CANADA - Salmon returns unexpected
Pink salmon are returning in near record numbers on the B.C. coast but no one is really sure why.
Estimates by fishery officers monitoring rivers in the Broughton Archipelago show returns of pink salmon this year already significantly higher than the brood year in 2007.
“They have over replaced the brood year in at least three of the systems,” said Pieter Van Will, DFO program head for North Island stock assessment. For example, the estimated returns to the Kakweiken River system for the 2007 season were 37,000 returns. But the offspring of those fish returning to spawn were already estimated to number about 270,000 by the first week of September this year. In the Glendale system, the 2007 brood year was estimated at 264,000. The estimates for this year are already at 297,000. The same trend is evident in other Broughton Archipelago rivers and all along the B.C. coast.
“We are having strong returns coast wide,” confirmed Andrew Thomson, acting regional director of Fisheries and Oceans Canada (DFO) in the Pacific region. “The Quinsam River in Campbell River has record returns. I think it speaks to the larger picture that pink salmon fluctuate greatly. We don’t understand all the factors for this fluctuation. It is a very complex picture.”
But Thomson said pink salmon returns are typically lower in odd years and the reason for the strong returns this year is unclear.
“There are any number of environmental conditions that have an impact on the survival of pink salmon,” said Thomson. Those factors could include, along with others, ocean conditions, feed availability, juvenile mortality and flow conditions.
Overall the strong return of pinks are good news.
A study co-authored by local researcher and environmentalist Alexandra Morton, predicted in 2007 the demise of the pinks by 2011. The study pointed at fish farms for increasing the numbers of sea lice that in turn threatened juvenile salmon headed for the ocean each spring. The study concluded that “sea lice typically killed over 80 percent of the fish in each salmon run” and that “if sea lice infestations continue, affected pink salmon populations will collapse by 99 per cent in ... four years.”
Morton, who is happy to see the pinks return, said the extinction forecast hasn’t materialized because fish farms are doing a better job of managing farms.
“The extinct prediction was based on nothing changing,” said Morton. “Since then there have been significant changes.” Those changes include better and earlier administration of the drug SLICE by fish farmers to control sea lice infestations, said Morton.
“It is effectively bringing the lice numbers down,” said Morton.
But while Marine Harvest Canada, operator of the majority of fish farms in the Broughton Archipelago, appreciates the kudos, they say nothing has changed in how they treat their fish for lice.
“Yes farm management is always improving, but we haven’t changed the way we administer SLICE in five or six years,” said Ian Roberts, spokesperson for Marine Harvest. The pinks returning this fall would have migrated through the Broughton in the spring of 2008.
“There was no big corridor of fallowed farms on an out-migration route that year,” said Ian Roberts, spokesperson for Marine Harvest Canada that operates the majority of the farms in the area. “We fallowed three farms. We were managing sea lice as we have in previous years.”
Marine Harvest generally manages sea lice by administering SLICE to kill sea lice on their fish. Last year the company used 15 kg of SLICE to treat 80,000,000 kg of farmed fish.
“Lice levels near or far from farms have dropped in the last five years,” said Roberts. “The returns must be due to other variables in the ocean.
“We are consistent. We are still operating and treating for sea lice the same way. We’re consistent so there’s obviously another factor at play (in fluctuating salmon returns),” said Roberts. “We’ve seen good years and we’ve seen bad years. We have been here for both.”
[North Island Gazette: http://www.bclocalnews.com/vancouver_island_north/northislandgazette/news/59391342.html]