Highest Rated Comments

oceanxorg42 karma

Lucy Howey: There are satellite tags that can report to the satellites when an animal’s at the surface, however, because these are deepwater sharks that never go to the surface, we use archival tags (they’re kind of like a Fitbit in that they’re a small device that records and stores a bunch of data but to send it later). When the tag pops off it sends the data to a satellite.

There’s a small piece of metal that attaches the tag to the animal and after a certain amount of time there’s an electrical current that corrodes the piece of metal and it floats to the surface.

So the tag doesn’t “check in” but the data does take a few weeks to download because there are only short periods of time when satellites are actually overhead to receive the signal over the course of a day, or even how many satellites are available to that part of the planet. It can also take a long time if there’s a lot of data in the tag/if the memory is full.

oceanxorg36 karma

Dr. Dean Grubbs: They don’t ever surface but it’s not the depth that determines their habitat; it’s the temperature. Everywhere we’ve tracked these things they spend their days at 5°C and their nights at 16°C, so whatever depth that corresponds to. In colder climates like the Northeast Pacific they’ll come to depths that divers can actually swim with them. In the Atlantic, off Virginia we tracked them 100 to 400 meters; Hawaii it was 600-250 meters; in Eleuthera, Bahamas, where we tagged them, it’s 400-1200 meters. We deliberately took the sub and waited at a depth where the temperature was ~16°C because we knew that’s where they would head when the sun set. During the day, they’re deeper than the submersible max depth.

oceanxorg23 karma

Gavin Naylor: I saw so many animals down there that I had only ever seen as line drawings in a textbook.

Lee (sub-pilot) did this completely goofy thing, perhaps mostly for my benefit, but it was fantastic: He switched all the lights off and put the thrusters on in the submarine halfway up the water column on the way up. And we had the most spectacular bioluminescence show. It made the New Year fireworks display look like a joke. It was spectacular. All of these things were agitated, and the whole of the sub was shrouded in bioluminescence. That is a pretty cool party trick.

oceanxorg23 karma

Lucy Howey Jordan: We haven’t got the data back yet but—funny story—on the third dive a grouper swam up and tagged itself and we did get data back from that.

Re: “Lastly, are sharks the only species that can survive such a wide range of depths? The pressure difference when bringing them to the surface must be huge”

Dr. Gavin Naylor: That’s a great question. So, fish achieve buoyancy through a gas-filled internal balloon called a swim bladder. If they’re deep sea fish, this naturally expands as they get closer to the surface and causes all sorts of problems (crushes their organs, causes their eyes to pop, etc). Sharks achieve neutral buoyancy by having a huge, very oily liver (the same way oil floats on water—it’s less dense) so it allows them to transition very rapidly from one depth to another. However, just because they’ve got an oily liver doesn’t mean they have don’t have biochemical challenges.

Dean Grubbs: For example, one reason sixgill sharks can survive coming to the surface is because they’re big. My colleague Brendan Talwar has been studying about how a lot of the small deep-water sharks cannot survive being brought to the surface because they get too hot. Their big livers in this case become a hazard. But one reason the sixgill survives is partly because they’re big they don’t get hot as quickly.

oceanxorg21 karma

Dr Gavin Naylor: The way that you would try to address that is look at the rates at which new species are being discovered over time. And if we are getting close to understanding all of the sharks in the ocean, then it should get slower and slower (the rate of discovery). But it’s not. We’re still discovering them at the same rate. So it’s entirely possible that there are 50 percent of the world’s sharks are yet to be discovered. (PS That's a guess, not an estimate.)