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Consider: the Angular Roughshark

Updated: 3 days ago

Has any animal been more villainized by Hollywood than the shark? Ever since Jaws splashed its way into cinema history half a century ago, sci-fi and horror movie producers have figured out just about every conceivable way to make sharks into movie monsters. We have giant sharks, cave sharks, land sharks, dino sharks, sharktopi, mecha-sharks, and of course the ever-popular Sharknado. Discovery Channel hasn’t exactly done sharks any favors either, with Shark Week documentaries often focusing on shark bite incidents or making great whites look as much like the John Wicks of the sea as possible (that seal decoy killed his dogfish and stole his car). Just about everywhere you look, film producers want you to think of sharks as monsters, often to the detriment of real-life sharks, which are unfairly persecuted as man-eaters.

But not all shark species fit so easily into the monster mold. While great whites rocket through the sea turning seals into midair surf-and-turf, this shark spends its time lazing along the ocean floor like a predatory vacuum cleaner, minding its business and waiting for the perfect moment to strike. Yet, despite its tame lifestyle, this shark’s population is declining and the species is at serious risk. What can this strange animal teach us about sharks as a whole, and about how we treat our planet’s oceans? Consider: the Angular Roughshark, Oxynotus centrina.

Roughshark angular roughshark green eyed shark triangle shark deep sea shark
Image Attribution: Alessandro Pagano

I love animals that are so ugly they wrap back around to being adorable (like pugs, or Steve Buscemi), and this shark is no exception. My man looks like a pig stuck in a sleeping bag, or perhaps like the hash-slinging slasher (whether the lights flicker on and off in its presence is not known). Angular roughsharks are a prominent member of the Roughshark family Oxynotidae. Five species of roughshark swim our planet's oceans, with two species in the Pacific and three in the Atlantic. Angular roughsharks can be found along the eastern Atlantic coast, from Norway down to Senegal and into the Mediterranean and Black seas. They grow to a maximum length of 150 cm (~5 ft), with a compressed, muscular frame that gives them a triangular profile from the front (thus the name). They have large, forward-facing spiracles, nostril-like holes which help the shark breathe (and also propose porcine physical comparisons).

Angular roughsharks are deep-sea specialists, found between 50 and 1300 meters (~160 to 4300 feet) below sea level. They are bathydemersal, meaning that they spend most of their time floating just above the seafloor, and are primarily nocturnal. While some shark species spend their time hurtling through the ocean like rabid meat torpedoes (great name for a metal band), angular roughsharks behave more like deep-sea roombas (less great name for a metal band), floating along the seafloor and vacuuming up prey. They primarily eat marine worms known as polychaetes, though have also been observed snacking on starfish, crustaceans, and the egg cases of catsharks, which they grab onto and suck the contents from like particularly wet and slimy ice pops. Aiding these roughsharks in their hunts are two different sets of specialized teeth: bladelike lower teeth for slicing through flesh and crocodile-like conical upper teeth for grabbing hold of slippery prey.

Angular roughsharks have a triangular body profile with two disproportionately-large dorsal fins. The front dorsal fin contains a shark spin which these sharks use to defend themselves from predators. Fishermen have also reported that angular roughsharks will sometimes swim upside down and use their dorsal spines to dig up prey, though this behavior has yet to be documented by researchers. Image Attribution: Alessandro Pagano

These aren’t the only teeth that angular roughsharks have, though, Like all sharks, their skin is covered in denticles, essentially skin-teeth. Shark denticles really do have the same general structure as teeth, with three layers composed of pulp, dentin, and enamel. This differs significantly from the scales of bony fish, which are composed of calcium carbonate and collagen. Nowadays, only cartilaginous fish such as sharks and rays have denticles, but they were widespread among early bony fish as well, so much so that paleontologists debate whether teeth originally evolved on the surface of the skin or in the mouth. While all sharks and rays have dermal denticles, roughshark denticles are particularly large and pronounced (they must hate flossing).

