Overcrowded oceans threaten wild salmon: researchers
Billions of hatchery-bred fish are out-competing natural populations for food and habitat - By Randy Shore, Vancouver Sun October 5, 2010
Wild salmon stocks in the north Pacific are being eroded as the fish are forced to compete for food and shrinking habitat with billions of hatchery fish released into the oceans each year, a new study by scientists in B.C. and Washington state says.
This warning comes as the population of sockeye, pink and chum salmon across the Pacific Rim is higher than it has been in many decades.
"The total number of salmon out there is at an all-time high, in fact, the abundance is about double what it was in the 1950s," said Randall Peterman, a fisheries management scientist at Simon Fraser University and a co-author of the newly published study.
But releasing large numbers of hatchery fish to supply a food fishery is harmful to the natural salmon populations, he said.
"Hatchery fish have been causing deterioration in the wild population for some time."
The authors of the study, published in the peer-reviewed journal Marine and Coastal Fisheries: Dynamic Management and Ecosystem Science, are calling for the creation of an international forum to regulate the production of hatchery fish.
"The fact is that hatchery fish from one nation can influence the health of salmon stocks in another nation," Peterman said.
Hatchery output, particularly in Alaska and Japan, has reached about five billion fish a year and continues to climb, creating a triple threat for wild stocks.
Faced with increased competition for food, wild salmon return to their spawning grounds underweight and less able to spawn successfully.
"Both hatchery and wild fish are going to face slower growth if the have to compete for food," Peterman said. But hatchery fish are born to be eaten, not spawn in the wild, while wild stocks must be healthy in order to successfully reproduce.
Interbreeding between wild salmon and hatchery fish that stray into spawning grounds weakens the wild stocks. The fish that hatcheries release are raised in a protected environment not subject to the same threats -- also called "selection pressure" -- in the early stages of life as wild salmon and are genetically inferior to wild salmon, Peterman said.
"This has been shown to degrade genetic diversity and could make wild salmon less able to cope with variations in natural conditions," he explained.
"The decline in the robustness of the wild fish could make them less able to cope with the pressures of climate change."
And finally, the artificial abundance created by huge hatchery output leads to overfishing that further depletes wild stocks.
The combined abundance of wild and hatchery fish encourages fisheries managers to allow a higher harvest rate, Peterman warned.
But since the fishery is non-selective -- wild and hatchery fish are both harvested at a higher rate -- that leads to overharvesting of the wild stock.
Hatchery salmon represent about 20 per cent of the total salmon population, but runs as high as 76 per cent in Asian waters for species such as chum.
"The proportion of hatchery fish is rising and will continue to rise if hatchery plans that are on the books are built," he said.
