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Hawksbill Sea Turtle

 

Image modified from wikipedia; 
original image by Thierry Caro
HAWKSBILL SEA TURTLE (Eretmochelys imbricata)

Okay so this one is going to be a little bit biased because hot golly gee god damn do I enjoy turtles. Especially sea turtles. I just really think they're neat. Anyway, I'm going to try really hard not to give them undeserved points here, unlike my other reviews, where points are awarded based on extremely stringent criteria.

Appearance

Adult hawksbill turtles are, on average, one meter long, and weigh about 80 kg (roughly 3 ft and 150 pounds in freedom units). This seems pretty big for a turtle, but when compared to an absolute monster like the leatherback sea turtle, which grows up to 3 meters long and weighs as much as my old Kia, you realize that hawksbill turtles are the dainty lads of the sea, surpassing only the Ripley sea turtle in size.

They are a rare combination of beautiful and adorable. Like, they have doofy little flippers and faces like grandmas, but they've also got a striking black and white crackle pattern on their heads an flippers, and elegant tortoiseshell colouration on their carapaces (which proved to be their downfall for reasons I'll get into later). Adding to their mystic beauty is that fact that they're fucking biofluorescent, glowing red and green when bright LED light is shone on them. There's some speculation that this is due to them eating biofluorescent corals and stealing their glowiness, but there hasn't been enough research to shine a light on whether or not that's the case. I didn't know this before writing this review, but biofluorescence is pretty common in nature, seen in a whole shitload of invertebrates and fish, and recently observed in loggerhead turtles, a bunch of amphibians, and some geckos. But of all the biofluorescent tetrapods, hawksbill turtles were by far the first ones we knew about.

Points: 0.75/1 because they're kind of small but they more or less make up for it by being cute, pretty, and glowing.

Behaviour

Speaking of biofluorescence and speculations, male hawksbill turtles glow more brightly than females, which suggests that glowing might somehow be involved in turtle sexytime. Maybe they're like fireflies, and the glow helps them identify opposite-sex members of their species. Maybe they're like peacocks and male brightness is an indicator of virility. The study that reported this didn't look at very many turtles, so maybe the males that they peeped just happened to be a bit brighter than the females by chance. Maybe I'm thinking too hard about this.

It's sort of a moot point because sea turtles aren't very social, so it's hard to tell why they do what they do. Also - I've talked about this before and I'll talk about it again - it's really hard to study things that live in the ocean, especially if they are really big and not very numerous. Like little fish, we can pull them out of the water and look at them to learn their secrets, but we're extremely limited in what we can do with turtles. 

Points: 0.5/1 out of privacy

Distribution

Hawksbill sea turtles are turtles that live in the sea, but they're very widely distributed. As we all learned from the acclaimed nature documentary Finding Nemo, sea turtles often migrate spectacular distances. Now Crush, the turtle in the film, was a green sea turtle, but hawksbills also migrate, with females travelling hundreds or even thousands of kilometers every few years to the beaches where they were born.

When they're not doing that, they hang out on coral reefs and monch on various invertebrates. Coral reefs are having a hard time right now, so any animals that associate with them regularly are in for a reckoning pretty soon. Hawksbill turtles are going to need to get their shit together and start living in garbage patches if they want to survive.

Points: 0.5/1

Ecology

Here's something that really chapped my ass while I was researching this review: a lot of sources describe hawksbill turtles as "omnivorous" because they eat invertebrates and also sponges. I want you to stand up and say the following three words out loud to yourself: Sponges. Are. Animals. There, now you know something that most non-specialists who write articles about sea turtles apparently don't.  Anyway, eating sponges is pretty hardcore because a lot of species (including some of the ones that hawksbills like to eat) have internal skeletons made of silicate spicules, AKA shards of fucking glass. That makes hawksbill turtles the marine reptiles equivalent of that dude that ate glass that time.

Now, hawksbill turtles actually are omnivorous because they eat invertebrates (including sponges), and also algae. In fact, one study suggested that red algae made up the bulk of their diet. Other studies say they eat mostly sponges, so their diet probably varies a lot by location and time of year. Many of the things that they eat, including sponges, algae, and maybe jellyfish, produce toxic compounds which accumulate inside the turtle and make their meat toxic. This is a reasonably effective anti-predator measure against humans - except the ones that want them for their shells.

Points: 1/1

Evolution

Sea turtles have been around for a really, really, really really, really long time. Slightly more specifically, they've been around for about 120 million years. For context, crocodilians first emerged around 100 million years ago, your favourite dinosaur probably existed somewhere between 100 and 65 million years ago, and people have been around for a piddly 0.3 million years.  Ancient sea turtles would have been absolutely terrifying - Archelon ischyros, one turtle known from Cretaceous fossils, was 4.6 meters long and researchers think it could have weighed over 2000 kg. If you, like me, fear the sea, just imagine how bad it would have been with those things swimming around. Thankfully, the end-Cretaceous extinction event happened and now the beaches are relatively safe.

Like whales, seals, and manatees, marine turtles went from having feet with cute little toesies to having undifferentiated flappers at some point during their evolutionary history. Hawksbills, and a couple other species, still have claws on their flippy flaps, and actually use their front limbs for feeding - they hold the food in their little hands and take bites out of it, like a raccoon! Contrast this with whales, who have existed for a fraction of the time that sea turtles have (~55 million years) but don't have any claws or anything left. This is probably because sea turtles are not fully aquatic - they still lay hard-shelled eggs, which constrains them to reproducing on land.

