Fall Walleye Index Netting at Sandy Lake, Alberta, 2013

Transcription

1 Alberta, 2013 Fisheries Management Upper Athabasca Region, Slave Lake

2 Fisheries Biologist(s): Myles Brown, Kristy Wakeling, Mike Banko Disclaimer This is a summary report prepared for public distribution by Alberta Environment and Sustainable Resource Development, Fisheries Management Branch. This report has been peer reviewed, but may be subject to revision pending further data analysis. Abstract Sandy Lake was surveyed between September 18 th and 19 th, 2013 utilizing the Alberta standardized Fall Walleye Index Netting (FWIN) protocol to assess the stock status, relative abundance, structure, and reproduction (recruitment) of primarily the Walleye (Sander vitreus) population as well as northern pike (Esox lucius), yellow perch (Perca flavescens) and lake whitefish (Coregonus clupeaformis). This information was used to evaluate the status of the sportfish populations and ensure that current management actions, such as the Sport Fishing Regulations for Sandy Lake are in alignment with the stock status of the fish populations. In total 927 fish were captured in 12 nets comprised of 57 Walleye, 100 Northern Pike, 5 Lake Whitefish, 180 Yellow Perch, 583 Cisco (Coregonus artedi), and 2 Spottail Shinners (Notropis hudsonius). The Walleye catch per unit effort (maximum likelihood estimate) was 4.6 fish/100m 2 /24hr (95% C.I ) and the mean catch per unit effort estimated at 4.5 fish/100m 2 /24hr (95% C.I. 3-6). This catch rate is considered low and is indicative of a collapsed stock. The Walleye in Sandy Lake display very narrow size and age-class distributions with 95% of the captured Walleye (n=54) being young-of-the-year (yoy) and only two mature Walleye being detected; female Walleye (n=1), age 5 and male Walleye (n=1) age 5. There are several full year class failures evident in the population and due to the structure of the population it is not possible to determine 50% age or length at maturity or length at age (growth parameters), no Gonadosomatic Index (GSI) ratio could be derived. The northern pike catch per unit effort (maximum likelihood estimate) was 8 fish/100m 2 /24hr (95% C.I ) and the mean catch per unit effort was estimated at 8 fish/100m 2 /24hr (95% C.I. 7-9). This catch rate is considered low and indicates a stock status of vulnerable (ESRD Fisheries Management, unpublished data). Female pike (n=60) ranged in age from 1 to 13 years-old (2 full year class failures), due to the low sample size no maturation schedule could be derived as nearly all female (n=59) pike were mature and ranged in size from 251mm 1010mm total length (figure 4 and 5). Male pike (n=39) ranged in age from 2 to 15 years-old (three year class failures), due to the low sample size no maturation schedule could be derived as all male pike were mature and ranged in size from 477mm 809mm total length. The catch rate and biological metrics measured from the 2013 FWIN are indicative of a vulnerable northern pike population exhibiting signs of growth overfishing. The yellow perch catch per unit effort (maximum likelihood estimate) was 13.2 fish/100m 2 /24hr (95% C.I ) and the mean catch per unit effort was estimated at 14 fish/100m 2 /24hr (95% C.I. 6 22) (table 2). Female yellow perch (n=36) ranged in age from 1 to 3 years-old and ranged in size from 110mm 254mm total length. Due to the low sample size no accurate maturation schedule could be derived, all females were mature at 3 years of age. Male yellow perch (n=78) ranged in age from 1 to 3 years-old and ranged in size from 90mm 189mm total length. Due to the low sample size no maturation schedule could be derived as all male yellow perch were mature at 1 year of age. The low-moderate catch rate of yellow perch detected in the 2013 FWIN is indicative of a growth overfished vulnerable population. The lake whitefish catch per unit effort was 0.4 fish/100m 2 /24hr (95% C.I.0-1). As a result of the low sample size (n=5) the biological metrics for the lake whitefish population could not be adequately described. Compared to FWIN catch rates provincially, the low sample size detected in the 2013 index netting is indicative of a collapsed lake whitefish population. Page 2 of 13

