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Proposed Recovery Strategy for Vancouver Lamprey
2. Description of Needs of the Species
2.1 Biological Needs, Ecological Role and Limiting Factors
Ecological Role.-- After metamorphosis, Vancouver lamprey are external parasites of other fish species, and as such play a role in limiting abundance of those species. They feed primarily on coho salmon (Oncorhynchus kisutch) and coastal cutthroat trout (O. clarki clarki), although other salmonids such as Dolly Varden char (Salvelinus malma) are also preyed upon (Beamish 1998). Lamprey are also preyed upon by fishes and other wildlife and thereby form part of the food base of those species. Ammocoetes are most vulnerable to predation immediately after emerging from their burrows (Close et al. 2002). Both live and spawned out adults of Pacific lamprey are a significant component of some fish and wildlife diets (Close et al. 2002), though the extent of predation on Vancouver lamprey is not known.
Limiting Factors.-- The environmental factors that limit Vancouver lamprey have not been well-studied. We assume that populations are affected by competition, predation, habitat quantity and quality, and food availability, though the relative effect of each is not known. It is evident that to persist over the long term, all species require sufficient rearing and spawning habitat and a healthy food base.
2.2 Habitat Needs
Vancouver lamprey have been reported only in Cowichan and Mesachie lakes on Vancouver Island. Cowichan Lake is 30 km long, 6204.3 ha in area, 152 m maximum depth, 50.1 m average depth, and has an elevation of 164 m (Province of BC 2005). It is the second largest lake on Vancouver Island, and drains eastward into the Cowichan River. Mesachie Lake is considerably smaller: 59.3 ha in area, 32 m maximum depth, and with an elevation of 167 m (Province of BC 2005). It is entirely within the Cowichan Lake watershed and drains into the southwestern corner of Cowichan Lake. Both lakes are oligotrophic, a nutrient status typical of coastal lakes in the area. The Cowichan Valley experiences a variable climate that is generally warm and dry in summer and mild and wet in winter.
A variety of other fish species have been reported from the lakes, including chinook (O. tschawytscha; Cowichan Lake only), coho salmon, cutthroat trout, Dolly Varden, kokanee (O. nerka), prickly sculpin (Cottus asper), rainbow and steelhead trout (O. mykiss), threespine stickleback (Gasterosteus aculeatus), plus three non-native species – Atlantic salmon (Salmo salar; likely not self-sustaining), brook trout (Salvelinus fontinalis) and smallmouth bass (Micropterus dolomieui; Cowichan Lake only) (Province of BC 2005).
The spawning habitat requirements of Vancouver lamprey are not known in detail. Beamish (1985, 1998) indicated that they use nearshore lake habitat for spawning, rather than the stream habitats typically used by Pacific lamprey. However, ammocoetes have been found in the lower portions of some lake tributaries (Beamish 1982), indicating that some spawning does occur in these tributaries. Beamish (1998) describes spawning aggregations on shallow gravel deltas near the mouth of tributary creeks, in water depths of 0.2 to 2 m. Spawning behaviour in the lab is similar to that of Pacific lamprey (Beamish 1998), which construct nests in areas of gravel, where eggs are deposited and fertilized, and subsequently rear. Hatching generally occurs a short time after fertilization. Other lamprey species require clean gravels with interstitial flow or groundwater upwelling for spawning and incubation. We assume that Vancouver lamprey have similar requirements. Distribution into deeper habitats has not been investigated.
After hatching, ammocoetes drift a short distance from the nest, where they burrow into soft fine sediments or sand (Scott and Crossman 1973). Vancouver lamprey ammocoetes are usually found within the lake in close proximity to tributary creeks (Beamish 1998). Larval habitat is thus generally defined as fine sediment areas in close proximity to lake tributaries, but the depth and spatial distribution of larval habitat remains poorly understood.
Little is known about Vancouver lamprey biology between the time of metamorphosis and spawning. Active feeding occurs in the warmer months, and considerable growth occurs from metamorphosis to time at spawning (Beamish 1982). We assume that during this time, the lamprey seek prey in a variety of locations within the water column. The habitat requirements of this life stage are not known.
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