Douglas J. Peck 1, John R. Foster 2, Joseph C. Lydon 3, Kevin J. Poole and Mark D. Cornwell 2

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1 The effectiveness of spring stream electro-fishing, trap netting and lake electro-fishing for determining walleye (Sander vitreus) abundance in Otsego Lake, NY Douglas J. Peck 1, John R. Foster 2, Joseph C. Lydon 3, Kevin J. Poole and Mark D. Cornwell 2 Abstract: This study was conducted to determine an efficient and accurate method of monitoring walleye populations in Otsego Lake. Catch per unit effort and mark and recapture data were collected using trap nets, stream electro-fishing, spring and fall boat electro-fishing, and fall gill netting. All sampling methods had flaws that limited their usefulness in monitoring walleye abundance. While electro-fishing samples of walleye in their spawning streams were strongly biased toward males, stream electro-fishing to conduct mark and recapture determinations of walleye abundance appear to be the most efficient way of monitoring walleye populations in Otsego Lake. INTRODUCTION (Sander vitreus) is an apex predator that is a critical component of the fisheries and ecology of many New York lakes and reservoirs (Festa et al. 1987). In order to monitor the populations of this important game fish, fisheries managers and researchers require accurate measures of abundance. Direct measures of walleye abundance, such as mark and recapture population estimations, are time consuming and expensive (Rogers et al. 2005). More often relative measures of abundance, such as angler success, netting, or electro-fishing indices of catch per unit effort are utilized (Hansen et. al 2000; Irwin et al. 2008; VanDeValk et al. 2008). In New York walleye population estimates follow the Percid Sampling Manual (Forney et al. 1994) developed by Cornell s Warm-water Fisheries Unit and the NYS Department of Environmental Conservation. This approach, which has been applied to many walleye lakes and reservoirs, makes use of catch per unit effort data from night boat electro-fishing, gill netting, trawling as well as mark and recapture studies (Brooking et al. 2002, 2004; VanDeValk et al. 2008). The Percid Sampling Manual was utilized to determine the relative abundance of Otsego Lake s walleye population using catch per unit effort data from boat electro-fishing, gillnetting (Cornwell & McBride 2007) and from mark and recapture studies (Lydon et al. 2008). The population estimates calculated by Lydon et al. (2008) were significantly less than the number of walleye indicated by electro-fishing and gillnet catches (Cornwell and McBride 2007). The discrepancy may be due to the highly mobile character of Otsego Lake walleye, differences in their habitat utilization, or catchability compared to that found in shallow weedy lakes and reservoirs utilized in previous studies of walleye abundance (Stich et al. 2007; Byrne et al. 2008). 1 Fisheries & Aquaculture Student, Fisheries & Wildlife Dept., SUNY Cobleskill, NY. 2 Fisheries & Wildlife Dept., SUNY Cobleskill, NY. 3 Robert C. MacWatters Intern in Aquatic Sciences BFS/Fisheries (1997) & Wildlife Dept., SUNY Cobleskill, NY.

