Aquatic Ecosystems & Water Resources Research |
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Marine EcologyEnables management of key marine species such as sharks, turtles, and crocodiles and provides a conceptual framework for understanding the dynamics of highly diverse and complex tropical ecosystems. Active research programmes in marine ecology include:
Recently completed research programmes include: |
Developing Non-lethal Method for Estimating Age and Habitat Use for Australian Sawfish PopulationsProject Team: Dr Iain Field, Assoc Prof Corey Bradshaw, Dr Mark Meekan (AIMS) Funding: DEW Partners: Australian Institute of Marine Science Worldwide, populations of sawfishes are in decline. Given the vulnerable status of these species, non-lethal techniques are required to obtain information on life history parameters useful for defining extinction risk. This project will use rostral teeth to recover non-lethally vital data on age structure, growth and mortality patterns of various sawfish populations. Additionally, analysis of the chemical fingerprints from teeth will provide information on habitat use and site fidelity of these species. The specific aims of this project are to develop tools that will:
Estimating Fishing-related Mortality and Designing Sustainable Management Protocols for Shark Fisheries in Northern AustraliaProject Team: Assoc Prof Corey Bradshaw, Dr Iain Field, Dr Rik Buckworth Our research aims to (1) implement an intensive tagging study to estimate fishing-related and natural mortality of two commercially important species - black-tip (Carcharhinus tilstoni) and spot-tail (C. sorrah) sharks, (2) develop a series of mathematical models incorporating mortality estimates to evaluate fishing mortality rates and susceptibility of populations of these sharks under current and alternative future management arrangements and (3) prescribe new and additional monitoring protocols and management arrangements leading to better spatial and temporal management of shark fisheries in northern Australia. Go to Shark Tagging Project page. Selected mediaABC Northern Territory ABC North Queensland The Age ABC News feature National Radio Bush Telegraph
Movement, migration and habitat use of reef sharks at the Rowley Shoals
Gene profiling shark catches: do we really know what we are catching?Project Team: Dr Iain Field, Assoc Prof Corey Bradshaw, Dr Rik Buckworth (NT Fisheries), Dr Mark Meekan (AIMS), DR J Ovenden (QDPIF) Funding: Sea World Rescue and Research Foundation Partners: Sea World, NT Fisheries Globally, recent quantitative estimates of shark catches have revealed high levels of uncertainty about harvest numbers and catch compositions. This uncertainty has caused much concern over the sustainability of directed fisheries or incidental by-catch. A cornerstone of fisheries management in Australia is the logbook and observer dataset, although presently there are no estimates of the magnitude and extent of the error inherent in many shark fisheries reporting procedures. Our work will be a preliminary study using genetic analyses of sampled catches to determine the ‘true’ identity of currently mis-identified species and estimate the recording error rate. The data and results will have profound implications for future Australian and international shark conservation and fisheries management.
Distribution and Abundance of Glyphis spp. in Northern Australia and their Potential Interactions with Commercial FisheriesProject Team: Dr Iain Field, Assoc Prof Corey Bradshaw, Dr Mark Meekan Dr Rik Buckworth At present the distribution, abundance and habitat of endangered speartooth sharks (Glyphis spp.) in northern Australia are unknown. These species are known to have a large potential range and vary their distribution seasonally. Glyphis are caught as by-catch by recreational and commercial fisheries, but the extent of this threat is not known. Our project has two core elements. 1) We propose develop a monitoring protocol that will also 2) determine the distribution and abundance of Glyphis spp., integrating commercial and recreational fishery catch data and fishery-independent surveys. 3) By combining the data for distribution and abundance with commercial catch records we will estimate the interaction and impact of commercial and recreational fishers. Furthermore, although not the main focus of this study, we will also collect the same information for sawfish (including Pristis microdon) during surveys. Go to Freshwater and Estuarine sharks page
Tracking Extreme Dispersal in Saltwater CrocodilesProject Team: Prof Grahame Webb, Assoc Prof Corey Bradshaw Saltwater crocodiles have significant tourist, commercial, indigenous and ecological value. As populations recover, crocodiles now exist in upstream freshwater recreation areas, putting local residents and tourists at risk. Conflict between swimming and crocodiles is a potentially major threat to the Top End’s tourist industry, yet our understanding of the ecology of saltwater crocodiles in freshwater habitats in poor. We propose to document the existing crocodile population in freshwater areas, understand what dictates their presence or absence, using proven satellite technology to understand their movements in freshwater. This will be used to formulate management strategies to mitigate the impacts of crocodiles on recreation and tourism. Selected mediaABC News feature
