FISHERY DATA SERIES NO. 53 MOVEMENTS AND STOCK COMPOSITION OF NORTHERN PIKE IN MINT0 FLATS1. Rolland A. Holmes and Alan Burkholder

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1 FISHERY DATA SERIES NO. 53 MOVEMENTS AND STOCK COMPOSITION OF NORTHERN PIKE IN MINT0 FLATS1 Rolland A. Holmes and Alan Burkholder Alaska Department of Fish and Game Division of Sport Fish Juneau, Alaska August 1988 Reprinted June This investigation was partially financed by the Federal Aid in Sport Fish Restoration Act (16 U.S.C K) under Project F-10-3, Job Number N-8-4.

2 The Alaska Department of Fish and Game operates all of its public programs and activities free from discrimination on the basis of race, color, national origin, age, sex, or handicap. Because the department receives federal funding, any person who believes he or she has been discriminated against should write to: O.E.O. U.S. Department of the Interior Washington, D.C

3 TABLE OF CONTENTS Page LIST OF TABLES... LIST OF FIGURES... LIST OF APPENDICES... iii ii iv ABSTRACT... 1 INTRODUCTION... 2 Study Objectives... 2 METHODS... 5 Age and Sex Composition... 7 Length Composition... 7 Length-Weight Relationship... 7 Mixing Rates... 8 RESULTS... 8 Age and Sex Composition... 8 Length Composition Length-Weight Relationship Radio Telemetry DISCUSSION ACKNOWLEDGEMENTS LITERATURE CITED APPENDICES i

4 LIST OF TABLES Table Page 1. Sampling areas in Minto Flats Age composition of northern pike sampled from Area I and Area II of Minto Flats, May - June Age composition of northern pike sampled from Area I and Area II of Minto Flats, July - August Age composition of northern pike sampled from Area I and Area II of Minto Flats, September - October Age composition of northern pike sampled from Area III of Minto Flats, May - October Mean length-at-age for male and female northern pike from Minto flats, Mean lengths for northern pike sampled from Minto Flats, Estimates of mean length, mean weight, condition factor, and parameters of the length-weight relationships for male northern pike sampled in Areas I and II of Minto Flats during spring and autumn, Estimates of mean length, mean weight, condition factor, and parameters of the length-weight relationships for female northern pike sampled in Areas I and II of Minto Flats during spring and autumn, ii

5 LIST OF FIGURES Figure Estimated harvest of northern pike in Alaska, the Arctic Yukon Kuskokwim Area (AYK), and the Tanana Drainage, Minto Flats drainage and major sampling areas... Length frequencies of male northern pike sampled in Areas I and II during the spring and autumn... Length frequencies of female northern pike sampled in Areas I and II during the spring and autumn... Length frequencies of male, female, and all northern pike sampled in Minto Flats during Frequency of condition factors (K) for male northern pike sampled in Areas I and II of Minto Flats during spring and autumn, Frequency of condition factors (K) for female northern pike sampled in Areas I and II of Minto Flats during spring and autumn, Predicted length-weight values for male northern pike sampled during the fall and female northern pike sampled in the spring in Minto Flats, Log transformations of length versus weight of male northern pike sampled from Minto Flats during the spring of Log transformations of length versus weight of female northern pike sampled from Minto Flats during the fall of Percent of radio tagged northern pike that remained stationary or moved to a different area of Minto Flats between time of tagging and 4 December Page iii

6 LIST OF APPENDICES Appendix Table Page 1. Length frequency distribution of northern pike sampled from sport and subsistence harvests in Minto Flats Mean lengths of northern pike sampled from subsistence and sport harvests in Minto Flats Minto Flats northern pike sport fishing statistics iv

7 ABSTRACT Over 2,000 northern pike Esox Lucius were sampled from the population in Minto Flats during 1987 using gill nets, trap nets, hook and line, and a boat mounted electroshocking system. All fish were sampled for size, sex, and age data and all fish larger than 300 millimeters were tagged. In addition, movements of 98 northern pike implanted with radio transmitters were monitored. A concentration of spawning northern pike was located in the vicinity of Big Minto Lakes (Area I) and overwintering concentrations were located near the Big Lakes and the lower Tolovana River (Area III). Length at age and maximum age of northern pike sampled from Minto Flats were higher than those of northern pike populations sampled from lakes of interior Alaska. KEY WORDS: Northern pike, Esox Lucius, Minto Flats, length frequency, lengthat-age, length-weight relationship, sex ratios, radio telemetry, movements.

