Shark week 3: free stuff for the shark-obsessed
November 8, 2022
Couple of fun things here. First, if you’d like to play with — or print — 3D models of megalodon teeth, there are a bunch of them on Sketchfab, helpfully curated by Thomas Flynn, the Cultural Heritage Lead there. As of this writing there are 24 meg teeth in the collection (link), and by my count 14 of them are downloadable, 11 for free and 3 for sale. If you’re not already on the ‘fab, it takes like 2 minutes to create a free account, and then all you gotta do is click on the download icon next to each freely downloadable tooth.
Second, I obviously named this post series after Shark Week on the Discovery Channel, but the sad fact is that Discovery Channel documentaries long ago took a steep nose dive into being mostly garbage. I guess if you like seeing the same footage half a dozen times in a 40-minute documentary, being repeatedly beaten over the head with the same three very basic facts (or, too often, “facts”), and wondering which thing the creators have more contempt for, the actual science or you, the audience, then go ahead, knock yourself out.
If, on the other hand, you like non-repetitive, vibrant footage, non-repetitive, useful and informative narration, and coherent programming you can actually learn from, let me suggest the Free Documentary – Nature channel on YouTube.
“Rise of the Great White Shark – A History 11 Million Years in the Making” is excellent, with tons of great footage and some very nicely-done explanations of the sensory and thermoregulatory adaptations of great whites and other sharks — and, whaddayaknow, a fact-based, non-sensationalized, and still awesome segment on megalodon.
I also learned a lot from “Shark Business”, about the growing ecotourism business of boat- and scuba-based shark tours or shark encounters. Two things in particular stood out: first, because sharks don’t have hands, their exploratory way of interacting with objects in their environment is to give everything a test bite. The vast majority of shark “attacks” on humans consist of a single bite, with a quick disengagement and no pursuit of the human by the shark. It’s just that sharks have super-sharp teeth and incredibly powerful jaws, and even a comparative gentle (to the shark) test bite can leave a person severely injured or dead. That sharks most often don’t intend any harm is probably cold comfort to people who have been subject to test bites, but it’s a useful thing to understand if you’re genuinely interested in sharks.
The other thing that jumped out at me is the 50-second segment that starts at 7:45, in which a tour guide is shown pushing on the snouts of great white sharks with his bare fingers as they approach the boat. The sharks roll their eyes back, open their mouths, and seem to go catatonic for a bit. Although they don’t make this connection explicitly in the doc, sharks generally roll their eyes back when they go in for a bite, presumably to protect their eyes from the object they’re sampling. I wonder if the nose touch signals to the shark that it’s bite time, and it rolls its eyes back, opens its mouth, and waits for something to bite down on. It seems like a useful thing to be aware of in case a shark is ever coming at you — a gentle push on the snout might put the shark into zombie mode for long enough to get out of the way. On the flip side, if you push the shark’s snoot and don’t get out of the way, it might be super-primed to take a hunk out of you. Note: I am not a shark expert, this is not professional advice, and I assume no liability if a shark eats your arm off. I just thought it was an interesting bit of shark biology that could conceivably pay off in an emergency.
Is this really going to be a whole week of shark posts? Beats me! I’m making this up as I go. Let’s find out.
Sauropod Vertebra Picture of the Week 
November 8, 2022 at 6:34 am
I’d been under the impression that the touch (or punch) to the snout probably produced catatonia because of literal sensory overload – besides the lateral line type sensors most fish have, sharks (I thought) had another system either in, or converging at the nose. But your theory probably explains the eye roll and mouth gape just as well – protect the eyes and present an obvious defense against the unexpected touch. People kind of do both (close eyes and relax the jaw) when knocked out, so it’s hard to tell. I’m neither a shark, nor a shark expert.
Which reminds me: SETI is surely worth something, but being able to communicate with and understand how species we share this planet with, how they think and even just perceive the world – would be of more immediate value. [Though someone drew a comic about how they had invented a device that let them understand their own dog: the inventor says, “I shouldn’t have been surprised by this!” when their dog keeps repeating, “Oh, there you are! So happy to see you! Ooo, what’s that over there? Is that food? Oh – there you are!”]
November 8, 2022 at 7:22 am
You are correct that sharks have another sensory system in their snouts — the electroreceptive ampullae of Lorenzini.
Now, with the usual caveat that I’m not a shark researcher and could be talking right out my backside, I’m skeptical that the sharks are actually going catatonic when touched on the snout. I think that’s anthropomorphic projection. What they actually seem to do is open their mouths super wide and keep swimming, while rolling their eyes back, which seems like a really useful reflex. If feeding, it means they’re mouth open, eyes back, ready to bite, and moving toward food, and if defensive, it means they’re mouth open, eyes back, with their deadliest weapons pointed at trouble. (Why not turn and swim away? I reckon by the time the offending element has literally booped their snoot, that ship has sailed.) Either way, they’re primed for action. Probably nothing in their whole evolutionary or individual histories has prepared them for something that can boop the snoot and yet not be there to get bitten.
I’m also talking about gentle touches rather than punches. With olfaction, the electroreceptive organ, and the lateral line all converging at the snout, I wouldn’t be surprised if an actual punch could temporarily overload their senses, like some combination of flashbang grenade and stink bomb.
Your point about how sharks perceive the world is well-taken. I wonder about the lateral line system of sharks and other fishes. In the same way that we can be in a crowded restaurant and hear dozens of people talking at once, yet still tune in to particular conversations if they’re clear enough, I’ll bet that sharks and other fishes can keep track of dozens of objects moving in the water around them just with their lateral lines (and not counting vision, olfaction, and electroreception). After all, we manage to isolate meaningful signals out of all that babble with comparatively tiny receptor organs. If we define hearing as turning pressure waves into meaningful signals, then sharks “hear” vibrations in the water with organs roughly as long as they are. That’s a loooong baseline, implying possibly very high angular discrimination.
Dang it. I started this series for fun. I do _not_ have time to actually read up on sharks.
November 9, 2022 at 1:38 am
You want sensory overload; imagine a shark with ultrasensitive ampullae of Lorenzini getting anywhere near an electric ray; that would hurt.