caring for cultus lake - map of sockeye salmon
from Caring For Cultus Lake booklet
The Cultus sockeye is a genetically unique population of salmon. Sockeye usually spawn in rivers and streams but Cultus sockeye spawn exclusively in the lake. They are also the latest to spawn of all the Fraser River sockeye. Cultus sockeye have a unique adaptation to spawning time: eggs that are spawned later actually develop faster. The fry also behave unlike most other sockeye fry: they school and move into deeper waters immediately after swimming up from the gravel, likely an adaptation to the many predators in Cultus Lake.

Cultus Lake sockeye have been counted and studied since the 1920s, longer than any other in B.C, making this salmon population one of the world’s best-documented.

In 2002 Cultus sockeye were designated by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as “endangered”.

The Pikeminnow Problem
pikeminnow The northern pikeminnow is a native resident fish species. They are major predators of juvenile sockeye salmon in Cultus Lake. There are now fewer sockeye in Cultus Lake than pikeminnow and this creates a significant threat to salmon survival.

A tagging program begun in 2004 found an estimated population of 60,000 to 70,000 adult pikeminnow in Cultus Lake. Greater knowledge of pikeminnow locations and movements at all times of the year, using acoustic tags and underwater receivers, is helping to assess their impact on sockeye and assist in their removal when necessary. Research to date suggests that pikeminnow predation on juvenile sockeye is likely highest in the fall and winter months.

The Sweltzer Creek Corridor
The sockeye have survived deep sea fisheries. They’ve made it up the Fraser River. They are almost home to Cultus Lake, but there is one more gauntlet to run: Sweltzer Creek.

Sweltzer Creek is short and relatively shallow with little channel complexity or large woody debris. Water temperatures can exceed 25C in August and September, although cut-off seepage channels from the Chilliwack River and groundwater infiltrating pools may provide cooler refuge areas. Prolonged exposure to high temperatures can be lethal to sockeye. Any delays while swimming up Sweltzer Creek may decrease spawning success or increase mortality.

For the population to have a chance at recovery, these areas need to be minimally obstructed or disturbed so that the fish pass through the three kilometres as quickly as possible. Activities that may threaten the population are those that would delay fish in the creek, including recreation in and near the creek and at the lake and creek outlets. Some activities of concern are angling near the mouth, swimming at a campsite in the middle reaches, swimming in the upper reaches and around the lake outlet, boating and the operation of a low level weir (to control lake levels) at the lake outlet. The population is more vulnerable here than at any other point on the migratory corridor (with the possible exception of net fisheries) so it is very important to minimize disturbance.

Another major threat is the colonization of Eurasian Milfoil.

COSEWIC Assessment: Endangered (2003)
Reason for designation:
The Cultus population has unique genetic and biological characteristics (migratory delay of adults at the Fraser estuary, protracted lake residency before spawning, exclusive lake spawning, late spawning date, deepwater life of fry). The lack of success with previous attempts to transplant sockeye to Cultus Lake and other lakes suggests that Cultus sockeye are irreplaceable. The Cultus population has collapsed primarily due to overexploitation, including directed and incidental catches in mixed-stock fisheries at levels above those that can be sustained. An additional key source of impact on spawning adults since 1995 has been very high pre-spawn mortality, associated with unusually early migration into freshwater and with Parvicapsula parasite infestation. There are also ecological impacts to the lake habitat from colonization by Eurasian Watermilfoil, land development, stream channelization, nutrient input, and recreational use. Under present conditions, there is a high probability of extinction of the Cultus sockeye.
Species At Risk Act (SARA) : Public Registry website