Thresher Shark
The high season (July to October) is normally highlighted by the chance to see the Mola (Sunfish). Though this has been true for this high season, we have also had increased sightings of thresher sharks; another amazing and rare creature!
Thresher sharks have been seen around Lembongan before, but it was a rare occasion and often deep (30 – 40 meters). Through the months of September and October, the chance of seeing a thresher has jumped up dramatically.
These thresher sharks have been spotted shallower than normal, around 20 – 30 meters, cursing by our divers on the north coast of Nusa Penida. Not all the thresher sharks have been spotted that deep. One was spotted during a PADI Discover Scuba Dive and another was spotted during dive 4 of the PADI Open Water course.
Lets take a look at some interesting facts about Threshers
- How to identity a thresher shark
- How do thresher sharks hunt
- Threats to thresher sharks
How to Identify Thresher Sharks
Named for their exceptionally long, thresher (Scythe)-like tail, which can be as long as the total thresher’s body length. The thresher shark has a short head and a cone-shaped nose. The mouth is generally small.
Some species of threshers can be as long as 6 meters in length. The big eye thresher shark, which is the species spotted around Lembongan, can reach up to 4.5 meters.
Most of the big eye thresher sharks that have been spotted over the last two months have been small. Ranging from around 1.5 meters to 2.5 meters, fin tip to nose.
Thresher sharks are fairly slender, with small dorsal fins and large, recurved pectoral fins.
Thresher sharks are primarily pelagic; they prefer the open ocean, venturing no deeper than 500 meters.
How do Thresher Sharks Hunt?
Threshers are solitary creatures which keep to themselves. Some species however do occasionally hunt in a group of 2 or 3 contrary to their solitary nature.
Thresher sharks tend to eat pelagic schooling fish; such as bluefish, juvenile tuna, and mackerel. Squid and cuttlefish are also primary food items. They are known to follow large schools of fish into shallow waters. Crustaceans and occasionally seabirds are also taken.
Threshers are active predators. They use their tail as a weapon to stun / kill prey.
The thresher accelerates towards a ball of fish and brakes sharply by twisting its large pectoral fins. It lowers its snout, pitches its whole body forward, and flexes the base of its tail. This slings the tail tip over its head like a trebuchet, with an average speed of 50kmh.
It’s fast, aggressive and violent. Everything can happen to these whipped fish; from swim bladder ruptures to broken spines to parts afloat. The sharks then swim round and swallow the pieces at their leisure.
The threshers are only successful on a third of their strikes but during these victories, they always kill / stun several fish at once. That’s far more efficient than chasing after agile individuals in a confusing shoal.
Threats to Thresher Sharks?
All three thresher shark species have been listed as vulnerable to extinction by the World Conservation Union since 2007.
Threshers are highly vulnerable to over fishing. Besides being hunted for their meat, threshers are also hunted for their liver oil, skin (for leather), and their fins, for use in shark-fin soup.
Threshers use to be fished in Lembongan and there have been stories from a few years ago of people seeing local fishermen with up to 7 thresher sharks on their boats. Since this, there has been a ban on fishing sharks around these islands and Indonesia.
Speaking with locals now, they say that thresher sharks have not been fished here for about a year. This could be why we are starting to see an increase in sightings on dives.
This could be a great sign that the threshers are here to stay. It may only be while the water is cooler but how amazing would it be if high season became mola and thresher Season!
Despite the ban on fishing some species of sharks in Indonesia, it is still common to see many different types of sharks at the Tanjung Luar Fish Market on Lombok Island, which is notorious for the selling of sharks and mantas. Tanjung Luar is one of the most illegal fishing markets in the world.
