QUIRK CREEK BROOK TROUT SUPPRESSION PROJECT 29 Alerta Sustainale Resource Development Fish and Wildlife Division Cochrane, Alerta
QUIRK CREEK BROOK TROUT SUPPRESSION PROJECT 29 Prepared y Jennifer E. Earle 1, Jim D. Stelfox 1 and Brian E. Meagher 2 March 21 1 Alerta Sustainale Resource Development, Fish and Wildlife Division, Box 142, #228, 213-1 Street West, Cochrane, Alerta T4C 1B4 2 Trout Unlimited Canada, Suite 16, 6712 Fisher St. S.E., Calgary, Alerta T2H 2A7
For information aout this report, please contact: Alerta Sustainale Resource Development Fish and Wildlife Division Box 142, #228, 213-1 Street West Cochrane, Alerta T4C 1B4, Canada Telephone: (43) 932-2388 Cover photo: Brook trout Suggested Citation: Earle, J.E., J.D. Stelfox and B.E. Meagher. 21. Quirk Creek rook trout suppression project 29. Unpulished report, Fish and Wildlife Division, Alerta Sustainale Resource Development, Cochrane, Alerta. Quirk Creek Brook Trout Suppression Project 29 ii
TABLE OF CONTENTS Page LIST OF FIGURES...iv LIST OF TABLES...v ACKNOWLEDGMENTS...vi EXECUTIVE SUMMARY... vii 1. INTRODUCTION... 1 1.1 Project Overview... 1 1.2 Study Area... 2 2. METHODS... 3 2.1 Fish Identification Education... 3 2.2 Angling... 3 2.3 Electrofishing... 3 2.4 Hyrids... 4 3. RESULTS AND DISCUSSION... 5 3.1 Angling... 5 3.2 Electrofishing... 9 3.3 Catch-per-unit-effort... 12 4. CONCLUSIONS... 13 5. REFERENCES... 14 6. COLLECTION OF FIGURES... 17 7. COLLECTION OF TABLES... 32 Quirk Creek Brook Trout Suppression Project 29 iii
LIST OF FIGURES FIGURE 1 QUIRK CREEK STUDY AREA AND LOCATION OF SAMPLING SITES...18 FIGURE 2 NUMBER OF HOURS FISHED BY ANGLERS ON SUPERVISED AND UNSUPERVISED OUTINGS ON QUIRK CREEK...19 FIGURE 3 BROOK TROUT CATCH RATES FOR ANGLERS ON SUPERVISED AND UNSUPERVISED OUTINGS ON QUIRK CREEK...19 FIGURE 4 PERCENTAGE OF HARVESTED BROOK TROUT CAUGHT BY ANGLERS ON UNSUPERVISED OUTINGS ON QUIRK CREEK...2 FIGURE 5 FISHING EFFORT AND BROOK TROUT HARVEST RATES IN THE UPPER REACH OF QUIRK CREEK....2 FIGURE 6 FISHING EFFORT AND BROOK TROUT HARVEST RATES IN THE LOWER REACH OF QUIRK CREEK....21 FIGURE 7 MEAN LENGTHS OF BROOK TROUT HARVESTED BY ANGLERS FROM THE LOWER AND UPPER REACHES OF QUIRK CREEK....21 FIGURE 8 LENGTH FREQUENCIES OF BROOK TROUT HARVESTED BY ANGLERS IN THE UPPER REACH OF QUIRK CREEK, 1998 28....22 FIGURE 9 - LENGTH FREQUENCIES OF BROOK TROUT HARVESTED BY ANGLERS IN THE LOWER REACH OF QUIRK CREEK, 2 29....23 FIGURE 1 LENGTH FREQUENCIES OF BULL TROUT CAPTURED BY ANGLERS IN THE UPPER REACH OF QUIRK CREEK, 1998 28...24 FIGURE 11 LENGTH FREQUENCIES OF BULL TROUT CAPTURED BY ANGLERS IN THE LOWER REACH OF QUIRK CREEK, 2 29...25 FIGURE 12 LENGTH FREQUENCIES OF CUTTHROAT TROUT CAPTURED BY ANGLERS IN THE UPPER REACH OF QUIRK CREEK, 1998 29....26 FIGURE 13 LENGTH FREQUENCIES OF CUTTHROAT TROUT CAPTURED BY ANGLERS IN THE LOWER REACH OF QUIRK CREEK, 2 29....27 FIGURE 14 ESTIMATED BIOMASS AND HARVEST OF BROOK TROUT IN THE UPPER REACH OF QUIRK CREEK....28 FIGURE 15 ESTIMATED BIOMASS AND HARVEST OF BROOK TROUT IN THE LOWER REACH OF QUIRK CREEK....28 FIGURE 16 ESTIMATED PERCENTAGE OF THE NUMBER OF LARGE (>15 MM) BROOK TROUT IN THE POPULATION THAT ANGLERS HARVESTED IN THE LOWER AND UPPER REACHES OF QUIRK CREEK...29 FIGURE 17 - ESTIMATED PERCENTAGE OF THE BIOMASS OF LARGE (>15 MM) BROOK TROUT IN THE POPULATION THAT ANGLERS HARVESTED IN THE LOWER AND UPPER REACHES OF QUIRK CREEK...29 FIGURE 18 DENSITIES OF LARGE (>15 MM) BROOK TROUT AND ALL BROOK TROUT IN THE LOWER AND UPPER POPULATION ESTIMATE SITES ON QUIRK CREEK....3 FIGURE 19 SIZE DISTRIBUTION OF BROOK TROUT HARVESTED IN 1999 AND ELECTROFISHED ON 16 AUGUST 1999 FROM THE UPPER REACH OF QUIRK CREEK....3 FIGURE 2 PERCENT COMPOSITION OF BROOK TROUT IN THE ANGLING AND ELECTROFISHING CATCH IN THE UPPER REACH OF QUIRK CREEK....31 FIGURE 21 PERCENT COMPOSITION OF BROOK TROUT IN THE ANGLING AND ELECTROFISHING CATCH IN THE LOWER REACH OF QUIRK CREEK....31 Quirk Creek Brook Trout Suppression Project 29 iv
LIST OF TABLES TABLE 1 ANGLING DATA SUMMARY FOR QUIRK CREEK, 1998 29...33 TABLE 2 FISH POPULATION ESTIMATES FOR, AND BROOK TROUT KNOWN TO BE HARVESTED FROM, QUIRK CREEK...34 TABLE 3 PERCENT OF ANGLER-CAUGHT FISH >25 MM IN THE UPPER AND LOWER REACHES OF QUIRK CREEK, 1998 29...36 TABLE 4 NUMBER OF CUTTHROAT TROUT >15 MM CAUGHT BY ANGLING IN THE UPPER AND LOWER REACHES AND BY ELECTROFISHING IN THE UPPER AND LOWER POPULATION ESTIMATE SITES OF QUIRK CREEK...37 TABLE 5 BIOMASS AND NUMBER OF BROOK TROUT REMOVED BY ANGLING IN QUIRK CREEK...38 TABLE 6 BIOMASS AND NUMBER OF BROOK TROUT REMOVED BY ELECTROFISHING IN QUIRK AND HOWARD CREEKS....39 TABLE 7 CATCH-PER-UNIT-EFFORT SUMMARY FOR BROOK TROUT CAPTURED BY ANGLING AND ONE- PASS ELECTROFISHING IN QUIRK CREEK....4 Quirk Creek Brook Trout Suppression Project 29 v
ACKNOWLEDGMENTS The Quirk Creek Brook Trout Suppression Project is a collaorative effort involving the Fish & Wildlife Division of Alerta Sustainale Resource Development and Trout Unlimited Canada (TUC). Previous TUC staff Dean Baayens (1998-21) and Greg Eisler (22-23) spent considerale time administering the fish identification test to volunteer anglers, coordinating and supervising outings, sampling harvested rook trout, and collecting and entering creel data. Ultimately, this project would not have een possile without the participation of many volunteer anglers over the years and, in particular, those dedicated anglers who have harvested most of the rook trout in recent years on unsupervised outings. This project was supported y funds from the Alerta Conservation Association (22 23; 28 29), the Alerta Sport, Recreation, Parks and Wildlife Foundation (1999 2), Anadarko Canada Corporation (2 23) and Applied Aquatic Research Ltd. (22 23). Quirk Creek Brook Trout Suppression Project 29 vi
