth, the pregnant porbeagle shark was expected to give birth soon, when one of the two tracking tags attached to the shark by marine scientists resurfaced near Bermuda.
Surprisingly, the tag emerged much earlier than anticipated. It had been affixed to the 7-foot-long shark only 158 days prior, after conducting an ultrasound scan off the coast of Cape Cod, Massachusetts, in October 2020. The tag was supposed to remain attached for about a year.
“Something seemed amiss,” stated Brooke Anderson, a shark researcher at Arizona State University during that time.
The second tag, which was designed to transmit a signal when the shark’s fin breached the surface, never sent a signal again.
Data collected from the retrieved “pop-off” tag revealed an unusual pattern: for the initial five months, the depth and temperature information appeared normal for this species, but then deviations started to occur.
“Unexpectedly, temperatures suddenly spiked and remained high even at depths of 600 meters,” recounted Anderson.
The diving patterns of the creatures also became peculiar.
John Dodd
“All the data pointed in one direction: she had been consumed,” remarked Anderson.
The researchers ascertained that the irregular readings from the tag were due to it having been inside another animal’s stomach for several days.
Their conclusions were detailed in a study published in the Frontiers in Marine Science journal, shedding light on the fact that porbeagle sharks are being preyed upon by much bigger animals.
Naming a few possible predators, the researchers narrowed down their suspects based on biological characteristics – the data didn’t align with a mammal like a killer whale, leading them to focus on warm-blooded sharks with some heat-generating capacity.
“The predator needed to elevate its body temperature above the ambient water, have the size to inflict damage on the porbeagle, and reside in the area of the predation,” explained Anderson.
The researchers inferred that a great white shark or mako shark likely devoured the pregnant porbeagle, temporarily swallowing the tag.
“Our estimation is that it was a mature female great white shark, possibly exceeding 15 feet in length,” disclosed Anderson.
Previously, the notion that porbeagle sharks might fall prey to larger creatures had not been considered, she added.
Originally, their team aimed to track pregnant porbeagle sharks during their gestation period and pinpoint where they typically give birth.
Across two Atlantic seasons, they located and tagged a total of 11 porbeagle sharks, hauling each one onto the boat, treating them with aerated seawater, and concealing their eyes with wet towels.
“We operated like a NASCAR pit crew,” described Anderson. Eight of these sharks were pregnant.
Their expectations didn’t encompass uncovering a profound deep-sea mystery.
Matt Davis, a marine resources scientist from the Maine Department of Marine Resources not involved in the research, acknowledged that the study’s conclusions were plausible.
This incident underscores the continued need for scientific exploration of mid-depth ocean life and predator-prey interactions, added Davis.
The porbeagle shark is categorized as an endangered species by the International Union for Conservation of Nature. Overfishing activities began in the 1960s, causing a population decline of 75 to 80 percent by 2001, as per Anderson.
While the species is recuperating due to fishing regulations, their longer lifespan and lower reproductive rate mean a protracted recovery process.
“We must continue tagging and monitoring these sharks to understand the frequency of such incidents,” emphasized Anderson regarding the predation. “In an instant, this critically endangered species lost not just its essential breeding females, but all its developing offspring as well. It is crucial to grasp both the frequency and impact of such events.”
Their research could play a pivotal role in restoring a healthy shark population in the Atlantic, where sharks prey on sharks.
Source: www.nbcnews.com
