South Sector 5, Lake of the Woods: Fall Walleye Index Netting, 2007 Tom Mosindy

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1 Ministry of Natural Resources South Sector 5, Lake of the Woods: Fall Walleye Index Netting, Tom Mosindy Introduction This update presents results of fall walleye index netting (FWIN) conducted on South Sector 5 by the Lake of the Woods Fisheries Assessment Unit (LWFAU) during September and October. These are compared with indicators from previous FWINs of this sector in and (Mosindy and Mucha 26), in order to determine if the status of walleye (Sander vitreus) and other large fish community components have changed. This work supplements a long-term fish community index netting (FCIN) program that has been regularly conducted in this sector by the Lake of the Woods FAU since 1982 (Mosindy 1983). Study area South Sector 5 is the largest sector in Ontario waters of Lake of the Woods, covering 71,8 ha and extending from the mouth of the Rainy River northwards to Miles Bay (Figure 1). This sector is typically shallower and more turbid than the northern sectors. These waters tend to be homothermous and well oxygenated during most of the year with water clarity limited to secchi disc readings of 1 to 2 m. Late summer blooms of blue-green algae, primarily Aphanizomenon sp., can reduce secchi disc readings to <.6 m. Sector 5 has an estimated potential fish yield of 4.25 kg ha yr 1 and a morphoedaphic index (MEI) of 12.5 (Ryder 1965), based on a mean depth of 5.5 m and total dissolved solids (TDS) of 86 mg L 1. Walleye, sauger (Sander canadensis), northern pike (Esox lucius), muskellunge (E. masquinongy), whitefish (Coregonus clupeaformis), cisco (Coregonus artedi), yellow perch (Perca flavescens), lake sturgeon (Acipenser fulvescens) and white sucker (Catostomus commersonii) are native to this area. Smallmouth bass (Micropterus dolomieu), largemouth bass (Micropterus salmoides), black crappie (Pomoxis nigromaculatus) and rainbow smelt (Osmerus mordax) were introduced during the last century. Methods Netting in followed the FWIN protocol (Morgan ), and was stratified equally between two depth strata (i.e. 2 5 m and 5 15 m). All fish caught were identified to species, measured for both total and fork Buffalo Bay Warroad Manitoba Ontario Manitoba Minnesota 7 Shoal Lake Northwest Angle Big Traverse 1 miles 1 kilometres U.S.A. Winnipeg River 6 Big Is. Canada 2 Bigsby Is. 1 Kenora Aulneau Peninsula 5 Rainy River Rainy River Baudette Whitefish Bay 3 Sabaskong Bay Morson Figure 1. Location of Ontario sectors, Lake of the Woods. 4 Sioux Narrows length (mm), weighed (g), and examined to identify their sex and state of maturation. Stomach contents were examined and at least two calcified tissues were removed from each fish for ageing (Mann 1993), except sauger,yellow perch, cisco and white suckers which were subsampled at the rate of every fourth fish. Mature ovaries from walleyes were collected in the field and preserved in 7% ethanol for later analysis. Fecundity was estimated gravimetrically based on egg counts of ovary subsamples (Morgan et al. 23). Data were analyzed using FISHNET 2. software (Lester et al. 1989). Relative abundance was expressed both as the arithmetic mean number of fish caught per lift, pooled across all strata, and as the geometric mean catch per lift, based on the average of individual observations transformed to Log 1 (x + 1). The students Nestor Falls

