Wildlife of the Julian Rocks Marine Park
By Rowena Mynott
Julian Rocks is located within the Julian Rocks Marine Park off the coast of Byron Bay, New South Wales, Australia.
The local indigenous peoples, the Bundjalung people, tell the story of a jealous husband standing on the cliff watching his wife canoe out to sea with her lover. Becoming frustrated he threw a spear, which landed in the canoe breaking it in two halves. Each end sticking out of the water has formed the rocks that make up the Julian Rocks today.
The rock itself is part of the local volcanic system formed from an eruption 23 million years ago. Located at the most easterly point of Australia, the warm waters from the north and cooler waters from the south mix around the rocky outcrop to form an eclectic visual sensation of over 600 species of tropical and temperate fish.
It is not only home to an abundance of marine life, but is also a nesting ground for many marine birds such as gulls, terns and cormorants. Water temperatures, currents and food resources fluctuate with the seasons and with these changes come seasonal visitors.
In our animal line-up this issue we look at the top 10 critters to find at the Julian Rocks Marine Park over the next couple of months.
Manta Ray (Manta birostris)
The largest and most impressive species of ray, mantas have been know to display curiosity around humans, swimming close to divers and snorkelers. This makes for an impressive experience with an animal that can measure up to seven and a half metres across and weigh up to 2300 kilograms. They feed on plankton filtered from the seawater passing through their gills as they glide along. They are known to frequent cleaning stations where small fish such as wrasse, remora and angelfish swim in the manta’s gills and over its skin to feed, in the process cleaning it of parasites and dead tissue.
Manta rays are known to live in excess of 20 years. They have low fecundity, giving birth to a single pup, possibly two pups on occasion. Different populations show differences in movement habits and site fidelity. Like many elasmobranchs, manta rays are highly vulnerable to fisheries given their life history and population structure. The IUCN Red List categorizes them as near threatened.
Zebra Shark (Stegostoma fasciatum)
Absent over the winter months, the Zebra Shark is a common sighting around the Julian Rocks area at this time of year. Also referred to as a “Leopard Shark” they reach an average size of around two and a half to three metres. Zebra Sharks are usually solitary animals, but can be found in large aggregations resting on sandy bottoms or near coral reefs in coastal waters. Easily identifiable by its spotty leopard-like colouration, this shark possesses a long crescent shaped tail and large rounded head.
These docile sharks are harmless to humans, feeding mostly on crustaceans, molluscs and small fishes. They are capable of ram ventilation enabling them to lie motionless on the ocean floor whilst using their mouth to pump water across their gills to breathe.
Zebra sharks are oviparous (egg layers), producing three to four egg capsules per month. The eggs are oval shaped, about 17centimetres in length and are very well camouflaged to resemble a piece of seaweed. They have a fibrous material attached that anchors the egg to a reef or rocky outcrop. After around six months, the pup hatches, measuring approximately 25-35cm in length, beginning its life already completely independent of its mother.
In most parts of the world, these sharks are classed as vulnerable to extinction by the IUCN. Their population numbers are being depleted by commercial fisheries, degradation of their reef habitat by human development and destructive fishing practices such as dynamiting or poisoning. However in Australia, population numbers are greater as only low levels of by-catch from commercial fishing have an impact on them.
Common Lionfish (Pterois volitans)
Their long poisonous spines, giving the appearance of a mane, support the spectacular fins of the lionfish. It is one of the most venomous fish on the ocean floor. Though they are not aggressive toward humans, envenomation from a lionfish sting is normally excruciatingly painful. They are voracious predators, feeding on a diverse diet of reef fishes, but their spines are used mainly for defense. They comprise five genera of the Scorpaenidae family. Commonly adults measure 30 cm to 35 cm in length.
They are native to the Indo-Pacific oceanic region. There have been recent introductions into the warmer regions of the Atlantic Ocean and Mediterranean, Caribbean and Red Seas where, because of their aggressive predatory nature and strong defense to predation, they have the potential to cause significant changes to the ecology of these regions.
Humpback Whale (Megaptera novaeangliae)
Visiting the calm waters around Julian Rocks, the humpback whale at this time of year is completing its northerly migration. The migration takes place each year as the humpbacks head to warmer waters to give birth and mate. Humpback calves are born with very little blubber and would not survive the cooler southern ocean waters, so the first couple of months of the calves’ lives are spent basking in the warm coastal Australian waters.
Part of the baleen whale family, humpbacks possess brush like fibers instead of teeth and feed on a diet of krill. The majority of krill can be found in Antarctica, the starting point for their migration. Having gorged on krill before leaving, they will not eat for their entire journey, an impressive feat especially for a mum feeding a newborn calf.
As they make their northern migration past Julian Rocks, they will often show the aerial acrobatics they are most famous for as they propel their up to 40 tonne, 15m long bodies into the air. Lucky divers and snorkelers can hear their haunting song underwater, and might on occasion be lucky enough to be offered a glimpse as they pass.
Hunted once from 200,000 animals on the east coast of Australia down to just 100, this population of humpbacks was in danger of becoming extinct. Now due to protection, their numbers are steadily increasing and starting once again to reach healthy proportions.
Cuttlefish (Sepia apama)
Cuttlefish are among the most intelligent of the invertebrates. They have a remarkable ability to rapidly alter their skin colour. They use this for camouflage and counter-shading but also for communication with other cuttlefish.