8 INTRODUCTION Northern pike Esox lucks have become increasingly popular with interior Alaska anglers in recent years. Next to Arctic grayling Thymallus arcticus, northern pike are the most sought after indigenous sport fish species in interior Alaska (Holmes 1987). Harvests of northern pike in interior Alaska averaged about 14,500 fish between 1977 and 1984 with more recent harvests being about 15,500 fish (Mills 1987). Interior Alaska accounts for 75% to 90% of the harvest of Alaskan northern pike on an annual basis and Tanana River Drainage waters alone account for about 65% of the harvest (Figure 1). Minto Flats, George Lake, and Volkmar Lake are the three most popular northern pike fishing areas in the Tanana River Drainage. Minto Flats is located approximately 50 km west of Fairbanks. It is a 200,000 hectare myriad of marsh and lakes interconnected by numerous sloughs and four major rivers (Figure 2). The four rivers that feed this system are the Tolovana River, the Chatanika River, the Tatalina River and Goldstream Creek. The rivers are slow flowing and meandering. The lakes are shallow and contain large areas of dense aquatic vegetation. Useable habitat for northern pike in Minto Flats consists of an estimated 6,000 hectares (Holmes and Pearse 1987). Access to the area is attained by float equipped aircraft, by road to Minto Village, or by road from Murphy Dome to the lower Chatanika River. Minto Flats has supported the largest northern pike sport fishery in Alaska every year but one since 1977 (Mills ). In addition, there is a subsistence fishery by the people of Minto Village. They harvest northern pike mainly in the spring and fall using gillnets and hook and line. In 1983, the estimated subsistence harvest was 3,003 fish (Andrews, in preparation). From 1981 to 1984 the average sport harvest in Minto Flats was 2,279 northern pike. However, in 1985 a new sport fishery developed on a concentration of overwintering northern pike in the lower Chatanika River. This fishery accounted for an increase in the sport fishery harvest in Minto Flats to 4,665 fish in 1985 and 4,903 fish in Additionally, angler reports and limited creel survey sampling (Appendix 1) indicated that a large portion of the harvested fish from this new fishery were prespawning females. Concern that increasing harvests could be exceeding sustainable yield prompted the Department to close the winter sport fishery for northern pike by emergency order in January The Department initiated this study to evaluate the stock composition of the northern pike of Minto Flats, and to determine if present management practices are sufficient to maintain this important fishery. Studv Obiectives The goal of this project is to identify stocks of northern pike in Minto Flats, to locate concentrations of northern pike, and to assemble data on the growth and mortality of northern pike for each stock. The specific objectives for 1987 were:

9 T moi NORTHERN PIKE HARVEST w --our= &- Estimated harvest of Kuskokwim Area (An<), a: brthern pike in Alaska 1 the Tanana Drainaee the Arctic Y -w-,,'ox wtf 'ukon