Ecology of Whale Sharks at Ningaloo ReefProject Team: Assoc Prof Corey Bradshaw, Prof Barry Brook Increasing exploitation of whale sharks threatens the future of these large pelagic animals. Photo-identification is used to produce estimates of population size and structure at Ningaloo Reef, Western Australia. Continuous records of a sizeable aggregation of whale sharks at Ningaloo Reef, Western Australia show that mean shark length declined and relative abundance was reduced by approximately 50 % over the last decade. These reductions have occurred despite the total protection of whale sharks in Australian waters. As this species is highly migratory, such changes in demography probably reflect increasing fishing mortality in other parts of their range. Effective conservation of whale sharks will require international protection and collaborative tagging studies that identify and monitor the migratory pathways of these animals. We are also developing new techniques to improve individual marking for long-term population monitoring and modelling. Selected mediaBBC News feature
Recently completed researchPopulation and Harvest Models of Saltwater CrocodilesProject Team: Assoc Prof Corey Bradshaw, Prof Barry Brook It has been demonstrated repeatedly that the degree to which regulation operates and the magnitude of environmental variation in an exploited population will together dictate the type and magnitude of sustainable harvest achievable. Yet typically, harvest models fail to incorporate uncertainty in the underlying dynamics of the target population by assuming a particular (unknown) form of endogenous control. We use a novel approach to estimate the sustainable yield of saltwater crocodile (Crocodylus porosus) populations from major river systems in the Northern Territory, Australia as an example of a system with high uncertainty. We used multi-model inference to incorporate three levels of uncertainty in yield estimation: 1) uncertainty in the choice of the underlying model(s) used to describe population dynamics, 2) the error associated with the precision and bias of model parameter estimation and 3) environmental fluctuation (process error). Bradshaw, CJA, Fukuda, Y, Letnic, MI & Brook, BW. In press. Incorporating known sources of uncertainty to determine precautionary harvests of saltwater crocodiles. Ecol. Applic.
Foraging Ecology and Population Models of Southern Elephant SealsProject Team: Assoc Prof Corey Bradshaw, Prof Barry Brook The demography of high level Antarctic predators is ultimately determined by the oceanic processes that influence the spatial and temporal distribution of primary productivity. We are quantifying the links between the foraging performance of southern elephant seals and a range of oceanographic parameters, including sea surface temperature, productivity and bathymetry. These data are a crucial component to our understanding of how Antarctic predators will respond to changes in the distribution of marine resources as a result of global climate change or commercial fishing.
Foraging Ecology of Olive Ridley Turtles in the NTProject Team: Assoc Prof Corey Bradshaw This project aims to use satellite tracking to determine the movement patterns, diving behaviour and feeding ecology of olive ridley (Lepidochelys olivacea), an important food item for local Aboriginal people in terms of eggs and meat. We aim to establish foraging patterns, migration routes and infer diving physiological patterns from collected data.
Diving Physiology of Marine TurtlesProject Team: Associate Professor Corey Bradshaw For air-breathing diving species such as cetaceans, pinnipeds, penguins and marine turtles, the requirement to return regularly to the surface to breathe imposes a potential conflict between achieving maximal oxygen stores for a dive and minimising the cost of swimming. In other words, there is trade-off between maximising oxygen through full inspiration at the surface and the degree of difficulty in descending. Although it has long been known that hard-shelled marine turtles can modify their inspired lung volume to adjust the level of buoyancy during dives, they can also modify the volume of air inspired prior to the dive commencing in anticipation of the next dive. However, at some point the maximum volume of inspired air is limited by lung capacity, and this will determine the maximum depth of neutral buoyancy achievable. Thus, a turtle must maintain near-neutral buoyancy during the bottom phase of a dive such that a larger inspiration at the surface preceding a deeper dive is required. Because lung volume scales to mass, longer apnoeic periods in larger turtles are most likely the result of a higher capacity to store oxygen. However, data on sea turtles are too few to examine the allometry of diving capacity, so detailed measurements of lung capacity relative to individual size are desperately required. To address this, we dissected a number of hard-shelled marine turtle species that had died in captivity. Our aims are to: (1) establish the lung volume-body size relationship for hard-shelled marine turtles, (2) examine the data for any differences among species studied, and (3) refine the dissection techniques used to maximise the probability of obtaining reliable data from the fastidious dissection of delicate lung tissue.
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