Along the Harrison River in B.C.sa国际传媒檚 Fraser Valley, thousands of eagles are gathering to gorge on salmon that have reached the spawning ground.

David Hancock, a biologist who has been studying eagles for about 65 years, says the worldsa国际传媒檚 largest congregation of bald eagles happens on the river in the little community of Harrison Mills, about 100 kilometres east of Vancouver.

sa国际传媒淟ast Saturday morning I did a survey off the river and there were just over 7,000 eagles in the area,sa国际传媒� he said in a recent interview. sa国际传媒淭his is the most wesa国际传媒檝e ever had in November.sa国际传媒�

About 35,000 eagles gather in the lower Fraser Valley between November and February, and some days about 2,000 to 3,000 raptors move in, Hancock said.

sa国际传媒淚tsa国际传媒檚 the biggest single accumulating area because the Harrison River is the single most productive river,sa国际传媒� said Hancock. sa国际传媒淚tsa国际传媒檚 the only river in Canada called a salmon stronghold river.sa国际传媒�

The Harrison River is a tributary of the Fraser River and runs about 18 kilometres in length.

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As rivers in Yukon, Alaska and northern British Columbia ice up food supplies freeze too, which forces the eagles south.

sa国际传媒淥ur salmon are just beginning to die so the table is set down here,sa国际传媒� said Hancock.

But there are other factors that contribute to the number of eagles that descend on the area.

sa国际传媒淪ometimes the north doesnsa国际传媒檛 freeze up and the eagles donsa国际传媒檛 need to come,sa国际传媒� he added. sa国际传媒淪ome years we donsa国际传媒檛 get as many salmon so the table isnsa国际传媒檛 as generously set.sa国际传媒�

The eagles remain in the area until February although a few thousand may fly further south into Washington, Oregon and California as winter deepens.

Hancock said this year, the Harrison River does not have enough salmon.

sa国际传媒淭his was not a good year for spawning,sa国际传媒� he said.

When the salmon carcasses are gone, he said the eagles feed on spawned herring and oolachin, a smelt.

In about four years the area might not see as many eagles because overharvesting means there wonsa国际传媒檛 be as many salmon carcasses for them to feed on, he said.

Hancock said in the last two decades researchers have learned about the connection between the huge trees in forests in the area and spawned salmon. The carcasses of spawned salmon give nutrition to the soil, he added, which helps trees grow.

sa国际传媒淲ithout those salmon there are no big forests,sa国际传媒� Hancock said. sa国际传媒淭hatsa国际传媒檚 the lesson we learned in the last 20 years of ecology.sa国际传媒�

The Canadian Press

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