Freshwater salmon stocks have increased dramatically in Okanagan lakes this year, even though populations of Pacific salmon have plummeted in the nearby Columbia River system.
A recently released provincial government survey found kokanee spawners in Okanagan Lake, for example, reached a high of 336,500 – the largest quantity since the province started keeping track of the population in 1992.
Restored habitat, better watershed data and volunteer efforts have been given credit for allowing the first full recreational kokanee fishery this year in four years.
"The Okanagan showed exceptional numbers of spawning for adult kokanee this year – up to doubling, or even tripling of the average numbers," said Kim Hyatt, a research scientist at Fisheries and Oceans Canada.
The welcome increase comes after the population was brought to its knees in the mid-1990s, when the invasive opossum shrimp was introduced into the waters in an effort to stimulate trout populations. The shrimp would undercut the kokanee's food supply, ultimately driving the population of spawning adults down to 13,000 – a 99-per-cent decrease from spawning numbers 30 years prior to that.
The population recovered with the development of the Okanagan Lake Action Plan, a 20-year effort to rebuild declining kokanee stocks. The plan was successful, until the species took another major hit in the 2011 spawning season.
"We don't know exactly what caused the population decline [in 2011]," said Hillary Ward, a fisheries stock biologist with the Ministry of Forest, Lands and Natural Resource Operations. "But it was likely because water temperatures were too warm and there was not enough oxygen [for the kokanee to survive]."
But as this year's salmon run comes to a close, not all of the province's salmon stocks are booming.
After an excessively hot summer, it was estimated that the total sockeye salmon spawning in rivers and streams in British Columbia's South Okanagan region would be as low as 18,000 due to higher-than-normal water temperatures. Recreational fisheries throughout the region were suspended in a response to the low projections.
Mr. Hyatt said the number of surviving sockeye that ended up making the trip to the Southern Okanagan via the Columbia River system appear to be even smaller.
"[Initially], we expected that we might have as many as 180,000 reach spawning grounds in the Okanagan," Mr. Hyatt said Monday.
"But at this stage in the game, it looks like there's about 10,000 adults in the spawning grounds."
It remains uncertain how quickly these populations will recover given likelihood of similar conditions in the future, he said.
"Because of climate change, we're anticipating the extreme weather conditions we saw this year to likely increase in frequency."
The warm weather patterns have also influenced salmon populations across the coast of British Columbia, but in a very different way.
"What we [also] have seen are widespread reductions in the average size-at-age of the salmon," said Mr. Hyatt, who emphasized that the trend has been noticed all along the province's coast.
The decrease in size is likely because of warming waters in offshore rearing and overwintering areas of the North Pacific Ocean, creating living conditions that aren't optimal for salmon growth.
Commercial fishermen in the region have witnessed this change first hand, although some of them have trouble attributing it to the changing temperatures.
"The fish between 2003 and 2011 were all benefactors of having sardines available," said Mike Marriott, commercial fisherman and founder of Ucluelet's Long Beach Charters.
"We were catching 20-pound coho on a daily basis. I had never seen that before."
Mr. Marriott maintains that a plentiful food supply led to larger-than-usual salmon.
"Then the sardines disappeared," he said.