3 Introduction Alberta Environment and Sustainable Resource Development implements strategies to manage sport fisheries for long-term sustainable harvest. Monitoring is required to evaluate the effectiveness of these strategies and to recommend alternate strategies where evidence supports change. The objective of Fall Walleye Index Netting is to estimate relative abundance, population structure and growth of Walleye, but we also collect data for northern pike, yellow perch and lake whitefish. These data are essential to provide sustainable harvest allocations for sport fish and to ensure the current management strategies in place for the sportfish species monitored are in alignment with the current status and structure of the populations. Sandy Lake is a 2793 ha lake located approximately 44 km southeast of Wabasca-Desmarais and 134 km north of Athabasca, Alberta. Sandy Lake is bordered on the south west corner of the lake by the community of Sandy Lake. There are several residences bordering the lake with low grad private boat launches and docks present at some residences and one public boat launch suitable for launching large size boats. There is a moderate amount of landuse and disturbance in the area around Sandy Lake. This disturbance is primarily attributed to oil field exploration with some timber harvest and agriculture. The sportfishing pressure on Sandy Lake in currently unquantified, however it is probable that the angler pressure will increase corresponding to the increased industrial activity in the Wabasca-Desmarias area as has been observed in other jurisdictions in Alberta. Sandy Lake supports a large number of licensed First Nations and Metis harvesters however the current level of harvest by First Nations and Metis food fishers is also currently unknown and will require additional investigation and assessment in order to identify potential future management objectives and options. Historically, Sandy Lake had supported commercial fishing opportunities. The commercial fishery was suspended in 1993 following decline in fish stocks in the lake and following communication between the Big Stone Cree First Nation and Fisheries Management staff at that time. Currently, the commercial fishery remains as a result of the high degree of use by First Nations and Metis food fishers and low relative abundance of several target and bycatch species in the lake. The current sportfishing regulations on Sandy Lake & tributaries & outlet for 1 km are: May 15 to March 31 - Walleye limit 0; Pike limit 3 over 63cm; Perch limit 15; Lake Whitefish limit 10; Burbot limit 10. Apr. 1 to May 14 Closed. Tributaries and outlets are closed Nov. 1 May 31. Methods A comprehensive description of equipment and methodology may be found in the Manual of Instructions Fall Walleye Index Netting (FWIN) (Morgan 2002) and the FWIN protocol used at Sandy Lake was in accordance with the Standards for Index Netting of Walleye in Alberta. Sites were selected randomly and were weighted by depth stratum. The number of nets set was by conducting power analyses of net catches to achieve a predetermined level of precision measured by a coefficient of variation of less than 0.2 (Haddon 2001, Morgan 2002). In total 14 nets were set, three nets were set in shallow depth stratum < 5m water, four nets were set in 5 15 meter medium depth stratum, and five nets were set in the > 15 m depth stratum, unique to lakes in this geographic area of Alberta. The FWIN nets consisted of eight panels, 1.83 m deep x 7.62 m in length with stretched mesh sizes of 25, 38, 51, 64, 76, 102, 127, and 152 mm. Nets were set for approximately 24 hrs before being cleared of fish and reset at a new location. The date and time the nets were set and pulled were recorded. Nets were set perpendicular to depth contours, and minimum and maximum depths were recorded. The net location was recorded in Universal Transverse Mercator (UTM) projection coordinates using the North American Datum 1983 (NAD 83) using handheld GPS units. Surface water temperature was also recorded for most net locations. The FWIN protocol requires that sampling occur at surface temperatures of 10 to 15 C. All fish species were kept for biological sampling. Catch was recorded by net location and mesh size. A net ID, date, mesh size, and count of each species of fish caught were recorded for each panel for catch-per-uniteffort (CPUE) calculations. All fish were measured for fork length (FL), and total length (TL) to the nearest millimetre, and weighed in grams, with individual data recorded on a sample envelope for each fish. Walleye, northern pike, yellow perch, and lake whitefish were also examined for gender and maturity, and a bony structure was removed for ageing. Page 3 of 13

