Shark behavior, especially after capture and release, has long intrigued researchers. One such phenomenon that has puzzled scholars is the contraction of the shark's stomach, particularly in response to capture stress and release efforts. Scientists have been observing stomach eversion in elasmobranchs and pelagic fish, especially those caught by hook and line fishing, for many years. This fascinating behavior of the stomach turning upside down is thought to act as a mechanism to expel harmful and indigestible substances from the gastrointestinal tract. This behavior is often caused by stress during capture, especially in hook and line fisheries where the hook itself can act as an eversion stimulus. “Circle hooks, commonly used in catch-and-release fishing, have been reported to be less likely to root than J-hooks, and thus may reduce the chance of ectropion,” said the postdoc. explains Dr. Samantha Andrzejczyk. At Stanford University's Hopkins Marine Station.
However, the effects of capture and release on shark physiology remain relatively elusive. Concerns about post-release mortality highlight the urgent need for scientists to understand the recovery process of released sharks after research, especially as shark populations decline. I have to. This is especially true for people whose stomachs have turned upside down. Stomach contractions and the associated energetic costs play an important role in post-capture recovery.
“Stomach eversion is relatively common in fish raised from deep water, a phenomenon known as barotrauma. In this case, the rapid release of pressure causes the gas inside the fish to expand, often forcing the stomach out of the mouth. This is different from the mechanism observed in sharks (which do not have swim bladders). “Like sharks, sport-fished marlin are often observed to evert their stomachs during capture, but their ability to successfully retract their stomachs during release is unknown,” Andrzejczyk said. “Across different shark species, this behavior has not been widely studied. While this has been noted in sharks that are commonly caught in fishing, it is very rarely observed in natural environments. The prevalence of the pattern suggests its usefulness as a natural strategy for removing harmful substances from the stomach. Nevertheless, its ability to recede after a prolonged period of ectropion, especially in fishing situations, remains poorly understood in most of these species.
In a groundbreaking study published in the latest issue of Fisheries Research, scientists take a closer look at the complex process by which sharks' stomachs retract, focusing specifically on tiger sharks caught and released off the coast of Western Australia. I guessed. Andrzejczyk's team used state-of-the-art animal video and triaxial accelerometers to record the shark's behavior after its stomach contracted and released. Their discovery revealed a surprising series of events. Captured tiger sharks' stomachs were everted, and their stomachs remained intact even after they were released. However, within minutes of release, the shark exhibited violent movements, including bursting its tail beat and retracting its stomach into its normal position.
“Although gastric eversion has previously been recorded in line-caught tiger sharks, subsequent stomach contractions when released have not been observed, so we are wondering how these sharks recover,” said Dr. There was a limited understanding of whether or not they would survive such events,” Andrzejczyk said. “Our video and accelerometer tags showed that the tiger shark not only retracted its stomach immediately after release, but also resumed normal swimming behavior. This suggests that it does not cause any negative effects beyond capture and confinement.”
Despite the energetic costs associated with stomach contractions, the tiger sharks quickly returned to normal swimming behavior. Nevertheless, it remains unclear how well other species of sharks, especially those with high stress and mortality rates during capture, are able to retract their flipped stomachs. Perhaps in their natural habitat, the ability to constrict their stomachs is widespread among sharks. However, in capture scenarios where sharks endure stress and incur high energetic costs, the ability to retract the stomach upon release may vary between species. ”
The study also highlighted potential risks associated with prolonged gastric ectropion, including increased vulnerability to predation and competition. Andrzejaczek is not currently conducting further research into these behaviors, but the increasing use of biologging techniques such as camera tags among different shark species may allow for the possibility of recording these phenomena in the future. I believe that there is an increased possibility that this will occur. “Overall, this is an exciting time in shark science, with such novel behaviors being recorded remotely for the first time.”
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