2 2 t-test and analysis of variance (ANOVA) were used to test for statistical significance (at α =.5) in differences between means, depending on the type of samples being compared (Statistix7 2). Age total length keys were used to derive age distributions for sauger, yellow perch and cisco from their observed length distributions and aged subsamples using Ketchen s stratified sub sampling method (Ketchen 195). Condition was expressed as a weight total length relation: W = 1αL β, where W = round weight, L = total length, α = the intercept and β = slope. Weights at standard total lengths were calculated for male and female walleye from various years for comparison (Morgan et al. 23). Walleye maturity was assessed based on external condition of the gonads, according to criteria outlined in Duffy et al. (2). The Shannon Diversity Index (Krebs 1989) was used to evaluate the health and stability of the female walleye population. This index was calculated from the number of mature females and the number of age groups containing mature females in the population. Growth comparisons were based on observed mean total lengths-at-age data for both males and females. Pre-maturation growth (h) for walleye (Lester et al. 2), which was defined as the growth rate up to 35 mm total length (TL) for the sexes combined, was calculated as: h = 35 mm/ (T 35 +1), where age at 35 mm (T 35 ) was interpolated from mean total lengths of two consecutive age groups whose lengths fell around 35 mm. Total length and age at 5% maturity were based upon logarithmically transformed (Log 1 ) age and length-at-maturity schedules (i.e. the percent mature at age or length) for males and females which were then fitted to a logistic regression (modified Abrosov; Lysack 198). Total annual mortality (A) was calculated as A = 1 S; where S is the estimator of survival (Robson and Chapman 1961) for age groups in the observed catch. Results A relative standard error (RSE) of 9.7 % was reached after 6 net lifts in, as compared to an RSE of about after 68 lifts in. Netting commenced on September 17 th and was completed on October 5th, within a surface water temperature range of C. Overall, fish were slightly fewer but larger in the catch when compared to previous FWIN programs. The arithmetic mean catch by number decreased slightly from 85.5 fish lift 1 in to 78.9 fish lift 1 in, but mean catch by weight increased from 18.1 kg lift 1 to 23.3 kg lift 1 between sampling years (Table 1). Major changes in species composition included an increase in cisco numbers and biomass with a corresponding decline in yellow perch (Figures 2 and 3). Walleye Most characteristics of the walleye catch during the FWIN had improved over those observed in and, with the exception of a decline in relative abundance (Table 2). The geometric mean catch of walleye dropped from 1.5 and 11.1 fish lift 1 in and (Mosindy and Mucha 26) to 8.6 fish lift 1 in, which is below a geometric mean catch of 1.7 fish lift 1 for walleye in northwestern Ontario lakes (Morgan et al. 23). Although the vast majority of the catch was still comprised of fish age six and younger (Figure 4), the walleye age class structure had broadened to include 17 age groups in, up from 14 in. All age groups up to age 14, with the exception of age 7, were represented. Total annual mortality (A) estimates for fish age 5 (Table 2) declined from 47 to 4 for males and 32 to 26% for females during and. The Shannon Index, which was used to measure age diversity amongst mature females, remained high (.93) and indicative of a healthy stable population. The geometric mean catch of fish >age 6, which represent the majority of male and female spawners, increased significantly from.24 to.49 fish lift 1 between and (t = 5.44; df = 126; p<.1). Table 1. Catch per unit effort by species expressed as the geometric mean number and mean weight (kg) per net lift in FWIN gill nets during, and, Sector 5, Lake of the Woods, Ont. The arithmetic mean is given in brackets. Species Geometric mean number per lift Mean kg per lift (28.5) (13.3) (25.8) N.pike (.6) (.9) (1.2) W.sucker (2.2) (2.3) (1.5) B.crappie (1.9) (1.7) (1.5) Y.perch (28.4) (35.7) (1.7) Sauger (5.8) (13.2) (22.2) Walleye (15.2) (14.8) (1.9) All species (86.4) (85.5) (78.9) Total no. of lifts

