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NW Fishletter #381, May 7, 2018

[1] No Room For Chinook? An Oceanful Of Pinks, Chum And Sockeye

While fish managers look for ways to boost numbers of migrating fish in the Columbia and Snake rivers, scientists studying overall salmon abundance in the North Pacific Ocean are singing a different tune.

A study published April 4 in Marine and Coastal Fisheries found that overall, the Pacific has more salmon now than at any other time in the last 90 years. What's more, the scientists believe the Pacific Ocean may have reached its carrying capacity for salmon in recent decades.

The study, by marine scientists Gregory Ruggerone and James Irvine, is the most comprehensive compilation of data for natural- and hatchery-origin salmon in the North Pacific Ocean to date. It builds on Ruggerone's 2010 abundance study, calculating the annual abundance of pink, chum and sockeye salmon since collection of relatively comprehensive statistics began in 1925.

These numbers show that from 2005 through 2015, the ocean--from the coasts of Washington and British Columbia to Alaska, Russia, Japan and South Korea--is virtually teeming with adult salmon, an average of 721 million annually. By weight, they add up to about 1.32 million metric tons.

By numbers, the Pacific Ocean now averages more than twice as many salmon as it had from the mid-1940s to the mid-1970s, and 36 percent more than its last peak in the late 1930s. Only now, about 40 percent of adult and immature biomass stems from hatcheries.

The study does not include abundance of Chinook, coho or steelhead because "considerably more effort is needed" to estimate the hatchery and naturally-spawning components of these species. Also, together, they comprise only about 4 percent of the total salmon catch across the Pacific Rim. "While very important in the Columbia River Basin, Pacific-wide, those three species are not highly abundant," Ruggerone told NW Fishletter.

A research scientist at Natural Resources Consultants, Ruggerone is also a member and former chair of the Independent Scientific Review Panel, and has served as a member and chair of the Independent Scientific Advisory Board. His co-author Irvine does research at Fisheries and Oceans Canada, Pacific Biological Station, in Nanaimo, B.C.

Ruggerone said compared to the last 25 years, Chinook, coho and steelhead once enjoyed a higher percentage of overall salmon in the Pacific, but not significantly higher. However, the surge in abundance of the ocean's big three--pinks, chum and sockeye--helped along by the 1977 ocean regime shift and by hatchery production, may be contributing to depressed numbers of the other salmon species, he said.

"In the state of Alaska, where habitat is largely pristine, Chinook salmon throughout the state are depressed," he said, adding that numbers have declined even though there are relatively few dams, and many rivers are largely intact.

The returning adults are also getting smaller and returning at a younger age, on average. "That has led some of us to think part of the decline in abundance in Alaska, statewide, is partly related to increased mortality during late marine life," he said. And that, he said, may be from competition for food in the ocean. A dissertation by a colleague, Nancy Davis, found quite a bit of overlap in the diets of larger pink salmon and Chinook in offshore marine areas, he said, and found that in odd years when pinks are highly abundant, Chinook reduced their food consumption, including key prey such as squid and fishes.

While there are implications for salmon and steelhead that return to the Columbia River, Ruggerone's abundance study focuses on the numbers and total biomass of pink, chum and sockeye salmon, and the proportion that originate in hatcheries, in 21 regions of the ocean since 1925.

The study indicates that total numbers of adult salmon were highly variable in the early years of the study, peaking in the late 1930s at about 530 million fish, and then declining in the mid-1940s to about 310 million fish, where it remained until the mid-1970s.

The numbers increased to about 543 million fish after the 1976-1977 ocean regime shift, from 1977 until 2004. They have become most abundant in the last 25 years, averaging 665 million fish from 1990 to 2015. That average jumps to 721 million fish during the decade 2005 to 2015.

From 1990 to 2015, pinks dominated the numbers, comprising about 67 percent, followed by chum at 20 percent and sockeye at 13 percent.

