Meet some of our oddest, oldest fishes — as they rapidly approach extinction

Largetooth sawfish

Few people on earth have encountered a largetooth sawfish at full size, according to the EDGE of Existence project, and it’s doubtful that any will ever forget the experience.

A species of ray that grows to more than 20 feet in length and a half-ton in weight, Pristis pristis looks rather like a flattened shark except for its front end: 6 feet or so of flat, bony bill, both edges sporting big, sharp teeth, the overall design suggesting a ripsaw fashioned for cutting up cars.

Nowadays you’d be lucky to see one half that size, and even that chance is dwindling. Once common throughout the global tropics, in the shallow ocean as well as brackish estuaries and freshwater streams, the species’ range and numbers have contracted dramatically into four sub-populations of uncertain size. On the Red List of struggling creatures by the International Union for Conservation of Species, it is classed as “critically endangered,” the last step before “extinct in the wild.”

It’s also a rarity in another sense. With sharks and skates, it belongs to a class of cartilaginous fishes known as Chondrichthyes, little changed over the last 100 million years. More specifically, it is in the family pristidae, which contains just four sawfish species, and only one of the largetooth type.

Thus its special importance to the EDGE project, a young program of the Zoological Society of London that attempts to focus conservation effort, and public attention, on species with the unhappy dual distinction of being both Evolutionarily Distinct and Globally Endangered. Like some other recent work, it underscores the point that species way out at the end of a branching lineage have special importance as repositories of earth’s evolutionary history.

Last week the program issued a report listing the world’s top 50 sharks and other chondrichthyans that fit both criteria, with the longtooth sawfish at the top:

The sharks, rays and chimeras … are one of the oldest groups of species that have inhabited the planet. Many members of this group swam in the ocean while dinosaurs roamed the Earth. Some of the modern sharks, rays and chimeras on the EDGE list represent particularly large amounts of unique evolutionary history; many have unusual and striking morphology, behaviours and genetic make-up.

Sadly, this wealth of uniqueness is highly threatened by unsustainable fisheries, as well as by the degradation of marine ecosystems — particularly coastal areas. Many of these species’ populations are declining at an alarming pace, with the most evolutionarily distinct shark and ray species also tending to be the most threatened ones. [EDGE uses a classification scheme that groups the mostly deep-ocean chimeras, also known as ghost sharks, with the chondrichthyans; other systems give them the separate order Chimaeriformes.]

To scroll through the rest is a powerful lesson in the shape of modern extinction trends, and how little we may know of what we’ve got till it’s gone, or nearly so:

  • The ornate eagle ray, Aetomylaeus vespertilio, whose gold color and patterning make it look rather birdlike — especially, I imagine, when one breaches the sea surface on a sunny day. Classed as critically endangered on the Red List, it comes in at number 11 on the new EDGE roster.
  • The giant freshwater whipray, Urogymnus polylepsis, whose 6-foot diameter and 1,300-pound weight make this river dweller the largest of the whiptail stingrays and, for that matter, one of the world’s freshwater fish in any category. Number 43 on the EDGE list, the Red List classes it as endangered, a step below the ornate eagle ray and largetooth sawfish.
  • The African wedgefish, Rhynchobatus luebberti, also known as Lubbert’s guitarfish, which despite growing to lengths approaching 10 feet is so rarely seen that the EDGE report carries a drawing rather than photo of it; this oddity is number 42 in the EDGE report and is Red Listed as endangered.

Little known to science

A remarkable feature of the EDGE list is its frequent reference to how little is known to modern science about many of these unusual species, or the exact reasons each has become so vulnerable to extinction:

Despite the fearsome reputation of the great white shark and the well-recognised appearance of the hammerhead, sharks are one of the least-studied groups of animals — some so elusive they’ve never been captured on camera….

EDGE sharks coordinator and marine biologist Fran Cabada said: “Sharks, rays and chimeras — making up the cartilaginous fish, have been around since the age of the dinosaurs, but due to human activities, their modern relatives are facing threats all over the world. They’re found in almost every aquatic environment and as many are apex predators — i.e., at the top of the food chain — they’re crucial to maintaining healthy ecosystems.

“Unfortunately, sharks have a bad image. This means people often can’t see beyond the negative, and usually exaggerated stories, and don’t understand just how threatened and important they are.”

While ignorance may well explain a lower level of public passion for saving sharks versus, say, whales, there is far deeper knowledge of the cartilaginous fishes, their habits and habitats among humans who make a living by killing them.

Shark meat is sold as food, but mostly to the world’s poor, so that’s not where the real money is. Fins of both sharks and rays are a high-demand item in Asian cuisines, prized for both culinary value and supposed health benefits: As supplies have dropped in recent decades the market values have risen to place them among the world’s priciest seafood items by weight.

Cartilage, livers, ovaries, brains and other tissues are made into products for traditional medicine; skins are tanned for leather; teeth are still sold as curios.

Sawfish are targeted for some of the same market niches, but the main draw is the saw: A few minutes of Googling will turn up no recipes for sawfish soup, but many an amputated rostrum on offer as décor, typically mounted on a pedestal and sometimes fitted with a thermometer or other kitschy adornment, at prices that are both breathtaking and stomach-turning.

(Wait, you say: Can it still be legal to cut up an endangered sawfish and sell the rostrum? Nope. But then isn’t the market drying up? Of course not.)

The problem of ‘bycatch’

Besides deliberate targeting, these ancient species are also heavily burdened by losses to “bycatch,” collateral killing in which a fishing boat dragging nets or lines for more popular food species will pull in considerable numbers of non-target sharks and rays unintentionally. Typically it is illegal to unload these unfortunates for sale, but there’s no requirement to be gentle in returning them to the water, nor even to return them alive.

Decades ago, bycatch awareness around dolphins and turtles led to changes in gear and technique to protect them, but sharks and sawfish aren’t getting that kind of help (and the latter, because of that striking anatomical projection, are especially prone to getting tangled in nets).

As with other species in decline as the planet’s sixth great extinction progresses, the cartilaginous fishes are also pressured by the indirect consequences of development, such as habitat loss and degradation, with climate change also expected to play an important role.

But they also would seem, as a group, to be unusually burdened by direct human predation — willful, accidental, and in the gray area of negligence in between.

***

Earlier EDGE reports have dealt with such groupings as birds, mammals, reptiles, amphibians and corals; a searchable database is here.

In addition, the group has a list of more than 70 species for which it helped to organize special conservation efforts, and this, too, is a tour of wondrous biodiversity (as well as human indifference) across the animal kingdom, from the Chinese giant salamander to the black rhinoceros, the Bengal florican to the Ganges River dolphin, the Bactrian camel to the Hawksbill turtle. That material can be found here.

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