Volcanoes, Eelgrass Suspect in Changing Salmon Habitat

NOAA Fisheries researchers say the combined forces of volcanoes and eelgrass are likely suspects in the gradually disappearing nearshore habitat for young salmon and other wildlife at Chignik, Alaska.

The report, published online in ScienceDirect, is the first to quantify shallowing of the seafloor in the Chignik area, and to identify possible causes.

Large runs of sockeye salmon spawn in lakes in the area of Chignik, which lies on the Pacific Ring of Fire, surrounded by active volcanoes. Eelgrass beds serve as nurseries for young salmon to feed and acclimate to saltwater. Loss of inshore habitat is of great concern to natural resource managers and area residents who fish commercially and for subsistence.

The 2017 summary on the Chignik area from the Alaska Department of Fish and Game noted that a total of 897,489 reds were commercially harvested, which was well below the most recent 5-year and 10-year average harvests. NOAA researchers said the shallowing of Chignik waters may have a significant, long-term impact on the local salmon run, and other fish, birds and wildlife that feed and shelter there. The researchers hope their findings will help managers and communities to understand the vulnerability of these areas so that they can respond proactively.

These unexpected changes in the nearshore habitat were discovered in an Alaska Fisheries Science Center (AFSC) project led by biologist Mark Zimmermann to create fish habitat maps based on old hydrographic maps called smooth sheets.

As he studied the smooth sheets for the 1990s, Zimmermann found notes about seafloor shallowing in Chignik, but no explanation of why it might be happening. He recruited a multidisciplinary team of experts, who determined that eelgrass beds were entrapping and stabilizing volcanic ash flowing into the area.

“Volcanoes and eelgrass were working together to turn a large portion of the Chignik sites into land,” Zimmermann said. “Although this phenomenon has gone unnoticed until now, it is probably widespread, especially throughout the North Pacific, where volcanoes, eelgrass, and salmon are common components of the ecosystem.

“The world’s biggest eelgrass bed is nearby, at Izembek Lagoon, just west of Chignik on the Bering sea side of the Alaska Peninsula,” he added. “A similar dynamic could operate there and in other areas. Understanding it could provide insight for marine coastal management of commercially valuable species like salmon.”

The study, said Zimmermann, underscores the importance of long-term monitoring programs and correctly using historical hydrographic surveys to understand inshore habitat change and vulnerability and not taking habitat for granted.”

The complete study, published in journal ScienceDirect, can be found online at https://www.sciencedirect.com/science/article/pii/S0272771417306716?via%3Dihub