Response of Fish Populations to Weir Construction in Arden Creek

Transcription

1 Response of Fish Populations to Weir Construction in Arden Creek Tracy A. Michalski Fisheries Section British Columbia Ministry of Environment, Lands and Parks 2080 Labieux Road, Nanaimo, BC, V9T 6J9, Canada George E. Reid Fisheries Section British Columbia Ministry of Environment, Lands and Parks 2080 Labieux Road, Nanaimo, BC, V9T 6J9, Canada ABSTRACT In 1996, the Courtney Fish and Game Protective Association constructed 2 wooden weirs and 1 rock weir in a channelized portion of Arden Creek, Vancouver Island, B.C. The Association added an additional wooden weir in Volunteers from the Association, students from Puntledge Park and Lake Trail schools, and Urban Salmon Habitat Program staff conducted fish assessments at weir (treated) and control (untreated) sites in 1996 and We found more fish at treated sites in both years. In 1996, 66% of the fish sampled were associated with weirs, and in 1997, 80%. The density of fish at treated sites was 0.67 fish/m 2, compared to 0.35 fish/m 2 at control sites in 1996, and 0.29 fish/m 2 at treated sites compared to 0.07 fish/m 2 at control sites in We estimated the biomass to be 3.32 g/m 2 at treated sites and 2.4 g/m 2 at control sites in In 1997, we estimated the biomass at 3.87 g/m 2 at treated sites and 0.35g/m 2 at control sites. When we compared the population and biomass statistics between weir types, we found that wooden weirs produced greater absolute numbers, higher densities, and higher biomass. The mean length of sampled coho increased significantly between 1996 and 1997, due mainly to density dependent factors. We make a number of recommendations for future work on Arden Creek. Key words: coho, cutthroat, Oncorhynchus clarki, Oncorhynchus kisutch, habitat restoration, weirs. Arden Creek is a small, urban creek located in the municipality of Courtenay on Vancouver Island, B.C. (Fig. 1). The creek has undergone extensive channelization, resulting in a loss of habitat complexity. Approximately 1 km in length, Arden Creek flows unaltered for approximately 200 m through a protected, wooded wetland before entering School District 71 property. The remaining 800-m section of the creek has been straightened and follows the boundary along Puntledge Park Elementary School. The creek supports both coho (Oncorhynchus kisutch) and cutthroat trout (O. clarki). It has historically suffered from low summer flow (Law 1994). Raven River Habitat Services conducted a survey of habitat enhancement opportunities in the Comox Valley in 1992 and recommended augmenting the flow and increasing the habitat complexity in Arden Creek (Baldwin 1992). The federal Department of Fisheries and Oceans (DFO) and the British Columbia Ministry of Environment, Lands and Parks (MELP) cooperated to address these recommendations in 1993 and constructed a flow diversion structure to channel 0.03 m 3 /sec of water from Morrison Creek into Arden Creek. Complexes of large woody debris (LWD) were cabled into several locations upstream of the channelized portion of the creek. In 1996, The Courtenay Fish and Game Protective Association applied for funding from the Urban Salmon Habitat Program (USHP) to enhance the complexity of Arden Creek habitat where it flows through School District 71 property. The Association successfully obtained this funding, and in 1996 and 1997 constructed 3 wooden weirs and 1 rock weir in the channellized area of the creek. The objective of the project was to create additional habitat for rearing fish. Weirs encourage downstream scour and create dammed pools upstream (Murphy 1995, Koning and Keeley 1997). Constructing these structures would restore the pool habitat critical to the survival of both coho salmon and cutthroat trout. Volunteers from the Courtenay Fish and Game Protective Association, students from Puntledge Park and Lake Trail schools, and USHP staff conducted fish assessments at weir and untreated (control) sites in 1996 and Our objective was to monitor changes to fish populations as a result of the installation of the weirs. In this paper we present the results of these assessments and make suggestions for future work on Arden Creek. L. M. Darling, editor Proceedings of a Conference on the Biology and Management of Species and Habitats at Risk, Kamloops, B.C., Feb.,1999. Volume Two. B.C. Ministry of Environment, Lands and Parks, Victoria, B.C. and University College of the Cariboo, Kamloops, B.C. 520pp. 873

2 MICHALSKI AND REID Figure 1. Location of Arden Creek, Courtenay, Vancouver Island, B.C. 874 Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., Feb

