Maugean skate

Abstract: A new species of rajin skate, Zearaja maugeana sp. nov., is described on the basis of specimens from two estuaries in remote southwestern Tasmania. The species, known locally as the Maugean Skate, has been assessed as Endangered in the IUCN Red List of Threatened Animals based on its rarity and very narrow geographic range. It is also one of the few skates worldwide to occur mainly in brackish water. The Maugean Skate belongs to a group of anatomically conservative, Dipturus-like skates conforming to the currently unrecognized genus Zearaja Whitley. This ancient group, with a Gondwanan lineage possibly dating back to the Cretaceous, contains at least two other species: Z. nasuta from New Zealand and Z. chilensis from South America. The skeletal morphologies of the Zearaja species are compared with typical Dipturus skates and their phylogenetic position discussed.

Abstract: The Endangered Maugean skate Zearaja maugeana is a relic species restricted to two isolated estuaries, Bathurst Harbour and Macquarie Harbour, in south-western Tasmania, Australia. Over a 1-year period, dive, tagging and net surveys provided information on the biology and ecology of this species. In all, 96 Maugean skates were caught during five trips to Macquarie Harbour, with four additional individuals observed underwater; however, no animals were located in the single trip to Bathurst Harbour. Morphometrics and the sex of the animals were recorded for 95 individuals. Crustaceans dominated the diet, with the majority of animals feeding on the crab Paragrapus gaimardii. Recapture rates were very low, with only one of 82 pit-tagged skates recaptured, and that occurred on the day of release. One acoustically tagged male skate was tracked for 5 km along the harbour margin for 24 h, whereas a female skate tracked for 46.5 h showed high site fidelity, suggesting that multiple factors potentially influence habitat utilisation. Although Macquarie Harbour represents the stronghold for this species, this estuary is also experiencing major environmental disturbance and change. Conservation management of this Endangered skate requires specific consideration of aquaculture, recreational fishing and mine drainage effects, as well as ongoing monitoring.

Abstract: The Maugean skate, Zearaja maugeana, is endemic to two isolated western Tasmanian (Australia) estuaries. The species' persistence in one of these estuaries (Bathurst Harbour) is uncertain, while the other estuary (Macquarie Harbour), potentially the remaining stronghold for the species, is an anthropogenically impacted system. Key life‐history parameters were studied to inform conservation actions for this species. Reproductive information was obtained using non‐lethal methodologies, circulating concentrations of sex steroids and ultrasonography. Growth and age parameters were estimated based on vertebral sections from a small sample of individuals. Females and males reached 870 and 760 mm total length, respectively. The species reached a maximum age of at least 10 years. Females and males attained 50% sexual maturity at 665 and 633 mm total length, respectively, probably maturing somewhere between four and six years of age. Females displayed an asynchronous, discontinuous reproductive cycle, being able to reproduce throughout the year, with a probable decline in reproductive activity during summer. No egg cases were observed in‐utero. Males produce sperm all year round, with a peak in testosterone production during spring–autumn. Conservation strategies for Z. maugeana will need to focus on reducing anthropogenic impacts on the environmental health, the primary impacts being altered river flows associated with the production of hydroelectricity and increased nutrient load associated with salmonid aquaculture. There is a need to better understand how reproductive success, egg survival and recruitment are affected by these environmental challenges if the future well‐being of this species is to be secured.

Abstract: The endangered and range-restricted Maugean skate (Zearaja maugeana) is subjected to large environmental variability coupled with anthropogenic stressors in its endemic habitat, Macquarie Harbour, Tasmania. However, little is known about the basic biology/physiology of this skate, or how it may respond to future environmental challenges predicted from climate change and/or increases in human activities such as aquaculture. These skate live at a preferred depth of 5–15 m where the dissolved oxygen (DO) levels are moderate (~55% air saturation), but can be found in areas of the Harbour where DO can range from 100% saturation to anoxia. Given that the water at their preferred depth is already hypoxic, we sought to investigate their response to further decreases in DO that may arise from potential increases in anthropogenic stress. We measured oxygen consumption, haematological parameters, tissue–enzyme capacity and heat shock protein (HSP) levels in skate exposed to 55% dissolved O2 saturation (control) and 20% dissolved O2 saturation (hypoxic) for 48 h. We conclude that the Maugean skate appears to be an oxyconformer, with a decrease in the rate of O2 consumption with increasing hypoxia. Increases in blood glucose and lactate at 20% O2 suggest that skate are relying more on anaerobic metabolism to tolerate periods of very low oxygen. Despite these metabolic shifts, there was no difference in HSP70 levels between groups, suggesting this short-term exposure did not elicit a cellular stress response. The metabolic state of the skate suggests that low oxygen stress for longer periods of time (i.e. >48 h) may not be tolerable and could potentially result in loss of habitat or shifts in their preferred habitat. Given its endemic distribution and limited life-history information, it will be critical to understand its tolerance to environmental challenges to create robust conservation strategies.