EXECUTIVE SUMMARY In southern Alerta, non-native rook trout Salvelinus fontinalis populations have generally increased while native westslope cutthroat trout Oncorhynchus clarkii lewisi and ull trout Salvelinus confluentus populations have declined. Since their introduction to the Elow River watershed in 194 and Quirk Creek in 1947, rook trout colonized the entirety of Quirk Creek, comprising 92% of the fish population y 1995. To reduce the rook trout population, angling was used from 1998 29, as part of a rook trout suppression project. The ojective of this study was to determine whether angling could e an effective method for reducing densities of rook trout, to facilitate recovery of the native trout populations. Anglers participating in the project were required to pass a fish identification test and harvest all rook trout caught. The stream was divided into an upper and lower reach and anglers recorded all fish caught on supervised and unsupervised outings. The fish identification key proved to e effective in teaching anglers how to identify fish, as only 15 (.2%) of the 9585 fish harvested y anglers participating in the project were not rook trout. Fishing effort and rook trout harvest rates peaked in the early years of the project. Effort was generally higher in the more accessile lower reach, ut declined sustantially in oth reaches. Higher catch rates of anglers on unsupervised outings, in conjunction with a decline in the numer of supervised outings, resulted in an increase in the relative importance of unsupervised outings for rook trout harvest, especially in the lower reach. Based on their larger size and higher catchaility, ull trout and cutthroat trout have the potential to provide a etter quality fishery in Quirk Creek. Since initiation of the project, only 5% of the rook trout caught y anglers have exceeded 25 mm in length, compared to 24% of cutthroat trout and 28% of ull trout. The estimated percentage of the large (>15 mm) rook trout population that anglers harvested in the upper reach peaked at 61% in 1999, ut has declined consideraly since then, to less than 2%. However, in the lower reach, the percentage of the large (>15 mm) rook trout population harvested y anglers has een sustantially higher, averaging 4%, and has never een lower than 25%. A comparison of rook trout catch-per-unit-effort (CPUE) indicates that electrofishing resulted in oth a higher numer and iomass of rook trout caught per person-hour when compared to angling. However, angling CPUE was generally higher for unsupervised than for supervised outings, which was the primary method of removing rook trout from the lower reach in the last few years. In conclusion, angling, particularly unsupervised outings, appears to have een sufficient on the lower reach of Quirk Creek to keep the numer of large rook trout at a low enough level that the iomass of cutthroat trout has increased to near record levels. For the more remote upper reach, however, we have een unsuccessful in getting anglers to exert sufficient pressure on a sustained asis to reduce and keep the rook trout population at a low level. It appears that the suppression of rook trout populations y angling has the potential to work on other streams, provided that the streams selected are readily accessile to anglers and sufficient angling pressure can e sustained. Quirk Creek Brook Trout Suppression Project 29 vii
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1. INTRODUCTION 1.1 Project Overview Brook trout Salvelinus fontinalis, although not native to Alerta, are present in many montane and foothills waters as a result of extensive stocking. In southern Alerta, rook trout populations have generally increased while native westslope cutthroat trout Oncorhynchus clarkii lewisi and ull trout Salvelinus confluentus populations have declined. Brook trout life-history attriutes (early spawning age, reduced longevity and low catchaility) have resulted in the replacement of native ull trout and cutthroat trout fisheries with fisheries for smaller, less-catchale, non-native rook trout. Brook trout colonized Quirk Creek susequent to their introduction to the Elow River watershed in 194 and Quirk Creek in 1947. Although native cutthroat trout and ull trout were the only fish captured in Quirk Creek in 1948, rook trout had colonized the lower 3 km of the creek y 1978, where they comprised 35% of the electrofishing catch (Tripp et al. 1979), and spread throughout the entire creek y 1995, comprising 92% of the fish population (Paul and Post 1996). Electrofishing surveys of Quirk Creek continued in 1996 with the addition of two more sampling sites; however, results were similar to 1995 in that rook trout comprised greater than 9% of the total catch (Paul and Post 1997). These changes occurred despite the implementation of reduced ag limits and minimum-size limits designed to provide more protection for native trout (Stelfox et al. 21a). Since 1998, harvest of all fish has een prohiited in Quirk Creek, except y anglers participating in the rook trout suppression project. Management programs to reduce or eliminate non-native trout populations often involve piscicides and/or electrofishing (Moore et al. 1983; Buktenika 1997; Kulp and Moore 2). However, Larson et al. (1986) suggested that experimental angling programs might offer a costeffective, alternative method for reducing densities of non-native trout. Although Larson s study only ran nine weeks, it appeared that anglers reduced the non-native trout population y aout 1%. Since piscicides are only suitale in certain situations, and there are insufficient resources to attempt removal of non-native trout y electrofishing in all streams where native trout populations appear to e threatened, the option of selectively removing non-native trout y angling provides an appealing alternative. Our ojective in this study was to determine whether angling could e an effective method for reducing densities of non-native rook trout in Quirk Creek, to facilitate recovery of the native trout population. Data on the angling component of the project was previously presented in Stelfox et al. (21a, 24) and Earle et al. (27a, 28a, 29a). The following report summarizes new angling data collected in 29 and compares it to data collected from 1998 to 28. Quirk Creek Brook Trout Suppression Project 29 1