10 MXNTO FLFIl-S \ \ \ Figure 2. Minto Flats drainage and major sampling areas. \

11 1. to estimate the mixing rates of northern pike among their major spawning, summer-rearing, and over-wintering areas in Minto Flats; 2. to estimate the sex and age composition of the population(s) and of the harvests by northern pike sport and subsistence fisheries in Minto Flats; 3. to estimate the mean length of the population(s) and of the harvests by northern pike sport and subsistence fisheries in Minto Flats; and, 4. to estimate the parameters in length-weight and age-length relationships for the population(s) of northern pike in Minto Flats. All objectives were addressed during the 1987 field season. However, due to the complex nature of the study, sampling has been continued in This report summarizes results obtained during the first year of this project. METHODS Sampling was conducted from 19 May through 13 October 1987 throughout Minto Flats. Sampling gear included: fyke nets and hoop traps with leads, gill nets, hook and line, and a pulsed D.C. boat-mounted electroshocking system. In addition, anglers and subsistence fishermen contacted during sampling activities were interviewed and their catches sampled. After capture, northern pike were weighed to the nearest 50 grams and measured to the nearest millimeter of fork length. Sexual products or the external characteristics described by Casselman (1974) were used to identify sex. Scales were taken from which to estimate age. Each fish over 300 mm in length was given a fin clip and tagged with a Floy FD-68 internal anchor tag prior to being released. The capture location of each fish was recorded as one of 23 subareas of Minto Flats (Table 1). For evaluation of major movements and stock identification, these subareas were grouped into three major areas (Figure 2; Table 1): (I) the upper Chatanika River, Goldstream Creek, and Big Minto Lakes complex; (II) the lower Chatanika River, Tatalina River, and upper Tolovana River drainages; and (III) the lower Tolovana River and Swanneck Slough Drainages. Scales were used for estimating age. Previous analysis (Peckham and Bernard 1987) indicates estimated ages from scales, sagittal otoliths, and cliethra are similar. Scales were stored in coin envelopes and were later removed for cleaning and mounting on gum cards. Gum cards were used to make impressions on 20 mil acetate using a Carver press at 60,000 kg/cm2 (20,000 psi) heated to 93' C for 30 seconds. Annuli were counted along the dorsal radius using a Micron 770 Microfiche reader. Scales, cliethra, and vertebrae were taken from northern pike killed during sampling.

12 Table 1. Sampling areas in Minto Flats. Area Section No. Number Location 1 1 Big Minto Lake No Big Minto Lake No Big Minto Lake No Big Minto Lake No Goldstream Creek (upstream of Caches) 1 6 Goldstream Creek (Caches to Chatanika) 1 7 Chatanika (upstream of access road) 1 8 Chatanika (Goldstream to access road) 1 9a Chatanika (Birch Cr. Sl. to Goldstream) 2 9b Chatanika (Birch Cr. Sl. to Tolovana R.) 2 10 Tatalina (Chatanika to South Fork) 2 11 Main Tatalina (upstream of South Fork) 2 12 South Fork of Tatalina 2 13 Tolovana (Chatanika to Minto Village) 2 14 Tolovana (upstream of Minto Village) 2 15 Lakes south of Tolovana 2 16 Lakes north of Minto 2 17 Lakes northwest of Minto 2 19 Rock Island Slough 3 18 Tolovana (Chatanika to Swanneck Slough) 3 20 Tolovana (Swanneck to Tanana) 3 21 Swanneck Slough 3 22 Grassy Slough 3 23 Tanana River 6

13 Age and Sex Comnosition Age and sex composition was evaluated in each of the three major geographical areas of Minto Flats during each of three time periods. The percent age composition and associated variances were estimated as multinomial proportions using the following formulas (Cochran 1977): (1) ii - 2 n (2) V&) - P,(l n-l - P,), where: ni - the number of fish of age i in the sample: and, n = the number in the sample. Length Comoosition Mean length-at-age was calculated as the arithmetic mean for male and female northern pike. The mean length of northern pike sampled by sex in each of the three major areas and time periods was also estimated. Variances and standard errors for mean lengths were also calculated using standard normal procedures. Length frequency distributions by area, sex, and time were compared. Length-Weight Relationships The two parameters of the length-weight relationship were estimated for male and female northern pike in Areas I and II of Minto Flats during various times of the year. Area III was excluded from the analysis because too few fish were captured for meaningful analysis. Parameters of the length-weight relationship were estimated though iterative least squares fitting with a computer program of the Marquardt algorithm. The algorithm was estimated using a search over a set of starting values (a: 2 to 10 by 2 and b: 2.0 to 4.0 by 0.2). The set of estimates with the lowest least squares was selected by the best fit for the data set. Condition factors of northern pike by area, sex, and time were calculated according to Carlander (1969): (3) K = W x 105/L3, where: K = estimated condition factor; W = weight; and, L = length.

