Climate Change Impacts on Pelagic Fishes and Sharks in Australia
Pelagic fishes and sharks.
In A Marine Climate Change Impacts and Adaptation Report Card
for Australia 2012
Alistair J Hobday, Tim Ward, Shane Griffiths
Pelagic fishes and sharks occupy surface waters from the coast to the open ocean. There are ~260 pelagic species around Australia. While some of the most well known are the large offshore apex predators such as tunas, billfish and sharks, the midtrophic level small pelagic species, such as sardines, anchovies, and squids, are critical to ecosystem function. In Australia, both small and large pelagic species have high ecological, economic and social value. Observed impacts of climate change are restricted to changes in local abundance and distribution, particularly southward range extensions. Little is known regarding changes in phenology, physiology or community structure. In future, general ocean warming around Australia and in particular on the east coast, in combination with predicted strengthening of the East Australian Current, is likely to see the distribution of a range of pelagic species extend southwards from present limits. Recent years have seen a number of reports of fish detected south of their typical range limits on the east coast. On the west coast, changes in the strength of the Leeuwin Current are likely to have major implications for the distribution and abundance of some species, including western Australian salmon and Australian herring in waters off South Australia. Recent extreme events on the west coast have also seen pelagic species reported far to the south of their normal distribution. Changes in productivity, for example due to increased coastal upwelling, may lead to increases in abundance of some species, particularly of small coastal pelagic fishes, such as sardines and anchovy, in the upwelling system between Cape Otway and the central Great Australian Bight. Confidence in observed impacts is generally low to medium as observed changes are limited. Similarly, confidence in future impacts is also generally low to medium, as lack of data on observed impacts makes prediction difficult. Impacts on sharks are poorly known compared to teleost fishes. Overall, impacts in southern Australia are more commonly reported than in northern Australia. Knowledge gaps include an absence of information on species habitat tolerances and methods to detect changes. Recent efforts to develop empirical models for future prediction of species ranges and potential abundance changes are in agreement with earlier projections (Report Card 2009). The adaptation potential is high for many species because of significant opportunity for large-scale movements of most pelagic species, and thus the main impacts are likely to be localized changes in the composition of pelagic fish community. The impact of such changes in community composition is unknown. To address knowledge gaps, focused regional studies on the relationship between climate variables and the distribution and abundance of species of high interest are one way to improve understanding of the potential impacts of climate change. Predictive modelling at appropriate scales is also reliant on downscaled climate models, which can generate a range of environmental variables at the scale of individual fish movements.
Marine Climate Change in Australia
Impacts and Adaptation Responses 2012 REPORT CARD