The initial benefit of having skin covered in teeth is somewhat obvious: dentin is one of the hardest biological materials, so a suit of teeth works like biological chainmail, protecting the shark from attackers without sacrificing flexibility. Incidentally, this is why I wore a suit of human teeth to high school everyday; bullies gave me a wide berth, though sadly so did potential lovers—tradeoffs. New research has shown that denticles are more than just armor, though. In one experiment, researchers studied the hydrodynamics of denticles and found that they can reduce drag by breaking up the flow of water across a shark's skin, allowing them to swim faster and more efficiently. The irregular structure of denticles has also been shown to inhibit the growth of colonial organisms such as bacteria, algae, and barnacles, keeping the sharks clean. Why angular roughsharks in particular have such pronounced denticles is still a mystery, unfortunately. Experts hypothesize that these extra-large and rough denticles act to keep the sharks clean and to defend them from predators; after all, there’s always a bigger fish.

Dermal denticles as viewed under a scanning electron microscope. While generally scale-shaped, the exact shape of dermal denticles can vary across the body of a shark to optimize swimming and prevent gill flaps from chafing. Image Attribution: Pascal Deynat under CC BY-SA 3.0.

The mating behaviors of angular roughsharks are also poorly-understood. We do know that these sharks give birth only once every few years. As such, their population grows slowly. This is a common trait of deep-sea organisms: nutrients in the deep sea can be scarce, so animals there often find it more energy-efficient to have a few strong offspring than many smaller ones. Angular roughsharks exhibit a sort of gestation known as aplacental viviparity (yet another great name for a heavy metal band). Essentially, roughshark embryos develop inside of an egg case within the mother’s oviduct (the shark equivalent of an ovary), but the case is never laid. Instead, the shark embryos hatch inside of the oviduct and spend more time developing inside until they have developed enough to be born. During this time, the shark pups feed on a nutritious yolk produced for them by their mothers as well as mucus secretions along the sides of the oviduct. One may picture the pregnant angular roughshark like a Fabergé egg modeled by David Cronenberg: teeth on the outside, mucus on the inside. At least the pups don’t each each other like sand tiger shark pups do (no seriously, they really do. I can’t wait to see that happen in the next Sharknado).

Angular roughsharks are struggling in the age of international fisheries. The species is listed as Endangered by the International Union for the Conservation of Nature (IUCN), though within the Mediterranean and other inland European seas, the situation is much more dire. Angular roughsharks have vanished from much of their traditional range in the Mediterranean as well as most of the Adriatic sea and the sea of Marmara in Turkey. While once abundant around the Canary Isles off the coast of northwest Africa, the species hasn’t been sighted there recently, suggesting it may be locally-extinct.

The decline in angular roughshark populations is primarily attributed to fishing bycatch. Bycatch is the process by which a species is accidentally caught by a fishing operation that is trying to catch a different species. While very few people eat angular roughsharks, they end up unintentionally caught by humans quite commonly. The fishing method that threatens angular roughsharks the most is known as bottom trawling. In this process, fishing boats drag a net along the seafloor, dredging up sediment and capturing anything that can't fit through the holes in the net. Fisheries primarily use trawlers to catch bottom-dwelling marine species such as flounder, halibut, crabs, and shrimp. While used worldwide, trawling has come to be a cornerstone of the European seafood industry and is responsible for ⅓ of all seafood harvested in the European Union.

angular roughshark pig nosed shark pig-nosed shark shark mediterranean shark
Angular roughsharks are a common commercial bycatch species in the Mediterranean and along coastal Europe. They are not alone: half of all sea life in the Mediterranean is threatened by human activity, many by the effects of commercial fishing. If societies and industries along the Mediterranean don’t soon make changes to protect their wildlife, the world’s largest inland sea may become less of an ecosystem and more of a swimming pool. Image Attribution: Biodiversitygr under CC BY-SA 4.0.

Trawling has a litany of environmental consequences. Like some other forms of net fishing, trawling catches indiscriminately, harvesting any large animal that the net happens to dredge up. In the past, trawling nearly led to the extinction of many species of sea turtle, which were frequently caught as bycatch, though many countries now require turtle exclusion devices to be implemented into trawling nets. Bycatch is just the tip of the iceberg when it comes to the kind of environmental damage trawling can do to roughshark habitats. Angular Roughsharks eat animals that spend most of their lives burrowed in seafloor sediments. Trawlers force these creatures from their homes, which over time can deplete their populations, causing roughsharks to starve.

