Western Australian salmon (Arripis truttaceus) are not true salmon (salmonid) but one of four species of fish (including Australian herring) belonging to the Arripidae family, which are only found in Australia and New Zealand.
The salmon is a pelagic fish species found along the coast from north of Perth stretching south across the Great Australian Bight to western Victoria and Tasmania.
They are a moderate size fish with a powerful streamlined body and large, symmetrical forked tail with a darker blue-green colouration along the upper body, fading to a silvery white underneath.
Salmon typically form immense schools of up to a hundred tonnes or more, composed of thousands of individuals. They are carnivorous and very fast swimmers. Salmon will feed en masse by co-operatively ‘herding’ baitfish up to the surface.
Distribution and habitat
Salmon form a single breeding stock across southern Australia.
In Western Australia they are found in cooler southern waters, but are also common in waters north of Perth metropolitan area during winter months.
Adults most commonly frequent the clear, shallow waters along surf beaches, rocky reefs and coastal estuaries, however some schools are found in deeper offshore waters.
Salmon are responsive to ocean temperatures, and their seasonal movement is closely related to the strengths of the Leeuwin Current and Capes Current and subsequent water temperatures. In some years warmer coastal waters result in the fish aggregating in deeper, cooler waters offshore.
In 2015 and 2016 very large schools of salmon were observed in south-western waters and as far north as Exmouth, which is further north than ever previously reported. This suggests the salmon stocks are in a healthy state.
Lifecycle
Western Australian salmon are relatively long lived, known to grow up to one metre in length and can reach weights in excess of nine kilograms each (though the average fish caught would be five kilograms or less).
Adults undertake a westwards migration along the southern coast of Australia to the lower south-west coast in late summer, where they spawn during autumn months. The Leeuwin Current disperses eggs and larvae to protected coastal nurseries, distributed from the west coast of WA along the south coast of Australia as far east as Victoria. After spawning, adult fish migrate back to the south coast of WA.
Juveniles spend their first three to four years in nursery grounds within estuaries, inlets and sheltered bays. On reaching sexual maturity, fish between South Australia and Tasmania migrate westward to the south coast of WA where they join local schools.
Diet
Adult western Australian salmon feed mostly on small baitfish.
Predators
Salmon are a natural food source for large marine predators including dolphins, seals, sea lions and a wide range of shark species, which are known to follow large salmon schools along the coast.
Illustration © R. Swainston/www.anima.net.au