3 3 Recent recruitment fluctuated with evidence of both a weaker than normal year-class in 2 and stronger than average year-class formation in alternating years; 25, 23 and especially 21. Estimated ages at 5% maturity increased from 2.9 to 4.4 years for males and from 5.9 to 7.4 years for females when and FWIN samples were compared (Table 2). Growth, expressed as mean total lengths-at-age for walleye (Figure 5), continued an overall decline when compared with and values (Mosindy and Mucha 26). Observed mean total lengthsat-age were within the range of average values for northwestern Ontario populations (Morgan et al. 23). Pre-maturation growth (h) also declined from 134 and 117 mm yr 1 in and to 12 mm yr 1 in. Condition, expressed as calculated weight (g) at a standard 45 mm total length (Table 2), improved slightly for both male and female walleyes since the FWIN, but remained below mean values for northwestern Ontario populations. Calculated weights at 45 mm total length for male and female walleye in were 82 and 798 g, as compared to 856 and 853 g for northwestern Ontario populations (Morgan et al. 23). Walleye fecundity, estimated at 65.1 eggs g 1 (SD = 14.6), was based on a sample of 6 females ranging from mm TL (mean = 537 mm, SD = 18.3) and 4 18 years old (mean = 8.3 yr, SD = 3.5). Relative fecundity had decreased from an estimate of 75.7 eggs g 1 in (Mosindy and Mucha 26). Sauger Sauger abundance continued to increase in Sector 5 FWIN catches, from a geometric mean catch of 3.7 and 1.4 fish lift 1 in and to 14.8 fish lift 1 in. Mean catch of sauger by weight also increased from 1.28 and 2.28 kg lift 1 in and to 2.95 kg lift-1 in (Table 1). A shift to smaller and younger fish was observed when and catches were compared. Mean size had declined from 27 mm to 245 mm TL, while mean age also declined from 3. years to 2.2 years old in and, respectively. Although all age groups were represented up to age 1, almost 75% of the catch sample was comprised of fish age 2 and younger (Fig. 6). Maturity rates, based on age at 5 percent maturity, increased from 1.8 years for males and 3.3 years for females in to 2.2 years for males and 3.8 years for females in. This continued a trend of increasing age at maturity for saugers in FWIN samples since. Total annual mortality rates, calculated for fish age 4, were about 55% for the sexes combined, 5 for males and 58% for females. Rates were comparable to those observed in, but considerably lower than total annual mortality rates of 74% for males and 77% for females in (Mosindy and Mucha 26). (N=5811) Sauger 15% Walleye 17% (N=4733) Sauger 28% Walleye 14% Y.perch 14% 16% Y.perch 42% B.crappie 2% N.pike 33% W.sucker 3% Spottail shiner Trout-perch 3% B.crappie 2% N.pike 2% W.sucker 2% Spottail shiner 2% Trout-perch 3% Figure 2. Percent species composition of the FWIN catch by number in and, South Sector 5, Lake of the Woods, Ont. Northern pike Northern pike also increased in both number and total weight per net lift in FWIN samples. The geometric mean number of pike per lift increased from.4 in to.6 in and.9 in, but remained well below a provincial average of 2.2 fish lift 1 in FWIN nets (Malette and Morgan 25). The mean total weight per lift increased from 1.43 kg in to 2.76 kg in and 3.99 kg lift 1 in. While northern pike represented less than 2% of the total catch by number (Figure 2), they comprised almost 17% of the total catch weight, surpassed only by walleye and cisco (Figure 3). Both age and size compositions continued to broaden with increased representation of older and larger fish in

