Thresher Shark Encounter

[iainwilliams]

Hello – Number 1 here (check the first thread of this forum).

I’m just back from the Philippines where I spent 4 weeks diving in several areas. My travels initially took me to Malapascua Island north of Cebu Island in the central region of the archipelago. The island is renown for the thresher sharks that migrate daily into shallow water at the top of reef for cleaning.

Conditions during my week were rough and 2-3 meter swells with strong winds were the norm. The depth to the top of the circular shaped reef was 25 meters and the reef dropped sharply to deeper depths. The water was a very green colour and visibility was between 7 – 18 meters due to plankton. Diving starts early at 0530 as the sharks move back into deeper water after the early hours.

I waited about 35 minutes for my first encounter, staring into the gloom wondering what on earth I was doing here feeling cold in a thermocline 4 degrees colder than the usual warm water! – waiting. To occupy myself I watched nudibranchs, white anemones and three very colourful eels.

Then the thresher emerged out of the green swimming directly toward me. Its bulk was large and the black eye initially reminded me of diving with a white shark. At 5 meters distant the thresher moved to the right and swam past me. The shark was a large female approximately 3 meters in length (body only without tail), the unmistaken elongated upper caudal trailing behind her torso. The thresher then turned and swam back in front of me before turning once again and disappearing into the gloom.

All to soon the encounter was over, however, like all shark encounters of such magnitude the memory is permanently burnt on the retina!

The Common Thresher Shark (Alopias vulpinus) is a shark whose tail fin has a greatly elongated upper lobe. This shark is a very strong swimmer and can even leap out of the water. The Common Thresher Shark is not an aggressive shark, but it can be provoked. The thresher's large tail can injure divers.

The Common Thresher Shark swims from the surface to a depth of about 1,150 feet (350 m). It lives in tropical and temperate waters, including the eastern and western Atlantic, the central Pacific, and the Indo-west Pacific. The Common Thresher is decreasing in numbers because of overfishing (it is hunted for meat and for its fins).

Anatomy: The Common Thresher has a countershaded body, dark blue-gray above and white underneath. It has small jaws, but can use its tail to corral and even kill fish. The first dorsal fin is much, much bigger than the second; the pectoral fins are curved. Like other mackerel sharks, it has an anal fin, 5 gill slits, 2 dorsal fins, no fin spines, the mouth behind the eyes, and no nictitating eyelids. The Common Thresher shark ranges from 16.5 to 20 ft (5 to 6 m) long.

Teeth and Diet: The Thresher eats s quid and fish, corralling them with its elongated tail; it catches prey with its very sharp (but small) teeth.

Classification: Kingdom Animalia, Phylum Chordata, Class Chondrichthyes, Order Lamniforms, Family Alopias (Thresher sharks), Genus Alopias, Species vulpinus.

 

[Mako Mark]

one of my most memorable shark dives was a thresher too. There is something very special about them, they do look like a little great white or Mako.

I saw my first while I was living in Bali, on teh wreck of the USS liverty in Tulumben. I had dropped off the end of the wreck ad was descending at about 35 meters whent this thing blasted through like a rocket, scattering all the bait fish that were hanging out on top of the wreck. It then took a lazy turn and came and had a quick look to see what the heck we were, then dissapeared into the blue.

shak was 2.5 to 3 meters (not including the tail) distance about 5-8 meters viz 40 meters.

 

[iainwilliams]

Wow seeing a threasher belting through at speed would be a good sight to see. The ones I've seen look pretty sluggish.

I'm always aurprised at the speed a shark can move if it wants to!

I was in PNG last September (my usual diving haunt 3 times a year) and we were diving a virgin site to see if it was suitable for "guests". My friend was rubbing the plastic bottle at 25 m to see what we could attract. Within 2 minutes we had 3 large grey whalers and 2 medium sized silvertips swimming about along with a white tip. They were very curious and my inexperienced bottle rubber kept rubbing the bottle like some jeannie lamp! Next minute a grey whaler did a 180 degree turn on it tail some 40 m out and charged us pectral fins down to about 5 m away. He then flipped over and swam off erratically before another whaler made a similar pass. Neadless to say my friend does not like rubbing bottles anymore! After we stopped bottle rubbing the sharks disappeared into the blue.

