8840209 Appendix A 1

RAINBOW (Oncorhynchus mykiss)

Ecology and Life History The is a member of the family and the life history of this species is extremely variable and depends on a variety of factors (Scott and Crosman, 1973; Roberge et al, 2002). The native fishes’ range occurs along the western coast of , from to Alaska. The rainbow trout is a native fish of Okanagan Lake, although some stocking of the lake with multiple different strains did occur up until 19601. However, in the fish has been introduced into many lakes for sport fishing and now occurs throughout most of the country (Scott and Crossman, 1973). The rainbow trout has also been introduced throughout the world, and at times is considered to be an invasive species. The rainbow trout has a variable diet and will forage throughout the water column on a variety of items (Coker et al, 2002), depending upon the strain of the fish. In general, the fish’s diet changes with the seasons, and generally the species forages near the bottom or near structure (Scott and Crossman, 1973). Rainbow trout of large lake systems (e.g., Okanagan) are typically larger, and smaller fish tend to form a large component of an adults diet. In smaller lake systems, rainbow’s are primarily insectivorous, foraging on Dipetera (e.g., chironomids), Ephemoptera (mayflies), Plecoptera (stoneflies), Crustacea (e.g., amphipods such as Gammerus sp.) etc. (Scott and Crossman, 1973; Coker et al, 2001; Roberge et al, 2002). Rainbow trout are stream spawning, typically using smaller tributary streams of rivers or inlet or outlet streams of lakes (Scott and Crossman, 1973; Roberge et al., 2002). The age at maturity varies between systems and life histories but fish typically mature between 3 to 5 years and males usually slightly faster than females (Scott and Crossman, 1973). This fish species spawns over fine gravel substrates in streams, typically in riffle/pool areas (both above and below pools) that have vegetated banks for cover (Roberge et al, 2002; Scott and Crossman, 1973). Eggs are deposited over substrates in a prepared nest that is excavated by the female (Scott and Crossman, 1973; Roberge et al, 2001). Males will court females during the digging process and are very aggressive on the spawning grounds (Scott and Crossman, 1973). Spawning typically occurs in the early spring, when water temperatures are 10 to 15 ºC (Scott and Crossman, 1973; Roberge et al, 2002). In BC, spawning typically occurs between March and June (Roberge et al, 2002) and EBA has previously documented spawning around May 20th in low elevation mountain lakes in the region. Okanagan Lake System In the Okanagan Lake system the relative abundance of young of the year (YOY) rainbow trout was 1.4% of the total population sampled using beach seine techniques during the spring season. During spring sampling using beach seines, abundance of YOY was greatest in close proximity to stream mouths that were used for spawning (e.g., Mission Creek, Bertram Creek, Bellevue Creek, etc.). For instance, in the Mission Creek mouth area, rainbow trout YOY made up 9.8% of the beach seine community, highlighting the importance of this area to YOY. YOY fish in the Mission Creek mouth were strongly associated with loose, large woody debris along the shoreline.