4 4 (N= kg) Walleye 24% (N=14.6 kg) 24% Walleye 23% Sauger 12% Y.perch 7% B.crappie R.Bass W.sucker 6% N.pike 15% Sauger 13% W.sucker 12% Y.perch 3 N.pike 17% Burbot B.crappie Figure 3. Percent species composition of the FWIN catch by weight during and, South Sector 5, Lake of the Woods, Ont. catch samples. All age groups from young of the year to age 12 were represented in the FWIN (Figure 7). Northern pike averaged 663 mm TL and 4.2 years in, 759 mm and 5. years in, and 748 mm and 5.2 years in, which were well above the Ontario averages of 581 mm and 4.3 years for this species (Malette and Morgan 25). All males appeared to be capable of spawning at age two while all females age 4 and older were mature. Total annual mortality (A) for the sexes combined, calculated for fish age 3, declined from 4% in to 28% in and 25% in. Yellow perch A comparison of and catches with the FWIN indicated a declining trend in yellow perch abundance. Yellow perch comprised 14% by number and 7% by weight of the catch, as compared to 42% by number and by weight in the FWIN (Figures 2 and 3). The geometric mean number of perch per lift fell from 14.4 in to 11.9 in and 7.1 in. The mean weight of perch per lift also declined Table 2. A comparison of FWIN diagnostics for walleye caught during fall walleye index netting,, South Sector 5, Lake of the Woods, Ont. Diagnostic No. of year-classes (including young-of-theyear) present No.of missing year-classes up to age 14 Maximum age of mature fish up to first missing year-class Mean age (yrs) Mean catch (GM) Mean catch (GM) age Probability per net Shannon Diversity Index Prematuration growth (h) Condition given as Wt 45 mm TL males females % maturity 1 males females Mortality (A) 2 males ( 5 yr) females ( 5 yr) Relative fecundity (eggs per gram total fish weight) 1 Lysack (198) 2 Chapman and Robson (1961) n/a from 2.41 kg in to 1.79 and 1.59 kg lift 1 in and (Table 1). While a decline in abundance between and surveys was accompanied by a shift to younger and smaller perch, increased numbers of older, larger fish were noted in catches (Figure 8). Mean size and age of yellow perch in catch samples increased from 168 mm TL, 74.2 g and 2.9 years in to 28 mm TL, g and 3.1 years old in. The mean catch of perch 25 mm TL and age 4 more than doubled from 1.6 fish lift 1 in to 3.3 fish lift 1 in. Strong year-classes in 21 and 23 were partly responsible for this shift. Growth rates for both male and female perch, based on a comparison of mean total lengths-at-age (Figure 9), appear to have increased during and. Maturity rates for Sector 5 yellow perch were similar to those observed in

5 5 7 6 n = 85 X = 1.3 yrs S.E. =.6 Figure 4. Age frequency comparison of walleye caught in fall walleye index gill nets during,, and, South Sector 5, Lake of the Woods, Ont. Percent frequency n = 1 X = 2.1 yrs S.E. =.7 n = 653 X = 3.3 yrs S.E. = Mean total length (mm) Figure 5. Mean total length-atage comparison for walleye (sexes combined) caught in fall walleye index gill nets during,, and, South Sector 5, Lake of the Woods, Ont n = 34 X = 2.9 yrs S.E. =.6 Figure 6. Age frequency comparison of sauger caught in fall walleye index gill nets during,, and, South Sector 5, Lake of the Woods, Ont. Percent frequency n = 896 X = 3. yrs S.E. =.5 n = 1314 X = 2.2 yrs S.E. =

6 6 Percent frequency n = 35 Mean = 4.2 yrs S.E. =.26 n = 58 Mean = 5. yrs S.E. =.31 n = 73 Mean = 5.2 yrs S.E. =.32 Figure 7. Age frequency comparison of northern pike caught in fall walleye index gill nets during,, and, South Sector 5, Lake of the Woods, Ont Percent frequency n = 484 Mean = 2.9 yrs S.E. =.8 n = 642 Mean = 3.1 yrs S.E. =.7 Figure 8. Age frequency comparison of yellow perch caught in fall walleye index gill nets during and, South Sector 5, Lake of the Woods, Ont Mean total length (mm) Males Males Females Females Figure 9. A comparison of mean total lengths-at-age for male and female yellow perch caught in fall walleye index gill nets during and, South Sector 5, Lake of the Woods, Ont

