14 Homing in Salmon

Key Idea: King (chinook) salmon migrate as adults from the ocean to headwaters to spawn, possibly using magnetic fields, polarised light, and scent to help navigate to the river in which they were spawned. King salmon (Oncorhynchus tshawytscha) are anadromous, meaning they migrate from the sea to fresh water to spawn. Salmon possess one of the most remarkable homing instincts of any animal. Young fish travel from the river of their birth to sea where they grow to maturity. When ready to spawn, they return to the river they left as juveniles. Travelling hundreds of kilometres in the open ocean, they locate their home river and swim upstream to spawn in the same tributary in which they were hatched. Their navigation from the open ocean may involve using the Earth’s magnetic field or polarised light. Once close to their homeland coast, they rely on smell to detect the unique odour of their home river.

1. (a) Describe the mechanism salmon use to return to the stream where they hatched:

(b) Using the map above, describe the evidence indicating that this method of navigation is not foolproof:

(c) Describe the adaptive advantage of returning to the natal stream to spawn:

2. Salmon may be removed (as eggs or fry) from their stream of origin and farm reared before being released to grow at sea. These fish generally fail to return to their natural headwaters to breed. Suggest why these fish do not return:

3D King salmon (Oncorhynchus tshawytscha) occupy the Paringa River drainage on the west coast of the South Island. The Lake Paringa salmon stock includes both landlocked (non-migrating) and anadromous individuals. Out-migrant salmon live and grow to maturity in coastal water to the north and south of Paringa drainage. Salmon enter the mouth of the Paringa River and move into Lake Paringa via the Hall River. Some incidence of straying by salmon into the Ohinemaka drainage.

Immature salmon spend varying periods (up to 3+ years) in Lake Paringa before completing the marine phase of their life cycle. Eventually the young fish migrate to the Tasman Sea as smolts.

Tasman Sea

Hall River

Lake Paringa

Paringa River Ohinemaka Riv er

Highway 6 To Hokitika

Salmon moving upstream to spawn congregate in the lake off the Windbag River mouth while developing to sexual maturity.

Area enlarged on map to the right

Highway 6To Haast Windbag River

Principal salmon spawning areas.

(Information kindly supplied by Dick Hutchinson, Dept. of Conservation)

Some spawning occurs in the upper reaches of the Paringa River during years of high abundance.