Tuesday, Mar 30, 2021
What have these 19 sharks got in common?
Friday, Oct 02, 2020
These 19 sharks are all targeted by Queensland's Shark 'Control' Program.
The waters around Australia are home to a rich diversity of sharks with some 180 species occurring around our coastline. But many of these are in trouble, with some even facing extinction.
Among sharks under threat are some of the 19 species targeted by the Queensland government’s nets and drumlines. Two of these are listed as Critically Endangered in the Red List of Threatened Species drawn up by the International Union of the Conservation of Nature (IUCN), seven species are Near Threatened and three species are listed as Endangered.
Great Hammerhead (Sphyrna mokarran)
This species has been described as one of evolution's most eccentric creations with its wide hammer-shaped head. But the unusual shape serves many useful purposes including; boosting its hunting prowess through more efficient manoeuvrability, increasing its power of smell, and giving it 360-degree vision, enabling it to see prey above and below at the same time.
Sadly, the Australian hammerhead shark populations are in decline. They are particularly vulnerable to being caught in nets because of the unique shape of their heads. In six years (2012-2018) 592 hammerheads have been culled in Queensland’s Shark Control Program (QSCP) even though hammerhead sharks have never been involved in a fatal incident.
Oceanic Whitetip Whaler (Carcharhinus longimanus)
Formerly, the most abundant oceanic pelagic shark in tropical and warm temperate waters, this species is also in sharp decline. Previously living in abundance far offshore in the open sea, the oceanic whitetip rarely comes close to land, but it has been recorded off the coast of the south of WA and the east coast of NSW and QLD.
An impressive shark to observe, it is slow-moving but active day and night, cruising slowly on or near the surface with huge pectoral fins outspread. This species is very inquisitive and persistent, especially when investigating divers, but its very inquisitive nature makes it highly catchable, and the shark’s huge fins have a very high value in the international fin trade.
Bull Whaler (Carcharhinus leucas)
The bull shark is the only widely distributed shark that stays in freshwater for long periods to feed and breed. Females sometimes give birth in river mouths where the young will live for up to five years. It is a massive, solid, broad-headed greyish shark with a broad, bluntly-rounded snout, small eyes and large angular pectoral fins. But despite its appearance and reputation, the bull shark is a popular species in shark tourism with divers remarking on their gentle, graceful movements. Bull sharks usually cruise slowly near the seabed in waters less than 20-metres deep but are agile and quick when attacking prey. Young sharks have been seen spinning out of the water. The critical inshore habitats of bull sharks have been badly damaged by a wide range of human activities, including Queensland’s nets and drumlines.
Blacktip Shark (Carcharinus limbatus)
Physically, the Australian blacktip shark and the common blacktip look the same and can only reliably be distinguished by the number of vertebrae. However, the common blacktip, which has a worldwide distribution, is listed as near threatened, while the Australian blacktip is regarded as 'of least concern'. The common blacktip occurs on continental and insular shelves, usually close inshore (off river mouths, in estuaries, shallow muddy bays, saline mangrove swamps, island lagoons and coral reef drop-offs). It is heavily fished and susceptible to habitat degradation. This is a popular commercial and sport fishery species, with valuable meat and fins. In Australia it occurs in WA, NT, QLD and NSW waters.
Blue Shark (Prionace glauca)
This is one of the most strikingly beautiful sharks in the ocean. Its long slim body is distinctively coloured with a dark blue back and bright blue flanks, long conical snout, large eyes and long narrow scythe-shaped pectoral fins. Its beauty doesn’t stop it from being the most heavily fished shark in the world, and from being targeted in Queensland’s Shark Control Program. It occurs worldwide and is widely distributed in Australia, its migrations often following major trans-oceanic currents. Blue sharks cruise slowly at the surface with the tips of their dorsal and tail fins out of the water.
Grey Reef Whaler (Carcharhinus amblyrhynchos)
This is an active, strong swimming, highly social species which aggregates by day in or near reefs or lagoons and becomes even more active at night. Found in tropical waters throughout the Indo-west and central Pacific, in Australia it is recorded from the central WA coast, around the tropical north and south to southern QLD. It has an inquisitive nature, often investigating disturbances and approaching divers.