2 In order to provide a critical measure of the success of past and future walleye stocking efforts in Otsego Lake an efficient and accurate measure of walleye population abundance was needed. Thus, the primary goal of this study was to evaluate different approaches for measuring the abundance of adult walleye in Otsego Lake. In order to meet this goal, walleye populations were surveyed in the lake using spring and fall boat electro-fishing, fall gill netting, spring trap netting along with stream electro-fishing. MATERIALS AND METHODS This study was conducted on Otsego Lake, Otsego County, New York (42.40⁰ N, 74.55⁰ W). Otsego lake has a surface area of 1,711 ha., a maximum depth of 50.5 m and an elevation of m (Harman et al. 1997). Marked Sample The marked sample of walleye were captured in six foot Oneida trap nets set on Sunken Island, and in the mouths of Shadow Brook, and Hayden, Cripple, and Leatherstocking Creeks from 9-25 April 2008 (Figure 1). were removed from the nets daily, measured, marked and returned to the opposite side of the net from which they were captured. In 2008 a total of 628 walleye were marked with a hole-punch at the base of the third dorsal fin spine and injected with a visible implant elastomer (VIE) behind the left eye. VIE marks were color coded to indicate capture site. Within this group of 628 marked walleye, 490 fish also received a NYSDEC numerically coded jaw-tag. In April, 320 walleye were marked after capture in six foot Oneida trap nets set at the mouth of Cripple Creek, Hayden Creek, Shadow Brook, and Leatherstocking Creek (Figure 1). In 2008, hundreds of walleye were observed upstream of the blocking trap nets. These fish had moved past the trap nets in the stream mouths without being captured. The same phenomena occurred in. Consequently backpack shocking was conducted upstream of the trap nets to increase the number of the walleye marked in. Smith-Root and Halltech backpack shockers were utilized to capture and mark 179 walleye upstream of the traps in Cripple Creek (below Clarke Pond), Shadow Brook (at Mill Road) and Hayden Creek (County Road-53). All walleye captured in were checked for previous marks, measured, hole-punched in the anal fin and injected with a color coded elastomer tag on the isthmus. that were > 300mm were marked. In Otsego Lake a walleye of that size was approximately three years of age. Samples Three recapture samples were made in Otsego Lake using a Smith-Root SR-16 boat electro-fisher. Otsego Lake s entire shoreline plus Sunken Island shoal were boat electro-fished in the spring of 2008 and, and in the fall. Electro-fishing occurred at night on 9, 10, 15, 31 of May 2008; 3, 4, 9, 16 June and 21, 22, 26, 27 October. A different section

3 of the lake was shocked each night. Boat electro-fishing effort expended was 16 hours in the spring of 2008, 11 hours in spring of and 9 hours in the fall of. Figure 1. Trap net (black dots) and gill net locations (Stars) in Otsego Lake, NY (from Cornwell and McBride In the September 2008 a recapture sample was collected during NYSDEC s warm-water gillnet survey. Monofiliment gill nets (150 ft) consisting of six 25 foot panels of 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 stretch mesh were set overnight at 10 different locations. Nets were set on the east shore 0.5 miles north of Clarke Point, off the west edge of sunken island, west shore just north of six mile point, center of Hyde Bay, west shore 0.2 miles south of five mile point, east shore 0.8 miles south of five mile point, west shore 0.1 mile south of three mile point, east shore 0.2 miles south of kingfisher tower, west side in rat cove, and east shore 0.3 miles north of lake outlet (Figure 1). In recapture samples were collected in Cripple Creek, Hayden Creek, and Shadow Brook from trap nets set on 2 April. Leatherstocking Creek s net was set on 7 April. All of the nets were removed on 2 May at the end of the spawning run.

4 were removed from the trap nets every hours. Captured walleye were examined for tags, measured, hole-punched in the anal fin, and injected with a color-coded elastomer tag on the isthmus before being returned to the opposite side of the net. Smith-Root and Halltech backpack electro-shockers were used in Cripple Creek (below Clarke Pond, Shadow Brook (at Mill Road) and Hayden Creek (County Road-53) to collect a recapture sample. Sampling locations were upstream of the trap nets. Electrofishing surveys for recaptured fish occurred from 8 pm to midnight on 16, 17, 18 April. All walleye were checked for marks, measured, hole-punched in the anal fin, and injected with a color-coded elastomer tag on the isthmus. Petersen mark-recapture population estimates were calculated using Bailey s (1951) modification. The minimum size for recaptured walleye included in the fall gill net or spring trap net samples was 367 mm. This figure is based on the expected 60mm annual growth of a 300 mm walleye. Mark Sample RESULTS The sex of the walleye in the marked sample differed significantly from 1:1 ratio (Table 1, P <.001). Males dominated in both the downstream trap nets and in the upstream backpack collections. Further, the per cent of females captured upstream in the electro-fishing sample was significantly lower than the per cent captured in the trap net sample (chi square test P <.001). Table 1. The occurrence of male and female walleye in marked samples. Sample Year Sampling Method/Location Males Females Per Cent Females 2008 Downstream Downstream Upstream % % % Collecting and processing walleye for marking in trap nets set in the mouth of four streams required a minimum of four hours per day. Further, in most locations a boat was needed to access the nets. In 2008 and, approximately 64 and 62 hours of team effort were utilized, respectively, to sample trap nets. This resulted in the capture of 10.6 and 5.8 walleye per team hour. In contrast, only 12 hours of effort was expended in on stream electro-fishing over 3 nights, resulting in the capture and processing of 14.9 walleye per team hour.

