in 2015 confirming this trend. As of 2021, the population has recovered to an estimated population exceeding 240,000 animals. The fishing ban for the whole of northern Spencer Gulf was extended until 2020, prohibiting their capture in all Spencer Gulf waters north of Wallaroo and Arno Bay. In 2020 the closed area rolled back to the same limited spatial closure that was in place in 2012, encompassing the waters of False Bay, from Whyalla to Point Lowly and extending northwards towards the Point Lowly North marina. Population estimates Figure '0' is used to represent years in which surveys did not occur, and no estimation was made. 1999–2017 data sourced from SARDI Approximate 2016 population estimate was published in the Whyalla News and approximate 2017 numbers were first published by PIRSA. A slightly larger estimate for the 2017 season was published in 2018 by the ABC (reflected in the graph). Effect of local industrialisation The mass aggregation sites of Upper Spencer Gulf are proximate to a number of industrial pollution sources, and prospective sites for further development. As of 2021, operations that publicly report their pollution discharges to the sea in a controlled and measured manner include the Whyalla steelworks, the Port Pirie lead smelter owned and operated by Nyrstar. The pollutants of primary concern to cuttlefish recruitment are changes of salinity (due to discharges from desalination plants) and nutrient enrichment, discharged by the steelworks, lead smelter, municipal wastewater treatment plants and farming of yellowtail kingfish. Nutrient enrichment Northern Spencer Gulf is an oligotrophic inverse estuary with naturally low levels of nutrients cycling through it. A potential exists for anthropogenic nutrient pollution to cause eutrophication in the region with associated ecological impacts to the cuttlefish and wider ecology. A long-term industrial nutrient pollution source exists to the west of the cuttlefish breeding reef at the Whyalla steelworks. There, ammonia, a byproduct of its coking process for steel-making, and is discharged into Spencer Gulf via reed-beds and settling ponds. North of the cuttlefish aggregation, sea cage farming of yellowtail kingfish occurred commercially from the late 1990s until 2011. Fish farming is another nutrient pollution source, as uneaten feed and fish waste enter the water column and sediment. Concerns have been raised about an observed correlation between fish farming intensification, fish mortalities and the decline and eventual recovery of the giant Australian cuttlefish after fish farming ceased in upper Spencer Gulf. Hydrocarbon pollution