This shark is taken by multispecies fisheries in many parts of its range and used for various products such as shark fin soup and fishmeal. Site fidelity, restricted habitat, small litters and late age of maturity have made it sensitive to increasing fishing pressure. It also faces habitat degradation.
Long Nose Whaler/Spinner Shark (Carcharhinus brevipinna)
This shark is named for its long narrow pointed snout and spectacular spinning leaps out of the water when chasing fish. In Australia, the spinner shark is found across northern Australia, Queensland and southern NSW, and with its black- tipped fins is often mistaken for the blacktip shark. It is an active schooling species that prefers shallow coastal waters. In Australia, both juveniles and adults are targeted or taken as bycatch by commercial gillnet, trawl and longline fisheries. It is also popular in recreational fishing.
Silky Whaler (Carcharhinus falciformis)
A large, slender, fast-moving shark, deriving its English name from the smooth hide, covered with small, tightly packed overlapping denticles. It is distributed worldwide in tropical seas, in Australia it is known from south-western WA, around the tropical north and down the east coast to central NSW.. An active, swift, bold, inquisitive shark it displays an interesting range of behaviours. When in groups, Silky Sharks have been seen ‘tilting’ (presenting their full lateral profile towards each other, gaping their jaws and puffing out their gills. Sometimes they suddenly charge straight upwards, veer away just before reaching the surface then glide back down to deeper water.
Tiger Shark (Galeocerdo cuvier)
One of the most impressive sharks in the ocean, not just because of its huge size (it can grow to more than 5 metres) but also for its distinctive black stripes and its ability to travel long distances. A tiger shark tagged off Nigaloo Reef, WA swam as far north as Semba Island, Indonesia, then south to the Great Australian Bight during the summer, before returning to Nigaloo a year later. In Australia, the tiger shark is known from south-western WA around the tropical north and south to the south coast of NSW. Popular with divers. Tiger sharks should be listed as endangered in Australian waters, says the Australian Marine Marine Conservation Society (AMCS) and Humane Society International (HSI) after a study reported a shocking 71% decline in only three decades.
The authors of the study, in the journal Biological Conservation, commented that commercial fishing was likely a major cause of the plummeting numbers, while Queensland’s SCP was another significant cause.
Dusky Whaler (Carcharhinus obscurus)
This is another shark that is extremely popular with divers. They are regularly seen in the Shelly Beach/Fairy Bower areas of Sydney Harbour. From January to June, this area serves as a nursery ground to the delightful juvenile duskies. The dusky whaler is widespread around Australia. This species makes seasonal migrations with females moving into shallow coastal waters in warmer months to give birth. They reproduce slowly and are vulnerable to overfishing; both commercial and recreational.
Shortfin Mako (Isurus oxyrinchus)
Possibly the fastest shark in the world, Shortfin mako sharks can swim at speeds of 100km/hour in short bursts, and are able to jump right out of the water. This is a very active and powerful shark, coloured indigo blue above with a lighter blue on its sides and white below. They are highly migratory, undertaking very long journeys across ocean basins. One shortfin tagged off New Zealand travelled over 13,000 kms in 6 months, zipping back and forth between NZ and Fiji. The shortfin’s future is of serious concern, based on a severe depletion around the globe, including a 60% decline in the Atlantic over 75 years.
Longfin Mako ( Isurus paucus)
The longfin mako is rarer than the shortfin and less resilient to overfishing. It is distinguished from the shortfin by a less pointed snout. Urgent action is needed to halt the decline of makos after the IUCN upgraded their status in 2018 from vulnerable to endangered. “Despite being one of the fastest fish in the sea, mako sharks need our urgent intervention to outrun extinction,” according to Lawrence Chlebeck, HSI marine campaigner.
Sandbar Whaler (Carcharhinus pIumbeus)
Sandbar Sharks are a wide-ranging coastal species in tropical and temperate regions. Sandbar whalers can be found along most of the WA coastline and off northern Queensland extending to near Port Macquarie in NSW. It is a robust, greyish-brown to bronzy shark with a moderately long, rounded snout and a very largem dorsal fin. Sandbar sharks are taken in commercial and artisanal fisheries throughout their range and are heavily exploited for their fins in some areas. In Australia, it is believed female sandbar sharks approach shallower habitats near land to pup.
