WA Sharks, Shark Fisheries and Safety Tips

Figure 1 Shark Sizes

Sharks are a highly diverse group of fishes which have evolved to inhabit all marine habitats, from the surfline to the depths of oceanic trenches. More than 160 species of sharks are found in Australia and new species are still being discovered.

The largest fish on earth is the whale shark, Rhincodon typus, which grows to over 12 metres in length and feeds exclusively by sieving plankton from the water as it swims.

The smallest species of shark is the pygmy shark, Euprotomicrus bispinatus, a tiny dogfish, which only grows to about 25 centimetres.

One of the most common species of sharks in metropolitan waters is the Port Jackson shark, Heterodontus portusjacksoni, which is a small shark that feeds mainly on shellfish. Other common species include wobbegongs (family Orectolobidae), which lie motionless on the seabed waiting for their fish prey to swim past; small whaler sharks (family Carcharhinidae), gummy and whiskery sharks, which eat small fish, squid and octopus.

Several species of shark are caught commercially in Western Australia, including the gummy shark, whiskery shark, dusky shark (bronzie) and sandbar shark (thickskin). Commercial shark fishing targets the smaller species and juvenile whaler sharks. Shark is mainly sold through fish and chip shops although is becoming increasingly popular as a table fish.

In recent years, the value of shark fins, a delicacy in Asia, has increased dramatically. This has led to increased targeting of sharks purely for the value of their fins, but legislation passed in October 2000 now prevents fishers from catching sharks only for their fins in Western Australian waters.

Owing to their relatively low reproductive rates (the number of pups produced per year), and the length of time taken to reach sexual maturity, fished shark stocks require careful management if they are to be sustained.

Figure 2 Shark Fishery map

The shark fishery in Western Australia is managed as four separate zones, as shown in figure 2. Shark catches in these fisheries for the 2001/2002 season were as follows:

Despite their ‘man-eating' reputation, most sharks are entirely harmless to humans, preferring a diet of fish and invertebrates. As ‘apex predators', which occupy the very top level of the food chain, sharks play an essential role in maintaining the health of the marine environment and are deserving of our respect. As well as their environmental importance, sharks are a valuable resource for the fishing and tourism industries.

Of more than 160 known species of Australian sharks, only three are accepted as posing a significant risk to human safety. Most wild animals will bite when they feel threatened; sharks are no exception. No matter how big or small, all sharks are capable of biting and should be left alone.

The three most dangerous species are the great white shark (also known as the white pointer or white shark), Carcharodon carcharias; the tiger shark, Galeocerdo cuvier; and the bull shark (also known locally as the Swan River whaler), Carcharhinus leucas. Whaler sharks, wobbegongs and hammerheads, while usually timid, have also bitten humans (although rarely fatally), and should be avoided.

The great white is the largest predatory shark in the world, reaching about six metres in length when fully grown.

The diet of young great whites consists almost entirely of fish. Bigger white sharks have a generally broader diet, comprising of large fish, other sharks and rays, seals, dolphins and occasionally whales. Great white sharks may occasionally scavenge sick and dead whales as they pass on their annual migration.

The great white is a widespread but scarce species, occuring in most temperate waters of the world. The southern coast of Australia is recognised as being one of the last areas of relatively high white shark abundance, although numbers have been reduced through game fishing and accidental commercial catches. The lower west, and particularly the south coast of Western Australia, are considered part of the species' normal range.

Little is known about the biology of this species, largely because it is scarce and the cost of research is extremely high.

Scientists do know that great white sharks take a long time to reach sexual maturity and give birth to very few offspring when they do reproduce. This biology makes the species highly susceptible to over-exploitation, and due to anecdotal evidence indicating a decline in their numbers, the Commonwealth and State Governments have protected white sharks in almost all Australian waters. The grey nurse shark, a relatively harmless but easily overfished coastal species, and the whale shark are also protected throughout Australian waters.

Further reading

Edmonds, C. (1989). Dangerous Marine Creatures. Reed Books, Sydney.

State of the Fisheries Report 1998/1999. the Department of Fisheries (annual publication).