Lingering Heat Off West Coast Is Bad News for Salmon
A new report shows offshore heat in parts of the West Coast continues to work against the recovery of Pacific salmon stocks.
The California Current ▶cosystem Status Report (CC▶SR) issued annually by NOAA Fisheries’ two West Coast laboratories to the Pacific Fishery Management Council explains that ocean conditions off the West Coast have remained unusually variable since the arrival of a major marine heat wave in 2014 dubbed “the Blob.”
A marine heat wave rivaling the Blob emerged in the Pacific in the second half of 2019 and, while it waned in early 2020, the repeated warm events left a remnant reservoir of heat deep in offshore waters that could favor future heat waves.
Warm waters off the West Coast are generally associated with less productive conditions. By contrast, colder water from the north injects more energy-rich plankton into the marine ecosystem, therefore, young salmon entering the ocean during cooler conditions grow bigger faster and support stronger salmon returns to the rivers where they spawn.
The 2020 CC▶SR introduces a new ecological indicator known as the “habitat compression index.” It reflects how warm offshore waters run up against cold, deeper waters that well up near the coast. The result is a narrow, compressed band of coastal ocean with cool, productive waters that draw fish and their predators together.
The habitat compression index will provide a running barometer of how offshore heat is affecting nearshore waters and species that depend on them. “We will continue to study this metric in relation to other indicators in hopes of understanding why coastal
impacts in recent years have been so severe,” the report states.
“Through presenting ecosystem trends, our goal is to provide a snapshot of the health of the California Current ecosystem,” says Toby Garfield, co-editor of the report. “Understanding these changes is critical to preserving the productivity and sustainability of West Coast fisheries.”