3 Fish Populations and Weir Construction METHODS In October of 1996 and 1997 we sampled fish at the weirs and control sites of Arden Creek, with the assistance of the Courtenay Fish and Game Protective Association and students from Puntledge Park and Lake Trail schools. We used the Two-Pass method to sample the fish (Resource Inventory Committee 1993). We netted off areas above and below the sample sites to prevent fish migration and removed fish using an electroshocker. Once we had sampled the fish, they were anaesthetized, enumerated, identified to species, weighed, and measured. All fish were then returned to their capture location. We analyzed the data by comparing the total abundance, density (fish/m 2 ), and biomass (g/m 2 ) of sampled fish. We also examined species length frequencies by categorizing fish lengths into 10-mm classes and comparing frequencies by year and site. RESULTS COHO AND CUTTHROAT ABUNDANCE AND POPULATION DENSITY The number of fish sampled in Arden Creek in 1996 and 1997 totalled 130, of which 85% were coho (Table 1). We sampled 85 coho in 1996 and 25 in The difference between the 2 years was significant (P = 0.03). Cutthroat abundance displayed a similar pattern, but their numbers were proportionately reduced. We sampled 17 cutthroat in 1996 and 3 in We found more fish at treated sites than at control sites in both 1996 and 1997 (Table 1). In 1996, 67 fish were taken at the treated sites, compared with 35 at the control sites. Of the 67 fish sampled, 55 were coho and 12 were cutthroat, compared to 30 coho and 5 cutthroat from the control sites that year. We only sampled 28 salmonids in Twentyfive of these were coho, 80% of which were found at treated sites. Only 3 cutthroat were sampled in 1997; 2 were at treated sites. We compared population densities at each site by relating the number of fish sampled to the area sampled (Table 2) and found a significant decrease in the density of coho Table 1. Coho salmon and cutthroat trout abundance sampled at treated and control sites in Arden Creek in 1996 and Total Treated Control Treated Control Area sampled (m 2 ) n/a Coho Cutthroat Total between the two years (P = 0.07). We then examined the difference in density between treated and control sites for both years. In 1996, the population density at treated sites was 0.67 fish/m 2, 65% higher than the 0.35 fish/m 2 sampled at the control sites. In 1997, we sampled 0.29 fish/m 2 at the treated sites compared with 0.07 fish/m 2 at the control sites. Treated sites produced higher densities for individual species in both 1996 and The density estimates for coho between 1996 and 1997 at the treated sites were 0.55 and 0.12 fish/m 2 respectively, compared to 0.3 and 0.06 fish/m 2 at the control sites. The pattern for cutthroat was similar. COHO AND CUTTHROAT BIOMASS We did not find any difference in the total amount of biomass produced between 1996 and In 1996, treated sites produced 3.32 g/m 2, control sites 2.4 g/m 2 (Table 2). In 1997, the biomass at treated sites was 3.87 g/m 2, 91% higher than the 0.35 g/m 2 sampled at control sites. Coho biomass declined significantly between the 2 years, while cutthroat biomass increased significantly in that same period, accounting for the small total difference between years (P 0.001). When we combined biomass for both species for both years, treated sites produced 7.25 g/m 2, and controls site 2.75 g/m 2. The total biomass of coho captured at treated sites in 1996 was 2.86 g/m 2, significantly higher than that at control sites (P = 0.004). The biomass of cutthroat was 63% higher at the treated sites in In 1997, cutthroat biomass was higher at treated sites; however, we only captured 3 fish, 1 of which was a 2+ fish (parr) which accounted for most of the total biomass. Table 2. Coho salmon and cutthroat trout densities (fish/m 2 ) and biomass (g/m 2 ) at treated and control sites in Arden Creek in 1996 and Treated (n = 67) Control (n = 35) Treated (n = 22) Control (n = 6) Density Biomass Density Biomass Density Biomass Density Biomass Coho Cutthroat Total Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., Feb

4 MICHALSKI AND REID COHO AND CUTTHROAT LENGTHS The mean length of coho increased significantly between years, from 59.8 mm in 1996 to mm in 1997 (P < 0.001; Fig. 2). In 1996, coho ranged between 44 and 90 mm, with a modal length of mm. In 1997, the length of coho ranged between 55 and 90 mm and the modal length had increased to mm. The cutthroat sampled in 1996 ranged between 40 and 87 mm. The modal length of these fish was mm. This compares to 1997, when the length ranged from 72 to 168 mm. The 1996 samples were made up entirely of 0+ fish (fry), while in 1997, the 3 fish sampled represented 3 different age classes. We found larger coho at control sites in both 1996 and 1997 (Fig. 3). In 1996, the mean length of coho at control sites was 62.9 mm; this was almost 5 mm larger than the coho sampled at treated sites. The mean length of coho sampled at control sites in 1997 was 75.4 mm