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Sawfish could soon become completely extinct if we don’t stop overfishing, says a study

A new study from the Simon Fraser University (SFU) warns that one of the most distinctive marine species — sawfish — are at real risk of extinction due to overfishing.

Image via Pixabay.

Sawfishes have already disappeared from roughly half of their known range, the authors report, as overfishing is driving their numbers into the ground. The species used to be quite a common sight for around 90 coastal countries around the globe, but are now one of the most threatened family of ocean fish and presumed extinct in 46 of those nations. A further 18 countries presume at least one species of sawfish to be locally extinct, while 28 others presume at least two.

A fish in need

“Through the plight of sawfish, we are documenting the first cases of a wide-ranging marine fish being driven to local extinction by overfishing,” says Nick Dulvy, one of the two authors of the paper.

“We’ve known for a while that the dramatic expansion of fishing is the primary threat to ocean biodiversity, but robust population assessment is difficult for low priority fishes whose catches have been poorly monitored over time. With this study, we tackle a fundamental challenge for tracking biodiversity change: discerning severe population declines from local extinction.”

Sawfishes get their name from the highly distinctive rostra they sport. These are long and narrow noses lined by teeth, making them very similar to sawblades. According to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, three of the five species of sawfish alive today are critically endangered, with the other two being endangered.

According to the authors of this study, overfishing is to blame. The animals’ long rostra and the teeth they sport can easily become entangled in fishing nets. They can fetch a high price on the market as their fins are among the most pricy shark fins. Rostra can also be sold for a variety of reasons, from folk medicine and novelty to spurs used in cockfighting.

Although we have no reliable global account of sawfish numbers, Dulvy says that the data we do have paints a very bleak picture. Unless an effort is made to stop overfishing and protect the habitats these species live in, there’s a very real risk of them going completely extinct.

In regards to solutions, the team recommends a concerted international conservation project focusing on Cuba, Tanzania, Columbia, Madagascar, Panama, Brazil, Mexico, and Sri Lanka, where such efforts are likely to see the greatest payoff. Fishing restrictions in these countries could also help. Australia and the United States both have solid protections already in place and retain populations of sawfish — they should act as “lifeboat” nations to ensure the species doesn’t go the way of the dodo.

“While the situation is dire, we hope to offset the bad news by highlighting our informed identification of these priority nations with hope for saving sawfish in their waters,” says Helen Yan, the paper’s other co-author.

“We also underscore our finding that it’s actually still possible to restore sawfish to more than 70 percent of their historical range if we act now.”

The paper “Overfishing and habitat loss drive range contraction of iconic marine fishes to near extinction” has been published in the journal Science Advances.

Giant sawfish exhibit virgin birth, reproducing without sex

A routine DNA test came up with some extremely surprising results – female sawfish in Florida reproduce without mating with males. This is among the very few times this process was observed in vertebrates and might force scientists to rewrite biology books.

Image via Dutch Shark Society.

“This could rewrite the biology textbooks,” study co-author Kevin Feldheim of the Pritzker Laboratory at the Field Museum of Natural History in Chicago, where the DNA fingerprinting was conducted, said in the statement. “Occasional parthenogenesis may be much more routine in wild animal populations than we ever thought.”

Parthenogenesis is a form of asexual reproduction in which growth and development of embryos occur without fertilization. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. This type of virgin birth is not as uncommon as you’d think – it’s often seen among invertebrates, and rarely happens in vertebrates. For example, the Komodo Dragon the world’s largest living lizard, is known to give birth through parthenogenesis. Also, the same thing has been observed in certain shark, snake and fish species living in captivity. But researchers were really not expecting to see it in sawfish.

“There was a general feeling that vertebrate parthenogenesis was a curiosity that didn’t usually lead to viable offspring,” said one of the researchers, Gregg Poulakis from the Florida Fish and Wildlife Conservation Commission.

Sawfishes, also known as carpenter sharks are actually a family of rays characterized by a long, narrow, flattened  nose extension, lined with sharp transverse teeth that resemble a saw. Sawfishes should not be confused with sawshark, which have a rather similar appearance. The discovery was made when researchers were conducting DNA tests on the DNA of 190 smalltooth sawfish captured in southern Florida faced with extinction. They wanted to see whether the sawfish are breeding with their own relatives due to the very small population, but they came up with an even more surprising conclusion – they breed… with themselves.

The toothy snout of a juvenile smalltooth sawfish in Florida’s Charlotte Harbor estuarine system.
Credit: Florida Fish and Wildlife Conservation Commission (FWC)

“What the DNA fingerprints told us was altogether more surprising: female sawfish are sometimes reproducing without even mating,” said lead author Andrew Fields from Stony Brook University in the US. In fact, one population of sawfish was made up of 3 percent parthenogenesis births.

In other words, you could consider it a miracle – the species is trying to avoid extinction through virgin births.

“Vertebrate animals that we always thought were restricted to reproducing via sex in the wild actually have another option that does not involve sex,” study co-author Demian Chapman, a marine biologist at Stony Brook University in New York, said in a statement. “Rare species, like those that are endangered or colonizing a new habitat, may be the ones that are doing it most often. Life finds a way.”

But if we want to say the full story on this one, humans are the reason the sawfish are going extinct in the first place. Overfishing and habitat destruction have destroyed 99% of the population in the past 25 years, and desperate times call for desperate measures. While in the long term, parthenogenesis leads to reduced genetic diversity and makes the species vulnerable to new threats, in the short run, it may just be the thing that saves them.

“This should serve as a wake-up call that we need serious global efforts to save these animals,” said Feldheim, stressing the importance of conservation measures.