5 Stream Sample A stream recapture sample was made by trap net and backpack shocking to see if the walleye population spawning in a particular stream could be estimated. Overall, the trap net recapture sample contained a much smaller per cent (2.9%) of the 628 walleye marked in 2008 than expected (Table 2). In, the per cent of recaptured walleye (that were marked in 2008) was lower in the trap net catch (18/ %) than in the electro-fishing (25/ %) catch further upstream. Table 2. Statistics for stream recapture of 2008 marked walleye. Location Year Method- Location Number Marked Number* # Marked % Marked Fish Population Estimate 95% Confidence interval Shadow Brook Downstream % Cripple Creek Downstream % Hayden Creek Leatherstoc king Creek Shadow Brook Downstream Downstream Upstream % % % Cripple Creek Upstream % Hayden Creek Upstream % Leatherstoc king Creek Upstream *Denotes recapture sample adjusted for one-year growth % For many individual streams the data collected for population estimates were inadequate (Table 2). Consolidating the stream electro-fishing and trap netting data from the four sample streams was used to develop the overall population estimates for 2008 given in Table 3.

6 Table 3. Stream recapture of 2008 marked walleye. Year Method Number of Marked Number* # Marked Fish Per Cent Population Estimate 95% Confidence interval Trap Net Electrofishing % 10, % 4, *Denotes recapture sample adjusted for one-year growth Lake Sample Boat electro-fishing and gill netting was used to collect lake recapture samples for walleye marked in 2008 (Table 4). Boat electro-fishing in the spring of 2008 and resulted in adequate samples of marked and unmarked walleye. However, fall gill netting resulted in much lower capture rates of marked and unmarked fish. Gill net samples also resulted in a high mortality. Table 4. Otsego Lake recapture of 2008 marked walleye. Year Method Number Captured # Marked Fish Per Cent Population Estimate 95% Confidence interval 2008 Spring Boat Electrofishing % Fall Gill Net % Spring Boat Electrofishing 266* % *Denotes recapture sample adjusted for one-year growth. Fall and spring boat electro-fishing was utilized to collect a recapture sample of walleye tagged in (Table 5). So few walleye were captured in the fall electro-fishing sample that population estimates could not be made (Table 5).

7 Table 5. Otsego Lake recapture of marked walleye. Year Method Number* Captured # Marked Fish Per Cent Population Estimate 95% Confidence interval Fall Boat Electrofishing Spring Boat Electrofishing % % Males dominated the boat electro-fisher recapture samples (Table 6). However, the per cent of females was significantly higher (Chi square test, P <.01) than in the stream samples (Table 1). Table 6. Occurrence of male and female walleye in boat electro-fisher recapture samples. Sample Year Sampling Method/Location Males Females Per Cent Females 2008 Boat % Boat % Population Estimate Petersen Mark and formula with Bailey s modification (Bailey 1951), was used to estimate adult walleye population size. When trap nets were used to collect marked samples and spring boat electro-fishing was used to collect recapture samples 5338 adult walleye were estimated to occur in Otsego Lake in 2008 (Table 4) and 7995 in (Table 4). However, different data combinations gave widely different predictions. When recapture data was collected in the fall using gill nets (Table 3), 8714 fish were estimated to make up the adult walleye population in But, when boat electro-fishing data was used, the adult walleye population was estimated to be 4118 adult fish in In, stream electro-fishing and trap netting recapture samples, indicated that the adult walleye population in 2008 was 4019 and fish, respectively (Table 3). Changes in Population Abundance Catch per unit effort measures of population abundance of walleye indicate that the walleye population decreased in compared to 2008 (Table 7). Trap netting in the different

