Along the Harrison River in B.C.鈥檚 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鈥檚 largest congregation of bald eagles happens on the river in the little community of Harrison Mills, about 100 kilometres east of Vancouver.

鈥淟ast Saturday morning I did a survey off the river and there were just over 7,000 eagles in the area,鈥� he said in a recent interview. 鈥淭his is the most we鈥檝e ever had in November.鈥�

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.

鈥淚t鈥檚 the biggest single accumulating area because the Harrison River is the single most productive river,鈥� said Hancock. 鈥淚t鈥檚 the only river in Canada called a salmon stronghold river.鈥�

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

READ MORE:

READ MORE:

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

鈥淥ur salmon are just beginning to die so the table is set down here,鈥� said Hancock.

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

鈥淪ometimes the north doesn鈥檛 freeze up and the eagles don鈥檛 need to come,鈥� he added. 鈥淪ome years we don鈥檛 get as many salmon so the table isn鈥檛 as generously set.鈥�

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.

鈥淭his was not a good year for spawning,鈥� 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鈥檛 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.

鈥淲ithout those salmon there are no big forests,鈥� Hancock said. 鈥淭hat鈥檚 the lesson we learned in the last 20 years of ecology.鈥�

The Canadian Press

Like us on and follow us on .