1.2 Study Area Quirk Creek is located 5 km southwest of Calgary in a designated off-highway vehicle (OHV) area. A good dirt road comes within.5 km of the creek for most of its length. Anglers participating in this project were allowed direct vehicle access to this road y fording the Elow River, ut only on supervised outings under the direction of the volunteer coordinator. A locked gate prevents anglers on unsupervised outings from crossing the Elow River y vehicle. Most of Quirk Creek meanders through a large wet meadow dominated y grasses and low (<1 m) shrus. Although cattle and OHVs have degraded streamanks in a few areas, most of the streamanks are undamaged and provide good fish haitat, consisting of deeply undercut anks with overhanging terrestrial vegetation. The lower 2 km of creek flows through a narrow valley efore joining the Elow River at an elevation of 153 m. There are no permanent arriers on the creek, although eaverdams up to 1.5-m high are scattered along the creek. Water temperatures were recorded at 3-minute intervals from July 19 to Octoer 5, 26 using HOBO U22 Water Temp Pro v2 data loggers. Maximum recorded water temperatures in 26 were 12.1 C in the upper reach (11U 66125 E 5628781 N) on July 24 and 16.8 C in the lower reach (11U 656812 E 5632769 N) on July 26. A ridge, located near Mac Creek, divides Quirk Creek into a 6.48-km upper reach and a 6.18- km lower reach, with the lower reach serving as a control during the first two years of the project (Figure 1). Surface areas of the upper and lower reaches were calculated to e 1.63 and 3.5 ha, respectively, ased on mean stream widths of 2.5 and 4.9 m, respectively, which were otained y measuring stream widths every 2 m in oth reaches in 24. From 1987 to 1997, the entire length of Quirk Creek was open to angling under the general sportfishing regulations for Alerta s eastern slopes. In 1987, minimum-size limits of 25 cm for cutthroat trout and 4 cm for ull trout were implemented. In 1995, the harvest of ull trout was prohiited. In 1998, Quirk Creek was designated a catch-and-release stream. However, eginning in 1998, anglers who had passed a fish identification test and were participating in an outing supervised y a volunteer coordinator were permitted to harvest all rook trout they caught in Quirk Creek upstream of the ridge near Mac Creek (Stelfox et al. 21a). In 2, the area of rook trout harvest was extended to include all of Quirk Creek and, eginning in 21, a select group of anglers were permitted to harvest rook trout on unsupervised outings in either reach. A detailed summary of prior fishing regulations for Quirk Creek can e found in Stelfox et al. (21a). Quirk Creek Brook Trout Suppression Project 29 2
2. METHODS 2.1 Fish Identification Education To participate in the project, all anglers had to pass a fish identification test on an annual asis to demonstrate their aility to identify the three fish species found in Quirk Creek. If a person failed the test on their first attempt, they were given a dichotomous key with pictures of the keyidentifying features (a list of key-identifying features in 1998) and were permitted to take the test a second time with the key (list) in front of them. In addition, anglers were shown pictures of juvenile fish of all three species, as well as rook trout x ull trout hyrids, and the keyidentifying features were discussed. For a more detailed discussion of the fish identification test and results up to 2, refer to Stelfox et al. (21 and 24). 2.2 Angling Participating anglers were required to harvest all rook trout caught and were initially only allowed to harvest rook trout from the upper reach of Quirk Creek on supervised outings. However, eginning in 2, anglers also harvested fish from the lower reach to assess rook trout immigration and, starting in 21, some of the more skilled anglers harvested fish on unsupervised outings. Anglers only fished from June to Octoer, could not use ait and were required to release all ull trout and cutthroat trout after recording the length of each fish in 5-cm size classes. All harvested rook trout were delivered whole to the volunteer coordinator at the end of each outing for measuring (fork length, nearest 1 mm) and weighing (nearest 1 g) and then returned to the angler. Anglers on unsupervised outings recorded fork lengths (nearest 1 mm) of all rook trout caught and filled in creel cards. Weights for rook trout caught on unsupervised outings were derived using length-class-specific condition factors from fish captured during supervised outings that year. In a few instances, an angler on an unsupervised outing forgot to record rook trout lengths, ut recorded on the creel card the numer of rook trout harvested in each size category. In these cases, a length was assigned to each fish y using the mid-point of the 5-cm size category on the angler s creel card (e.g., 17.5 cm for the 15 2-cm size category). 2.3 Electrofishing As part of the rook trout suppression project and, initially, a project looking at ull trout population dynamics throughout Alerta (Paul and Post 1996, 1997), electrofishing surveys were conducted in Quirk Creek from 1995 to 29 (Paul et al. 21; Paul 23; Paul 24; Dormer and Paul 25; Earle et al. 27, 28, 29, 21). Aundance estimates were determined y removal-depletion methods at an upper and lower site. In addition, ecause removal of rook trout y angling had not produced the desired reduction in rook trout y 23 (Paul et al. 23; Paul 24), one-pass electrofishing was used in addition to angling to selectively remove rook trout aove Mac Creek from 24 to 28. In order to assess the response of the rook trout population to angler harvest alone, no one-pass electrofishing harvest of rook trout has een conducted since 28. For detailed methods and results of the electrofishing component of the study, refer to Earle et al. (27, 28, 29, 21). Quirk Creek Brook Trout Suppression Project 29 3
For the calculation of catch-per-unit-effort for one-pass electrofishing, person-hours were ased on an electrofishing crew of three and the numer of volunteers, which varied according to day and year. Travel time was not included in the estimates. From 26 to 28, a group of field ecology students (>15 people) assisted the crew; however, for those years, a volunteer crew size of seven was used in the calculation of total time, since this was considered an ideal crew size and was comparale to the sampling efforts in the previous years. The estimated iomass (kg/ha) of rook trout present in the creek was determined in each year y extrapolating the iomass estimates from each population estimate site to the surface areas of the upper and lower reach. The angler harvest of rook trout (kg/ha) was then compared to the estimated iomass in each reach. To estimate the percentage of the large (>15 mm) rook trout population harvested y angling, we extrapolated the numer of large (>15 mm) rook trout estimated to e present in each population estimate site to the entire reach and then added this estimate to the numer of large (>15 mm) rook trout harvested from the reach that year prior to the electrofishing date. This roughly estimated the numer of large (>15 mm) rook trout present at the start of each angling season, and was then compared to the numer of large (>15 mm) rook trout harvested during the entire angling season in that reach. 