Actually this is probably the first time I've actually been scared diving with sharks, other than swimming with a great white - but that's another story. See ya.........Iain

 

[Humuhumunukunukuapua'a]

What's "rubbing the bottle"? I gather it attracts sharks?

 

[iainwilliams]

Rubbing a plastic bottle half filled with water and air simulates a low frequency noise that replicates the frequency of a struggling fish, that may be trouble. We can hear the noise the bottle makes when we rub it - this is not the noise that attracts the sharks. Rather it is the sound that we cannot hear when we rub the bottle - this is the low frequncy sound.

Furthermore, any unusual noise we normally attract a shark. I've used scrapping my knife in my tank or banging it, the bottle routine and tapping my slate. Usually the shark tires of these irritating noises after several encounters, however, if your reef is rarely dived then the fish will always be keen to check out what is new in their domain....Iain

 

[AzSnake]

Rubbing a plastic bottle half filled with water and air simulates a low frequency noise that replicates the frequency of a struggling fish, that may be trouble. We can hear the noise the bottle makes when we rub it - this is not the noise that attracts the sharks. Rather it is the sound that we cannot hear when we rub the bottle - this is the low frequncy sound.

Furthermore, any unusual noise we normally attract a shark. I've used scrapping my knife in my tank or banging it, the bottle routine and tapping my slate. Usually the shark tires of these irritating noises after several encounters, however, if your reef is rarely dived then the fish will always be keen to check out what is new in their domain....Iain

Ok is this done with 2 thumbs? Or with your palm? Please elaborate.

 

[hornetplt]

Ok is this done with 2 thumbs? Or with your palm? Please elaborate.

Take a standard plastic water bottle (with lid attached) underwater(i like to store inside my wetsuit). At depth, take out bottle, open lid and fill with air. Screw top back in and hold bottle between palms of your hands. While holding the bottle firmly(you have to, otherwise it will shoot to surface), roll the bottle as vigorously as possible between your hands like you would do trying to warm your hands up on a cold day. Do this continuously & if there are sharks or other predators in the area, they WILL cruise by to check you out. You may really piss some of them off and they may come a little to close for comfort. Remember, you now "sound" like a wounded fish. When this is done around some species of schooling travely, they will sometimes surround you, almost like they are trying to protect their buddy who isn't having such a good day. I have found that this is a very effective tool to draw in predators and if it becomes too much for you to handle, just stop rubbing the bottle and they will soon leave. Some sharks may become VERY agitated......just a fair warning!

 

[AzSnake]

Take a standard plastic water bottle (with lid attached) underwater(i like to store inside my wetsuit). At depth, take out bottle, open lid and fill with air. Screw top back in and hold bottle between palms of your hands. While holding the bottle firmly(you have to, otherwise it will shoot to surface), roll the bottle as vigorously as possible between your hands like you would do trying to warm your hands up on a cold day. Do this continuously & if there are sharks or other predators in the area, they WILL cruise by to check you out. You may really piss some of them off and they may come a little to close for comfort. Remember, you now "sound" like a wounded fish. When this is done around some species of schooling travely, they will sometimes surround you, almost like they are trying to protect their buddy who isn't having such a good day. I have found that this is a very effective tool to draw in predators and if it becomes too much for you to handle, just stop rubbing the bottle and they will soon leave. Some sharks may become VERY agitated......just a fair warning!

Great explanation.
Thanks!
I will be careful. I plan on trying this out in waters with less aggressive and dangerous sharks. I will be in Cozumel in 3 weeks. You never know whats around but You typically see nurse, black tips and hammerheads in Cozumel, possible a lemon shark if your lucks.

 

[JustAddWater]

I've seen thresher shark from the boat; slapping its tail at the baitfish on the surface, but I've never seen one underwater. I bet they are a pretty impressive sight.

 

[Wijbrandus]

Great explanation.
Thanks!
I will be careful. I plan on trying this out in waters with less aggressive and dangerous sharks. I will be in Cozumel in 3 weeks. You never know whats around but You typically see nurse, black tips and hammerheads in Cozumel, possible a lemon shark if your lucks.

If we don't hear from you again, we'll know this isn't a smart thing to do.

Good luck.