Post-spawning death of salmon in Fraser River after visiting their natal river

postspawning death salmon run fraser river natal river salmon run ecological impact annual fish migration life cycle british columbia bc fish migrate birth streams spawn chum river nature fraser valley circle of life harrison mills wilderness wild places canadian outdoors wildlife canada migration nature scene wild fauna canadian countryside outdoors no people swim upstream water animal current struggle nobody natural salmonid spawning area keystone species magnetoreception ecological consequences lifecycle hatching grounds