River sharks

Legislative protection

Environment Protection and Biodiversity Conservation Act 1999

The speartooth shark Glyphis glyphis is listed as critically endangered under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).
EPBC Act Status and Documents - Glyphis glyphis — Speartooth Shark

The Northern River Shark Glyphis garricki is listed as endangered under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).
EPBC Act Status and Documents - Glyphis garricki — Northern River Shark

Information about these species is scarce due to the lack of specimens in research collections and the fact that encounters are rare and identification may be confused with other shark species. Following is information currently available about the biology and distribution of Glyphis glyphis and Glyphis garricki.

Recovery plan

A combined recovery plan for the listed sawfish and the two species of river shark (Glyphis glyphis and Glyphis garricki) was released in November 2015.

Biology

Glyphis glyphis and Glyphis garricki are two of possibly four or five Glyphis species belonging to the family Carcharhinidae. These medium-sized whaler sharks are greyish with small eyes, without distinctive color pattern, with short and broadly rounded snouts, and erect, broadly triangular, serrated upper teeth (Last & Stevens, 1994).

The small eyes and slender teeth of the Glyphis sharks suggest that they are primarily fish-eaters that have adapted to hunting in cloudy estuarine and river waters. The maximum size of these species is unknown but they may grow to a length of 2-3 metres (Last & Stevens, 1994). Glyphis glyphis and Glyphis garricki can easily be confused with the Bull shark, Carcharinus leucas, as these three species occur in the same habitat and possibly occupy similar ranges during some lifecycle stages. However, Glyphis seem to be particularly adapted to low oxygen environments, more so than Bull sharks (Last, pers comm).

Distribution

In the past Glyphis glyphis was recorded in the Bizant River, Queensland and the Adelaide River, Northern Territory, but it is now considered that these two populations are actually two different species. Scientists were able to make the distinction between the two populations based on the fact that they had different numbers of vertebrae (Last & Stevens, 1994). Subsequently, it has been determined that Glyphis glyphis are found in the Bizant River and Glyphis garricki are found in the Adelaide River. Recent collection of additional specimens has shown that both Glyphis glyphis and Glyphis garricki occur in the Alligator River within the Kakadu National Park, Northern Territory.

Within the Bizant and Adelaide Rivers these species are known to occur in relatively shallow, upper freshwater, and possibly brackish, reaches of the river and associated floodplains. Similarly, certain areas of Kakadu National Park (such as the Alligator River) may also provide important habitat but further investigation and identification are required within the area (Pogonoski et al., 2001). Outside Australia Glyphis species are known to occur in New Guinea and Borneo.

It is thought that Glyphis glyphis and Glyphis garricki are naturally rare with specific habitat preferences and low reproductive rates, which makes populations vulnerable to any form of exploitation. Threats to the survival of Glyphis glyphis and Glyphis garricki include recreational line fishing, gill netting and habitat degradation.

Last, P.R & J.D Stevens (1994). Sharks and Rays of Australia. CSIRO Publications, pp259-260.

Pogonski, J.J, D.A Pollard and J.R Paxton (2001). Conservation Overview and Action Plan for Australian Threatened and Potentially Threatened Marine and Estuarine Fishes. Environment Australia, Canberra.

Dr Peter Last, personal communication, CSIRO Marine Research, Hobart.

Resources