14 Mixing Rates Stock identification and mixing rates will be evaluated using Floy Tag recoveries obtained from sampling in subsequent years. In addition, a radio telemetry study was initiated during the 1987 field season. From 20 August to 6 October, Wildlife Materials radio transmitters (model HLPI-2150-LD) were implanted in 98 northern pike captured in Minto Flats. Forty-eight fish were tagged in Area I and 30 and 20 fish were tagged in Areas II and III, respectively. Transmitters were surgically implanted in the abdominal cavity above the pectoral girdle of each northern pike. The transmitter antenna extended through the abdominal wall and trailed behind the fish (Ross 1982). Locations of radio-tagged fish were determined by overflights of Minto Flats and the surrounding area. From 12 October through 4 December, 10 separate flights were made to locate radio tagged fish. Exact location of each fish was recorded on a map. Only information associated with overwintering movements is presented in this report because radio transistor monitoring and Floy tag recovery are ongoing. A more complete discussion of mixing rates will be presented in a separate report following the 1988 field season. Age and Sex Comnosition RESULTS A total of 2,274 northern pike were sampled in Minto Flats from 19 May to 13 October Males were captured more frequently than females during the spring spawning period, May and June. During May and June, 541 males (58%) and 387 (42%) females were captured in Area I (Table 2). During the same time period in Area II, 89 (54%) males and 76 (46%) females were captured. During mid summer (July and August) and autumn (September - October) sex composition in both Area I and II were approximately equal (Tables 3 and 4). In Area I, 108 males (46%) and 125 females (54%) were sampled in July and August, and 137 males (52%) and 129 females (48%) were samples in September and October. In Area II, 89 males (54%) and 76 females (46%) were sampled in July and August and 53 males (51%) and 50 females (49%) were sampled in September and October. Age composition of sampled female northern pike was older on average than males (Tables 2-4). In Area I, 10.5% of females and 2.6% of males were age 10 or older. In Area II, 8.8% of females and 2.6% of males were older than age 10. Age 6 was the modal age class for females in Area II while Age 4 was the modal age class for males. In Area I, age 7 was the modal age class for females and age 6 was the modal age class for males. In Area III, age 6 was the modal age for combined samples of male and female northern pike (Table 5). Through the summer, the age composition of males, females, and sexes combined remained stable in Area II (x2 not greater than 5.08, df=4, p>o.25). However, in Area I, the age composition of both males and females changed during each sampling period (x2 not less 8.37, df-4, p<o.lo). The proportion of larger northern pike in Area I decreased as the summer progressed (Table 2-4). In May and June, the age composition of both sexes of northern pike differed 8

15 Table 2. Age composition of northern pike sampled from Area I and Area II of Minto Flats, May - June Males Females Combined Sample Sample Sample Age Size Percent SE Size Percent SE Size Percent SE AREA Total AREA II Total

16 Table 3. Age composition of northern pike sampled from Area I and Area II of Minto Flats, July - August Males Females Combined Sample Sample Sample Age Size Percent SE Size Percent SE Size Percent SE AREA Total AREA II Total

17 Table 4. Age composition of northern pike sampled from Area I and Area II of Minto Flats, September - October Males Females Combined Sample Sample Sample Age Size Percent SE Size Percent SE Size Percent SE AREA I Total AREA II Total

18 Table 5. Age composition of northern pike sampled from Area III of Minto Flats, May - October Age Sample Size Percent SE Total

