Sawfishes sure can wield a saw (w/ video)

Mar 05, 2012

Sawfishes wouldn't be sawfishes if they didn't come equipped with long toothy snouts—their saws. Now, researchers reporting in the March 6 issue of Current Biology, have figured out what they use those saws for, and it turns out the answer is quite impressive. It might even help save the critically endangered and incredibly elusive sawfishes.

"I was surprised to see how skilled sawfish are with their saw," said Barbara Wueringer of the University of Queensland. "They use their saw to impale prey on the rostral teeth by producing several lateral swipes per second."

Unlike sawfishes in the wild, the animals she and her team caught on hidden cameras were fed on dead fish, "but their strikes were sometimes strong enough to split those fish in half." The animals then proceeded to swipe their meals onto the floor and dig in.

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Sawfishes wouldn’t be sawfishes if they didn’t come equipped with long toothy snouts -- their saws. Now, researchers reporting in the March 6 issue of Current Biology, a Cell Press publication, have figured out what they use those saws for, and it turns out the answer is quite impressive. It might even help save the critically endangered and incredibly elusive sawfishes. Credit: Current Biology, Dr. Barbara Wueringer

Sawfishes don't use their saws just to kill and manipulate prey, but also to sense their next mark in the first place. That's contrary to other jawed fishes whose long "noses" are generally used for one or the other purpose, not both, the researchers said.

Wueringer's team earlier found that the saws of freshwater sawfishes are covered in thousands of electroreceptors. Those tiny sensors enable sawfishes to detect the electric fields of other animals in their midst. Tiny canals in the skin covering the saw also allow them to detect water movements. The two senses together give them an edge as hunters in the dark and murky waters in which they live.

In the new study, the researchers observed recently captured sawfishes in action. They watched as those sawfishes tore into already dead fish and responded to weak electrical fields that mimicked live, hidden prey.

"Now we know that sawfish are not sluggish bottom dwellers as previously believed, but agile hunters that hunt in the three-dimensional space of the water," Wueringer said.

What the researchers observed is contrary to what you might read in any textbook, she added. The sawfishes' saw had been considered more like a rake, used by the fish to sift through sand in search of something to eat.

Wueringer said this new view might even lead to changes in the fishing practices that are allowed in prime territory, noting that the saw is partly to blame for sawfishes' global decline: their saws are easily entangled in fishing gear.

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User comments : 9

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RitchieGuy
1.8 / 5 (5) Mar 05, 2012
Nice find by Dr. Wueringer and her team. It appears that the very same advantages that make sawfishes more adept at hunting their prey may also be contributing to their undoing by, once again, man-caused trapping of man's own prey. So what can be done about the demise of the sawfish species? I suggest eliminating the nets that haul everything in including unwanted fish.
An expensive alternative would be to build large plastic tunnels underwater with an inlet on one end and an outlet on the other and an equally strong plastic gate panel in the middle. In effect, it would be SIMILAR to having livestock in a corral who have to go through a gate individually to be weighed or powdered with insecticide. A TV camera could be used to monitor what fish are passing through and the fish that are desirable can be let through to the outlet while the middle panel is closed to keep other fish out. The fishermen could form a cooperative that will pay for the maintenance of the tunnel. It would work,
RitchieGuy
1 / 5 (4) Mar 05, 2012
and a stiff net or a large cage could be affixed to the outlet that can be swung away from the outlet to let any undesirable fish a way out of the tunnel. Then when the camera shows that there are only desirable fish in the outlet side, the outlet can be opened and the fish swim toward the net or cage and are hauled up to the boat. There are other details that would need to be worked out, but in addition to the big expense, each tunnel would need to be maintained by a group who are interested in saving sawfish from destruction and who don't mind the expense. It would also be better for the ocean environment because there is nothing to get snagged on coral and anemone on the sea floor and young fry can still get through the small holes in the sides of the tunnel. The plastic will likely degrade over time and will need to be replaced or repaired by divers. But the initial expense would be great and that might be too prohibitive for some.
TheGhostofOtto1923
Mar 05, 2012
This comment has been removed by a moderator.
RitchieGuy
Mar 05, 2012
This comment has been removed by a moderator.
Au-Pu
not rated yet Mar 06, 2012
An original and theoretically practical approach.
Commercial fishermen wouldn't go for it. They believe they have a right to rape the seas. They are one of our non productive enterprises. They contribute nothing to the production of their harvest.
You will be better off to sell your idea to conservationists and or to save various species groups.
Governments could help by introducing a two tiered tax system. If you produce your harvest, you are taxed at a lower rate. If you do not produce your harvest you pay a substantially higher tax.
That would greatly upset the oil, mining, forestry, law, accounting, real estate and all similar non productive industries.
But I think it would be a good idea.
Cluebat from Exodar
not rated yet Mar 06, 2012
Good luck getting any national factory ship to pay your non-productive enterprise tax. This idea will only serve to collapse the american fishing industry. People will still get their canned tuna, but through imports from poorly regulated nations instead.
TheGhostofOtto1923
1 / 5 (3) Mar 06, 2012
An original and theoretically practical approach.
??Perhaps one might consider the difficulty in getting fish to cooperate in swimming through a tube in the open ocean? Nets are dragged to catch fish because they try to avoid getting caught. Yes?
RitchieGuy
1 / 5 (1) Mar 06, 2012
Cluebat says:
Good luck getting any national factory ship to pay your non-productive enterprise tax. This idea will only serve to collapse the american fishing industry. People will still get their canned tuna, but through imports from poorly regulated nations instead.


The point being that sawfish have become an endangered species because their saws get caught in the usual fishnets clearly necessitates an alternative method of fishing before extinction of the sawfish by mishandling. Environmentalists could view such a tunnel with approval.

@Au-Pu
I don't think an unfair tax on non-productive industries would be necessary. They're taxed enough already. Schools of food fish could be lured by bait inside the tunnel inlet. Only the right sized fish would be trapped within the tunnel and the smaller ones would have access to the outside through graduated holes so that bigger fish can't get out. Sawfish will chase the fish, but their saws can't get caught, leaving them free to get
RitchieGuy
1 / 5 (1) Mar 06, 2012
out through the outlet at the end. I think for a clear plastic round tunnel of the right circumference and length would require a very large fishing boat that would need to suspend the tunnel over the side in such a way that the tunnel doesn't rise and fall with the motion of the boat. . . maybe including a suspension system with pontoons.
I'm sure there are fishing fleet owners who might be able to afford this tunnel and its maintenance. Important thing is it's environmentally friendly and humane.
TheGhostofOtto1923
1 / 5 (2) Mar 08, 2012
So ritchie how big is this tube of yours?

"A factory stern trawler is a large stern trawler which has additional onboard processing facilities and can stay at sea for days or weeks at a time. A stern trawler tows a fishing trawl net and hauls the catch up a stern ramp. These can be either demersal (weighted bottom trawling); pelagic (mid-water trawling); or pair trawling, where two vessels about 500 metres apart together pull one huge net with a mouth circumference of 900 meters."

-1/4 mi diameter? Your tube going to feed factory ships?
TheGhostofOtto1923
1 / 5 (2) Mar 08, 2012
The point being that sawfish have become an endangered species because their saws get caught in the usual fishnets
Their saws get caught... Then how do you suppose swordfish, sharks, dolphins, turtles etc get caught in those same nets? A minor point but it shows you're (not) thinking. Look up gill nets. It will be good practice.