• Energy Research

Abstract Several lines of evidence show that ocean warming off the east coast of Tasmania is the result of intensification of the East Australian Current (EAC). Increases in the strength, duration and frequency of southward incursions of warm, nutrient poor EAC water transports heat and biota to eastern Tasmania. This shift in large-scale oceanography is reflected by changes in the structure of nearshore zooplankton communities and other elements of the pelagic system; by a regional decline in the extent of dense beds of giant kelp ( Macrocystis pyrifera ); by marked changes in the distribution of nearshore fishes; and by range expansions of other northern warmer-water species to colonize Tasmanian coastal waters. Population-level changes in commercially important invertebrate species may also be associated with the warming trend. Over-grazing of seaweed beds by one recently established species, the sea urchin Centrostephanus rodgersii , is causing a fundamental shift in the structure and dynamics of Tasmanian rocky reef systems by the formation of sea urchin ‘barrens’ habitat. Formation of barrens represents an interaction between effects of climate change and a reduction in large predatory rock lobsters due to fishing. Barrens realize a loss of biodiversity and production from rocky reefs, and threaten valuable abalone and rock lobster fisheries and the local economies and social communities they support. This range-extending sea urchin species represents the single largest biologically mediated threat to the integrity of important shallow water rocky reef communities in eastern Tasmania. In synthesizing change in the physical ocean climate in eastern Tasmania and parallel shifts in species' distributions and ecological processes, there is evidence that the direct effects of changing physical conditions have precipitated cascading effects of ecological change in benthic (rocky reef) and pelagic systems. However, some patterns correlated with temperature have plausible alternative explanations unrelated to thermal gradients in time or space. We identify important knowledge gaps that need to be addressed to adequately understand, anticipate and adapt to future climate-driven changes in marine systems in the region.

Communicating the performance of commercial fish stocks is a fundamental role of fisheries management. This is often undertaken by reporting stock status relative to limit reference points (LRP). Reporting against LRP is effective in drawing attention to stocks that are overfished but does not identify fisheries where performance could be improved by shifting stocks closer to target reference points (TRP), that is, benefit can be foregone despite stocks being fished sustainably. This study examined the performance of Australian fish stocks against a TRP of 40–60% of unfished biomass, the level at which economic performance is generally optimised. Stocks examined were drawn from the 2016 Status of Australian Fish Stocks report, which is designed to report on stock status relative to LRP at a national level. Only stocks with an estimate of biomass or status relative to explicitly defined reference points were considered. Of 123 stocks evaluated, 41 (33%) were at target biomass levels, 28% were above and 39% below. This result, in combination with the major output of the 2016 SAFS report, shows that although most Australian stocks are not overfished, many are outside levels that would deliver greatest benefits. While maintaining all stocks at target levels may be impractical given the dynamic nature of fisheries, failing to maximise the number of stocks at target levels reflects lost ecological, economic and social potential. Assessing stocks relative to TRP in addition to LRP would highlight opportunities for improving fisheries while still addressing the fundamental requirement of preventing stock depletion.