Port Jackson Shark

Port Jackson sharks The Port Jackson shark is a nocturnal, bottom dwelling shark that is found in the temperate waters off of the southern half of Australia. One of the more well-known species observed in Sydney harbour is the Port Jackson shark (Heterodontus portusjacksoni). During the day they are found in flat areas with some shelter from currents (i.e. caves). Records indicate the largest Port Jackson shark was 65 inches (165cm) in total length. However, it is uncommon for Port Jackson sharks to grow more than 53.9 inches (137cm) in total length. Reportedly, Port Jackson sharks can live more than 30 years. Port Jackson sharks are found both close to shore and off the shelf in waters as deep as 275m. This species feeds primarily on echinoderms, crustaceans, molluscs, and some small fish. Sea urchins and large gastropod molluscs (sea snails) are noted in almost every study on the diets of Port Jackson sharks. This shark has a small mouth containing small, molar-like teeth in the rear of the mouth used to crush prey. Not much is known about predators of Port Jackson sharks. Juveniles are more likely to become prey for other marine life, than the adults. There are some reports indicating adult male Port Jackson sharks prey upon Port Jackson shark egg capsules, however some speculate that those reports were cases of mistaken identity with crested horn sharks. There are some speculations that Port Jackson sharks could fall prey to larger sharks, such as the white shark or bluntnose sevengill shark. The Port Jackson shark is not used for food by humans, and is rarely targeted in fishing. This shark is caught as bycatch. Recent studies suggest Port Jackson shark populations suffer from high embryonic mortality rates, and thus should be monitored closely to insure the populations are not being overfished as bycatch. The fact that Port Jackson sharks reach maturity later in life, along with the limited number of eggs produced each year, and high embryonic mortality rates could all contribute to a decrease in the population. The Port Jackson shark is currently listed as “Lower Risk/Least Concern” on the World Conservation Union (IUCN) Red List. Crested Hornshark This lookalike ratbag egg robber is still cute. The Crested Hornshark resembles the Port Jackson Shark, which has a harness-like pattern on the sides of the body and lower ridges above the eyes. It is found in NSW from shallow inshore waters, down to depths of around 90 m, feeding off echinoderms, crustaceans, molluscs and small fish. They have been seen several times eating Port Jackson shark egg cases. 14 Autumn is Orgy Season in NSW Every year Port Jackson sharks arrive from their southern Australian feeding grounds to mate and lay their eggs. Port Jacksons are not permanent residents of Sydney Harbour. The sharks migrate from as far south as Tasmania to lay their eggs at specific sites. Sexual maturity for females occurs between 11 and 14 years old. Males reach maturity from 8-10 years old. Late winter/early spring is Port Jackson mating season and that’s when these sharks aggregate. The Port Jackson shark breeding season lasts from late August to mid November, during which time a female will lay a pair of eggs every 10- 14 days. Scientists have noted that a female can lay up to 16 eggs during each breeding season. Males reach peak sperm production around May, but females do not begin laying eggs until late August. Mating occurs some time prior to laying the eggs and the females store the sperm within their shell glands until ready to fertilize the eggs. Port Jackson sharks are oviparous, meaning they lay egg capsules instead of giving live birth. An embryo develops for 10-11 months before hatching from its egg capsule completely. A typical Port Jackson shark hatchling is 180- 220mm long. Recent studies have suggested that egg capsules suffer 89.1% mortality, primarily from predation. What is remarkable is that Port Jacksons sharks use the same resting sites and places where they lay their eggs every year. Following tagged sharks scientists suggested that Port Jacksons form ‘visual cognitive maps’ along their migratory route which allows them to find back to their ‘most favourite’ locations. They even pass on their knowledge to the next generation so most of these resting sites have been used for many years. At some sites Port Jacksons have been reported for more than 30 years. Depending on the season, Port Jackson sharks migrate between feeding and egg-laying sites. Port Jackson sharks may intimately know and recognise between 400-2400 individual resting sites along the southeast coast. In Sydney Harbour, the researchers found four resting areas at South Bondi to which the sharks regularly return. When disturbed, move directly from one site to another. If transferred by boat to different localities within the harbour, up to 3 km away, they return to their original resting sites. Particular sharks were hanging out in a non-random fashion. They were choosing to be with particular individuals, as if they have their own group of friends. There is some evidence that suggests that Port Jackson sharks are in groups segregated by gender and level of maturity. If you remove those key individuals, the population could potentially fall apart. They are common near fishing jetties where they have a reputation as bait robbers, often leading to occasional and senseless killing of PJs by anglers. Pipsqueak Predator “Generally, Port Jackson sharks are considered to be harmless”. Not so! According to the International Shark Attack File, “there are no confirmed attacks by Port Jackson sharks”. In 2011, diver Andrew Houston went for a dip in Port Phillip Bay. He felt something latch onto his leg. “It felt like the real thing, like a big one, you know?” But when he whirled around in the water he was confronted with a pint-sized Port Jackson shark that wasn’t letting go. He was forced to swim to shore with the animal still attached to him. When he reached Elwood beach the diver and a passerby took several more minutes to dislodge the animal from his calf. The shark swam back out into the bay. All the shark attack victim had to show from his close encounter was a bruised calf and a torn wetsuit. The incident didn’t deter him from diving. [In a tragic postscript to this funny story, we regretfully have to report that Andrew died in a diving accident in May 2013]. 15 Tassie News Managing Devastating Urchin Barrens Primary Source; Rebuilding Ecosystem Resilience: Assessment of management options to minimise formation of ‘barrens’ habitat by the long?spined sea urchin (Centrostephanus rodgersii) in Tasmania, Johnson, Ling, Sanderson, et al. An ambitious urchin barren research project at Elephant Rock on the East Coast of Tasmania has ended, with surprises for everyone. Try to imagine that you are walking along through the bush at say Mt Buffalo, the Blue Mountains, or Lamington, listening to a radio shock jock tell you that climate change is all bulldust. Then you repeat the same walk a couple of years later, except this time there are no trees. Your favourite wilderness spot has basically become an open desert dotted with patches of sick-looking scrub. This is what has already happened to large sections of Tasmania’s East Coast sub-tidal reef. Its position on the southern end of the Eastern Australian Current means that Eastern Tasmania has been experiencing abnormally large changes in sea temperature since the 1950’s. Loss of nearly all giant kelp in recent decades has been followed by the appearance of large populations of NSW black urchins (Centrostephanus rodgersii). As waters have warmed the urchins have extended their range into Tasmania in vast numbers. Inshore reef in places like St Helens have been destroyed and replaced by desolate urchin barrens. It is a disaster for environmentalists and fishermen. What do we do? Well for a start we need to learn more about the phenomenon. Earlier research had identified rising sea temperatures and declining stocks of large lobsters as the main causes of the problem. Ideas to fix it ranged from smashing