There are no known records of sexually mature (adult) Glyphis glyphis. ANYWHERE. EVER.
This is one of the reasons the Barry Lyon from Australia Zoo commenced researching the G.glyphis (otherwise known as the speartooth shark) in 2012.
The speartooth shark is listed on the EPBC Act as critically endangered and the Wenlock River appears to be the current stronghold for the species in Queensland. G.glyphis recorded in the Wenlock River range from juveniles with umbilical scars to sub adults with a total length of 1.57 metres. They have all been located in tidal, brackish and highly turbid water.
As very little is known about the shark, Barry’s research is looking at the ecology and it is hoped that when more is understood about the shark’s ecology, management and conservation practices will be enhanced.
To learn more about the species, Barry is capturing and tagging the sharks with acoustic pingers (see picture). Thanks to the extensive research on crocodiles undertaken by Australia Zoo, CSIRO and University of Queensland, the Wenlock River is already full of receivers, so the shark research is able to use technology already in place. So far 55 speartooth sharks have been tagged, and of these 39 have provided long term data, all of which are juveniles and sub-adults.
What is known about the shark
Barry is currently analysing the data recorded so far, and results indicate:
- Females may come to the mouth of river (in Port Musgrave) to give birth to pups. It is still unknown at what age they start having young, because adults have never been captured.
- During September and October, juveniles swim upstream, to where the fresh water first mixes with salt, and the water is slightly saline.
- The new data shows that all the speartooth sharks inhabit the upper estuary in the mid-late dry season.
- When the river first really floods, there is a total migration to the lower estuary and the mouth of the Wenlock, with some sharks moving into Port Musgrave.
- After the wet until the end of June, all the sharks undertake ranging movements between lower and upper estuary.
- From July for rest of dry, the sharks remain in the upper estuary.
- Sub adults appear to have a larger home range than the juveniles.
- The sharks also move with the tides. Data so far suggests they travel up to 25 km in a 24 hr period utilising tidal movement.
- Bull sharks dominate the upstream clearer waters.
The Wenlock River is the crucial river for the species in Queensland. It is thought this is because its tidal sections are highly turbid, and being perennial, the Wenlock features fresh water inflow all year, unlike many other rivers on Cape York. A combination of sandstone and bauxite springs drive the perennial nature of the Wenlock River. This highlights the importance of the broader ecological connection been the catchment and the river itself. Barry has found the fresh water inflow has a big influence on which part of the river the sharks inhabit, however he is not sure if that is related to food sources or other drivers.
About the speartooth shark
Speartooth sharks are thought to grow to three metres or more in length. They have small eyes, and like the bull shark which is well adapted to hunting in dirty water, they have a large number of electro-receptors on their heads to help detect prey. The speartooth shark has approximately 670 of these electro-receptors, more than twice as many the bull shark. This suggests it is well adapted to hunting in dark and turbid water. Its distinguishing feature is a series of teeth shaped like spear heads (see picture). The second dorsal fin is also at least half the height of the first fin, and much higher than that of a bull shark (see picture).
The main threats to the species’ survival are considered to be commercial gill netting, insensitive recreational fishing, and habitat modification.
What the public can do to help save the speartooth shark
Juveniles are known to enter crab pots, and may occasionally take baits of line fishers, so anglers are encouraged to release any they find with great care. Speartooth sharks have not been known to take hooked fish from anglers’ lines, so should not be seen as a threat.
What’s next? The science will be used to inform management actions into the future, to raise awareness about the speartooth shark, and to identify further gaps in knowledge for future research.