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Western Australian Salmon

Western Australian Salmon

Arripis truttaceus

Western Australian salmon are the largest (growing up to 96 centimetres) of only three species in the Family Arripidae.  Despite their common name, however, they are not related to the salmon (family Salmonidae) found in the northern hemisphere.  Western Australian salmon are countershaded with greenish grey to steely blue back with small dark spots on the upper sides, and pale yellow-green to silvery white below.  The pectoral fins are bright yellow.  Juveniles which are often referred to as salmon trout are silvery white with several rows of large golden or brown spots on the back and sides.  They have a black spot at the base of its pectoral fin and a thin black line along the edge of its tail fin.  These smaller fish are sometimes confused with adult herring which occupy the same habitat.  The distinguishing features between the two, is the herring has a much larger eye and black spots on the tips of the tail fin.  The body shape of the Western Australian salmon is streamlined and fusiform  with a large and powerful forked tail.

Western Australian salmon inhabit coastal waters including estuaries, around rocky headlands, near reefs and in the surf zone and also to deeper waters to depths of 80 metres.  Juvenile Western Australian salmon are found over soft substrates in shallow and sheltered coastal waters, and are often found over seagrass beds.  They form immense schools with hundreds to thousands of individuals, both adults and juveniles.  Western Australian salmon are voracious carnviores feeding on a varied diet of small fish, krill, copepods and other zooplankton and also feeding from the seafloor on benthic invertebrates such as shellfish, crabs and annelid worms.  Occasionally they are observed to be co-existing with other predatory fish species such as trevally, and use a herding technique of co-operatively bullying baitfish to the surface for a feeding frenzy.  A technique thought to benefit seabrids also.  Western Australian salmon form an important part of the diet of orcas, bottle nosed dolphins, several species of large shark and the Australian Sealion.

Adults undertake seasonal migrations over vast distances, moving westwards into deeper water during winter months to spawn.  Salmon eggs are planktonic and drift south and eastwards with the aid of the warm Leeuwin Current, until the develop and settle.  Young salmon spend the first 2 to 5 years in sheltered coastal bays, inlets and estuaries until they become sexually mature and move to more exposed coasts.  Western Australian salmon are relatively long-lived fishes and may live up to 26 years.  Their breeding habits and well known migration routes have made the species vulnerable to fishing pressures over the years having supported a substantial beach seine net fishery, as well as declining stocks of their primary diet of baitfish from overfishing.  Western Asutralian salmon are restricted to southern Australian waters,occurring from Kalbarri, WA to Eden, NSW and around Tasmania.

Other common names include:  Cocky salmon, blackback salmon, bay trout, salmon trout , buck salmon, colonial salmon, kahawai.

Occurrence at the Busselton Jetty: 

The Western Australian salmon are seasonal and occur in large numbers in Geographe Bay in autumn.  A large predatory fish they are observed from the underwater observatory in pursuit of yellow-tail and herring.  It is not uncommon to see individual large adults hovering in the protection in the largeness of the structure of the jetty and the observatory nursing large injuries potentially from bottle nosed dolphin attacks.