Poster Sjac2362

Lifecycle and jaw adaptations of Australian Elasmobranches Whale Shark (Rhincodon typus) Size: 4m-12 (Max 20m) Habitat and Distribution: A pelagic shark, found in warm tropical waters on the northern coast of Western Australia, Queensland and the Northern Territory. It is unique in that it is the only member of its order than is not benthic. It has been tracked at depths as low as 1200m, and in water temperatures as low was 3.4 degrees C (Brunschweiler, Baensch, Pierce and Sims, 2009). The shark is believed to follow migratory patterns that are similar to their prey. Lifecycle: They are ovoviviparous, giving birth to live young from eggs that hatch inside the mother, and specimens have been observed that contained over 300 eggs in the uteri (Stevens , 2006). Due to the myste rious nature of these large fish, little is known about the mating rituals of these sharks. Scientists believe that there are numerous breeding grounds and nurseries throughout the tropics, and it is of great importance to protect these habitats for further study. Jaw Structure: They have a wide and varied diet, feeding mostly on krill and zooplankton. They are filter feeders, using a short-burst suction method, rather than a flow-through method. The suction method also means that the shark does not have to be moving forward through the water column to capture prey. The shark sucks water in through its mouth, passing it out through the gills, food is trapped on the dermal dentricles and the sieve-like structures that cover the gills (Picture A). The head of the shark will sway from side to side as it filter feeds through the water column (Martins and Knickle, 2009). The shark has over 600 small, rasping teeth, however they serve no purpose in feeding (Picture B). Shortfin Mako (Isurus oxyrinchus ) Size: 1.8 – 2.5m (Max 4m) Habitat and Distribution: A pelagic shark , it is wide ranging and found in all ocean s and areas of water above 16*C, and is thought to migra te with warm water currents. This large range and distribution can be attributed to the constant body temperature that the shark can maintain, increasing the temperature range in which the species can survive. It minimises heat lost through the gills by passing blood through the rete mirabile heat exchangers before entering and after exiting the gills, and is one of only four species of shark that can maintain a constant body temperature (Block and Carey, 2004). The only area of Australia that it has not been caught is off the coast of the Northern Territory. It is the fastest shark in the ocean, reaching speeds of 70km/h, and has the highest levels of white muscle tissue (Hamlett, 1999). The shark is also heavily streamlined with numerous contours on the skin (Picture E), ideal for long-range cruising and able to reach depths of 150m. Lifecycle: Exhibits sexual dimorphism with females growing up 30 per cent lar ger than males, and giving birth to a few large young, the shark is ovoviviparous. There is frequently a separation of the sexes, with large groups of males being isolated from large groups of females. This is thought to be brought on by the aggressive courtship rituals which often leave females wounded, and as a result they seek an avoidance response (Mucientes, Querizo and Sousa, 2009). Jaw Structure: The diet of this species consists of most large pelagic fish, as well as other sharks and it has been known to hunt dolphin s. Recent studies indicate that the species must consume approximately 4.6% of their body weight per day to fulfil energe tic demands (Wood, Wetherbee z, Juanes, Kohler and Wilga, 2009). In order to accommodate such a large intake of food the shark has numerous serrated teeth designed for tearing flesh, these teeth are visible even when the mouth is closed. The upper anterior teeth broaden with increasing size, with individuals over 3m long having wide, flat, and triangular teeth that are ideal dismembering large prey (Picture G). Thus, large individuals may be able to feed and break up prey that is too big to be swallowed whole (Elasmo-research.org). Ornate Wobbegong (Orectolobus ornatus ) Size: 730mm – 830mm (Max 1m) Habitat and Distribution: Found along the Eastern coast of Australia, from Queensland to New South Wales. Found at depths of 50m, usually around inshore reefs, and is a benthic shark found in clear water. They are nocturnal, and sleep under rocky crevasses during the day, this behaviour may be related to predator avoidance (Carraro and Gladstone, 2006). Lifecycle: An ovoviviparous species, it produces up to 18 eggs, which develop and hatch internally, feeding first on the egg yolk-sac and then on the nutrient- rich uterine fluid secreted by the mother. It is believed that theshark’s sense of smell plays a significant role in mate detection as studies have found that the shark has olfact ory recept ion of equal or gre ater abi lit y tha n mos t elasmobranches (Theiss, Hart and Collin, 2009). Jaw Structure: It is an ambush predator, and hunts predominantly at night. It lies motionless of the sea floor as a sit-and-wait predator, feeding mostly on octopi and cuttlefish. The colouration on the skin of the shark provides ideal camouflage against the reef habitat, and the nasal barbels that protrude from the mouth are used as a lure to attract prey (Picture C). Sometimes, prey may be too big to swallow whole whist still alive, and may be left impaled on the jaws of the shark until death, where it will be eaten without much struggle (Bester, 2009). The anterior teeth are larger and more razor-like, whilst the posterior teeth are smaller and needle-like, suggesting that this shark may feed on a large variety of prey (Picture D). The jaw itself is also more prognathic, allowing for a flatter head, ideal for the bottom-dwelling lifestyle of the shark. Port Jackson shark (Heterodontus portusjacksoni ): Size: Males – 770mm, Females – 900mm (Max 1650mm) Habitat and Distribution: Heterodontus sp. is found in southern Australian waters from southern Queensland south to Tasmania and west to the central coast of Western Australia. However, debate is still ongoing that there are two distinct genetic populations, one found along the coast of New South Wales, and the other stretching from eastern Victoria to Western Australia (Tovar-Avila, Walker and Day, 2007). They live in the benthic layer on the sea floor, and as a result of this have developed the ability to pump water across their gills without having to move through the water, allowing them to live a sedentary lifestyle (Hamlett, 1999). Being nocturnal, they spend large portions of the day in caves, where they are less exposed to water currents. Lifecycle: There is sexual dimorphism in the species with females typically being 130mm longer than males. The breeding season occurs from July to November, and the species is oviparous. Reproduction occurs when the male clasps the pectoral fin of the female, wrapping around her to insert one clasper (Powter and Gladstone, 2008). The female lays an egg which she then wedges in a rock crevice (Picture F). Jaw Structure: Have a unique jaw in comparison to other sharks, as their teeth are no serrated. They feed primarily on echinoderms, molluscs, crustaceans and fishes, and as a result of this, have two distinct types of teeth (Picture H). The anterior teeth are small, short and pointe d, designed to grasp prey items. Whilst the posterior teeth are flat and plate-like, and designed to grind and crush the shells (Burton, 2002). Elasmobranches form a large part of the Aust ralian Oc ean envi ronment, wi th many div er se species each wi th thei r own adaptations for survival. By looking at the habitats and lifecycles of four different species, each found in its own unique environment, we can see the effect this has had on feeding and jaw structure. Sam Jackson

Poster Sjac2362

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