4 Otoliths were collected and prepared following Watkins and Spencer (2009). Aging structures for the remaining species were collected and prepared following Mackay et al (1990). Walleye and northern pike ages were determined and verified by a second technician. Gonad weight was also collected for mature female Walleye. Walleye catch rates were calculated as walleye 100m-2 24hrs-1 and empirical confidence intervals to 95% were determined by bootstrapping net catches to 50,000 replications (Haddon, 2001). Size and age distributions, von Bertanlanffy growth curves, and maturity rates were calculated to assess the stock status according to modified guidelines of the Walleye Management and Recovery Plan (Berry 1995). Von Bertalanffy parameters were calculated using FAMS 1.0 software (Slipke and Maceina, 2010). The raw data can be found in Fish and Wildlife Management Information System (FWMIS). Walleye densities were estimated from the FWIN catch rate based on the regression y = x (where y = density (#/ha) and x = FWIN CUE) from unpublished Alberta Conservation Association and Fish and Wildlife data. Although not designed specifically for managing northern pike or other species captured, FWIN surveys may also be useful as a tool for assessing those populations as well. Fisheries Management Branch (FMB) is currently calibrating FWIN catch rates and structures of northern pike populations to other sampling methods currently used for this species. Biological data for northern pike, yellow perch and lake whitefish can be found in the Appendices. Results Index netting was conducted from September 18 th 19 th, Water temperature varied from o C at all 12 sampling sites. Nets were set for a mean time of 22 hours and 54 minutes, with soak times varying between 21 hours 24 hours and 50 minutes from site to site. In total 927 fish were captured in 12 nets comprised of 57 Walleye, 100 Northern Pike, 5 Lake Whitefish, 180 Yellow Perch, 583 Cisco (Coregonus artedi), and 2 Spottail Shinners (Notropis hudsonius). All fish that were in edible condition were distributed to members of the Bigstone Cree First Nation and other treaty status First Nations and eligible Métis individuals residing in the area of Sandy Lake. Walleye The Walleye catch per unit effort (maximum likelihood estimate) was 4.6 fish/100m 2 /24hr (95% C.I ) and the mean catch per unit effort estimated at 4.5 fish/100m 2 /24hr (95% C.I. 3-6) (table 2). This catch rate is considered low and is indicative of a collapsed stock (Sullivan 2003). The Walleye in Sandy Lake display very narrow size and age-class distributions (figure 2 and 3) with 95% of the captured Walleye (n=54) being young-ofthe-year (yoy) and only two mature Walleye being detected; female Walleye (n=1), age 5 and male Walleye (n=1) age 5. There are several full year class failures evident in the population and due to the structure of the population it is not possible to determine 50% age or length at maturity (table 3 and 4) or length at age (growth parameters), no Gonadosomatic Index (GSI) ratio could be derived. The Walleye population in Sandy Lake is at high risk of extirpation given the low abundance (collapsed stock) and limited nature of the size and age class distributions (table 5). Northern Pike The northern pike catch per unit effort (maximum likelihood estimate) was 8 fish/100m 2 /24hr (95% C.I ) and the mean catch per unit effort was estimated at 8 fish/100m 2 /24hr (95% C.I. 7-9) (table 2). This catch rate is considered low and indicates a stock status of vulnerable (ESRD Fisheries Management, unpublished data). Female pike (n=60) ranged in age from 1 to 13 years-old (2 full year class failures), due to the low sample size no maturation schedule could be derived as nearly all female (n=59) pike were mature and ranged in size from 251mm 1010mm total length (figure 4 and 5). Male pike (n=39) ranged in age from 2 to 15 years-old (three year class failures), due to the low sample size no maturation schedule could be derived as all male pike were mature and ranged in size from 477mm 809mm total length. Northern pike had moderate growth rates reaching 630mm Page 4 of 13

