The low survival rate of “spawning” kokanee salmon in Kootenay Lake has continued, according to fall totals from the 2021 provincial count.
Low survival rates for kokanee in the big lake have reduced the number of spawners – less than 40,000 in recent years – to around 24,000 spawning fish counted in 2021, a Ministry of Forests, Lands, Waterways periodical noted. ‘Natural Resource Exploitation and Rural Development (FLNRORD) published in December. .
A landlocked form of sockeye salmon, the number of spawning fish can vary each year – similar to oceanic forms of salmon.
“Abundant kokanee predators (rainbow Gerrard and bull trout) were the main driver of kokanee collapse and predation continues to keep kokanee survival below a level that allows for rapid recovery. “, notes the report.
Populations of rainbow trout and bull trout in Kootenay Gerrard Lake have remained above levels of conservation concern, as only a few spawners are needed to saturate the available juvenile habitat in streams.
“Survival of the youngest age class of kokanee continues to be low and therefore we will continue to take actions to improve kokanee survival,” the ministry said. “This means there is an additional margin to reduce kokanee predation without risking the conservation of these populations.”
Using the Kootenay Lake Angler Incentive Program – launched in June 2020 – the program has helped remove some kokanee predators from the lake (approximately 11,000 head were returned under the 2020-2021 program). To date, most actions to reduce predation pressure on kokanee have focused on increasing harvest through angling.
Although this program helped kokanee one to two years old last year, it did not affect survival in the lake of the youngest age category.
“The Department has liberalized Kootenay Lake angling regulations by increasing rainbow trout and bull trout quotas to ensure anglers are not restricted in fishing, opening up previously restricted areas to fishing and exploring tools to encourage greater angler participation,” the report explains.
The province will continue to stock the lake – an important part of recovery with 1.1 million eggs stored in 2021 – but the data indicates that stocking alone cannot enable recovery.
One of the kokanee resuscitation actions that has not been attempted is to reduce predation pressure by reducing the number of juveniles enough to bring down future Gerrard and bull trout populations.
The ministry revealed that an “expert advisory team has reviewed the risks and benefits of such actions and has suggested that benefits to kokanee recovery are likely”, with the risks described as manageable as long as the reduction is at short term (one to two years).
“Decisions will be made on these specific actions based on recommendations from our expert team and in discussion with First Nations over the next month,” the FLNRORD ministry report said.
Up or down?
Eight years ago, the population of kokanee salmon in the lake crashed from an average of around one million to “unprecedented numbers”, averaging between a record low of 12,000 in 2017 and about 90,000 in 2020.
These numbers reflected low survival from 2014 and a low cohort that spawned in 2017. When kokanee fall to such low abundance, they have more food available to them because there is less competition between fish, so they grow much faster and bigger.
This translates to many more eggs per female, so although the abundance of spawners is much lower, the total egg deposition for the entire run has not decreased as dramatically.
In 2020, all 90,000 spawners laid enough eggs to produce the long-term average number of fry before the collapse.
Five years ago, the ministry deposited more than 500,000 kokanee eggs in the spawning channels surrounding the lake, citing a hatch rate of 90%.
However, the species has thrived in some lakes in the region, but not others – such as Kootenay Lake – and research has shown that factors such as pollution, lake levels, climate change and loss of habitat contribute to the decline.
Once the balance is restored, kokanee are expected to become abundant again within one life cycle (approximately three to four years), and rainbow trout and bull trout follow in a few years.