With a name that means ‘head-footed’, this endearing little creatures can grow to 90cm and in some cases such as the Australian Giant Cuttlefish, almost as large as a man.
They have ten tentacles that they also use for communication and for prey capture. Their preferred diet is crabs and fish. Their eyes are among the most developed in the animal kingdom with several features similar to a humans eye although they are thought to have evolved independently from those of the vertebrates.
The cuttlebone, which can sometimes be found washed up on the shore, is an internal structure composed of aragonite and provide the cuttlefish with buoyancy.
Green Turtle (Chelonia mydas)
Australia is a lucky country as it is visited by six of the world’s seven endangered marine turtle species. At any time of the year, three of these species can be found at Julian Rocks. The most commonly spotted are the green, hawksbill and loggerhead turtles. Green turtles are the largest of these three species reaching lengths of up to one and a half metres and weighing in at 180 kilograms.
Named not for the colour of their shell, which is usually an olive or brown colour but for the colour of their green fat, made so by their algal diet, which is the traditional ingredient used to make turtle soup.
Scientists believe that a female green turtle returns each season to the same beach where she was born. This often takes the turtles on incredible journeys, travelling for 6000kms or more. Each time she breeds she will lay up to 1000 eggs and the temperature of the sand will determine the sex of the young turtle. Warmer sand produces female offspring and cooler sand, male. After eight weeks of incubation, the young turtles are off on their own to face many challenges in the oceans. Only one out of 1000 hatchlings will survive to adulthood. As an adult, green turtles will feed on a mainly vegetarian diet of marine algae, sea grasses with the occasional sea jelly.
Hunted for their eggs and flesh, numbers of green turtles are severely depleted. The main threats for these turtles comes from fishing gear as they are often caught as by-catch and from marine pollution such as plastic and cigarette ingestion. Worldwide green turtles are listed as endangered by the IUCN and CITES, however we are lucky in Australia as their populations are fairly healthy.
White Spotted Eagle Ray (Aetobatus narinari)
Found in tropical waters, these rays can be seen either alone or in swimming in larger congregations often close to the oceans surface. With a large disc shaped body, this beautiful ray can grow up to three and a half metres across and reach a total of nine metres in length. The snout is flat similar to a duck’s bill, which assists the ray in foraging for prey.
The main diet of the spotted eagle ray consists of clams, oysters, shrimp, squid and sea urchins. Possessing plates rather than teeth, their jaws are adapted to crush food rather than chew. This technique is so effective that scientists have found rays are able to separate the shells from the flesh of animals such as clams, oysters and whelks.
As one of the most acrobatic of the ray family, spotted eagle rays can sometimes be seen launching out of the water. It is not sure why they do this but a few suggestions are to remove parasites, avoid predators or chasing food.
Although not widely hunted as food, spotted eagle rays are considered near threatened by the IUCN due to other human influences such as entanglement in fishing nets and shark meshing. They are also often targeted for sport fishing.
White-Eyed Moray Eel (Siderea thyrsoidea)
Moray eels are part of the family Muraenidae and are widely distributed across the globe. Their scaleless skin is usually patterned for camouflage. They are characterised by a well-developed dorsal fin that extends from just behind the head, along the back, joining seamlessly with the caudal and anal fin. Most species do not have pectoral fins. They move using an anguilliform swimming motion, giving them a serpentine appearance. Of the approximately 200 species in 15 genera, there are at least 8 species that commonly inhabit Julian Rocks, the white-eyed moray being the most commonly seen.
The moray eel has a well-developed sense of smell but eyesight is generally poor. As they are nocturnal hunters, they usually preferring to spend their days hiding inside crevices. Morays are carnivorous, feeding on other fish, cephalopods, mollusks and crustaceans. Despite their reputation for being vicious or ill tempered, morays are shy and prefer to flee than fight.
Barrier Reef Anemonefish (Amphiprion akindynos)
Depending on the species, anemonefish or clownfish have an overall yellow, orange, reddish or blackish colour often with two or more white bands across their body. The 26 species of Anemonefish characteristically form symbiotic mutualisms with 10 species of sea anemones. Because of their mucus coating they are the only species of fishes that can avoid the potent poison of a sea anemone. However, scientists have yet to resolve whether the mucus originates with the fish, the anemone or some combination thereof. Anemonefish live in small groups within the tentacles of each anemone consisting of a breeding pair and a few smaller male anemonefish. These famous little fish are all born as males and exhibit a strategy known as ‘protandrous sequential hermaphroditism’. When the female dies, the dominant male changes sex and becomes the female.
Queensland Grouper (Epinephelus lanceolatus)
Also known as the giant grouper, it is the largest of the bony fishes found on coral reefs. They can grow as large as two and a half metres long and weigh up to 600kg with unconfirmed reports of much larger specimens. They feed on a variety of marine life, including small sharks and juvenile sea turtles.
Juvenile groupers have irregular black and yellow makings, while adults differ slightly as green-grey to grey-brown with faint mottling. Large individuals often have a ‘home’ cave in which they frequently stay.
It is likely that since a large area of reef is required to maintain such a large predator, numbers are typically low, even in unexploited areas. Overall they are listed as Vulnerable to extinction by the IUCN. Their primary threat is the marine aquarium fish trade and overfishing for the live reef food-fish trade, which targets smaller individuals, often before they have reached reproductive maturity.
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