19 between Area I and Area II (x2 = 85.85, df-6, p<o.ol), with Area I having more older fish than Area II. However, the age compositions were not significantly different between Areas I and II in September and October (x2-1.04, df=6, p>o.95). Insufficient samples from the sport and subsistence fisheries were obtained to accurately estimate age composition and mean length of the catch. However, length frequency distribution, mean length and corresponding standard error and catch-effort information from the sampled sport harvest and winter subsistence fishery were calculated and are presented in Appendices 1, 2, and 3. Lenpth Comnosition The mean length-at-age of northern pike older than age 3 was always larger for females than for males (Table 6). When adequate sample sizes were obtained, the mean length of sampled northern pike females in each of the areas of Minto Flats was always larger than that of males (Tables 7-9). The largest mean length of both males and females occurred in Area I, during the spring. Length frequency comparisons also demonstrate the tendency for larger size composition in Area I than Area II (Figures 3 and 4) and larger females than males throughout Minto Flats (Figure 5). Length-Weight Relationship Length-weight relationships were evaluated by area and by sex. Differences in condition factor were apparent between fish sampled in the spring and fall. For both males and females in Areas I and II, condition factor was higher in the spring than in the fall (Tables 8 and 9; Figures 6 and 7). Thus, lengthweight relationships were calculated for spring and fall separately. Regression of length and weight with non-linear procedures (for season-sexarea combinations) provided accurate estimates in only two cases: females in the spring in Area I and females in the spring in Area II (Table 9). In four cases, estimates with nonsignificant intercept estimates were obtained: females in Area II in the fall, males in area II in the spring, and males in Area I and Area II in the fall (Tables 8 and 9 ). In two cases (females in Area I in the spring and males in Area I in the spring), no convergence occurred and therefore no estimates of the parameters of the length-weight relationship were possible. In most cases, the failure to obtain accurate estimates of the length-weight relationship was due to the scarcity of data or to their limited range. Graphical comparison of the predicted values of the length-weight relationships for females during the spring and males during the fall were not significantly different between Areas I and II (Figure 8). For those combinations for which estimates were not possible (males in the spring and females in the fall) graphical comparisons were made using the log transformations of the raw data (Figures 9 and 10). Again, no differences in the length-weight relationship between areas were apparent. Because graphical comparisons exhibited no consistent differences, all data from Areas I and II were pooled to calculate a single length-weight 13

20 Table 6. Mean length-at-age for male and female northern pike from Minto Flats, MALES FEMALES Age Sample Mean SE Sample Mean SE _

21 Table 7. Mean lengths for northern pike sampled from Minto Flats, May - June July - August Sept. - Oct. Total Area Male Female Male Female Male Female Male Female Area I Mean SE n Area II Mean SE n Area III Mean SE n Total Mean SE n ,

22 Table 8. Estimates of mean length, mean weight, condition factor, and parameters of the length-weight relationships for male northern pike sampled in Areas I and II of Minto Flats during spring and autumn, AREA1 AREA II 19 May - 01 Jun 04 Aug - 29 Aq 10 June - 18 June 29 Aug - 13 Sep Length Weight I? Length Weight K Length Weight K Length Weight K Number Mean SD SE Minium Maximum Estimate' SE Estimate2 SE Estimate' SE No Convergence3 a = E-07 * a = 9.13E * P = * b = b = b = Corr(a,b) = Corr(a,b) = Cor(a,b) = * Estimated condition factor. Estimated parameters of the length-weight relationship. Data were not adequate to provide estimates of the parameters of the length-weight relationship. Estimate not significant at 95% level.

23 Table 9. Estimates of mean length, mean weight, condition factor, and parameters of the length-weight relationships for female northern pike sampled in Areas I and II of Minto Flats during spring and autumn, AREA1 AREA II 20 May - 01 Jun 05 Aug - 29 Aug 10 June - 19 June 29 Aug - 13 Sep Length Weight K1 Length Weight K Length Weight K Length Weight K Number Mean SD SE Minium Maximum Estimate' SE Estimate' SE Estimate' SE P = b = Corr(a,b) = No Convergence3 a = l.oje a = * b = b = Corr(a,b) = Corr(a,b) = * Estimated condition factor. Estimated parameters of the length-weight relationship. Data were not adequate to provide estimates of the parameters of the length-weight relationship. Estimate not significant at 95% level.

24 g Z 31y) am i?e ( Jo- 25- lo-18 JuN& lm7 IwslNAlluI T I s- l l l5 725 lizi MIDPOINT OF CELLS (mm FL) 12s s MIDPOINT OF CELIS (mm FL) Figure 3. Length frequencies of male northern pike sampled in Areas I and II during the spring and autumn.