2.4 Hyrids All rook trout x ull trout hyrids angled y the volunteer coordinators and captured during the one-pass electrofishing were harvested. Anglers were instructed to not harvest hyrids, so as to reduce the risk of ull trout eing mistakenly harvested as hyrids; however, some hyrids were harvested y the more experienced anglers, who had seen hyrids harvested y the volunteer coordinator. Brook trout x ull trout hyrids were identified in the field, primarily ased on the presence of pale spots and asence of lack markings on the dorsal fin (Plate 1). Genetic analyses conducted on 61 suspected hyrids collected from Quirk Creek during the 1998 22 period confirmed that they were all hyrids (Ryan Popowich personal communication). Hyrids were counted as rook trout in the analyses of angling and electrofishing data. For a discussion of hyrid aundance and distriution, refer to Earle et al. (27, 28, 29, 21). Quirk Creek Brook Trout Suppression Project 29 4
Plate 1. Brook trout x ull trout hyrids from Quirk Creek. Note pale spots on dorsal fins of hyrids, compared to prominent lack markings on the rook trout dorsal fin and the complete asence of markings on the ull trout dorsal fin. 3. RESULTS AND DISCUSSION 3.1 Angling The fish-identification key proved to e effective in teaching anglers how to identify fish, considering that only 15 (.2%) of the 9585 fish harvested y anglers participating in the project were not rook trout. This clearly indicates that the fish-identification testing of all anglers, as a condition of participation, was very effective in reducing misidentification and accidental harvest of fish. Average annual catch rates for rook trout in the upper reach were high (2.2 2.5 fish/h) during the first three years of the study, ut declined to.6 fish/h y 28 and. fish/h y 29 (Tale 1). In contrast, catch rates for rook trout in the lower reach changed relatively little from 2 to 28, ranging from.9 to 1.8 fish/h, ut declined to a low of.4 fish/h in 29. Aggregate catch rates in oth reaches were generally aout 1. fish/h higher than for rook trout alone (Tale 1). While the percentage of rook trout in the angler catch in the upper reach declined from 72% in 1998 to 26% in 25 and has remained low since then, it remained virtually unchanged (63 65%) in the lower reach until 24, when it declined to 3% (Tale 1). Since 24, it has gradually increased in the lower reach to 52% in 27, ut declined to 27% in 29. Quirk Creek Brook Trout Suppression Project 29 5
In the upper reach, the sustantial decline in relative aundance of rook trout in the angler catch was reflected y a decline in the electrofishing data. However, rook trout always comprised a higher percentage of the electrofishing catch, declining from 91% in 22 to 33% in 29 (Earle et al. 21). In the lower reach, the decline in relative aundance of rook trout in the angler catch has generally een accompanied y a decline in their relative aundance in the electrofishing catch, from a high of 86% of the electrofishing catch in 22 to a low of 3% in 28 (Earle et al. 21). In 29, rook trout accounted for only 37% of the electrofishing catch and 27% of the angler catch in the lower reach. The numer of hours fished on supervised outings has declined sustantially since initiation of unsupervised outings in 21, eing surpassed y unsupervised outings in 26, 27 and 29 (Figure 2). This, in conjunction with the consistently higher catch rates of anglers on unsupervised outings (Figure 3), initially resulted in an increase in the relative importance of unsupervised outings for rook trout harvest in oth reaches (Figure 4). By 27, aout 76% of all rook trout harvested in the lower reach were taken y anglers on unsupervised outings. In 28, however, the numer of hours fished on unsupervised outings was lower than on supervised outings (Figure 2) and catch rates were comparale for the two types of anglers, which resulted in unsupervised outings accounting for only aout half of the rook trout harvested that year. The importance of unsupervised outings increased in 29, when 75% of the rook trout harvested in the lower reach were taken y anglers on unsupervised outings. From 24 to 28, no unsupervised outings have een conducted in the upper reach. This was primarily ecause greater effort is required to access the upper reach without the vehicle assistance provided during the supervised outings and ecause another road accessing the upper reach, which was previously vehicle accessile to the pulic, was reclaimed in late 21. A small numer of unsupervised outings occurred in the upper reach in 29; however, no rook trout were caught. Fishing effort peaked at 43 h/ha in the upper reach in 1999 and 324 h/ha in the lower reach in 2 (Figures 5, 6). Since then, fishing effort has generally een higher in the lower reach, ut has declined sustantially in oth reaches. Brook trout harvest rates (fish/ha) closely mirrored effort in oth reaches (Figures 5, 6). Harvest rates peaked at 868 rook trout/ha (83.1 kg/ha) in the upper reach in 1999 and 539 rook trout/ha (55.7 kg/ha) in the lower reach in 2 (Tale 2), or 218 rook trout/km (21 kg/km) in the upper reach and 266 rook trout/km (27 kg/km) in the lower reach (Tale 2). Since then, harvest rates have declined sustantially in oth reaches, with only 17 rook trout/ha (1.8 kg/ha) eing harvested from the lower reach in 29 (Tale 2). The mean length of rook trout harvested in oth reaches initially declined following the start of harvest, ut has changed relatively little over the study, ranging from 173 to 28 mm during the 1998 29 period (Figure 7). The only exceptions were the sharp increases in mean length of rook trout harvested from the upper reach in 26 and 28, which should e viewed with caution, as they are ased on very small sample sizes (17 and 19 fish, respectively). No data were availale for 29 in the upper reach, as no rook trout were caught. Quirk Creek Brook Trout Suppression Project 29 6
