Wild steelhead in Puget Sound were recently added to the Endangered Species Act as a threatened species and subject to federal protection. The ESA listing has created a momentum for steelhead research and funding that may not have been available prior to being given protected status. The wild runs have been declining for over 20 years, but recent declines are a worry. Even though there has been a reduction in harvest of wild steelhead over the last decade, increases in wild steelhead abundance has not happened.
Research has revealed that Puget Sound smolt to adult steelhead survival rates have declined over the last 20 years, contributing to a marked decline in the adult runs.
A recent study by Moore, Berejikian and Tezak looked at steelhead migration time, behavior, and survival in Puget Sound and Hood Canal and came up with some answers.
“The estimated population specific survival rates for wild and hatchery smolts from the river mouths to the northern end of Hood Canal (18.6 to 50 miles) ranged from 55% to 86% in 2006 and from 62% to 84% in 2007.
Survival was much lower (23% to 49%) from the northern end of Hood Canal to the Strait of Juan de Fuca (89 miles) in 2006.
Travel rates through Hood Canal (5 miles to 6.2 miles per day) were significantly lower than those estimated as the fish migrated through northern Puget Sound and the Strait of Juan de Fuca (16 to 17.4 miles per day), while the mortality rates per unit of distance traveled were very similar in the two segments.
The high daily mortality rates estimated during the early marine phase of the steelhead life cycle (2.7% per day) suggest that mortality rates decrease substantially after steelhead enter the Pacific Ocean.”
The authors found that smolt release timing influenced migration rate. Those fish that were released later traveled faster from Hood Canal Bridge to the Strait of Juan de Fuca. They speculate that this suggests there may be an optimal time for smolts to reach the ocean, a window for maximum survival related to sea temperature, stability, and the amount of prey available. These ocean conditions affect the amount of prey available, influencing smolt survival.
Wild steelhead have a higher survival rate than hatchery steelhead. The authors refer to research by Beamish et al. (2006) indicating that salt water entry timing of wild coho salmon may be an important adaptive trait and help to explain why wild coho salmon have a higher survival rate than do hatchery coho.
The authors say that “Migration timing is likely an important factor in the survival of both hatchery and wild salmonids; however, hatchery practices that include single or few release dates probably limit the ability of smolts to regulate ocean entry time.”
The authors said they “found no differences in survival or migratory behavior between hatchery and natural origin steelhead smolts over the approximate 2 week residence in Hood Canal.” But they did find that hatchery fish suffer a greater mortality later in the marine environment compared to wild steelhead. “Overall smolt-to-adult survival of naturally produced steelhead has been shown to be substantially higher than smolt-to-adult survival of hatchery fish released in the same environment” according to research by Ward and Slaney 1990 and Kostow 2004.”
Over the last 40 years there have been large fluctuations in Puget Sound steelhead survival, and in recent years, “the low smolt-to-adult return rates…coincide with declines in population abundance,” the authors say. They also note that steelhead from coastal rivers have had higher smolt-to-adult survival rates and adult abundance than those in Puget Sound.
In Puget Sound the “early marine mortality probably is a strong limiting factor on these populations as over 58% of the population perished within 3 to 4 weeks,” the authors noted.
“In summary,” the authors say, “the mortality of the steelhead smolts migrating through Hood Canal appeared to be strongly related to the distance they traveled and less related to their rate of travel. Survival rates through Hood Canal were very similar between years. The estimated rates suggest that mortality for steelhead is greater during the first few weeks of their marine residence than it is later, when they grow larger and enter the open ocean.”
Upon reading this paper, Bill McMillan, said “I bet if they ever tracked steelhead smolts going out of the Nisqually, Puyallup, Green, and Cedar they would find even higher mortality than for the rest of Puget Sound. I have tried to indicate the high probability that southern Puget Sound stocks are the hardest hit because they have to migrate through the greatest density of competing hatchery fish, and potentially are even preyed on by resident hatchery stock chinook called "blackmouth" in these waters that sports fishermen love, as well as resident coho. Nevertheless, good to see that this work is being done.”
Moore, E, Megan, Barry A. Berejikian and Eugene P. Tezak. 2010. Early marine survival and behavior of steelhead smolts through Hood Canal and the Strait of Juan de Fuca. Transactions of the American Fisheries Society. 139: 49-61