Carrying Capacity: High Numbers of Pink, Chum
A record number of pink and chum salmon in the North Pacific Ocean may be contributing to the depletion of other salmon stocks, such as chinook salmon, according to a recent study.
A compilation of fisheries data in seas along the North Pacific Rim from the Bering Sea to the Columbia River shows that the number of pink, chum and sockeye salmon have been more abundant during the past 25 years than they have ever been since 1925 when record-keeping began.
In the ten-year period of 2005 to 2015, an average of 721 million salmon were swimming in the sea each year, which is approximately 36 percent more than their previous peak in the late 1930s.
"While it is good that the abundance of sockeye, chum, and pink salmon is high, there is growing evidence that this high abundance, especially of pink salmon, is impacting the offshore ecosystem of the North Pacific and Bering sea," said lead author Greg Ruggerone, a scientist at Natural Resources Consultants, INC. "These impacts may include the decline of higher trophic species of salmon, such as Chinook salmon in Alaska, the size, age and abundance of which has declined in recent decades even though their habitat is largely intact."
All species of Pacific salmon migrate thousands of kilometers through the open ocean in search of food, and the abundance of pink, chum and sockeye in the northern regions may be due to more favorable waters. Not only is habitat in the north less degraded than in other areas, the waters are also warming under climate change, making conditions cozier for them, according to a news release about the study.
The authors' estimates, which are based on the most comprehensive compilation of abundance data to date (1925 -- 2015), accounted for salmon born in both natural conditions and hatcheries throughout their native range in Asia and North America. Hatchery-born salmon represented about 40 percent of the seafaring adult and immature salmon.
Most of these hatchery salmon are chum, which typically spend more years at sea than their fellow salmon species before returning to freshwater spawning grounds, the final destination of any uncaught salmon's life journey.
Pink salmon were the most abundant overall, representing nearly 70 percent of all wild and hatchery Pacific salmon combined. While most pink are wild, the numbers born in hatcheries in the past 25 years have been exceptionally high at an average of 66 million adults per year, a number that exceeds total wild chum populations.
"Numbers and Biomass of Natural- and Hatchery-Origin Pink Salmon, Chum Salmon, and Sockeye Salmon in the North Pacific Ocean, 1925--2015" was published online April 4, 2018 in Marine and Coastal Fisheries: Dynamics, Management and Ecosystem Science. Its authors are Ruggerone and James Irvine, Fisheries and Oceans Canada, Pacific Biological Station in Nanaimo. British Columbia.
According to the study:
For example, there is growing evidence that the highly dense populations of pink -- the least desirable species for its small size, soft and pale meat and short shelf life, the study says -- are impacting the growth and survival of the more prized, but less plentiful chinook and coho.
"Density-dependent effects are apparent, and carrying capacity may have been reached in recent decades, but interaction effects between hatchery- and natural-origin salmon are difficult to quantify, in part because these fish are rarely separated in catch and escapement statistics," the study says.
Ruggerone explains their study highlights the importance of maintaining and improving efforts to monitor the numbers of hatchery salmon in fisheries harvests and spawning grounds to keep a better pulse on the status of wild salmon. Tagging or marking hatchery salmon to make them more identifiable when caught or spawning, as well as making the resulting data publicly available, are critical to preventing adverse effects on the growth and survival of wild salmon.
"Ultimately, we want fisheries agencies in all areas of the Pacific Rim to estimate the numbers of hatchery and wild salmon as a means to monitor wild salmon status," said Ruggerone, adding that there is a need to maintain habitat to support wild salmon abundance into the future.
The study recommends: 1- marking or tagging hatchery salmon so that they can be identified after release, 2- estimating hatchery- and natural-origin salmon in catches and escapement, and 3- maintaining these statistics in publicly accessible databases.
This study is the first to emerge from the State of Alaska Salmon and People (SASAP) project, which is an effort to synthesize all existing data about Alaska's salmon and the people who depend on them to support decision-making.
SASAP is a partnership between the National Center for Ecological Analysis and Synthesis and Anchorage-based Nautilus Impact Investing, and is funded by the Gordon and Betty Moore Foundation.
2018 Fishing Season: Gillnetting Begins For Salmon, Smelt In Limited Areas Of Mainstem Columbia Columbia Basin Bulletin, 2/2/18
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