Since initiation of this project in 1998, only 5% of the angler-caught rook trout have een longer than 25 mm, compared to 28% of the ull trout and 24% of the cutthroat trout (Tale 3). Bull trout appear to e slightly larger in the upper reach, as 32% of the ull trout caught y anglers were longer than 25 mm. Based on their larger size and higher catchaility, ull trout and cutthroat trout have the potential to provide a etter quality fishery in Quirk Creek. Paul et al. (23) determined that the catchaility of similar-sized ull trout and cutthroat trout was 2.5-fold greater than for rook trout. This higher catchaility, however, could prevent a recovery of the native trout population. Using a model developed with data from the Quirk Creek project, Paul et al. (23) calculated that ull trout and cutthroat trout populations in the upper reach would e extinct within five years at a hooking mortality rate of 1% and an angler effort of 656 anglerhours/year equivalent to the angler effort in 1999 and could still decline at hooking mortality rates of 2.5% and 5%. However, since 1999, there has not een a sustained decline in the ull and cutthroat trout populations. This is likely ecause the decline in angler effort has reduced the numer of times that ull and cutthroat trout were caught, and hence the proportion of the population that might die of hooking mortality. To estimate the approximate numer of times per year that each cutthroat trout >15 mm might have een caught y anglers, angling and population estimate data from Quirk Creek were compared (Tale 4). When fishing pressure was highest in the upper and lower reaches (1999 and 2, respectively), it is estimated that cutthroat trout >15 mm were caught almost four times per year. However, over the course of this study, it is estimated that the average cutthroat trout >15 mm was caught 1.2 and 1.6 times/year in the upper and lower reaches, respectively. Age-length data for Quirk Creek suggests that most cutthroat trout 15 mm long are age 3 and that most female cutthroat trout do not spawn until age 5. Therefore, it appears that most female cutthroat trout are likely vulnerale to hooking mortality for aout two years efore they spawn for the first time. Based on these assumptions, and the estimated average numer of times per year that cutthroat trout >15 mm were caught during the 1998 29 period, it is estimated that the likelihood of a female cutthroat trout succuming to hooking mortality efore spawning for the first time would have een no greater than 1% and 2% at hooking mortality rates of 2.5% and 5%, respectively. The minimum size of rook trout vulnerale to angling was generally in the 12 13 mm range (Figures 8, 9), ut fish as small as 71 mm were caught y angling. Although angler harvest appeared to have little impact on the size distriution of angled rook trout in the upper reach during the first three years of the study, the shift in size distriution of angled rook trout in the lower reach in 21 suggests that the initiation of harvest in the lower reach the previous year affected the population. Since angled ull trout and cutthroat trout were measured in 5-cm size classes, their length frequencies are presented according to these categories. In oth reaches, ull trout in the 2 25 cm size range usually dominated the ull trout catch (Figures 1, 11). However, in the lower reach in 27 and 28, an increase in the proportion of ull trout in the 15 2 cm (oth years) and 1 15 cm (28) size ranges suggests that there might have een an increase in recruitment, relative to the previous four years. Cutthroat trout captured in the upper reach were most frequently in the 2 25 cm size range (Figure 12). In the lower reach, cutthroat trout in the 2 25 cm size range were dominant in the Quirk Creek Brook Trout Suppression Project 29 7
first two years of the study; however, smaller (1 15 cm) fish dominated the catch from 22 to 24 (Figure 13). Since then, the proportion of large cutthroat trout has increased in the catch, possily reflecting the emergence of a strong year class. This was supported y lengthfrequency data from the lower population estimate site, which showed a strong young-of-theyear class in 23 (Earle et al. 27). While large cutthroat trout were still present in 29, smaller (1 2 cm) fish dominated the catch. Since the 1998 2 period, the iomass of rook trout in the upper reach has declined sustantially (Figure 14). However, the iomass of rook trout harvested y angling has declined even more, primarily due to a decline in angler effort (Figure 5), which has resulted in a decline in the proportion of the rook trout iomass harvested y angling in the upper reach. This likely contriuted to the increase in rook trout iomass in 24. To counteract this increase, starting in 24, rook trout were also removed from the upper reach y one-pass electrofishing (Figure 14). Given that angler harvest was virtually identical in 24 and 25, the electrofishing removal of an additional 25 kg/ha in 24 likely contriuted to the decline in iomass oserved in 25. Although angler harvest has declined in the upper reach since 25, rook trout iomass has remained at similar levels, likely due to removal y one-pass electrofishing. In 29, the rook trout iomass in the upper reach was the lowest recorded since the study started, even though no rook trout were harvested y angling in 29 and relatively few were harvested y electrofishing in 28 (Figure 14). In the lower reach, angling effort was typically higher (Figure 6) and this resulted in a greater proportion of the iomass eing harvested (Figure 15). The estimated iomass of rook trout in the lower reach has also declined sustantially since the 1998 2 period, with the lowest levels eing recorded in 28 and 29. In the lower reach, it therefore appears that angling has een, in part, responsile for keeping rook trout iomass at reduced levels. By adding each population estimate to the numer of rook trout harvested prior to the electrofishing date, we extrapolated the numer of large (>15 mm) rook trout present at the start of each angling season. Comparing the numer of rook trout harvested to this numer gives a more realistic estimate of the proportion of the rook trout population removed y angling, than is suggested y Figures 14 and 15. The estimated percentage of the large (>15 mm) rook trout population harvested y