[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)
        
 (HTM) web link (www.nature.com)
 (TXT) 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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       (page generated 2023-05-12 23:00 UTC)