5 TL 4 years for females and 5 years for males. Females (K= 0.218) are growing slightly faster than males (K= 0.197) and are reaching larger L (1009.8mm TL) than males (801.7mm TL) (figure 6).The catch rate and biological metrics measured from the 2013 FWIN are indicative of a vulnerable northern pike population exhibiting signs of growth overfishing. Yellow Perch The yellow perch catch per unit effort (maximum likelihood estimate) was 13.2 fish/100m 2 /24hr (95% C.I ) and the mean catch per unit effort was estimated at 14 fish/100m 2 /24hr (95% C.I. 6 22) (table 2). Female yellow perch (n=36) ranged in age from 1 to 3 years-old and ranged in size from 110mm 254mm total length. Due to the low sample size no accurate maturation schedule could be derived, all females were mature at 3 years of age. Male yellow perch (n=78) ranged in age from 1 to 3 years-old and ranged in size from 90mm 189mm total length (figure 7 and 8). Due to the low sample size no maturation schedule could be derived as all male yellow perch were mature at 1 year of age. The low-moderate catch rate of yellow perch detected in the 2013 FWIN is indicative of a growth overfished vulnerable population. Lake Whitefish The lake whitefish catch per unit effort was 0.4 fish/100m 2 /24hr (95% C.I.0-1). As a result of the low sample size (n=5) the biological metrics for the lake whitefish population could not be adequately described. Compared to FWIN catch rates provincially, the low sample size detected in the 2013 index netting is indicative of a collapsed lake whitefish population. Interpretation This was the first inventory of Sandy Lake using the Fall Walleye Index Netting protocol; previously it was assessed by the Alberta Conservation Association in 2002 using a previous netting protocol. Although the results are not directly comparable, the 2002 survey detected Walleye age 6-9 years old and between mm total length indicating that the Walleye population has declined since that survey as these ages and sizes of fish were not detectable in the 2013 FWIN survey. Currently the Walleye population is considered to be collapsed, exhibiting signs of recruitment overfishing and at high risk of extirpation as 95% of the Walleye detected were young-of-the-year and only two mature (1 male, 1 female) Walleye were found. The sportfishing regulation for Walleye on Sandy Lake is currently a zero bag limit; Sandy Lake has had a zero bag limit on it since at least 1998 according to historical Alberta Guides to Sportfishing Regulations. Despite this restrictive regulation, the Walleye population, specifically the mature/adult fish have still declined to the point where they are barely detectable. Historically, Sandy Lake sustained a moderate to high level of commercial harvest, including several harvest of thousands of kilograms of Walleye. Following requests and discussions with the Big Stone Cree First Nation and reported declines in fish stocks the commercial fishery was suspended in Given the current stock status of Walleye and Lake Whitefish, the commercial fishery on Sandy Lake will remain suspended. Currently, Sandy Lake supports an unquantified level of First Nations and Métis subsistence harvest and has been identified by the leadership and members of the Big Stone First Nation as an important local fishery. The allocation and use of Walleye in Sandy Lake needs to be assessed and it is recommended that additive conservation measures be investigated to promote the recovery of this Walleye population. The northern pike population in Sandy Lake can be characterised as being vulnerable, at a moderate abundance, exhibiting traits of growth overfishing and at moderate risk of collapse. There is broad age-class distribution with 13 age-classes present containing low densities of larger adult northern pike (figure 4 and 5) with no fish captured older than 15 years. There is evidence of multiple year-classes contributing recruitment to the population however densities are low with catch rates < 1 fish/100m 2 /24hrs for all but one (6 year olds) mature age cohort. Concurrently, there is a weak indication of recruitment with only two immature fish captured, all other northern pike (n=98) are mature. The low signs or recruitment in the 0-2 year old age classes are likely a result of the nets not being set in water less than 2m in depth and there are vulnerability and catchability uncertainties regarding Page 5 of 13