angling in the upper reach peaked at more than 6% in 1999 and has generally declined for oth numer and iomass since then (Figures 16, 17). In the lower reach, the estimated percentage of the large (>15 mm) rook trout population harvested y angling peaked in 23, declined for the next two years, then increased in 26, when anglers harvested 58% of the estimated numer and 69% of the estimated iomass of large rook trout in the lower reach. This increase also coincided with an increase in the numer of hours fished relative to the three previous years. Although there was a slight increase in the hours fished in the lower reach in 27 (Figure 6) and rook trout catch rates were comparale to 26 (Tale 1), the percentage of the large rook trout population removed y angling in the lower reach was less than half that in 26 for oth numer and iomass. In 28, although the numer of hours fished in the lower reach declined and the catch rate was similar to previous years, the percentage of the large rook trout population removed y angling increased to its highest level, with anglers harvesting 64% of the estimated numer and 75% of the estimated iomass of large rook trout in the lower reach. This was largely due to a sustantial decline in the estimated iomass of rook trout in the lower reach in 28 (Figure 15). In 29, the estimated iomass of rook trout in the lower reach was similar to that of 28; however, the Quirk Creek Brook Trout Suppression Project 29 8
percentage of the large rook trout population removed y angling was sustantially lower, primarily ecause the numer of hours fished was lower in 29 relative to 28 and catch rates were also lower. Since 2, anglers have removed a greater percentage of the large (>15 mm) rook trout population in the lower reach than in the upper reach, where the estimated percentage harvested has not exceeded 23% y either numer or iomass. The difference etween the lower and upper reach harvest rates is primarily due to the greater effort and higher rook trout catch rates in the lower reach. High angler harvest from the upper reach during the 1998 2 period, and in the lower reach starting in 2, may have contriuted to the decline in rook trout iomass. However, it is likely that other factors (e.g., environmental conditions and predation) also contriuted to the decline. In the early part of the study, mink were frequently oserved along and fishing in Quirk Creek, likely in response to the rapidly increasing food source. Beginning in 2, a widespread drought reduced flows in Quirk Creek for aout four years. This resulted in fish eing concentrated in smaller pools, which would have reduced the potential for fish to escape predation y mink. Evidence of mink predation was especially prevalent when electrofishing was conducted during spring 21, given that the proportion of captured fish earing scars consistent with having narrowly escaped predation y mink was much greater than during the spring 2 electrofishing (J. Stelfox personal oservation). Considering that there were far fewer fish captured during the spring 21 electrofishing than during the spring 2 electrofishing, and that the decline in fish numers was not just confined to rook trout, it appears that increased mink predation, facilitated y reduced flows due to the drought, may have een partially responsile for the sharp decline in the fish population during the 2 22 period. Regardless of what factors contriuted to the decline in the fish population, the increase in rook trout iomass in the upper reach in 23 following the decline in angler harvest suggested that other methods would have to e employed to prevent a resurgence of the rook trout population. Larson et al. (1986) showed that selective angler harvest has the potential to e a cost-effective method for reducing densities of non-native trout in a large mountain stream. However, the authors state that the angler harvest has little immediate impact on the smallest size classes of fish and suggest this may not provide satisfactory results when drastic reductions in the density of non-natives, including the smaller size classes of fish, are required. In such cases, the authors suggest that electrofishing (or a comination of angling and electrofishing) is proaly the most practical method to employ. In the following section, we discuss some of the results of the electrofishing component of the project and, in particular, how they relate to the angling data. 3.2 Electrofishing With the exception of 25 and 27, ull trout density has not exceeded 1 fish/ha in either reach and numers of ull trout captured have often een too low to otain valid population estimates (Tale 2). In 25, a ull trout population estimate of 265 fish/ha was otained for the upper reach. However, it appears that this increase was due to misidentification of young-of-theyear (YOY) hyrids as ull trout, given that no presumed age-1 ull trout (ased on size) were captured in 26, whereas most (97%) of the hyrids caught in 26 were presumed age-1 fish (Earle et al. 27, 21). Quirk Creek Brook Trout Suppression Project 29 9
In the lower reach, cutthroat trout declined from 571 fish/ha in 1987 to 25 fish/ha in 1995 and then increased to 872 fish/ha in 23 (Tale 2). Since then, cutthroat trout density has ranged from 113 fish/ha in 26 to a maximum of 1113 fish/ha in 29, largely due to an increase in the numer of YOY and presumed age-1 cutthroat trout (Earle et al. 21). Simultaneously, the iomass of cutthroat trout in the lower reach has also increased to record levels, reflecting an increase in the numer of large cutthroat trout in the population. In the upper reach, cutthroat trout density declined to 842 fish/ha in 29 after peaking at 1185 fish/ha in 27, while iomass declined in 28 due to a decline in large fish. Although iomass increased in 29, it was still lower than during the 25 27 period. Based on data from the population estimate sites, the rook trout population in the lower reach increased from 247 fish/ha in 1987, to a high of 284 fish/ha in 2 (Tale 2). After 2, rook trout density declined consideraly and was lower than the cutthroat trout density in 23, 24, 28 and 29. Brook trout iomass in the lower reach has also declined sustantially since removal of rook trout was expanded to the lower reach in 2; in 28 and 29, rook trout iomass was only aout ¼ that recorded in 1987 (Tale 2), when rook