7 7 ; males were mature and or maturing at the end of their second summer while most females were maturing by the end of their fourth summer. The total annual mortality rate (for ages age 3; both sexes combined) was 37%, a decline from 46% during the FWIN. Relative abundance of cisco appeared to have doubled from a geometric mean catch of 7.9 and 8. fish lift 1 in and to 16.2 fish lift 1 in. The representation of cisco in the total catch increased from about 16% by number and 24% by weight in to 33% by number and 3 by weight in (Figures 2 and 3). A slight decline in mean age and size from 3.6 years and 33 mm TL in to 3.3 years and 289 mm TL in was observed. All age groups from young of the year to age 1 were represented in the catch sample, although the 23 year-class (age group 4) dominated. Maturity rates were similar to those observed in ; all males were mature at age 2 while all females were maturing/mature at age 3. The total annual mortality rate for all fish age 3 had increased slightly from 47% in to 49% in. Other species The geometric mean number of white suckers per lift declined from 1.3 and 1.5 in and to 1. fish lift 1 in. The representation of suckers in the catch also declined from about 3% by number and 12% by weight in to about 2% by number and 6% by weight in (Figures 2 and 3). White suckers averaged 39 mm TL, 96 g and 4.8 years old in the sample, as compared to 397 mm TL, 956 g and 5.1 years old in. Black crappie relative abundance showed a slight decline between and FWIN samples (Table 1). Black crappie averaged 184 mm TL, 19 g and 1.9 years old in sample, and 189 mm TL, 127 g and 2. years old in. Crappies ranged in age from to 7 years old in FWIN catches. Troutperch (Percopsis omiscomaycus), a major forage species in South Sector 5, are regularly caught in smaller meshes of FWIN nets. Total lengths, weights and otoliths for age interpretation were collected during sampling. Troutperch numbers remained stable at about 2.7 fish lift 1 between and. Troutperch averaged 18 mm TL, 12 g and 1.6 years of age in. Fish ranged between mm TL and 1 3 years of age. Females represented almost 85% of the total catch (n = 161). Spiny water flea Spiny water fleas (Bythotrephes longimanus) (Figure 1) were identified in the stomachs of cisco, black crappie, yellow perch, walleye and sauger during routine diet analysis of fish caught during the FWIN. Spiny water flea were present in fish from at least 34 of the 6 FWIN set locations spread throughout South Sector 5 (Figure 11); from Black Point on Bigsby Island and Taylor Bay on the mainland along the eastern shore and northwards to Miles Bay. Although eight fish community index net (FCIN) sites spread throughout this area were sampled monthly, beginning in late May, no spiny water fleas were found in fish from these nets until they were observed in black crappie and cisco taken from Purdy Bay and Manitou Island netting sites during the last week of August. Spiny water fleas were present in almost 37% of all fish (n = 448) examined from FWIN nets. Highest percent occurrences were in species that normally fed heavily on zooplankton (Figure 12). Spiny water fleas were the most commonly identified diet items and zooplankton species in cisco and black crappie, occurring in 4 and 3% of all stomachs examined. They were also found in yellow perch (19%) and to a lesser extent in walleye and sauger (< ). Spiny water fleas were observed in all sizes of cisco (1 38 mm total length) and black crappie (14 35 mm), reflecting the full size range of each species vulnerable to the netting gear. In contrast, spiny water fleas were found more frequently in larger yellow perch, especially mature individuals greater than 2 mm total length, and in the smallest size classes of walleye and sauger that were sampled. Figure 1. Spiny water fleas, Lake of the Woods, Ont.