compared to 70.5 mm at treated sites. In 1996, the cutthroat sampled at control sites averaged 61 mm, while the average length at treated sites was 55.5 mm (Fig. 4). We did not compare lengths in FISH ABUNDANCE, DENSITY, BIOMASS, AND LENGTH AT WOODEN VS. ROCK WEIRS We sampled 67 salmonids at the 2 treated sites in 1996 (Table 3). Of these, 55 were coho, 69% of which were sampled at the wooden weir, and 12 were cutthroat, 83% of which were captured at the wooden weir. Density estimates were also consistently higher at the wooden weir in 1996 (Table 3). The total density sampled at both rock and wooden weirs was 1.58 fish/m 2. Of that, 1.23 fish/m 2 were captured at the wooden weir and 0.35 fish/m 2 at the rock weir. Coho density at the wooden weir was 0.87 fish/m 2, more than twice the estimated 0.35 fish/m 2 found at the rock weir. Cutthroat density at the wooden weir was almost 10 times the 0.04 fish/m 2 sampled at the rock weir. Biomass estimates were also higher at the wooden weir in 1996 (Table 3). The total biomass for all fish was 2.2 g/m 2 at the wooden weir and 1.1 g/m 2 at the rock weir. Wooden weirs produced an estimated 1.9 g/m 2 of coho, compared to 0.96 g/m 2 for the rock weir. The cutthroat biomass of 0.37 g/m 2 at the wooden weir was more than 2 times that at the rock weir. N = 85 N = 25 Average Length (mm) mm 62.9 mm mm 75.4 mm Treated Sites Control Sites Figure 3. Average lengths of coho sampled at treated and control sites in Arden Creek in 1996 and Figure 2. Comparison of length classes of coho salmon sampled in Arden Creek in 1996 and Figure 4. Average lengths of cutthroat sampled at treated and control sites in Arden Creek in Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., Feb

5 Fish Populations and Weir Construction Table 3. Comparison of total abundance, population, and biomass estimates at wooden and rock weir sites in 1996 and Wooden weir Rock weir Wooden weirs Rock weir (n = 1) (n = 1) (n = 3) (n = 1) Sample area (m 2 ) Coho No. sampled Population estimate (fish/m 2 ) a 0.26 Biomass (g/m 2 ) a 0.38 Cutthroat No. sampled Population estimate (fish/m 2 ) a 0 Biomass (g/m 2 ) a 0 All fish No. sampled Population estimate (fish/m 2 ) a 0.26 Biomass (g/m 2 ) a 0.38 a Indicates average for all sites sampled. We continued to find a greater absolute abundance at the wooden weirs in 1997 despite the fact that we found higher densities at the rock weir. We sampled 11 fish at the wooden weirs that year, compared to 9 at the rock weir. In contrast, the density of fish at the rock weir was 0.26 fish/m 2, compared to 0.16 fish/m 2 at the wooden weirs (Table 3). However, the biomass estimate for all salmonids at the wooden weirs was 1.1 g/m 2, significantly higher than the 0.38 g/m 2 estimated for the rock weir (P = 0.016). The average length of coho sampled at the rock weir in 1996 was mm, compared to 56.2 mm at the wooden weir. This difference was significant between the 2 weir types (P = 0.025). The pattern was the same for cutthroat that year, with larger fish being sampled at the rock weir. In 1997, the pattern was reversed for coho, with larger fish sampled at the wooden weir. No length comparison was done for cutthroat sampled in DISCUSSION COHO AND CUTTHROAT ABUNDANCE, POPULATION DENSITY, AND BIOMASS We found a decrease in abundance, population density, and biomass of coho, and a decrease in abundance and density of cutthroat trout in Arden Creek between 1996 and Decreases in fish population size and biomass between years are caused by changes in escapements, rearing densities, temperature, food supply, and/or changes in the amount of available habitat. Escapements of coho into the Puntledge River system in 1996 were below average, but strong enough to seed the available habitat (B. Allen, DFO, June 1998, pers. comm.), therefore, we do not attribute the decreases we saw to a decrease in escapement. The average temperatures were higher between April and October in 1997 (Environment Canada, 1998, unpubl. data from Courtenay/Meadowbrook AES weather station), but higher temperatures would have a positive effect on the population size and biomass. We do not believe that food supply was limited. The mean lengths of the coho we sampled in both 1996 and 1997 were consistent with the findings of Rounsefell and Kelez (1940), who reported that with moderate water temperatures and an abundant food supply, coho fry will grow from 30 mm at emergence in March to mm in September. In the summer of 1997, however, volunteers from the Courtenay Fish and Game Protective Association noted that Arden Creek was dry in several locations. The decrease in flow was due to accumulated debris and bedload in the Morrison Creek diversion. We believe this limited the amount of habitat available in Arden Creek. We attribute the decrease in fish populations in Arden Creek between