.[1] In this study, the annual and interannual variations of the Leeuwin Current at 32°S off the Western Australian coast are investigated. The mean annual cycle and the El Niño and La Niña composites of the Leeuwin Current temperature structures are obtained by linearly fitting a Taylor expansion to historical upper ocean temperature data. A temperature-salinity relationship is used to derive the salinity field and geostrophy is assumed to calculate the current velocity. The downward tilting of the isotherms toward the coast and the strength of a near-surface core of the low-salinity water indicate the seasonal variation of the Leeuwin Current. Seasonally, the Leeuwin Current has the maximum poleward geostrophic transport of 5 Sv (10 6 m 3 s À1) during June-July. Interannually, the Leeuwin Current is distinctly stronger during a La Niña year and weaker during an El Niño year. The annual average poleward geostrophic transports in the mean, the El Niño and La Niña years are 3.4, 3.0, and 4.2 Sv respectively. Variations of the Leeuwin Current structure on annual and interannual timescales are coastally trapped. A linear relationship between the coastal sea level deviation at Fremantle and the Leeuwin Current transport is derived, which justifies and calibrates the usage of the Fremantle sea level as an index for the strength of the Leeuwin Current. INDEX TERMS: 4516

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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.