8 streams showed widely varying levels of decline (Table 7), with the total number caught over the entire season declining by 47.1% (Table 8). If trap net CPUE is measured by the number of walleye captured per trap day, the decline from 2008 (8.1 walleye/trap day) to (2.4 walleye/trap day) was 71.8%. Table 7. Per cent change between 2008 and walleye trap net catches during the spawning runs of four streams on Otsego Lake. Sample Location Number Captured 2008 Number Captured Per Cent Change Shadow Brook % Cripple Creek % Hayden Creek % Leatherstocking % Similarly, CPUE based on boat electro-fishing gave inconsistent results (Table 8). The number of fish caught based on a survey of the entire lake indicated an increase of 12.2% between 2008 and. However, when the same data were examined in terms of the number of fish caught per hour of electro-fishing, the CPUE indicated an increase of 63.4% in (Table 8). Population estimates using mark & recapture data taken from spring electro-fishing surveys indicate a 49.8% increase in walleye population between 2008 and (Tables 4 & 5).

9 Table 8. Per cent change between 2008 and walleye catches in trap nets and boat electrofisher samples. Sample Method CPUE Measure 2008 Per Cent Change Stream Stream Boat Boat # new fish per season # new fish per trap day # fish per Lake Sample # fish per hour % % % % DISCUSSION A major advantage of using standard techniques, such as the Percid Sampling Manual, to monitor walleye populations is that it provides repeatable and comparable data. It has been utilized in sampling a number of New York lakes, such as Canadarago, Cayuta, and Oneida Lakes (Brooking et al. 2007; Van DeValk et al. 2008). However, the data presented by Lydon et al. (2008) indicated a poor correlation between gill net and electro-fishing CPUE and walleye population density. Further, there was no correlation between gill net CPUE and electro-fishing CPUE in New York Lakes (Lydon et al. 2008), which should both be measures of walleye abundance. In this study, changes in walleye population abundance between 2008 and as indicated by trap net CPUE were opposite of the indications from spring electro-fishing CPUE and mark and recapture data. Other concerns with the application of the Percid Sampling Manual to Otsego Lake s walleye population were raised in this study. Using gill nets to collect CPUE data or recapture tagged walleye requires a lot of effort and ultimately results in the destruction of a portion of the very population under study. In order to recapture enough walleye for adequate statistical analysis in mark and recapture studies (Robson & Regier 1965), substantially more effort was needed in Otsego Lake. Similarly, fall boat electro-fishing covering the entire shoreline also required tremendous effort and provided poor results (5 walleye). Such data is grossly inadequate for developing CPUE data or collecting a recapture sample for mark and recapture studies. In Otsego Lake only spring boat electro-fishing data should be used for CPUE studies or mark and recapture studies. Spring electro-fishing also has the advantage over fall electro-fishing because walleye marked during the spawning period are allowed adequate time to disperse around the lake, but inadequate time for juvenile walleye to recruit (grow) into the adult class that was being analyzed.

10 This study and others (Beverton and Holt 1957; Lydon et al. 2008) indicate that repeated measures of CPUE may not accurately reflect changes in population abundance. The data collected so far indicate that mark and recapture studies are the best way of monitoring walleye populations in Otsego Lake. However, the accuracy of the mark and recapture method in estimating the size of a population rests on a number of assumptions (Ricker 1975). One assumption violated in this study is that there is an equal chance for individual adult walleye in Otsego Lake to be caught during the initial marking period and the recapture period. Both mark and recapture samples had a strong bias toward males. There were significantly more males than females in the recapture sample and in the sample of marked fish. The stream electro-fishing data had the most male bias, which may be because the electro-fishing sample was collected toward the end of the spawning run. In 2010, stream electro-fishing will occur earlier in the spawning run to determine if the catchability of female walleye does not increase. In spite of the problems with male sampling bias in Otsego Lake, capturing walleye on their spring spawning run is the most efficient way to conduct population studies. An efficient electro-fishing crew can capture, measure, sex, and fin punch 50 walleye per hour. The utilization of stream electro-fishing to collect both the mark and recapture sample is both fast and easy. These data could be used to estimate the population size of spawning fish for each of Otsego Lake s tributaries. Thus, using mark and recapture data to track changes in the number of spawning walleye in each tributary may be the most efficient way of monitoring the walleye population in Otsego Lake. ACKNOWLEDGEMENTS SUNY Cobleskill students volunteered many hours trap netting and electro-fishing, especially David Johns, William Crawley, and Justin Potter. Equipment for this study was supplied by SUNY Cobleskill, SUNY Oneonta Biological Field Station, and Cornell Biological Field Station. Advice on the field work was provided by Matt Albright and Dr. Willard Harman from SUNY Oneonta BFS and Tom Brooking of the Cornell Biological Field Station. REFERENCES Bailey, N.T.J On estimating the size of mobile populations from recapture data. Biometrika, 38: Brooking, T. E., J. R. Jackson, and D. M. Green Surveys of fish and limnology at Canadarago Lake, NY in New York State Department of Environmental Conservation. Albany, NY. 25 pp. Brooking, T. E., J. R. Jackson, A. J. VanDeValk, and L. G. Rudstam Factors affecting survival of stocked walleye in New York lakes: The final year of stocking. Performance report NY Federal Aid Study VII, Job 102. New York State Department of Environmental Conservation. Albany, NY.