years to this. In 1997, we found a significant increase in the size of coho and cutthroat sampled in Arden Creek. We attribute this to a number of factors including: fewer fish in 1997 competing for food and space; and warmer temperatures between April and October 1997, resulting in earlier emergence and a longer growing season. In addition, the decrease in flow resulted in decreased flushing rates in Arden Creek. This would lead to pooling and, ultimately, increased temperatures in the pooled water, which would have a positive effect on fish growth provided the temperatures remained <20 C. FISH ABUNDANCE AND LENGTH AT TREATED VS. CONTROL SITES We found more fish as well as higher densities and biomass at treated sites in both 1996 and We attribute this to the Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., Feb

6 MICHALSKI AND REID creation of deeper pool habitats at the weir sites. Although coho are found in both pool and riffle habitat, they are best adapted to holding in pools (Hartman 1965). Researchers have found that the highest absolute and biomass densities of coho are correlated with depths of between 10 and 40 cm and that coho prefer depths of 30 cm or more (Glova and Masson 1976, Nickelsen 1975). The weirs in Arden Creek created upstream pool depths of between 26 and 36 cm, while the control areas had an average depth of only 13.3 cm. We found larger fish at control sites in both 1996 and Salmonids in streams defend territories from small, post-emergent juveniles until they become smolts or sexually mature. These fish increase the area they defend to meet increasing energetic requirements (Keeley and Slaney 1996). This results in decreasing population density as average body size within a cohort increases (Grant and Kramer 1990). In small or very small streams, a conflict of overlapping territories can inhibit growth, encourage emigration, or both (Marshall and Britton 1980). We postulate that as the number of fish increased at treated sites, fish emigrated to control sites, where there was more space. The lower densities of fish competing for territory and resources in control sites resulted in greater growth at these sites. FISH ABUNDANCE AND LENGTH AT WOODEN VS. ROCK WEIRS We also found more fish and higher biomass at wooden weirs in both 1996 and Both the rock and wooden weirs created similar pool habitat; the only difference is the location of the weirs. The rock weir is located at a stream crossing site used by students and members of the public. People walk across the top of the weir and dislodge the rocks. This traffic also causes bank sloughing, resulting in inputs of sediment into the stream. The effects of suspended sediment on rearing salmonids are twofold, affecting both the water column and the streambed (Griffith 1980). Light penetration to the streambed is diminished with increasing sedimentation, which, in turn, limits the primary production and availability of food. Thompson (1972) reported decreasing potential productivity with decreasing substrate particle size, silt being the least productive. Furthermore, salmonids are sight-feeders and Bachman (1958) observed the cessation of feeding by cutthroat at turbidity levels of 25 ppm. Herbert and Merkens (1961) report that sediment levels as low as 90 ppm can adversely affect the survival of trout. We conclude that the inputs of sediment and disturbance by foot traffic are likely responsible for the lower number of fish at the rock weir site. MANAGEMENT IMPLICATIONS The construction of weirs in Arden Creek has had a positive effect on the fish production of this small urban creek. We suggest, therefore, that the creek continue to be a focus for restoration activities by the club. Arden Creek was dry in several locations due to accumulated debris and bedload in the Morrison Creek diversion in the summer of This resulted in decreased rearing habitat in Arden Creek, which contributed to the decrease in the number of fish in the creek that year. DFO and MELP have now developed both short- and long-term prescriptions to address this situation. In the short term, constructing a weir in Morrison Creek will create an upstream pool and back water into the diversion and then into Arden Creek (R. Doucet, DFO, 1998, pers. comm.). The longer-term solution involves burying a pipe into the bed of Morrison Creek to ensure a permanent flow of water into Arden Creek. We found both rock and wooden weirs increased the number of fish in Arden Creek. Therefore, we recommend construction of additional weirs in the creek and suggest that the Courtenay Fish and Game Protective Association commission a study to determine appropriate locations for these structures. More natural-looking structures, such as Newbury weirs should be considered (Newbury et. al. 1997). These weirs are constructed out of boulders