A rare river shark
The Speartooth shark (Glyphis glyphis) is a rare river shark. The Speartooth shark belongs to the family Carcharhinidae. It lives in northern Australia and New Guinea in the tidal reaches of large tropical rivers and coastal marine habitats. It lives in a wide range of salinities, but exclusively to turbid and fast-moving waters. The first documented statistics on an adult happened in 2014 on Daru Island with two males and one female being caught in coastal waters just off the island. The Speartooth shark may or may not be the same as Glyphis Sp. A, Bizant River shark. Many believe that the Bizant River shark (Glyphis sp. A) and the Speartooth shark (Glyphis glyphis) are the same species, however there are noticeable differences in the shape of the lower anterior shape, and the size of the sharks.
Family: Carcharhinidae – Requiem sharks
Common Name– Ground Sharks
Common Name– Requiem Sharks
Status: IUCN Red List ENDANGERED
Average Size and Length: The first documented adult was recorded at a length of 8.5 feet.
Teeth and Jaw: The mouth of the Speartooth shark is big and arched with short furrows. The Speartooth shark has 26–29 upper and 27–29 lower tooth rows. The teeth are tall and upright. The ones in the upper jaw are wide and triangular with serrated edges and the ones in the lower jaw are narrow and spear-like with serrations only near the tip. Young sharks have tiny cusplets at the base.
Head: The Speartooth shark’s head is wide and short with a flat snout. It has small eyes with nictitating membranes, and large nostrils with skin flaps. They are divided into incurrent and excurrent openings. It has a large amount of ampullae of Lorenzini.
Denticles: The dermal denticles of a Speartooth shark are small, oval and overlap. They have 3 to 5 horizontal ridges that lead to marginal teeth.
Tail: The caudal fin is asymmetrical. The lower lobe is narrow and well-developed, while the upper lobe has a gently convex upper margin and a prominent notch in the ventral margin near the tip.
Demographic, Distribution, Habitat, Environment and Range: Research confirms that the sub adult and newborns only live in waters with muddy bottoms and fast tidal currents. The rapid water produces turbidity. The younger sharks have been found much further upstream than the older ones.
Documented living conditions were at <1% of sunlight penetrating at a depth of 3.3 feet. Salinity levels range from nearly fresh (0.8 ppt) to nearly marine (28 ppt), and temperatures range from 77 to 91 °F.
Very few Speartooth sharks have been found. The young adult and juvenile Speartooth sharks have been found in tropical rivers that are larger and that are lined with mangroves. The locations are in New Guinea from Port Romilly in Daru island and the Fly River, and in northern Australia in the Adelaide and Alligator Rivers. In Queensland, Australia there have been accounts in Ducie, Wenlock, Normanby, Bizant, Embly and Hey Rivers. They have been found in the estuary and as far as hundreds of miles upstream. Some research and possible sightings suggest even in the Ord River in Western Australia. The first 3 adults were found in 2014 off Daru island in coastal waters by scientists.
One record confirms a Speartooth shark in the South China Sea.
A study that tracked three individuals in the Adelaide River reported that they moved upstream with the flooding tide and downstream with the ebbing tide, averaging 10–12 km (6.2–7.5 mi) each way. The average swimming depth was determined for one individual to be 7.7 m (25 ft), in the middle of the water column. (Pillans, R.D.; J.D. Stevens; P.M. Kyne & J. Salini (25 August 2009). “Observations on the distribution, biology, short-term movements and habitat requirements of river sharks Glyphis spp. in northern Australia”).
Diet: Little is known about the feeding habits of adult Speartooth sharks, but many bony fish spines and a stingray spine were found embedded in the jaws of the only documented adult female. Juveniles eat prawns, burrowing gobies, catfish, threadfin, gudgeon, benthic croaker and bream.
Aesthetic Identification: The Speartooth shark is robust with a streamlined body with 5 pairs of gill slits with the first pair longer than the others. It is slate-gray above, including the upper surfaces of the pectoral and pelvic fins, and the caudal fin, and counter-shaded white underneath. The border between dark and light runs through the bottom rim of the eye, through the gill slits, over the flank well above the pelvic fins, and onto the upper caudal fin lobe. At the posterior margins, the fins get darker with a full black edge on the upper caudal fin lobe. The pectoral fins also have a black blotch underneath, near the tip. The eyes have white rings around them.
They have large pectoral fins that have convex leading and concave trailing margins, and blunt tips. The pelvic fins are triangular with nearly straight margins. The first dorsal fin originates over the pectoral fin insertions, and is broadly triangular with a narrow apex and a concave trailing margin. The second dorsal fin measures about 67–77% as tall as the first and is similar in shape (possibly to help them in the fast-moving currents); there is no midline ridge between the dorsal fins. The anal fin is almost as large as the second dorsal fin and lies slightly behind. It has a deep notch in the posterior margin.
Biology and Reproduction: The Speartooth shark is viviparous. Scientists believe that birthing happens from October to December, near the end of the dry season, with newborns measuring around 20–23 inches long. A female was captured and gave birth to 1 pup that was fully developed and was 2.13 feet long. Research suggests that litter sizes could range from 6 to 7. The growth rate could be around 7.5 inches per year.
Many believe that the Bizant River shark (Glyphis sp. A) and the Speartooth shark (Glyphis glyphis) are the same species, however there are noticeable differences in the shape of the lower anterior shape, and the size of the sharks.
Behavioral Traits, Sensing and Intelligence: Based on the data scientists have now, the Speartooth shark prefers darkness, so its activity levels probably aren’t impacted by the day/night cycle. It is known that they have small eyes and a lot of ampullae of Lorenzini, so therefore rely more on electroreception to hunt for prey.
Scientists don’t have evidence that they segregate by sex.
Speed: Research suggests that they are probably sluggish. The second dorsal fin is thought to help it through the strong currents. It moves with the currents to conserve energy.
Speartooth Shark Future and Conservation: The estimated global population of Speartooth sharks is thought to be around 2500. The Speartooth shark is caught incidentally by commercial fisheries using gillnets and longlines and recreational fisherman. Queensland has banned fishing in a river where this shark is known to live. They also face the threat of habitat degradation.
Speartooth Shark Recorded Attacks on Humans: The Speartooth shark is not a danger or a threat to humans.