11 Byrne, J. M., D. S. Stich, and J. R. Foster.. Diel movements and habitat utilization of walleye (Sander vitreus) in Otsego Lake, New York. In 41 th Ann. Rept., SUNY Oneonta Biol. Fld. Sta., Cooperstown, NY. Cornwell, M.D., and N.D. McBride (Sander vitreum) reintroduction update: stocking, gill netting and diet analysis In 40 th Ann. Rept. (2007). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Cornwell, M.D. and N.D. McBride.. Re-introduction Update: stocking, gill netting In 41 th Ann. Rept. ( 2008). SUNY Oneonta SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Festa, P.J., J.L Forney and R.T. Colesente management in New York State. NYSDEC Bureau of Fisheries. 104p. Forney, J.L., L.G. Rudstam, D.M. Green and D.L. Stang Percid sampling manual. Warmwater Fisheries Unit, Cornell Biological Field Station, Bridgeport, NY & NYS Department of Env. Cons., Albany, NY. Hansen, M. J., T. D. Beard, Jr, and S. W. Hewett Catch rates and catchability of walleyes in angling and spearing fisheries in northern Wisconsin lakes. North American Journal of Fisheries Management 20: Harman, W.N., L.P. Sohacki, M.F. Albright and D.L. Rosen The state of Otsego Lake Occas. Pap. No. 30. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Irwin, B. J., T. J. Treska, L. G. Rudstam, P. J. Sullivan, J. R. Jackson, A. J. VanDeValk, and J. L. Forney Estimating walleye density, gear catchability, and mortality using three fishery-independent data sets for Oneida Lake, New York. Can. J. Fish. Aquat. Sci. 65: Lydon, J.C., M.D. Cornwell, J.R. Foster, T.E. Brooking, and S. Cavaliere.. A markrecapture walleye population estimate of Otsego Lake, NY, 2008, with indications of overestimates based on catch per unit effort. In 41 th Annual Report (2008). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. Ricker, W.E Computation and interpretation of biological statistics of fish populations. Fisheries Research Board of Canada Bulletin 191, Ottawa, Canada, 382 pp. Robson, D.S. and H.A. Regier Sample size in Petersen mark-recapture experiments. Trans. American Fish. Society 93: Rogers M. W., M.J. Hansen, T. D. Beard Jr Relationships between recapture rates from different gears for estimating walleye abundance in northern Wisconsin Lakes. North American Journal of Fisheries Management 25:1,

12 Seber, G.A.F The Estimation of Animal Abundance. Edward Arnold, 2 nd edition, Griffin, London. Stich, D.S., B.F. Decker, J.C. Lydon, J.M. Byrne, and J.R. Foster Diel habitat utilization of walleye (Sander vitreum) in Otsego Lake. In 40 th Ann. Rept. SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta. VanDeValk, A. J., L. G. Rudstam, J. R. Jackson, T. E. Brooking, S. D. Krueger, J. L. Forney, W. W. Fetzer, R. DeBruyne, and E. L. Mills stock assessment and population projections for Oneida Lake, NY Federal Aid Study VII, Job 103. February NYSDEC, Albany, NY. 65 pp.