ANSWER 1

Shark Bay, on the mid-west coast of Western Australia, is a unique, shallow embayment strongly influenced by the El Nino and La Nina phases of the ENSO on seasonal and interannual timescales. ENSO affects the strength and timing of the Leeuwin Current, seasonal wind patterns and tropical cyclone activity. The embayment is also hypersaline, with ocean temperatures that are typically warmer than adjacent oceanic waters in summer and cooler in winter. For short-lived species such as saucer scallops, brown tiger prawns and western king prawns, there are currently no modelled long-term stock projections extending 10 years into the future. Recruitment can vary considerably from year to year and is strongly influenced by environmental conditions, the abundance of spawning adults and the availability of suitable habitat such as seagrass.

Saucer scallops are at the northernmost extent of their distribution in Shark Bay and, as a sedentary species, are unable to actively escape thermal stress, making them particularly vulnerable to marine heatwave (MHW) events. However, their short lifespan and high fecundity mean that populations can recover when environmental conditions are favourable. Under climate change, however, the period of suitable conditions between poor recruitment years is projected to decrease, potentially resulting in lower overall productivity and reduced opportunities for sustained stock recovery in the future. For prawns, in addition to marine heatwaves, they are also highly vulnerable to severe tropical cyclone systems, particularly those that track directly over or close to Shark Bay, causing flooding and the discharge of silty freshwater into the embayment, which can damage or destroy seagrass meadows that is key nursery habitat. 

Fortunately, Shark Bay’s scallop and prawn fisheries are considered to be well-managed with management plans and harvest strategies, extensive data from multi-stock surveys, and external certification through the Marine Stewardship Council (MSC). Nevertheless, recent climate-vulnerability assessments have identified these fisheries as being at high risk from future climate change, particularly under a rapidly warming scenario to 2050. For a region like Shark Bay, the swings between El Niño and La Niña years, together with the frequency and severity of extreme events in the next 10 years, will be truly telling of the status and productivity of these stocks.