Sharptooth Shark/Sicklefin Lemon shark (Negaprion acutidens)
This shark is a large, stocky, yellowish shark found in the tropical Indo-west and central Pacific oceans extending from South Africa to Australia and Oceania regions. Closely related to the better-known lemon shark. This species is found on continental and insular shelve and terraces, often on and around coral reefs and sandy plateaus and in lagoons, estuaries and mangrove swamps.
In Australia, this species is wide-ranging and captured in gillnets, beach-meshing and longlines on the east coast and Northern Territory. Outside Australia, it is heavily fished in unregulated and expanding inshore fisheries. This is another shark that is valuable for dive tourism.
Silvertip Whaler (Carcharhinus albimarginatus)
A medium-sized shark whaler with first dorsal, pectoral and upper caudal fin with distinct white tips. Found in northern Australian waters from Carnarvon in WA, across the Northern Territory to Bundaberg, Queensland. This is a large, slow- growing shark that is widely taken in bycatch and also targeted for its large fins and meat. Some very remote silvertip populations have reportedly been fished out by shark fin fisheries, but artisanal fisheries use most parts of this shark, including its liver, jaws and cartilage. Silvertip Sharks are very vulnerable to overfishing, particularly because they do not disperse widely between sites.
WHITE SHARK (Carcharodon carcharias)
White sharks are the largest predatory fish on earth and are about 16 million years old. Unfortunately, they are now facing an uncertain future. The white shark is protected internationally; however, in Queensland, the state government is permitted to catch and kill them as part of its Shark Control Program. This contradicts Australia's 'White Shark Recovery Plan', which aims to reduce the number of white sharks being killed both illegally and incidentally through commercial and recreational fishing, assisting in the recovery of the species.
These magnificent creatures can grow up to 7-metres long, according to the Queensland Museum. One of the biggest white sharks captured on camera is Deep Blue, filmed by divers in Hawaii in 2019. It is estimated to be 50 years old, more than 6 metres long and weighing 2.5 tonnes. It was tagged by scientists off Mexico 6 years earlier. The white shark can be found in the coastal surface waters of all the major oceans. One study puts the lifespan of white sharks at an estimated 70 years or more; well above the previous estimates. According to the same study, males take 26 years to reach sexual maturity. In comparison, females take 33 years to be ready to produce offspring. Whites can swim at speeds of 25 km/hr for short bursts and reach depths of 1200 metres.
CSIRO research estimates about 5,500 whites are cruising the waters off Australia’s east coast. The white is an intelligent and curious shark with complex social interactions that minimise conflict within aggregations. Recent research points to complex courtship displays. Satellite and genetic studies demonstrate that these sharks are highly migratory, regularly swimming thousands of kilometres to cross and re-cross ocean basins, but also there is a high degree of philopatry (homing behaviour). White sharks are warm-blooded, maintaining a high body temperature even in cold water.
Australian Blacktip (Carcharhinus tilstoni)
The Australian Blacktip shark is a medium-sized whaler that is endemic to tropical Australian waters. It is targeted and taken as bycatch in NT, Queensland and NSW inshore gillnet and line fisheries. After historical declines, stock reduction analysis has shown a 90% recovery of its unfished biomass.
Big Nose Whaler (Carcharhinus altimus)
The IUCN presently lacks enough information to assess the global conservation status of this species. However, the various fishing pressures within its range are cause for concern given its slow reproductive rate, and it may have already declined in the northwestern Atlantic and elsewhere.
Hunting close to the sea floor, the bignose shark feeds on bony and cartilaginious fishes and cephalopods.
Pigeye Whaler (Carcharhinus amboinensis)
A large, robust, greyish shark with a whitish belly, dusky fin tips and short, blunt snout and short eyes, the pigeye is similar in appearance to a bull shark. It is sensitive to fishing pressure due to its patchy distribution, low abundance, late age at maturity and low fecundity. Its occurrence in regions where intense fishing pressure is common suggests it is likely to have undergone declines.