trout comprised only 29% of the fish population (Stelfox et. al. 21). With the exception of 29, rook trout density has een higher in the upper reach than in the lower reach, peaking at 3473 fish/ha in 2. Brook trout density in the upper reach was also consideraly higher than that of cutthroat trout and ull trout until 28 and 29, when rook trout density dropped to its lowest levels since the study started. Brook trout iomass in the upper reach was highest in the first three years of the study (15 117 kg/ha), ut has since declined sustantially to a low of 1 kg/ha in 29. Angler harvest of 662 to 868 rook trout/ha in the upper reach during the 1998 2 period appeared to have very little impact on the density of large (>15 mm) rook trout in the upper reach relative to their density in the lower reach, which served as a control section until 2 (Tale 2; Figure 18). However, susequent to expansion of angler harvest to the lower reach in 2, the density of large (>15 mm) rook trout in the lower reach declined y 93% to 5 fish/ha in 24 (Tale 2; Figure 18). Since then, and despite an increase in angler harvest, the density of large (>15 mm) rook trout in the lower reach increased to 319 fish/ha in 27, ut susequently plummeted to 44 fish/ha in 28 and remained at a similarly low level in 29. In the upper reach, the density of large (>15 mm) rook trout also declined from a high of 1215 fish/ha in 1998 to a low of 92 fish/ha in 29. Although fishing effort (Figure 6) and angler harvest (Figure 15) have een low in the upper reach since 22, the density of large (>15 mm) rook trout has remained elow 4 fish/ha, likely due to the effects of removing a sustantial portion of the rook trout population y one-pass electrofishing during the 24 28 period (Figure 14). Several studies have indicated that the density of non-native trout can adversely affect the survival of native trout. Peterson et al. (24) found that, at mid-elevation sites, age- and age-1 Colorado River cutthroat trout survived at 13 times and two times higher rates, respectively, at sites where rook trout were removed. The investigators also indicated the data in their study was consistent with the hypothesis that iotic interactions with rook trout suppress cutthroat trout populations, particularly during the first two years of life. Larson and Moore (1985), in a Quirk Creek Brook Trout Suppression Project 29 1
study of stream populations of native rook trout and non-native rainow trout, found that aundance of age- fish of either species was greatly reduced in the presence of 3 or more adults/ha of the other species. A comparale relationship may exist etween rook trout and cutthroat trout in Quirk Creek, given that relatively good survival of the 1996 cutthroat trout yearclass occurred when there were 219 large (>15 mm) rook trout/ha, whereas relatively poor survival of the 2 cutthroat trout year-class occurred when there were more than 6 large rook trout/ha (Tale 2). If density of large rook trout is a major factor in the survival of cutthroat trout fry, then recovery of the cutthroat trout population will e contingent upon preventing the adult rook trout population from increasing to previous high levels. However, it is unlikely that this will e accomplished solely y angling on the upper reach, given that less than 2% of the extrapolated population of large (>15 mm) rook trout have een harvested y anglers since 22 (Figure 16). In contrast, angler harvest of etween 26% and 64% of the population of large rook trout in the more accessile lower reach appears to e having the desired effect, considering that the numer and iomass of cutthroat trout has increased sustantially in this reach since 26. A comparison of the length-frequency distriutions of rook trout caught y angling and electrofishing in 1999 (Figure 19) indicated that vulneraility to angling declined elow aout 21 mm and that anglers were very ineffective at catching rook trout smaller than 15 mm. Brook trout <15 mm comprised 5 7% of the electrofishing catch, ut only 3 11% of the angling catch in the upper reach during the 1998 2 period. Although electrofishing is less size-selective than angling, data on electrofishing efficiency indicates that it is also difficult to remove small rook trout y electrofishing. That smaller fish are less effectively caught than larger fish was apparent when two one-pass electrofishing events in 26 cumulatively removed only 5% of the rook trout in the 71 15 mm size range, compared to 89% of the large (>15 mm) rook trout (Earle et al. 27). To assess immigration of large (>15 mm) rook trout into the upper reach from the lower reach, the upper 2.5 km of the lower reach was electrofished on 6 May 2 and 2 June 21 to capture, mark and release large rook trout (Stelfox et al. 24). Of the 75 large (>15 mm) rook trout marked in 2, anglers susequently harvested 391 (52%) 349 (46%) in 2 and 42 (6%) in 21. Only eight (2%) of these marked fish were taken from the upper reach four in 2 and four in 21. The recapture rate of 46% was also surprisingly similar to the estimated 44% harvest rate for large rook trout from the lower reach in 2 (Figure 16). Of the 92 large rook trout marked in 21, anglers susequently harvested 33 (36%) in 21. None were taken from the upper reach. These results suggest that upstream movement was not sufficient to mask the effects of rook trout harvest in the upper reach, since only 2% of the recaptured rook trout had immigrated into the upper reach. In contrast, Gowan and Fausch (1996) found that movement was relatively common in their study, with rook trout usually moving in the upstream direction during and just after runoff, and also efore spawning. A comparison of percent composition of the catch illustrated that rook trout generally accounted for a greater proportion of the electrofishing catch than the angling catch in oth the upper and lower reaches (Figures 2, 21). Although the trends were generally the same, examining only the species composition of angled fish would have erroneously suggested that rook trout were less aundant, and hence cutthroat trout and ull trout were more aundant, than was actually Quirk Creek Brook Trout Suppression Project 29 11
