Misty Lake sticklebacks COSEWIC asessment and status report: chapter 8

Limiting Factors and Threats

In general, continued reproductive isolation between divergent forms of stickleback requires the maintenance of the specific selective regime that drives the divergence.  Changes to the selective regime can break down reproductive barriers and bring about hybridization (as seen in the benthic-limnetic pair found in Enos Lake, Vancouver Island). Populations can also be lost due to species introductions (as in Hadley Lake, Lasqueti Island, near Vancouver Island). Hybridization in lake-stream pairs may not be as great a concern as most of the inlet fish are believed to breed in the inlet, separate from the nesting sites of the lake fish (McPhail 1994).

The management issues identified in the Misty Lake Ecological Reserve Purpose Statement (BC Parks 2003) include: potential impacts of hydrocarbon and pesticide contamination from the adjacent highway and rest stop; water quality and hydrological changes due to nearby logging; non-native species introductions (fish and plants); and non-conforming recreational uses of the lake (canoeing and illegal fishing, which may increase the potential for detrimental impacts such as alterations to the aquatic community). Should crayfish be released to the lake, this could be detrimental to the lake population as reported for Enos Lake, which is also on Vancouver Island (COSEWIC 2002). Moodie (1984) identified increased beaver (Castor canadensis) activity as a threat to the giant black sticklebacks in Mayer Lake, Queen Charlotte Islands, resulting in potential lake level changes. The author indicated that fluctuating water levels could influence the availability of nesting sites. In the case of the Misty Lake inlet stream population, beaver dams constructed in the inlet could temporarily impede fish movements. However, beaver are native to Vancouver Island and do not appear to be a serious threat in this area.

Moore (pers. comm. 2005, 2006) noted an increase in algal growth in the inlet subsequent to the opening of the stream canopy with forest harvesting. This thick filamentous algae occurs in shallow sites with good light penetration and may have an effect on habitat use. Any effect will likely be temporary, and the density of algae will decrease as the riparian vegetation returns. Cumulative logging impacts may be a concern, particularly to inlet habitat from erosion, sedimentation, altered flows and changes to the benthic community; however, there have been no apparent long-term impacts to date as a result of previous forest harvesting activity in the watershed.  On small streams, green-up occurs quite quickly. Shrubs (like blackberry, salmonberry, red huckleberry, etc.) and alder grow in and provide shade relatively fast on the coast.  Logging plans for 2006 indicated the block was to be some metres removed from the stream so that should leave some shade cover as well. Sticklebacks are mostly found in deeper water not in the shallow sites discussed, although they may use those areas at times (some feeding forays perhaps). It is unlikely that they rely on these areas too heavily as they would likely be exposed to heavier predation. In summary, this watershed has been exposed to logging activities previously with no apparent lasting impacts to the stickleback populations to date; however, future logging is still a concern depending on the extent and proximity of these activities relative to the stickleback habitat.

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