[HN Gopher] Hammerhead sharks are first fish found to 'hold thei...
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Hammerhead sharks are first fish found to 'hold their breath'
Author : gmays
Score : 75 points
Date : 2023-05-12 17:33 UTC (5 hours ago)
HTML web link (www.nature.com)
TEXT w3m dump (www.nature.com)
| ugh123 wrote:
| What about fish that jump out of the water?
| amelius wrote:
| They were either not first, or they simply keep breathing
| regardless of availability of oxygen.
| HWR_14 wrote:
| IIRC, they keep blood pumping (inefficiently) through their
| gills while above water. This is less an analogue for "holding
| your breath" and more for "being on top of Mt. Everest." You're
| physically trying to get oxygen, it's just not working.
| hutzlibu wrote:
| "You're physically trying to get oxygen, it's just not
| working"
|
| Nitpick, but not working as good, because some humans do
| manage to get enough on Everest, to not need extra supplied
| oxygen.
| lostlogin wrote:
| I understood it as thing that could be tolerated for a
| short time by some humans. They will die as their
| saturations are falling, but they get up and then down
| within a narrow window.
|
| https://en.m.wikipedia.org/wiki/Death_zone
| hutzlibu wrote:
| You surely could not live there, but some people managed
| for astonishing amount of time.
|
| (and before they proofed it, it was thought to be
| literally impossible without extra oxygen)
| dj_mc_merlin wrote:
| > To understand how sharks were coping with the temperature
| changes, Royer and his colleagues developed a device consisting
| of instruments that measured depth, water temperature, location
| and movement, as well as a probe embedded into muscles near the
| dorsal fin that recorded the shark's core temperature.
|
| > In a paper published in Science1, the team reported that the
| sharks would dive several times -- six in an evening, for one
| shark -- into deep water at temperatures of 5-11 degC, around 20
| degC colder than at the surface, and remain there for 5-7 minutes
| at a time before surfacing.
|
| > Body temperature remained constant for most of the dive until
| the final stage of their ascent back to warmer waters, when it
| would decline rapidly.
|
| > Royer suggests that the sharks are keeping their core
| temperature stable by simply not opening their gills or mouth
| during the dive; effectively 'holding their breath'. "If you
| don't have water going over your gills, then you won't be dumping
| your body heat into the environment," he says.
|
| So they only measured the shark's temperature, the water
| temperature, and location (in 3 dimensions). Hammerhead sharks
| holding their breath is a hypothesis that aligns with the rapid
| heat loss as they ascend and reenter medium-temperature waters
| (and start breathing again presumably). It seems a bit early to
| say this is the exact mechanism, but I am no marine biologist.
|
| edit: ah, they have more evidence, including videos of sharks
| closing their gills
| https://www.science.org/doi/10.1126/science.add4445#sec-4
| dmbche wrote:
| For anyone not reading the article, they close their gills to (we
| assume) not lose heat when they are diving in deep and cold water
| - very interesting - hadn't thought that gills are the fastest
| way to exchange heat for fish. "Diving to over 1,000 metres from
| tropical temperatures at the surface down to just a couple of
| degrees centigrade to feed is a fairly extreme movement to do on
| a regular basis," Simpfendorfer says.
|
| !!
| kayodelycaon wrote:
| It makes a lot of sense when it's explained. Gills basically
| act like a heat exchanger for oxygen. Lungs work very
| differently. They don't have continuous flow and humans have
| mechanisms to heat up and moisturize air before it reaches
| their lungs.
| wil421 wrote:
| Salmon sharks are warm blooded and can stand temps down to
| about 36 degrees. I wonder if they have any adaptations in
| their gills to prevent heat loss or if they don't care
| because they warm their bodies.
| soperj wrote:
| > Lungs work very differently. They don't have continuous
| flow
|
| I was under the impression that bird lungs do have continuous
| flow.
| reubenswartz wrote:
| Water is a much more efficient heat exchanger than air.
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