Just like anglers, the Mandurah dolphins are taking advantage of the salmon run that has begun.
Each year, late autumn and early winter, the Western Australian salmon (Latin name Arripis truttaceus), which we shall refer to as salmon from here on, migrate west and up the coast to spawn.
This is when the Leeuwin current is strongest and the prevailing easterly winds ensure the larvae is distributed along the southern coast all the way to Victoria and even Tasmania.
Juvenile salmon spend three to four years in nursery grounds between South Australia and Tasmania before moving to Western Australia, around Esperance, and then joining the spawning run along the south west coast.
A fully grown salmon can be approximately 90 centimetres long and weigh up to 10 kilograms.
Surprisingly, despite their name, the Western Australian salmon do not actually belong to the salmon family, but to a group of salmon-shaped fish that occur only in Australia and New Zealand.
In the Peel-Harvey estuary and adjacent coastal waters, the schooling salmon is preyed upon by dolphins.
Salmon is considered high in its calorific value, providing substantial energy to the dolphin.
But just like salmon is renowned as a fighter on rod and reel, they also won’t go down without a fight when face to face with a dolphin. Thus dolphins also likely spend more energy catching salmon rather than the smaller fish in the system.
We have observed dolphins chase, toss and tire out salmon prior to catching it, breaking it into pieces and consuming it.
Although we have only visually observed this feeding behaviour, a study conducted in Scotland suggests that sound may play an important part in dolphins capturing large fish.
The study by Dr. Vincent Janik suggested that dolphins produce low frequency sounds to manipulate Atlantic salmon and brown trout, both fish which belong to the salmon family, to make them an easier catch.
Further investigation is required to understand whether Mandurah dolphins use a similar strategy to their Scottish counterparts.