1 Taken from: http://srmapps.gov.bc.ca/apps/fidq/stockedSpeciesSelect.do

Species summary - Rainbow Trout.doc 8840209 Appendix A 2

The relative abundance of juvenile and adult rainbow trout was 3.8, 1.0 and 0.85% (using gill nets) during the spring, summer, and fall, respectively. Adult rainbow trout were found at almost every site during spring sampling, except those with extremely large, sandy littoral shelves. Numbers of trout tended to be greatest along cliff/bluff, gravel beach, and low rocky shorelines, with moderate usage of marina and vegetated shoreline areas, and little if any use of sandy beaches. Juveniles (most likely Year 1 to 3) were only sampled along a gravel beach habitat that was in relatively close proximity to Bellevue Creek. The rainbow trout has long been affected by development in Okanagan Lake, and as early as 1939 spawning habitat was a limiting factor due to removal of water for irrigation purposes (Clemens, 1939). In our study, spawning areas were identified in Bertram Creek and Bellevue Creek based upon the presence of YOY and Year 1 trout. Presence of trout in Bellevue Creek was expected, but it was surprising to find YOY trout in Bertram since flows are unreliable and the stream has been previously documented to contain poor trout spawning habitat (Whightman and Taylor, 1978). Fish in this stream were sampled just below the culvert of Lakeshore Road using an electroshocker. Some reaches of this stream provide excellent cover for rearing rainbows, and there are some areas that could benefit from habitat restoration to improve spawning habitat. Also, several YOY fish were sampled in the mouth of Mission Creek. This area may be an important rearing area for juvenile rainbows, since it has been documented that 38% of the fish emigrate from the stream as YOY and 62% emigrate as yearlings (MoE, 1980). However, survival of fish that emigrated to Okanagan Lake less than 75 mm may only be 5%, indicating that in-lake rearing is not very successful (MoE, 1980). A cursory investigation of stomach contents and presence of gastrointestinal parasites was performed2 for rainbow trout during the spring and summer sampling events. Stomach contents of rainbows consisted of small insect larvae, terrestrial insects, and YOY sculpins and shiners. However, in many cases individuals had empty stomachs. Intestinal parasites were found in 40% of the individuals sampled during spring. The parasite assemblage consisted mostly of cestodes (i.e., tapeworms), but some liver cysts were also found in one individual. The relatively high prevalence of infection may be the result of the piscivorous nature of adult fish that results in them acting as paratenic3 or transport hosts, which is common in fish. Further investigation is required to characterise the parasite assemblage of rainbow trout in Okanagan Lake. The rainbow trout, next to Kokanee, is probably the most sought after sportfish in Okanagan Lake. The spawning and rearing habitat of this species is limited (MoE, 1980) and during the 1975 to 79 adult recruitment to spawning areas averaged 434 fish in Mission Creek (MoE, 1980). However, despite the appearance of limiting factors, Catch Per Unit Effort monitoring on Okanagan Lake indicates that the rainbow fishery has improved since 1996 (Webster, 2005). The rainbow trout is considered to be a species of importance within the system because of the small number of fish sampled, its value as a sports fish, and the habitat limiting factors. Highly important in lake habitats are stream mouth areas of spawning streams because a significant number of juvenile and YOY fish were sampled in these areas. Other habitats appear to be used relatively uniformly, and these areas appear to be used more for general living and foraging. Maintenance of riparian vegetation, and other factors will help

2 Individuals selected for dissection had not survived gill net sampling. No individuals were euthanized for this analysis. 3 A paratenic host is a parasite host that is not typically part of the life cycle, but may act as a carrier. Fish are often the final hosts in many parasite life cycles and piscivorous fish are often infected if they eat an infected fish, even though they are not the typical or target host for the species.

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improve trout habitat because these areas provide insect drop into the lake and terrestrial insects appear to be an important component of the fishes diet (Clemens, 1939). References Clemens, W.A. 1939. A biological survey of Okanagan Lake, BC: The fishes of Okanagan Lake and Nearby Waters. Bulletin of Fisheries Research Board of . LVI. Coker, G.A., C.B. Portt, and C.K. Minns. 2001. Morphological and Ecological Characteristics of Canadian Freshwater Fish. Fisheries and Oceans Canada. Laboratory for Fisheries and Aquatic Sciences. Canadian Manuscript Report of Fisheries and Aquatic Sciences #2554. January 2001. Ministry of Environment, 1980. Fisheries Management Plan for Okanagan Main Valley Lakes. Fisheries Staff. Okanagan Region. 1980. Roberge, M., J.M.B. Hume, C.K. Minns, and T. Slaney. 2002. Life history characteristics of freshwater fishes occurring in British Columbia and the Yukon, with major emphasis on stream habitat characteristics. Fisheries and Oceans Canada. Marina Environmental and Habitat Science Division. Canadian Manuscript Report of Fisheries and Aquatic Sciences 2611. Scott, W.B., and E.J. Crossman. 1973. Freshwater fishes of Canada. Department of Fisheries and Oceans. Fisheries Research Board of Canada. Bulletin 173. Webster, J. 2005. Okanagan Lake Rainbow Test Fishery – 2004/2005. Chara Consulting. Vernon, British Columbia. Whightman, J.C. And G.D. Taylor. 1978. Overview And Rating Of Production Capabilities And Enhancement Opportunities For Rainbow Trout And Kokanee In Tributaries To Upper Okanagan Lake Basins. Fish Habitat Improvement Section. Fish And Wildlife Branch. British Columbia. February 1978.

Species summary - Rainbow Trout.doc