6 detection of 0-2 year old pike. There is no evidence of truncation of northern pike at or below the current size restriction at 630mm TL with pike escaping out to past 1000mm TL. With the Walleye sportfishing regulation being at a zero harvest bag limit, continued attention will need to be focused on the pike population in subsequent index netting surveys to ensure that the sportfishing regulation is in alignment with the status and structure of the pike population. The age and size class structure of the yellow perch population is fairly narrow, with few large fish being detected in the sample. The catch rate of Yellow Perch has shown signs of improvement and has increased steadily since 2006 (table 1). Although the abundance of Yellow Perch is moderate relative to other lakes in the northern boreal region, the narrow size and age class structure are representative of a growth overfished vulnerable population at low risk of collapse. The catch rate of lake whitefish is very low relative to other lakes that have been assessed using FWIN in Alberta corresponding to a low relative abundance and is likely representative of a collapsed population (table 2). Tables and Figures Table 1. Species catch summary by site, Sandy Lake, September 30, 2013 Fish Count per Species Set Number UTM E UTM N Meridian Lift Date Soak Time (h) Max Depth (m) Min Depth (m) CISC LKWH NRPK SPSH WALL YLPR Set Total SD (Zone 12) 20-Sep SD (Zone 12) 20-Sep SD (Zone 12) 19-Sep SD (Zone 12) 20-Sep SD (Zone 12) 20-Sep SD (Zone 12) 20-Sep SD28A (Zone 12) 19-Sep SD (Zone 12) 20-Sep SD (Zone 12) 20-Sep SD (Zone 12) 19-Sep SD (Zone 12) 20-Sep SD (Zone 12) 19-Sep Species Total Table 2. Mean catch rate (fish/100m 2 /24hrs) for sportfish species monitored during the Sandy Lake, 2013 FWIN surveys Species Year CPUE 95% CI WALL ( ) NRPK ( ) YLPR ( ) Page 6 of 13

7 Figure 1. Map of the Fall Walleye Index Netting sampling location on Sandy Lake, Alberta, 2013 Figure 2. Age distribution of Walleye captured and sampled from Fall Walleye Index netting at Sandy Lake, Alberta, 2013 (n=57 ). Y-axis is catch per unit effort (fish/100m 2 /24hrs), the X-axis is age of Walleye in years. Page 7 of 13

8 Figure 3. Total length distributions of Walleye from Fall Walleye Index netting at Sandy Lake, Alberta, 2013 (n=55). Y-axis is catch per unit effort (fish/100m 2 /24hrs), X-axis is total length of Walleye in millimetres. Table 3. Walleye length composition (sample number, percent) of sexes combined, for males and female; number and maturing (percent) for Sandy Lake 2013 FWIN survey. Males Females Number Comp No. Mature No. Mature TL (mm) (N) (%) (N) (%) (N) (%) SUM Page 8 of 13

9 Table 4. Walleye age composition (sample number, percent) of sexes combined, for males and female; number and maturing (percent) for Sandy Lake 2013 FWIN survey. Males Females Number Comp No. Mature No. Mature Age (N) (%) (N) (%) (N) (%) SUM Figure 4. Age distribution of northern pike captured and sampled from Fall Walleye Index netting at Sandy Lake, Alberta, 2013 (n=100 ). Y-axis is catch per unit effort (fish/100m 2 /24hrs), the X-axis is age of northern pike in years. Page 9 of 13

