Nav: Home

Bigger doesn't mean better for hatchery-released salmon

November 14, 2019

Fish permeate the culture of the Pacific Northwest (PNW). In particular, the iconic salmon has been an important part of the region for thousands of years, from ancient Native American trade routes and legends to modern fishing and sporting. In the area of the Salish Sea - inland waterways including Puget Sound, the Strait of Georgia, and the Strait of Juan de Fuca - the cultures, economies, and technologies there are all impacted and influenced by salmon. It is no wonder, then, that salmon are of high conservation interest and constitute a large proportion of hatchery-raised fish in the region.

A recent study in the Ecological Society of America's journal Ecosphere examines hatchery practices in regard to how the Chinook salmon that are released back into the natural waterways in the PNW are affecting wild populations.

In the face of changing climate, ocean conditions, freshwater habitat loss, and increased human consumption, many salmon populations in the PNW are depleted relative to historical abundance. A large salmon, for instance, is a prized and sought-after catch for a sport fisher. There is a growing demand for salmon hatcheries to provide food security and to bolster fish populations; many hatcheries release fish after they reach a certain age or size, with a goal of increasing opportunities for commercial, recreational, and indigenous fishers.

Salmon hatcheries in the PNW, however, seem to be releasing young fish when they are the desired size for predators to prey upon. In this case, bigger does not equal better for the salmon population's survival.

Chinook salmon - named for the native Chinookan peoples, also known as King salmon - is the largest Pacific salmon species. As juveniles, they migrate to the ocean in their first or second year of life and return to freshwater to spawn as adults 1-6 years later. It is as juveniles that populations are most vulnerable to predators. "Survival during the first year at sea has a large impact on the total lifetime survival and adult abundance of Chinook salmon in the Pacific Northwest," says lead author Benjamin Nelson. "This is a problem for other species that depend on them, like endangered killer whales, and for people who depend on them, such as Native American communities and commercial fishers."

Researchers analyzed more than 65 years of records and data on hatchery-origin Chinook salmon in the Salish Sea to examine long-term changes in hatchery release practices. It appears that hatcheries have progressively released juvenile fish at bigger sizes and they are currently releasing them in a larger size range preferred by fish, bird, and marine mammal predators. A 2017 study using GPS tags found that harbor seal feeding increased shortly after hatchery releases of large coho salmon, but interestingly, the seals did not respond to far more abundant but smaller-sized Chinook releases a few weeks later. Many predators show similar large-size (over 10cm) preference in studies over the years showing that smaller juvenile salmon encounter fewer predators. Thus, hatchery-origin chinook are more likely to be eaten before they have a chance to spawn.

Not even the commercial fisheries benefit from hatcheries releasing larger fish. "Despite the fact that larger juvenile salmon are being released from some Salish Sea hatcheries," says Nelson, "the average size of the adult salmon captured by commercial fisheries has actually decreased along the west coast of North America. Some scientists have speculated these size trends could be because of poor ocean conditions, which may reduce the availability of food for growing salmon, while others believe that long-term size selectiveness by fisheries, or selective removals by predators (targeting larger, older fish) could play a role. It is likely that some combination of these factors is responsible."

Additionally, the researchers were surprised to find that hatchery Chinook are released in a narrow two-week window of time during May, while natural Chinook migrate to the ocean earlier in the year and over a much longer time frame. This could result in high survival if ocean conditions at that time are favorable,  but it could be detrimental when conditions are poor. Because ocean conditions change considerably from year-to-year, this could result in "boom or bust" dynamics.

"Just like a retirement portfolio," explains Nelson, "returns tend to be more stable when its assets are well-diversified. It is reasonable to believe this applies to salmon populations, as well. A more diverse group of hatchery releases could be more robust to changing environmental conditions, resulting in more stable returns of adult fish in the future."

With current marine survival rates at chronically low levels and with increasing demand for hatchery fish, understanding cumulative historical effects of hatcheries on ecosystems is essential for improving future hatchery practices and ensuring sustainable management. "Hatchery Chinook salmon in the Salish Sea have become increasingly similar over the last 50 years, in terms of both their size and the time at which they are released," remarks Nelson. "This loss of diversity could have several negative consequences, not just for salmon, but for other species that depend on them."


-end-
Journal

Nelson, Benjamin W. et al., 2019. "Ecological implications of changing hatchery practices for Chinook salmon in the Salish Sea." Ecosphere. DOI: 11002/ecs2.29220.

Authors

Benjamin W. Nelson; Contractor to the Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration; University of British Columbia, Institute for the Oceans and Fisheries.

