Hammerheads regulate body temperature in cold water by 'holding their breath'

Did you know that hammerheads regulate their body temperature when in cold water by 'holding their breath'?

The video above from 2012 off the coast of Tanzania and corresponding 2015 research shows a hammerhead at a depth greater than 1,000 metres. It was an opportune sighting and at the time was also "the deepest accurately recorded for this species and the first deep-water record for the Indian Ocean. The record adds support for the occurrence in deep water during night hours being a widespread and possibly common behaviour in this species". Interestingly, you can see in the video that the gill slits are shut tight on a closer look.

This earlier research supports the findings of a recent 2023 research article that notes "adult scalloped hammerhead sharks dive rapidly and repeatedly from warm (~26°C) surface waters to depths exceeding 800 meters with temperatures as low as 5°C." A summary of the article highlights that the body temperature of most fishes is "heavily regulated by their environment. This physiological feature can present a challenge for large, predatory fishes that must maintain a certain body temperature to fully function but must also venture into different thermal environments to find prey. Using state-of-the-art remote loggers, Royer et al. found that scalloped hammerhead sharks were able to maintain warmer body temperatures during deep (more than 800 meters) dives by closing their gill slits and thus preventing heat transfer. Functionally, these sharks hold their breath during dives to facilitate access to prey in deep, cold waters."



Sources:

2012 video, https://youtu.be/VyoNrDBf1AM

2015 article, https://www.cambridge.org/core/journals/marine-biodiversity-records/article/abs/deepwater-observation-of-scalloped-hammerhead-sphyrna-lewini-in-the-western-indian-ocean-off-tanzania/E8A14565DC3E2B30B9A058C3DDDBDA4B

2023 article, https://www.science.org/doi/10.1126/science.add4445