Northern river shark

The **Northern River shark**, or **New Guinea river shark** (*Glyphis garricki*) is a species of requiem shark, in the family Carcharhinidae in the genus *Glyphis*, found in scattered tidal rivers and associated coastal waters in northern Australia and in Papua New Guinea. This species of inhabits areas with poor visibility, soft bottoms, and large tides, with immature sharks ranging into fresh and brackish water. It is similar to other river sharks in having a stocky grey body with a high back, tiny eyes, and broad fins. It measures up to 2.5 m (8.2 ft) long.

Northern river sharks are likely piscivorous (fish-eating). This species is viviparous, with females bearing litters of 9 young possibly every other year before the wet season. Very rare and facing threats from commercial and recreational fishing, and perhaps habitat degradation as well, this species has been assessed as critically endangered by the International Union for Conservation of Nature. The Northern River shark has been found in rivers in Western Australia. Only juveniles of the species live in fresh and brackish water, while adults have only been found in Marine environments.

## Description

Like other members of the river shark family, the northern river shark has a stocky body with a high back. The head is wide and flattened, with a broadly rounded snout and minute eyes equipped with nictitating membranes. Each nostril is divided into a very large incurrent opening and a small excurrent opening by a triangular skin flap. The sizable mouth is broadly arched, with short furrows at the corners. Thirty-one to 34 tooth rows are in the upper jaw and 30–35 tooth rows are in the lower jaw; the upper teeth are upright and triangular with serrated edges, while the lower teeth are narrower and straight to slightly curved. In the largest individuals, the first few lower teeth from the jaw median are spear-shaped with serrations near the tip.

The pectoral fins are large and broad, with gently backward-curving margins and pointed tips. The pelvic fins are triangular with nearly straight trailing margins. The first dorsal fin is long-based and triangular, with the apex almost forming a right angle; the second dorsal fin is some two-thirds as high as the first. The origin of the first dorsal fin lies over the pectoral fin insertions, while that of second dorsal fin lies over the pelvic fin rear tips. No ridge exists between the dorsal fins on this species. The anal fin is smaller than the second dorsal fin and has a strong notch in the rear margin. The caudal fin has a strong lower lobe and a long, narrow upper lobe with a ventral notch near the tip. The dermal denticles are small, oval, and overlapping, bearing three horizontal ridges leading to marginal teeth. This shark is steel-gray above and white below; the color transition is sharp, located well below the eye, and becomes jagged on the sides of the trunk. The anal and caudal fins become dusky or black towards the trailing margins and tips. The maximum known length is 2.5 m (8.2 ft). This species differs from the extremely similar-looking speartooth shark (*G. glyphis*) in several morphological and meristic characters, including having fewer vertebrae (137–151 versus 213–222) and a lower, jagged gray-white color boundary.

## Habitat and Distribution

The northern river shark has been reported from King Sound, the Ord River, and Doctors Creek near Derby, Western Australia, the Adelaide and Alligator Rivers in Australia's Northern Territory, and the Daru region and possibly the Fly River in Papua New Guinea. It inhabits large rivers, estuaries, and coastal bays, all of which are characterized by high turbidity, silty or muddy bottoms, and large tides. Young and juvenile sharks are found in fresh, brackish, and salt water (salinity ranging from 2 to 36 ppt), whereas adults have only been found in marine environments. This indicates that, like the bull shark, the species is anadromous, with pups and juveniles living in freshwater while the adults dwell out at sea.

## Biology and Ecology

Northern River sharks are well adapted to hunting prey in low-visibility environments. The northern river shark has very small eyes, slender teeth, and high density of  ampullae of Lorenzini. In Doctors Creek, sharks may move to and from favored feeding areas with the tide. The shape of their teeth indicates a predominantly piscivorous diet.

## Reproduction

Like other requiem sharks, this species is viviparous, with the developing embryos forming a placental connection to their mother after exhausting their supply of yolk. Females give birth around October, before the start of the wet season, on possibly a biennial cycle. One female examined by researchers contained nine fetuses. The young are born at under 67 cm (26 in) long; males mature between lengths of 1.2 and 1.4 m (3.9 and 4.6 ft), while females mature between lengths of 1.4 and 1.7 m (4.6 and 5.6 ft).

## Conservation

The northern river shark appears to be extremely rare, though more subpopulations may remain to be discovered in Australia and Papua New Guinea. Based on present information, no more than 250 mature individuals are estimated to exist in the wild, with no more than 50 in any particular subpopulation. This species is caught legally and illegally by commercial fisheries using longlines and gillnets, as well as by recreational fishers; habitat degradation may pose a further threat to its survival. Because of its low natural abundance, limited distribution, stringent habitat requirements, and susceptibility to various human-caused threats, the IUCN has assessed the northern river shark as critically endangered. It has also been listed as endangered on the 1999 Commonwealth Environment Protection and Biodiversity Conservation Act, and on the 2000 Territory Parks and Wildlife Conservation Act. Kakadu National Park may be an important protected area for this species. No regulations restrict the capture of this species in Papua New Guinea.

## Interactions with Humans

Because of its rare nature, the northern river shark is at considerable risk from overfishing, pollution and habitat loss. Commercial and recreational fishermen represent the highest risk. With populations estimated to be no greater than 250 adults per subpopulation, it stands a substantial risk of population collapse.

Only one attack has potentially been attributed to the shark, after which the victim was interviewed by the film crew of *River Monsters*.

## In Popular Culture

A juvenile northern river shark was caught by *River Monsters* host Jeremy Wade. As the shark was foul-hooked, the record for catching it did not count. As dictated by Australian laws, the shark was only allowed to be handled for 60 seconds. The shark was quickly measured, tagged and released within the allotted timespan unharmed.