USA: Small fish size linked to poorer runs of chinook in Alaska’s biggest rivers

The shrinking size of Alaska salmon, a decades-long trend linked in part to warming conditions in the ocean, is hampering the ability of chinook in Alaska’s two biggest rivers to produce new generations needed to maintain healthy populations, a new study shows. The University of Alaska Fairbanks-led study shows how the body conditions of chinook salmon, combined with extreme heat and cold in the ocean and freshwater environments, have converged in the Yukon and Kuskokwim river systems to depress what is termed “productivity” — the successful reproduction that results in adult spawners returning to the same area. The study examines 26 different populations of chinook in those two river systems in areas from Western Alaska to the Yukon River uplands in Canada. Chinook runs in those rivers have faltered in recent years, and the situation has been so dire on the Canadian part of the Yukon that U.S. and Canadian officials earlier this year suspended all harvests of Canadian-origin ...