Andrew O. Shelton, Michael J. Ford, and Eric J. Ward; Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration

Joseph H. Anderson; Washington Department of Fish and Wildlife

Author Contact:

Benjamin Nelson      nelson.benjamin@gmail.com

The Ecological Society of America (ESA), founded in 1915, is the world's largest community of professional ecologists and a trusted source of ecological knowledge, committed to advancing the understanding of life on Earth. The 9,000 member Society publishes five journals and a membership bulletin and broadly shares ecological information through policy, media outreach, and education initiatives. The Society's Annual Meeting attracts 4,000 attendees and feat

Ecological Society of America

Related Salmon Articles:

What does drought mean for endangered California salmon?
Droughts threatens California's endangered salmon population -- but pools that serve as drought refuges could make the difference between life and death for these vulnerable fish.
Salmon provide nutrients to Alaskan streambanks
Nutrient cycling of stream ecosystems dependent on portion of salmons' lifecycle.
Melting glaciers will challenge some salmon populations and benefit others
A new Simon Fraser University-led study looking at the effects that glacier retreat will have on western North American Pacific salmon predicts that while some salmon populations may struggle, others may benefit.
Bigger doesn't mean better for hatchery-released salmon
A recent study in the Ecological Society of America's journal Ecosphere examines hatchery practices in regards to how Chinook salmon hatcheries in the PNW are affecting wild populations over the past decades.
Salmon get a major athletic boost via a single enzyme
A single enzyme anchored to the walls of salmons' blood vessels helps reduce how hard their hearts have to work during exercise by up to 27%.
Salmon are shrinking and it shows in their genes
Male salmon are maturing earlier and becoming smaller, and it shows in their genes.
Young salmon may leap to 'oust the louse'
A study by Simon Fraser University aquatic ecologists Emma Atkinson and John Reynolds reveals that young salmon may jump out of water to remove sea lice.
Fishy chemicals in farmed salmon
The American Chemical Society journal Environmental Science & Technology featured research by Carla Ng, assistant professor of civil and environmental engineering at Pitt's Swanson School of Engineering, on the cover of its June 19 issue.
A little water could make a big difference for endangered salmon
A trickle of water flowing through a stream could mean life or death for endangered coho salmon in coastal California.
Coho salmon die, chum salmon survive in stormwater runoff research
In a recent paper published in the journal Environmental Pollution, scientists found that coho salmon became sick and nearly died, within just a few hours of exposure to polluted stormwater.

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Our Relationship With Water
We need water to live. But with rising seas and so many lacking clean water – water is in crisis and so are we. This hour, TED speakers explore ideas around restoring our relationship with water. Guests on the show include legal scholar Kelsey Leonard, artist LaToya Ruby Frazier, and community organizer Colette Pichon Battle.
Now Playing: Science for the People

#568 Poker Face Psychology
Anyone who's seen pop culture depictions of poker might think statistics and math is the only way to get ahead. But no, there's psychology too. Author Maria Konnikova took her Ph.D. in psychology to the poker table, and turned out to be good. So good, she went pro in poker, and learned all about her own biases on the way. We're talking about her new book "The Biggest Bluff: How I Learned to Pay Attention, Master Myself, and Win".
Now Playing: Radiolab

Uncounted
First things first: our very own Latif Nasser has an exciting new show on Netflix. He talks to Jad about the hidden forces of the world that connect us all. Then, with an eye on the upcoming election, we take a look back: at two pieces from More Perfect Season 3 about Constitutional amendments that determine who gets to vote. Former Radiolab producer Julia Longoria takes us to Washington, D.C. The capital is at the heart of our democracy, but it's not a state, and it wasn't until the 23rd Amendment that its people got the right to vote for president. But that still left DC without full representation in Congress; D.C. sends a "non-voting delegate" to the House. Julia profiles that delegate, Congresswoman Eleanor Holmes Norton, and her unique approach to fighting for power in a virtually powerless role. Second, Radiolab producer Sarah Qari looks at a current fight to lower the US voting age to 16 that harkens back to the fight for the 26th Amendment in the 1960s. Eighteen-year-olds at the time argued that if they were old enough to be drafted to fight in the War, they were old enough to have a voice in our democracy. But what about today, when even younger Americans are finding themselves at the center of national political debates? Does it mean we should lower the voting age even further? This episode was reported and produced by Julia Longoria and Sarah Qari. Check out Latif Nasser's new Netflix show Connected here. Support Radiolab today at Radiolab.org/donate.