Greenback horse mackerel (Trachurus declivis) are an important commercial species with the main fishing grounds off the west coast of the North of New Zealand. Caught commercially with trawls, purse seines, traps and on line gear. The common jack mackerel or cowanyoung is found in coastal waters of southern Australia from Wide Bay, Queensland to Shark Bay, WA, including Tasmania (Wilson et al. 2009). 

There are three jack mackerel subpopulations in Australian waters: one in the Great Australian Bight, another in NSW waters, and the third off Tasmania. They are pelagic, forming schools over the continental shelf and outer shelf margin. Individuals have been found in depths of 460 m but this species is more commonly found between 20 m and 300 m (Wilson et al. 2009).

There is evidence of at least two biological stocks of Common Jack Mackerel in Australian waters: one off eastern mainland Australia, including eastern Tasmania, and the other extending from western Tasmania through to southern Western Australia. A separate biological stock also exists in New Zealand waters. These conclusions are based on morphological and meristic differences between fish from the Great Australian Bight and eastern Australia, genetic differences between fish from the Great Australian Bight and New Zealand, and a lack of genetic difference between fish from eastern Tasmania and New South Wales. While not conclusive, the above evidence was considered sufficient for the Common Jack Mackerel in the Small Pelagic Fishery (Commonwealth) to be managed as separate eastern and western biological stocks (Moore and Mazur 2016).

The bulk of the catch is caught by purse-seine (Ocean Hauling fishery) with small quantities landed by trawlers; most is sold for aquaculture feed or bait. This species was the subject of a large fishery off Tasmania in the 1980s, but recent catches have been very small. A lack of assessment data has led to the status of the jack mackerel stock being classified as ‘uncertain’ (Moore and Mazur 2016).