Looking at the biomass of adults only, the total weight of fish from 1925 until 1943 averaged 1 million metric tons. That dropped to about 600,000 metric tons from 1958 until 1976. And after 1977, total biomass increased steadily, reaching a plateau of about 1.32 million metric tons from 1990 to 2015. The adult biomass numbers are also dominated by pink salmon, with 48 percent of the total, followed by chum at 35 percent and sockeye at 17 percent.

Adding in immature fish, the ocean's salmon weigh about 4.3 million metric tons. Those numbers are strongly influenced by chum, which are larger and typically spend three or four winters in the ocean, compared with pinks, which spend just one winter in the ocean, Ruggerone said. When including biomass of immature fish, chum dominate with 60 percent of the combined biomass of all three species, followed by pink salmon with 22 percent and sockeye with 18 percent.

Ruggerone said a change known as the 1976-1977 ocean regime shift in the North Pacific Ocean--which also corresponded with a major shift in the Pacific Decadal Oscillation--had a huge impact on the central and northeast Pacific, which brought warmer sea-surface temperatures that tended to benefit pink and sockeye salmon.

"Both actually doubled in abundance after the regime shift in northern areas, largely because of very favorable conditions in that first year at sea," he said. But farther south, in the Pacific Northwest and Columbia River Basin regions, the regime shift led to a reduction in early marine survival for salmon, he added.

The study also tracked the increasing role that hatcheries play in salmon abundance. While generally favorable ocean conditions have improved production of natural-origin salmon, the study finds that some 40 percent of all three salmon species are from hatcheries, including 60 percent of chum, 15 percent of pink and 4 percent of sockeye. "The contribution of hatchery salmon to total abundance averaged less than 2 percent in the 1950s, and likely less than 1 percent in earlier years," the study states.

Hatchery salmon dominate the numbers in some areas, including Japan, South Korea, Alaska's southeast region and Prince William Sound, and the Sakhalin and Kuril islands of Russia. "For example, in Prince William Sound, approximately 76 percent of Pink Salmon, 73 percent of Chum Salmon, and 36 percent of Sockeye Salmon originated from hatcheries," the study says, noting that those numbers don't include numerous salmon that stray into streams within and outside Prince William Sound.

The paper includes a long discussion of potential impacts of increasing hatchery-origin salmon.

"Hatchery salmon are released into the ocean primarily so that returning adults can support salmon harvests by local fishermen. However, hatchery salmon can migrate long distances at sea and intermingle with distant natural-origin stocks, leading to unintended consequences when those natural-origin stocks are less productive," it says.

These effects are not usually considered by hatchery managers, even though the issue has been raised. The study concludes that a stable biomass in the ocean since 1993 suggests that the ocean may have reached its carrying capacity for salmon. "This finding leads to the question: would natural-origin salmon rebound if hatchery production was significantly reduced? Additionally, if the ocean becomes less favorable for salmon, as it was from the 1940s through the 1960s, will natural-origin salmon abundances decline more than they would without hatchery salmon?"

The study notes that those answers are beyond the scope of this research, but could be better explored with its recommendations--to ensure that all hatchery salmon are marked; that hatchery- and natural-origin numbers are estimated in the catch or spawning escapement; and that those numbers are maintained in publicly accessible databases.

Ruggerone said after his earlier 2010 abundance publication, member nations of the North Pacific Anadromous Fish Commission were encouraged to weigh in with their own estimates of wild and hatchery salmon abundance; and when they did not, he and Irvine worked to update numbers and expand the scope. "Ultimately we hope this paper, just like the previous one, will encourage countries to make their own estimates of wild-versus-hatchery salmon so that we can track the status of wild salmon across the Pacific Rim," he said.

The study was largely conducted with volunteer hours by the scientists, and with support from the Fisheries and Oceans Canada's International Governance Strategy, the State of Alaska's Salmon and People project, and the Gordon and Betty Moore Foundation. -K.C. Mehaffey

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Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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