Sampling juvenile salmon is key to understanding poor marine survival

The Tulalip Tribes coordinated a juvenile salmon sampling project in offshore marine areas throughout Puget Sound last summer, continuing efforts to learn more about poor marine survival.

“We know that early juvenile salmon growth after they enter the ocean is related to their survival, but we haven’t been sampling their growth consistently across the sound each year using the same methods and time period,” said Mike Crewson, Tulalip fisheries enhancement biologist. “This is way overdue. Every watershed needs it.”

Monitoring juvenile salmon in the offshore marine environment has been identified as a major data gap in efforts to improve the understanding of poor marine survival.

In July, Tulalip natural resources staff were joined by salmon ecology consultant Elisabeth Duffy to sample juvenile salmon and marine fish with a purse seine at 18 sites covering eight main marine basins in Puget Sound, from Bellingham Bay to the Nisqually reach, and additional sites in Hood Canal.

Some coho and chinook were retained to be analyzed later in Tulalip’s lab, but most of the fish were released after being weighed and measured. The researchers took length, weight and scale samples of the juvenile chinook and lavaged their stomachs before releasing them, while otoliths were collected from a smaller number of samples for analysis back at the Tulalip Stock Assessment Laboratory.

Salmon ecology consultant Elisabeth Duffy lavages the stomach of a juvenile chinook collected in Possession Sound.

The samples will provide growth rate data that will be used along with the stomach contents to help inform continued research in the Salish Sea Marine Survival Project. That project released findings in July that two of the main reasons for poor marine survival of salmon are a lack of prey and too many predators.

The timing of this sampling provides a snapshot of the out-migrating salmon that have been in the marine environment for a couple of months, before larger fish move out to deeper water later in the summer.

“Previous studies have shown many of the slower growing juvenile salmon offshore aren’t making it,” Crewson said. “We want to look at what they’re eating, the growth of scales and otoliths, and then look at the growth of the successful adults later.”

Funding from a Bureau of Indian Affairs Tribal Resilience Ocean and Coastal Management Planning grant enables the tribe to conduct marine fish monitoring through 2023, and helps institute a long overdue annual Puget Sound Juvenile Salmon and Forage Fish Sampling Program, Crewson said.

“This is widely recognized as a scientific priority to further our understanding of how climate change is affecting ocean conditions and the salmon we depend on,” he said. “This would be the last missing piece needed to develop an ecosystem indicators program that would combine the fish data with zooplankton and other physical oceanographic data that is already being collected.

“We need annual monitoring to document the effects of changing conditions to understand how climate is affecting prey availability, early marine growth and survival of juvenile salmon, along with the community dynamics of zooplankton and forage fish throughout Puget Sound.”

Above: Tulalip natural resources staff collect juvenile salmon from a seine in the offshore marine area of Possession Sound. Story and photos: Kari Neumeyer