Adult steelhead returns could decline 30 per cent due to juvenile die-off on Cowichan River
An estimated 84,000 rainbow trout fry died last summer in the upper Cowichan River, and that could result in about a 30-per-cent reduction in adult steelhead returning to spawn, a provincial fisheries specialist said Monday.
Mike McCulloch told the Cowichan Watershed Board that factors such as ocean survival could influence the ultimate returns for better or worse.
According to Fisheries and Oceans Canada, there are two forms of rainbow trout, a salmon-sized “Pacific Ocean sea-run strain known as steelhead and a smaller, landlocked (freshwater) variety.”
The majority of the 84,000 rainbow trout fry that died are thought to have been sea-run steelhead.
McCulloch explained that several factors contributed to environmental “chaos”on the Cowichan River last summer, including low water flows, warm summer temperatures, a “massive aggregation of algae,” and high levels of both pH and dissolved oxygen. (Originally, dissolved oxygen levels were thought to be low).
Conditions were “incredibly outside the range” of normal for the river, McCulloch said.
The target for water flows on the Cowichan River in summer is 7.0 cubic metres per second, but low water levels in Cowichan Lake resulted in river flows of 4.5 cubic metres per second.
There have been long-standing calls to increase the height of the weir at Cowichan Lake to allow more water storage for summer release. Last year, Crofton mill employed pumps to keep lake water flowing into the Cowichan River.
Had river flows been greater, dilution would have lessened the fish impact, including from the Town of Lake Cowichan’s sewage outfall ( https://bitly.ws/3bc2J )
Whereas phosphate levels are generally measured at about one microgram per litre, levels last summer on the Cowichan reached 10 to 15 micrograms per litre, McCulloch told the water board.
Last October, Lake Cowichan received more than $7 million from senior governments to help complete a $10.1-million wastewater infrastructure upgrade. ( https://bitly.ws/3bc3H )
As a result of last summer’s die-off, steelhead fishing is closed this winter on the upper Cowichan between 70.2 Mile Trestle and Skutz Falls.
McCulloch noted that the steelhead sport fishery is already mandatory catch-and-release. Anglers report catching one steelhead for every four days of fishing on average.
He added that recreational fresh-water sport fishing has a value approaching $1 billion, similar to salt-water fishing. “We have some obligation, I think, to support fresh-water fishing where we can do so in a sustainable way,” he said.
(Riverquest Charters photo: adult steelhead on the Cowichan River. sixmountains.ca photos: Mike McCulloch speaking to Cowichan Watershed Board; Town of Lake Cowichan sewage-treatment facility.)
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— Larry Pynn, Jan. 30, 2024