8 Science and Information Branch 8 Figure 11. Fall walleye index gill-net sites including those where spiny water fleas were observe in captured fish during September-October,, South Sector 5, Lake of the Woods, Ont B.Crappie Y.Perch Percent occurrence 35 3 Figure 12. Percent occurrence of various food items observed in stomachs of fish caught in fall walleye index gill nets during late September October, South Sector 5, Lake of the Woods, Ont Empty Digested Matter Spiny Water Other Flea Zooplankton Crayfish Mayflies Dipterans Fish Remains Stomach contents Discussion The status of walleye in South Sector 5 based on the FWIN results has continued to improve since. Overall walleye abundance, estimated at 8.6 fish lift 1 (geometric mean), had declined from and FWIN catches (Mosindy and Mucha 26). McLeod and Rob (29) noted a similar declining trend in walleye abundance from FWIN catches in the North Arm of Rainy Lake during the same time series ( ). They also observed the same variability in recent recruitment patterns, including an absence of walleyes from the 2 year-class, followed by an unusually large 21 year-class. The population age class structure in Sector 5 has broadened to include older age groups while the representation of older, mature fish has more than doubled from previous estimates. This reflects a long term decline in total annual mortality rates, a direct result of lower exploitation by both commercial and sport fisheries since the late 199s. A continuing decline in walleye growth rates and an increase in age at maturity since are indicative of decreased fishing pressure on walleye stocks in this area. Growth rates can also be affected by the cumulative thermal history

9 9 experienced by year-classes during their lifetime (Lester et al. 2). Year-classes exposed to cooler summers than previous cohorts can be smaller in average length. However, this factor could not account for observed differences in walleye growth when samples from and FWIN netting of Sector 5 were compared (Mosindy and Mucha 26). Although walleye growth appeared to have declined between and, all age groups sampled in had been exposed to higher cumulative growing degree days > 5 C than those sampled in. Reproductive potential remained high in the present study, with a favourable Shannon Diversity Index for mature females and a walleye fecundity estimate of 65.1 eggs g 1, which had decreased from but was still substantially higher than the northwest regional average of 4.7 eggs g 1 (Morgan et al. 23). Walleye fecundity is sensitive to changes in exploitation, food, energy availability, population density, population structure and behaviour (Baccante and Reid 1988). Walleye growth and maturity rates are currently lower than those observed for populations in nearby Sabaskong Bay (Mosindy ) and in Shoal Lake (Mosindy 28). A recovery in walleye stocks has been paralleled by improvements in populations of other species. Declines in total annual mortality, especially since, and/ or increased recruitment have been largely responsible for increases in the relative abundance and biomass of sauger, northern pike, and cisco. Although overall abundance of yellow perch declined, mean catches of older, larger fish has increased. A combination of factors including increased predation on younger age classes and a decline in targeted exploitation of older perch by the commercial fishery could account for this pattern. Spiny water flea (SWF), a predatory cladoceran which is native to Eurasian waters, invaded each of the Laurentian Great Lakes in the 198s. It was first observed in Saganagons Lake, near the southeastern boundary of Quetico Provincial Park in 23, in the South Arm of Rainy Lake in August 26 and in the Rainy River below the Fort Frances dam during the spring (Rob and Van den Broeck ). SWF presence in fish stomachs throughout South Sector 5 as far north as Miles Bay in the fall, a distance of well over 1 km, indicates that this zooplankter is capable of being dispersed quickly downstream. Although monthly FCIN netting along with water quality and zooplankton sampling throughout Sectors 5 and 6 began in late May, spiny water fleas were not observed until late August in two FCIN nets from Sector 5. By September October sampling, SWF densities had increased to the point that they represented the dominant zooplankton species and diet item in cisco and black crappies caught in Sector 5. Yan et al. (21) observed that spiny water flea abundance peaked in mid-summer, corresponding to a switch from parthenogenetic to gametogenic reproduction, during the initial invasion of Harp Lake, Ontario. However, a switch to resting-egg production during the fall is typical of this species in its native range in Eurasia. Spiny water fleas were not examined to determine their sex or state of maturity during the present study. While it is too early to assess impacts of spiny water flea on the native zooplankton and fish community, this species is the newest aquatic invader to arrive in Lake of the Woods, joining rainbow smelt and several nonnative crayfish, including the rusty crayfish (Orconectes rusticus). References Baccante, D.A. and D.M. Reid Fecundity changes in two exploited walleye populations. North American J. Fish. Manage. 8: Duffy, M.J., J.L. McNulty and T. Mosindy. 2. Identification of sex, maturity and gonad condition of walleye (Stizostedion vitreum vitreum). Ont. Min. Natur. Resour. Northwest Sci. & Technol. Thunder Bay, Ont. NWST FG pp. Ketchen, K.S Stratified subsampling for determining age distributions. Trans. Am. Fish. Soc. 79: Krebs, C.J Ecological Methodology. Harper & Row, New York. Lester, N.P., R.S. Kushneriuk, S. Orsatti, and D.G. Oliver FISHNET user manual. Ontario Ministry of Natural Resources, Toronto, Ontario. Lester, N.P., B.J. Shuter, R.S. Kushneriuk, and T.R. Marshall. 2. Life history variation in Ontario walleye populations: Implications for safe rates of fishing. Percid Community Synthesis. Population and Yield Characteristics Working Group. Ontario Ministry of Natural Resources. 34 pp. Lysack, W Lake Winnipeg fish stock assessment program. Man. Dept. Nat. Resour. Manuscript. Rep. No pp. Malette, M.D. and G.E. Morgan. 25. Provincial summary of northern pike life history characteristics based on Ontario s fall walleye index netting (FWIN) program 1993 to. Cooperative Freshwater Ecology Unit. Dept. Biology. Laurentian University. 138 pp.