Points: 0/1 because they've been around long enough to figure out the whole egg thing

Life History

Females lay about a hundred eggs per clutch, and can have multiple clutches per year, so by my math they produce, on average, an assload of babies. Now in Finding Nemo, the turtle travelled with his son, but in real life sea turtles fuck off after laying their eggs, leaving their babies to fend for themselves and, mostly, get eaten by stuff. But, y'know, if you had like five hundred kids you probably wouldn't be that sentimental about them either.

We don't know how long hawksbill turtles can live (again, because they live in the sea and are mysterious), but we can assume it's probably a pretty long time. Like me, they reach sexual maturity around age 20, so it's actually a good thing that most of their babies get eaten before they can reach the water, otherwise the ocean would be turtles all the way down.

This particular strategy is called "predator satiation", and the general idea is that if you have a lot of predators when you're young, but not so many when you're old, you compensate by having a ton of babies, so many that the predators couldn't possibly eat all of them. So even if only one or two baby turtles make it to adulthood, it's still a net win for the turtles. The downside is that the strategy doesn't work if your population experiences high adult mortality (which historically turtles haven't, but due to human activity now they do). The other downside is that we have all kinds of videos of little baby sea turtles getting eaten by every animal imaginable, from dogs, to birds, to that most disgusting of creatures, the crab.

Points: 0/1

Interaction with Humans

Lord, where do I even start here. Okay, so I mentioned above that the sea turtle strategy "shitload of babies, few survive, adults live forever" only works when the adults aren't getting killed by stuff. Unfortunately, hawksbill turtle shells make really pretty jewelry, so adults have been getting killed in rather large numbers for a very long time, leaving them critically endangered. In fact, people actually hunt females on the beaches when they're laying their eggs and are at their most vulnerable.

They also are caught as bycatch in a lot of commercial fisheries. They also get caught in discarded fishing equipment, which commercial fishers just dump unceremoniously into the ocean. They also get hit by boats because, being turtles, they don't understand the concept of shipping lanes. They also get fucked up by oil spills. They are also affected by global warming and beach erosion because females are generally tied to one nesting site and if that disappears they get confused. They also have problems with increasing development because that destroys beach habitat, and introduces artificial lighting which confuses the babies and reduces the already tiny number that makes it to the sea before they get eaten. So. Yeah. Not really a good time for the sea turts.

On the positive side, sea turtles are very culturally significant on a lot of south Pacific islands. And because they're really big and cool looking, there are ongoing efforts to preserve hawksbills and other sea turtle species. Is it enough to counteract the immense damage being done at all stages of their life cycle? Probably not, but at least it's something.

Points: 0/1 for not fighting back

Score: 2.75/7
Consensus: I definitely went overboard in my attempt to not award the sea turtle too many points

Further Reading
  • Bell I. 2013. Algivory in hawksbill turtles: Eretmochelys imbricata food selection within a foraging area on the Northern Great Barrier Reef. 34: 43-55
  • Diez CE, van Dam RP. 2002. Habitat effect on hawksbill turtle growth rates on feeding grounds at Mona and Monito Islands, Puerto Rico. Marine Ecology Progress Series. 234: 301-309
  • Fujii JA, McLeish D, Brooks AJ, Gaskell J, Van Houtan KS. 2018. Limb-use by a foraging marine turtle, an evolutionary perspective. PeerJ. 6:e4565
  • Gruber DF, Sparks JS. 2015. First observation of fluorescence in marine turtles. American Museum Novitates. 2015(3845): 1-8
  • Hirth HF. 1980. Some aspects of the nesting behaviour and reproductive biology of sea turtles. American Zoology. 20: 507-523
  • Lamb JY, Davies MP. 2020. Salamanders and other amphibians are aglow with biofluorescence. Scientific Reports. 10: article 2821. Open Access
  • Leon YM, Bjorndal KA. 2002. Selective feeding in the hawksbill turtle, an important predator in coral reef ecosystems. Marine Ecology Progress Series. 245: 249-258
  • Meylan A. 1988. Spongivory in hawksbill turtles: a diet of glass. Science. 239(4838): 393-395
  • Modh Top-Modh Tah M, Puan CL, Chuang M, Othman SN, Borzee A. 2020. First record of ultraviolet fluorescence in bent-toed gecko Cyrtodactylus quadrivirigatus (Gekkonidae: Sauria). Herpetology Notes. 13
  • Mortimer JA, Donnely M. 2008. Marine Turtle Specialist Group 2008 IUCN Red List status assessment: Hawksbill turtle (Eretmochelys imbricata). IUCN.
  • NOAA Fisheries. Hawksbill turtle. Link
  • National Geographic: "Glowing" sea turtle discovered. Video
  • Pavlin BI, Musto J, Pretick M, Sarofalpiy J, Sappa P, Shapucy S, Kool J. 2015. Mass poisoning after consumption of a hawksbill turtle, Federal States of Micronesia, 2010. Western Pacific Surveillance Response Journal. 6(1): 25-32
  • Sea Turtle Conservancy. Information about sea turtles: threats to sea turtles. Link
  • Smithsonian Ocean: What is the largest sea turtle? Link
  • Sparks JS, Schelly RC, Smith WL, Davis MP, Tchernov DV, Pieribone VA, Gruber DF. 2014. The covert world of fish bioluminescence: a phylogenetically widespread and phenotypically variable phenomenon. PLOS One. Open Access

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