the case. This underscores the importance of utilizing multiple sampling methods to otain population information. The total iomass and numer of rook trout removed y one-pass electrofishing in the upper reach from 24 to 28 was consideraly greater than that removed y angling (Tales 5, 6). However, the iomass removed from Section 2.6 4.7 y one-pass electrofishing in 27 was much lower than in the three previous years, likely reflecting the effects of removing a relatively large proportion of the rook trout population y one-pass electrofishing this section twice in 26 once in August and once in Septemer. Although a lower iomass was removed y onepass electrofishing in 27, this still appears to have reduced the rook trout population, as the iomass removed y one-pass electrofishing in 28 was even lower. One-pass electrofishing was not conducted in 29, in order to assess the response of the rook trout population to angler harvest alone. Brook trout were only removed from the lower reach y electrofishing on two occasions within the population estimate section in 24 and in a.3-km section in 26. However, if the ojective had een to remove rook trout y electrofishing, then a very large iomass could have een removed in 2, when one-pass electrofishing over a 2.7-km section of the lower reach, as part of the movement study, resulted in the capture (ut not removal) of 79 kg of rook trout. The capture of such a large iomass in one day of electrofishing in 2 reflects the fact that the rook trout population in the lower reach was near an all-time high of 88 kg/ha in 2 (Tale 2). When the totals for angling and electrofishing removals in oth reaches during the more recent (24 28) period are compared (Tales 5, 6), angling accounted for only 7% of the 4397 rook trout removed from the upper reach, ut 95% of the 1346 rook trout removed from the lower reach. However, y weight, angling accounted for a greater proportion of the rook trout removed 19% of the 178 kg from the upper reach and 99% of the 11 kg from the lower reach reflecting the fact that small (<15 mm) fish are more readily caught y electrofishing than y angling. The iomass numers do not, however, take into account the effort expended in each activity. Angling can e undertaken y a single person, whereas electrofishing involved a large crew and was more laour intensive. 3.3 Catch-per-unit-effort Electrofishing usually resulted in a higher rook trout catch-per-unit-effort (CPUE) when compared to angling (Tale 7). However, the amount of time spent sampling and processing fish during electrofishing had a sustantial effect on CPUE. For example, the greatest CPUE for rook trout (34 fish/h and 1.37 kg/h) was achieved y a three-man electrofishing crew in 23, when a short section of stream was shocked and all trout captured were measured and released without weighing. In the 25 28 period, the CPUE was only 3.8 6.9 fish/h (.11.31 kg/h) when all trout were measured (all years) and weighed (26 28 only) and all rook trout were killed. CPUE values were lower in 24 than in 25, primarily ecause a concerted effort was also made to catch young-of-the-year in 24. It is therefore apparent that, if the ojective were to simply remove as many rook trout as possile, without gathering data to monitor changes in the fish population, the most effective method would e electrofishing without sampling fish. Quirk Creek Brook Trout Suppression Project 29 12
Angling CPUE was generally higher for unsupervised than for supervised outings (Tale 7), which has een the primary method of removing rook trout from the lower reach since 25. The higher CPUE likely reflects the greater familiarity with the stream and higher skill level of the anglers authorized to harvest rook trout on unsupervised outings. Using anglers on unsupervised outings to remove rook trout may not result in as high a CPUE as with electrofishing, ut the cost of removing rook trout y this method is much lower than y electrofishing. This is ecause the only cost to the fisheries management agency is for staff to administer the fish identification test, issue the fish research licence and enter data provided y these anglers. However, the challenge with removal of rook trout y angling, especially on a remote stream, is to maintain a high level of angling effort over successive years. This can e difficult, as it depends not only on weather and stream conditions, ut also on maintaining a high degree of interest in the project, especially when rook trout catch rates decline as the rook trout population declines. 4. CONCLUSIONS For the more remote upper reach, it has not een possile for anglers on unsupervised outings to exert sufficient pressure, or to harvest enough rook trout, to sustantially reduce the population and maintain it at levels comparale to the lower reach. For this reason, rook trout removal using one-pass electrofishing was employed in the upper reach during the 24 28 period. However, in the lower reach, angler harvest of rook trout appears to have een sufficient to keep the numer of large rook trout at a low enough level for the iomass of cutthroat trout to increase to record levels. Based on population estimates, fishing pressure, and harvest rates over the past five years, it appears that aout 1 angler-h/ha may e sufficient to keep the rook trout population from reounding to previous high levels in the lower reach. The data from this project also suggest that it may e necessary to harvest at least 5% of the large (>15 mm) rook trout population to have an effect on that population. Brook trout harvest was suspended in the upper reach after 28 so as to determine whether the rook trout population reounds (as expected) and whether anglers are ale to harvest enough rook trout from the lower reach to prevent the rook trout population from reounding there. This project has also demonstrated that anglers, who have een educated in how to identify fish, can safely harvest many more rook trout than would otherwise e permitted y the current twofish ag limit. Of the 9585 fish harvested y anglers on Quirk Creek since this project started, only 15 (.2%) were misidentified (were not rook trout). The suppression of rook trout populations y angling may therefore have the potential to work on other streams, provided that the streams selected are readily accessile to anglers (relatively close to a road), the anglers are educated in fish identification, and sufficient angling pressure can e exerted over multiple years. Quirk Creek Brook Trout Suppression Project 29 13