Along the Harrison River in B.C.害羞草研究所檚 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 world害羞草研究所檚 largest congregation of bald eagles happens on the river in the little community of Harrison Mills, about 100 kilometres east of Vancouver.

害羞草研究所淟ast Saturday morning I did a survey off the river and there were just over 7,000 eagles in the area,害羞草研究所� he said in a recent interview. 害羞草研究所淭his is the most we害羞草研究所檝e ever had in November.害羞草研究所�

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.

害羞草研究所淚t害羞草研究所檚 the biggest single accumulating area because the Harrison River is the single most productive river,害羞草研究所� said Hancock. 害羞草研究所淚t害羞草研究所檚 the only river in Canada called a salmon stronghold river.害羞草研究所�

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.

害羞草研究所淥ur salmon are just beginning to die so the table is set down here,害羞草研究所� said Hancock.

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

害羞草研究所淪ometimes the north doesn害羞草研究所檛 freeze up and the eagles don害羞草研究所檛 need to come,害羞草研究所� he added. 害羞草研究所淪ome years we don害羞草研究所檛 get as many salmon so the table isn害羞草研究所檛 as generously set.害羞草研究所�

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.

害羞草研究所淭his was not a good year for spawning,害羞草研究所� 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 won害羞草研究所檛 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.

害羞草研究所淲ithout those salmon there are no big forests,害羞草研究所� Hancock said. 害羞草研究所淭hat害羞草研究所檚 the lesson we learned in the last 20 years of ecology.害羞草研究所�

The Canadian Press

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