10 Table 5. Criteria for classifying status of Walleye fisheries adapted from Alberta s Walleye Management Recovery Plan and modified by Sullivan (2003) for FWIN analysis. Category of Walleye Stock Parameter Collapsed Vulnerable Stable Old Growth Age-class Wide or Narrow Narrow Wide Wide Few old fish (>10 distribution distribution years) (>8 age classes) (>8 age-classes) Sandy Lake Age Classes Present Mean Age 6 to 10 4 to 6 6 to 9 >9 Sandy Lake (yoy) Age-Class Stability Sandy Lake 2013 Stable or Unstable 1-3 year classes 3-5 year-classes Low variance in Recruitment failures support fishery support fishery with recruitment No strong year classes 95% yoy, no Walleye over 5yrs old large variances in recruitment Length-at-age Fast Growing Moderate Slow Growing Slow Growing 50cm (TL) in 4-50cm (TL) in cm (TL) in 9-50cm (TL) in 12-7years years 12 years 15 years Sandy Lake 2013 Age 5 Age-at-Maturity Females 4-7; Females 7-8 Females 8-10 Females (50%)/ (100%) Males 3-6 Males 5-7 Males 7-9 Males Sandy Lake 2013 Females (5 / unknown) Males (5 / unknown) FWIN Catch Low <10 Rate Walleye/net Moderate; High >20 High >20 (CPUE) Walleye/net Walleye/net Walleye/net Sandy Lake Walleye/net Page 10 of 13

11 Figure 5. Total length distributions of northern pike from Fall Walleye Index netting at Sandy Lake, Alberta, 2013 (n=100). Y-axis is catch per unit effort (fish/100m 2 /24hrs), X-axis is total length of northern pike in millimetres. Figure 6. Length-at-Age scatter plot with von Bertalanffy growth equations for all northern pike sampled 2013; (n=100); K=0.288, L =889.4mm TL, t0= ), females (n=60); K=0.218, L =1009.8mm TL, t0= ), and males (n=39), K=0.197 L =801.7 mm TL, t0= ). Page 11 of 13

12 Figure 7. Age distribution of yellow perch captured and sampled from Fall Walleye Index netting at Sandy Lake, Alberta, 2013 (n=67 ). Y-axis is catch per unit effort (fish/100m 2 /24hrs), the X-axis is age of yellow perch in years. Figure 8. Total length distributions of yellow perch from Fall Walleye Index netting at Sandy Lake, Alberta, 2013 (n=167). Y-axis is catch per unit effort (fish/100m 2 /24hrs), X-axis is total length of yellow perch in millimetres. Page 12 of 13

13 Citations Berry, D.K Alberta s Walleye management and recovery plan. Alberta Environmental Protection, Natural Resources Services. Number T/ pp. Berry, D.K Alberta s Northern Pike management and recovery plan. Alberta Environmental Protection, Natural Resources Service. Number T/ pp. Government of Alberta Standards For Index Netting of Walleye in Albert. Technical Report. Prepared by Alberta Sustainable Resource Development, Fish and Wildlife Division, Fisheries Management Branch, Edmonton, Alberta, Canada. 20pp. Haddon, M Modeling and quantitative methods in fisheries. Chapman and Hall/CRC, Boca Raton, Florida, USA. 406 pp. Mackay, W.C., G.R. Ash, and H.J. Norris (eds.) Fish ageing methods for Alberta. R.L. & L. Environmental Services Ltd. in assoc. with Alberta Fish and Wildl. Div. And Univ. of Alberta, Edmonton. 113 p. Morgan, G.E Manual of instructions Fall Walleye Index Netting (FWIN). Percid Community Synthesis, Diagnostics and Sampling Standards Working Group. Ontario Ministry of Natural Resources. 34 p. Slipke, J., and Maceina, M. Fisheries Analyses and Simulations Tools- v2.1 (FAST). Department of Fisheries and Allied Aquaculture, Auburn University, AL, USA. Sullivan, M. G Active Management of Walleye Fisheries in Alberta: Dilemmas of Managing Recovering Fisheries. North American Journal of Fisheries Management 23: ,2003. Watkins, Owen B. and Stephen C. Spencer Collection, preparation and ageing of walleye otoliths. Fish and Wildlife Division, Alberta Sustainable Resource Development. 14pp. Von Bertalanffy, L A quantitative theory of organic growth. Human Biology 10: Page 13 of 13