Misty Lake sticklebacks COSEWIC asessment and status report: chapter 5

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Habitat

Habitat requirements

Misty Lake is located at an elevation of around 74 m. It is considered a natural ecosystem and appears to be stable at this time. The lake is small (35.6 ha in surface area) and relatively shallow (mean depth = 1.7 m; maximum = 6.1 m). Loose detritus covers both the lakeshore and bottom; dense beds of Potamogeton and Nuphar cover the littoral zone during the summer. Misty Lake is oligotrophic and relatively low in productivity; this is typical for small lakes on Vancouver Island. The outlet stream is located at the northwestern end of the lake and filters through a swamp before it develops and flows downstream to join the Keogh River. The water in the system is darkly stained with tannin lignins. Aside from Gasterosteus, native fish species in the watershed include Dolly Varden (Salvelinus malma), coastal cutthroat trout (Oncorhynchus clarki), coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss) and prickly sculpin (Cottus asper).

The headwaters of the system are at approximately 260 m in elevation. The total watershed area is about 12.2 km². The inlet crosses Highway 19 (the Island Highway), through a culvert about 900 m above the lake. At high water the culvert is passable to fish but at low water the downstream end of the culvert sits about 0.3 m above the water surface. The stream flows through 500 m of swamp before reaching the southeast corner of the lake. Irvine and Johnston (1992) provide some physical characteristics for the mainstem inlet and outlet streams: the inlet has a mean wetted width of 2 m, length of 5.3 km, mean gradient equals 1.5%, and the water temperature ranges from 1 to 19ºC; the outlet has a mean wetted width of 3 m, a length of 2.3 km, mean gradient of 1.0%, and water temperature ranges from 2 to15ºC.

The lake form feeds in the limnetic zone. Nesting sites are likely concentrated in shallow areas characterized by sand substrate, a gentle gradient and underwater vegetation as described for the Mayer Lake stickleback (Moodie 1984). McPhail (1994) noted that most of the breeding activity seemed to occur in either the lake or the stream in the Misty Lake system, although some gravid females of both the lake and inlet forms were collected in the inlet swamp (a transition zone). Deeply stained water makes detection of nest location difficult in both the lake and the streams.

The inlet form remains in the inlet swamp or inlet stream where it is commonly found in low water velocity areas of about 0.5 – 1.0 m in depth (Hendry et al. 2002) such as pools and sloughs. Moore (pers. comm. 2005, 2006) and Hendry (pers. comm. 2005, 2006) have observed that the number of inlet sticklebacks decreases with an increase in distance upstream from the lake (similarly numbers decrease in the outlet with distance downstream from the lake). McPhail (1994) reported that no nests had been observed in the stream and could not describe nesting habitat. Stream residents in the Little Campbell River, in the BC lower mainland, have been found to utilize stream habitats with fine substrate (mud), no current and heavy vegetation for nesting (McPhail 1994). Although the sticklebacks are less likely to use fast riffle habitats, these areas are required for benthic invertebrate production. A complex of natural stream habitat would be required to maintain the population.

Habitat trends

Misty Lake and its inlet were described in Lavin and McPhail (1993); the habitat is not believed to have changed significantly since that time. The inlet stream is small (watershed area is less than 9 km²). Much of the inlet watershed has been logged. Although forest harvesting impacts in this watershed have been relatively minor to date (R. Ptolemy, pers. comm. 2005), the recent loss of canopy cover has triggered an increase in algal growth resulting in some temporary loss of stickleback habitat (Moore, pers. comm. 2005, 2006). Since algal production is likely related to an increase in water temperature and sunlight, regeneration of streamside vegetation should restore the stream to pre-logging conditions within a short period. Logging is planned for at least two blocks in the watershed in 2006, including blocks outside of the protected area around the lake and alongside the inlet stream (although some metres removed from the channel); harvesting activities could lead to changes in channel morphology, water quality, and/or indirectly affect benthic prey availability in the stream (T. Michalski, pers. comm. 2006).

Habitat protection/ownership

Misty Lake and short sections of the lower portion of the inlet (less than 50 m) and the upper section of the outlet (both mostly swampy segments) are contained within the Misty Lake Ecological Reserve (Figure 5). The reserve was established under the Protected Areas of British Columbia Act in 1996 as a result of recommendations in the Vancouver Island Land Use Plan. Ecological reserves are areas in British Columbia selected to preserve representative and special natural ecosystems, plant and animal species (including distinct genotypes), features and phenomena. Consumptive uses such as hunting, fishing, camping and livestock grazing, or removal of materials, plants or animals are prohibited. The Misty Lake Ecological Reserve was primarily established to protect the lake form of Gasterosteus, which was red-listed by the BC Conservation Data Centre at the time the reserve was established. The secondary role of the reserve is to provide opportunities for biological research. The long-term effectiveness of the reserve may be compromised as the vast majority of the inlet tributary and the lake’s watershed remain outside of the current boundaries of the reserve.