An extreme marine heat wave which affected 2000 km of the midwest coast of Australia occurred in the 2010/11 austral summer, with sea‐surface temperature (SST) anomalies of 2–5°C above normal climatology. The heat wave was influenced by a strong Leeuwin Current during an extreme La Niña event at a global warming hot spot in the Indian Ocean. This event had a significant effect on the marine ecosystem with changes to seagrass/algae and coral habitats, as well as fish kills and southern extension of the range of some tropical species. The effect has been exacerbated by above‐average SST in the following two summers, 2011/12 and 2012/13. This study examined the major impact the event had on invertebrate fisheries and the management adaption applied. A 99% mortality of Roei abalone (Haliotis roei) and major reductions in recruitment of scallops (Amusium balloti), king (Penaeus latisulcatus) and tiger (P. esculentus) prawns, and blue swimmer crabs were detected with management adapting with effort reductions or spatial/temporal closures to protect the spawning stock and restocking being evaluated. This study illustrates that fisheries management under extreme temperature events requires an early identification of temperature hot spots, early detection of abundance changes (preferably using pre‐recruit surveys), and flexible harvest strategies which allow a quick response to minimize the effect of heavy fishing on poor recruitment to enable protection of the spawning stock. This has required researchers, managers, and industry to adapt to fish stocks affected by an extreme environmental event that may become more frequent due to climate change.

Ningaloo Niño refers to the episodic occurrence of anomalously warm ocean conditions along the subtropical coast of Western Australia (WA). Ningaloo Niño typically develops in austral spring, peaks in summer, and decays in autumn, and it often occurs in conjunction with La Niña conditions in the Pacific which promote poleward transport of warm tropical waters by the Leeuwin Current. Since the late 1990s, there has been a marked increase in the occurrence of Ningaloo Niño, which is likely related to the recent swing to the negative phase of the Interdecadal Pacific Oscillation (IPO) and enhanced El Niño-Southern Oscillation variance since 1970s. The swing to the negative IPO sustains positive heat content anomalies and initiates more frequent cyclonic wind anomalies off the WA coast so favoring enhanced poleward heat transport by the Leeuwin Current. The anthropogenically forced global warming has made it easier for natural variability to drive extreme ocean temperatures in the region.

The relatively high catch of invertebrate species compared with finfish off Western Australia is in sharp contrast to other regions of the world, where finfish production usually dominates. This low level of finfish production is primarily due to the Leeuwin Current, which consists of warm, low-nutrient waters flowing south along the edge of the continental shelf of the Western Australian coast. In contrast, the other eastern boundary currents in the Southern Hemisphere (Humboldt and Benguela) are associated with upwelling of cool, nutrient-rich waters flowing north and the high rates of primary production resulting in a large finfish production. The Leeuwin Current, being the dominant oceanographic feature off Western Australia, has a major influence on the abundance of many species. The larval phase is the stage mainly affected by the current, but not always with the same result. For example, the strength of the Leeuwin Current has a significant positive influence during the larval stage of the western rock lobster (Panulirus cygnus). However, the current has a negative influence during the larval life of the scallop, Amusium balloti, in Shark Bay. Similarly for the pelagic finfish species, the current has a negative effect on larval survival of pilchards (Sardinops sagax neopilchardus) but a positive impact for whitebait (Hyperlophus vittatus). Possible mechanisms for the effect of the current include transportation of larvae and temperature effects on spawning success and on survival and growth of larvae.

[1] The Leeuwin Current, a warm, poleward flowing eastern boundary current, dominates the surface circulation off the west coast of Australia and has profound influence on regional marine ecosystem and fisheries recruitment. In this study, the seasonal and interannual variations of upper ocean heat balance in the Leeuwin Current region are analyzed by using an eddy-resolving numerical model simulation, as a first step to quantify the climate impacts on regional ocean thermodynamics and marine ecosystem. The volume transport and heat advection of the Leeuwin Current are stronger during the austral winter on the seasonal cycle and are stronger during a La Nina event on the interannual scale. On both seasonal and interannual timescales, the mixed layer heat budget off the west coast of Australia is predominantly balanced between the variations of the Leeuwin Current heat advection and heat flux across the air-sea interface. On the interannual timescale, the variation of the Leeuwin Current heat advection tends to lead that of the air-sea (latent) heat flux by two months, which is likely a reflection of advection timescales of the Leeuwin Current and its eddy field. The interannual variation of the average February-April sea surface temperature off the west coast of Australia, which is crucial for the larval settlement of western rock lobster, is mostly influenced by the Leeuwin Current heat advection as well as the ocean memory from the previous austral winter, with the air-sea heat exchange playing a buffering role.

An individual-based model, incorporating outputs of a data-assimilating hydrodynamic model, was developed to investigate the role of ocean circulation in the recruitment processes of western rock lobster ( Panulirus cygnus ) during its 9- to 11-month larval phase off the west coast of Australia. During austral summer, strong northward alongshore winds aid the offshore movement of early-stage model larvae from midshelf hatching sites into open ocean; during austral winter, eastward flows that feed the enhanced Leeuwin Current facilitate onshore movement of late-stage larvae towards nearshore habitats. Stokes drift induced by swells from the Southern Ocean is critical to retain larvae off the west coast. Diurnal migration and temperature-dependent growth are also important. Model larvae hatched in late spring – early summer grow faster because of longer exposure to warm summer temperature, which allows them to be transported towards the coast by the strong onshore flows in winter and reduces their natural mortality. Preliminary source–sink relationship indicates that the population was well mixed off the coast, with higher likelihood of settlement success from hatching sites in the north, mostly due to higher surface temperature. Weighted with the breeding stock distribution, the area between 27.5°S and 29.5°S, including the Abrolhos Islands, is the most important hatching area to the success of settlement.