The damage done to ocean ecosystems by trawling extends past just this one shark species, though—trawling also contributes to the climate disaster which has made life so much more difficult for all of Earth’s species. The seafloor is the single largest carbon storage system on Earth. When living things in the ocean die, they sink down to the bottom of the sea, where they are eaten by bottom-dwelling decomposers. Over the hundreds of millions of years in which life has thrived in Earth’s oceans, the seafloor has become enriched with the naturally-occurring carbon in those animals, and it continues to accrue more carbon as dead things continue to rain down like a combination landfill and cemetery (convenient!). When trawling nets dredge up sediment, however, the carbon dioxide trapped within can dissolve into the seawater, causing a host of problems. Carbon dioxide reacts in water to form carbonic acid, which erodes the shells of mollusks and contributes to coral bleaching. Eventually, that carbonic acid can re-enter the atmosphere as carbon dioxide and contribute to global warming.

In response to trawling’s disastrous environmental effects, governments worldwide have begun to regulate it more closely. The European Union has banned bottom trawling below 800 meters and have placed limits on how many shark species a vessel can bycatch. Some marine protected areas within the Mediterranean have banned trawling completely, and roughshark populations have improved here. While once believed extinct in the Adriatic Sea, a recent survey found that angular roughsharks have returned to some protected areas there, and similar results have been seen in the Sea of Marmara. Despite these positive effects on the environment, the fishing industry has pushed back against European Union regulations. Fishing associations from 14 European countries have assembled like a smelly, bureaucratic Voltron to form the European Bottom Fishing Alliance (which I imagine doubles as a dating service for dominant gay men). The EBFA has argued that banning trawling from the EU will cause prices of common seafood such as halibut and shrimp to rise, turning these diet staples into luxury products and disrupting the culinary identity of many European regions.

The trawling debate mirrors many other climate-related societal debates, from agriculture to lumber to fossil fuel emissions. Conservative politicians often pontificate about rising prices and disruptions to daily life if we make choices to protect the environment, and these talking points often succeed in stymying progress towards a more environmentally-responsible society. This argument always functions as a binary choice: protect the environment or protect our wallets. But, when it comes to trawling, is this argument valid? Can we have our crab cake and eat it too?

It turns out that we can. In a landmark paper published in Nature in 2021, a team of researchers from around the world analyzed how preserving marine ecosystems would affect biodiversity conservation, food provisioning, and carbon storage. The team found that protecting just 28% of the world's oceans could save 90% of endangered marine species, preserve seafloor carbon stocks, and actually improve stocks of commercially-important seafood by over five million metric tons. That last point seems counterintuitive, but makes sense when you consider that fish do not stay in one place. As species within marine protected areas spawn and their populations grow, they diffuse into surrounding areas, including those areas where fishing is legal. As such, fishing areas adjacent to marine protected areas have a healthy reservoir of fish that will slowly trickle in, regenerating stocks as they are depleted. Research also shows that trawling itself can be more environmentally sustainable than other forms of meat production when managed correctly, and a minority of trawling operations currently follow regulations designed to protect ecosystems from destruction.

Angular roughsharks may not be coming to a Syfy B-movie near you anytime soon, but we still stand to gain a lot by giving them the attention they deserve. They are a great example of how poorly our collective imagination of sharks as open-ocean killing machines encapsulates the diverse array of sharks that swim our planet's seas. They also remind us that many of the problems that endangered species face also threaten the rest of life on Earth, humans included. Trawling kills angular roughsharks and destroys their habitats, but it also contributes to climate change, which has intensified storms, incited wildfires, and contributed to droughts around the world. Some might say that the economic burdens of regulating or ending trawling aren’t worth the hassle to save one homely-looking shark. Yet, protecting that shark will also lead to a decrease in emissions and an overall healthier planet, which will save money as well as lives. The only world scarier than one filled with sharktopi and mecha-sharks is one where life on Earth as we know it is destroyed by the consequences of our actions.

Image Attribution: Alessandro Pagano

Sources and More Information:

Consider Nature is written and published by Stephen Goralski. Editors for this article included Benjamin Gamble. Our web designer is Oli Platt. Olmungandr, the Consider Nature logo, was made by Maxwell Schumacher.

Y'all, there are six Sharknado movies. SIX. Why are there so many fucking Sharknados? Do you think they'll start naming Sharknados like hurricanes?

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