and are spaced to create continuous pool and riffle habitat. Large woody debris provides important physical and biological functions in the wide variety of habitats used by all species of Pacific salmon (Cederholm et. al. 1997). In their study of the summer microdistribution of coho underyearlings in the Big Qualicum River on Vancouver Island, Lister and Genoe (1970) reported that fry were in close association with bank cover, in back eddies, log accumulations, and rootwads. Even in the deeper, faster, mid-stream areas, juvenile coho still remain in close proximity to cover. Ward and Slaney (1997) compared differences in fish populations at sites with boulder deflectors, with and without LWD, in the Keogh River on Vancouver Island. Deflectors with LWD carried about twice as many juvenile steelhead parr and youngof-year coho. We recommend that LWD and rootwads be secured in Arden Creek, particularly along the channelled portion of the creek on School District 71 property and in the upstream pools created by the weirs. Not only would the LWD complexes provide biological benefits, they would also trap sediment. Cederholm et. al (1997) found that more than half of the total sediment stored in first to third order streams is retained by organic matter such as LWD. Sediment at the rock weir site is having a localized impact on fish and fish habitat at this location. There are numerous similar crossing sites throughout the School District 71 property and within the wooded wetland upstream. In his investigation, Baldwin (1993) noted that the substrate of much of Arden Creek was silt and organic muck over a layer of sand and gravel, and he speculated that the silt was probably coming from bank erosion caused by foot traffic. He suggested the construction of additional bridges and bank stabilization with riparian plants. We recommend this be done. In addition to the 878 Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., Feb

7 Fish Populations and Weir Construction impacts from people crossing the creek, upper Arden Creek has been subject to impacts from urban development. It is likely that some of the sediment also comes from these areas. Once sediment inputs are eliminated or minimized, there are a number of ways to dislodge the existing sediment. One is scarficiation, which involves excavating the streambed and exposing the substrates to the flushing effect of the stream. Another technique is hydraulic flushing, which uses high pressure jets of water and air to force the fines into the flow of the stream (Adams and Whyte 1990). Constructing instream deflectors will remove sediment and assist in the restoration of sediment-impacted channels by creating pools and increasing cover by narrowing and deepening the stream (Koning and Keeley 1997). We recommend that an assessment be undertaken to determine the sediment sources and to develop appropriate prescriptions to eliminate the inputs. We believe that instream structures combined with weir construction would create more habitat and increase the movement of sediment. Finally, we recommend continued monitoring of fish populations in Arden Creek. Monitoring provides valuable information regarding changes to fish populations and will expand the knowledge base about changes to fish populations as a result of restoration activities. In addition to monitoring fish, we recommend ongoing monitoring of all structures placed in the creek to ensure they are working appropriately and to determine whether any changes or adjustments should be made. Monitoring should include examining changes to the stream to ensure that the structures are having long-term, positive effects on restoring this small but valuable urban creek. ACKNOWLEDGEMENTS We sincerely thank the members of the Courtenay Fish and Game Protective Association for their dedication to the restoration and protection of Arden Creek. Their tireless commitment and long hours installing weirs in the summers of 1996 and 1997 not only helped to increase the fish production of this small creek, but also led to valuable information about the changes to fish populations in restored urban streams. We also thank the students from Lake Trail Secondary and Puntledge Park Elementary schools for their assistance in collecting some of the fish data. Our thanks to L. Carswell and C. Thirkill for their diligence during the field sampling, and G. Carswell for her enduring volunteer commitment to fish on Vancouver Island. LITERATURE CITED Adams, M. A., and I. W. Whyte Fish habitat enhancement: a manual for freshwater, esturarine, and marine habitats. Dep. Fish. and Oceans Can., Vancouver, BC. DF pp. Bachman, R. W The ecology of four north Idaho trout streams with reference to the influence of forest road construction. Dissertation, Univ. Idaho. 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