COSEWIC Assessment and Status Report : Misty Lake sticklebacks ,Gasterosteus sp.

Posted July 28, 2006 | Categories : 140,Research |


The Misty Lake sticklebacks, a highly divergent parapatric lake-stream pair of threespine stickleback, are found in a single small lake on Vancouver Island, British Columbia (BC). Similar parapatric lake-stream pairs have also been well documented in two other systems in BC, Mayer and Drizzle lakes on Graham Island (Queen Charlotte Islands). These pairs live in contact (parapatry) without a significant amount of overlap or interbreeding. Differences in body shape are believed to be adaptations to the different feeding strategies used by each member of the species pair. Genetic evidence suggests that each of the three highly divergent lake-stream pairs has evolved separately through parallel evolution. Of the lake-stream pairs examined to date, the Misty Lake inlet stream and lake populations appear to be the most genetically and ecologically differentiated from one another. The Misty Lake outlet stream population is intermediate in morphology between the inlet and lake populations and is considered part of the lake-stream complex.


The lake-stream pair of three-spine stickleback occurs only in Misty Lake and its inlet and outlet tributary system, on northeastern Vancouver Island, BC.
Misty Lake, its outlet and inlet are darkly stained and small in size. Sticklebacks in Misty Lake feed in the limnetic zone and spawn in the littoral zone, while those in the outlet are found in slower, deeper water. The inlet stream form remains in either the inlet swamp or the inlet stream, where it is commonly found in deeper, low water velocity areas such as pools and sloughs. Most breeding activity occurs in the stream, with very little in the swamp. Distribution within the inlet system has not been mapped, but appears to be stable.
The lake is considered a natural ecosystem and appears to be stable. The inlet watershed has been logged, but impacts from forest harvesting activities are minor. Misty Lake and short sections of the lower portion of the inlet and the upper section of the outlet are contained within the Misty Lake Ecological Reserve, a part of the provincial protected areas system. However, the majority of the lake’’s watershed lies outside the reserve boundaries.
Although there is ongoing research into the evolutionary biology of the Misty Lake sticklebacks, no detailed studies have been completed on the specific biology of the these fish. In the absence of specific information, it is assumed that they are similar in many aspects to similar forms of the threespine stickleback.
Both forms begin reproductive activity in April and are finished in July (gravid females are common during May and June). There is some information to indicate that the inlet sticklebacks live shorter lives and produce a higher number of eggs at each spawning than lake or outlet fish. Generally, the male stickleback provides parental care. He protects and fans the nest and continues to care for the young fish until they are capable of moving into cover to feed. Eggs take about 7 –– 10 days to hatch, depending on water temperature.
Mouth and gillraker morphology suggest that the lake population feeds on zooplankton in the open water of the lake and the stream populations feed on macroinvertebrates.
Studies have shown that the lake sticklebacks will move only in a downstream direction, while those in the inlet sticklebacks will move either upstream or downstream.
Population sizes and trends
Based on overall habitat stability, population trends are also likely stable, although in dry years decreasing water levels may lead to population declines.
Limiting factors and threats
BC Parks has identified potential threats to the stickleback populations within the Misty Lake Ecological Reserve. These include: hydrocarbon and pesticide contamination from the adjacent highway and rest stop; water quality and hydrological changes from nearby logging; non-native species introductions (fish and plants); and non-conforming recreational uses of the lake (canoeing and illegal fishing). The introduction of non-native species has been detrimental to the stickleback pairs in Enos Lake (also on Vancouver Island) and Hadley Lake (on Lasqueti Island, near Vancouver Island).
Special significance of the species
The parapatric stickleback pair found in the Misty Lake system is one of three well- studied lake-stream pairs that display ecotype differences similar to the level seen in the benthic-limnetic stickleback pairs. These highly divergent parapatric pairs are invaluable to the study of evolutionary processes. Genetic data strongly suggest that each highly divergent lake-stream pair has evolved separately through parallel evolution as neither the Misty inlet stream form nor its lake form showed the same genetic ancestry as the pairs from the Drizzle or Mayer lake systems on Graham Island.
Existing protection
The lake is located within the boundaries of the Misty Lake Ecological Reserve, which was established for the protection of the larger lake stickleback. Most of the habitat for the stream form is located upstream of the reserve; this area and much of the Misty Lake watershed is not included in the reserve, making it difficult to ensure the long-term protection of habitat for the whole lake-stream complex.