10 1 Mann, S.E Collection techniques for fish ageing structures. Ont. Min. Nat. Resour. Northwest Sci. & Technol. Thunder Bay. NWST Tech. Rep. TR pp. McLeod, D.T. and A. Rob. 29. Fall walleye index netting on the North Arm of Rainy Lake, Ontario,. Ontario Ministry of Natural Resources. Fort Frances District Report Series No pp. Morgan, G.E.. Manual of instructions fall walleye index netting (FWIN). Ontario Ministry of Natural Resources, Percid Community Synthesis Diagnostics and Sampling Standards Working Group. 35 pp. Morgan, G.E., M.D. Malette, R.S. Kushneriuk, and S.E. Mann. 23. Regional summaries of walleye life history characteristics based on Ontario s fall walleye index netting (FWIN) program, 1993 to 21. Ontario Ministry of Natural Resources, Percid Community Synthesis Diagnostics and Sampling Standards Working Group. 192 pp. Mosindy, T An assessment of the South Sector fishery, Lake of the Woods, Ont. Min. Natur. Resour. Lake of the Woods Rainy Lake Fish. Assess. Unit Rep pp. Mosindy, T. and J. Mucha. 26. Fall walleye index netting of South Sector 5, Lake of the Woods, Ontario ( and ). Ont. Min. Natur. Resour., Northwest Sci. and Info., NWSI Tech. Rep. TR pp. + append. Mosindy, T.. Fall walleye index netting (FWIN) of Sabaskong Bay, Lake of the Woods, Ontario: 2 and 25. Ont. Min. Natur. Resour., Northwest Sci. and Info., NWSI Tech. Rep. TR pp. + append. Mosindy, T. 28. Shoal Lake fall walleye index netting: 26. Ont. Min. Natur. Resour., Northwest Sci. and Info. NWSI Aquatics Update pp. Rob, A., and J. Van den Broeck.. Spiny water flea monitoring results, Fort Frances District. Fort Frances District Report Series No. 76. Ont. Min. Natur. Resour. 19 pp. Robson, D.S. and D.G. Chapman Catch curves and mortality rates. Trans. Am. Fish. Soc. 9: Ryder, R.A A method for estimating the potential fish production of north-temperate lakes. Trans. Am. Fish. Soc. 94: Statistix 7 2. Statistix for Windows. Analytical Software, Tallahassee, FL. Yan, N.D., A. Blukacz, W.G. Sprules, P.K. Kindy, D. Hackett, R.E. Girard, and B.J. Clark. 21. Changes in zooplankton and the phenology of the spiny water flea, Bythotrephes, following its invasion of Harp Lake, Ontario, Canada. Can. J. Fish. Aquat. Sci. 58: Mosindy, T. 21. South Sector 5, Lake of the Woods: Fall walleye index netting,. Ont. Min. Natur. Resour., Northwest Sci. & Info, NWSI Aquatics Update pp. 21, Queen s Printer for Ontario ISBN (PDF) Lake of the Woods Fisheries Assessment Unit Science and Information Branch Ontario Ministry of Natural Resources P.O. Box 58, 88 Robertson Street Kenora, Ontario P9N 3X9 Tel: Website: ontario.ca/nwsi Cette publication spécialisée n est disponible qu en anglais