25 sou&y-1juic;1w7 80- FwLLIUcJlEAI so- I lo-10 Jwc 1m 18- fmuar\nll ~ IO- 9- i 0 7-2aAlJa5T- 1s -WW RIwIrnAIuI lo- 0-12s t a5 523 es 72s 125 UIDWINT OF CELIS (mm FL) Figure 4. Length frequencies of female northern pike sampled in Areas I and II during the spring and autumn.

26 20, Females n: I All Northern Plko n:2,274 Mldpolnt of 50 mm Length Class Figure 5. Length frequencies of male, female, and all northern pike sampled in Minto Flats during

27 Mootmloom rr nlajs WmYAIuI Y) m )NuJ2l b- ywwllluu S- 2- MIDPOINT OF CPU (K) MIDPOINT OF CELL (K) Figure 6. Frequency of condition factors (K) for male northern pike sampled in Areas I and II of Minto Flats during spring and autumn, 1987.

28 som Mmu8l. la7 m- 24- a- m- 18- l loo- o J - 0. _ lb12 JUL lm7 m- lplallgiiallu tl a am 1.05 its 1.48 la2 UIDPDINT OF CELL (K) UIDPDIM DF CELL (K) Figure 7. Frequency of condition factors (K) for female northern pike sampled in Areas I and II of Minto Flats during spring and autumn, 1987.

29 15, lo FEMALES i DURING WRING 7- AREAI 6- s l- 0 I 1 I 1 I I I r I I I I I I I n MALE5 DURING FALL AREA1 2- I I I 1 I FORK LENGTH (hi) Figure 8. Predicted length-weight values for male northern pike sampled during the fall and female northern pike sampled in the spring in Minto Flats,

30 AREAII. AREAI M. 5 I I I I I I 1 I I I I LOG [FORK mmi(tm)] Figure 9. Log transformations of length versus weight of male northern pike sampled from Minto Flats during the spring of

31 AREAII. AREAI 5k;. l... l +* ;.. z iti B J l l 4$ * +*. i ; +++I- SC I-.. * : +. t l *. 5.8 I -- I I 1 I I I I I I I LOG [FORK m~m(tdtd)j Figure 10. Log transformations of length versus weight of female northern pike sampled from Minto Flats during the fall of

32 relationship. This was done only for the spring periods for males and females. This will allow comparisons with data from lakes in the interior of Alaska which were also obtained in the spring just after spawning. Parameters of the length-weight relationship for females (estimated on the raw data using the Marquardt procedure) were: a ~10-~; SE(a) - O.1938x1O-5; b = 3.105; SE(b) ; correlation (a,b) = ; and n = 448. For males the parameter estimates (using log transformed data and the least-squares procedure) were: a = ; SE(a) ; b = 3.163; SE(b) = ; correlation (a,b) ; and n Radio Telemetrv Ninety-three of the 98 tagged fish were located at least once from 12 October to 4 December. Forty-four of the 48 fish tagged in Area I were located, 29 of 30 fish tagged in Area II were located and 19 of 20 fish tagged in Area III were located (one fish each in Areas I and II demonstrated no movement and were assumed dead). Most major movements occurred by mid-october and most fish remained relatively stable after that time through early December. Therefore, these movements are assumed to be associated with overwintering. The majority (93%) of fish tagged in Area I remained in that area after tagging (Figure 11). A similar pattern occurred in Area III, where 83% of the radio tagged fish remained to overwinter. On the other hand, all but 10% of the fish tagged in Area II left the area after tagging. Fifty-two percent moved upstream into Area I and 38% moved downstream into Area III. DISCUSSION Research in 1987 provided a picture of the age, sex, and size composition of the northern pike population(s) in Minto Flats. These results can be compared with the three other northern pike populations in interior Alaska from which data are available: T Lake (Clark 1988), Volkmar Lake (Clark and Gregory 1988), and George Lake (Clark, Bernard, and Pearse 1988). As with other northern pike populations, sex ratios in Minto Flats were skewed toward females in the older and larger groups. For example, in Minto Flats females composed 47%, 37%, and 92% of the fish in the small ( mm), medium ( ), and large (>750 mm) size categories, respectively. Whereas, in T Lake females represented 34.8%, 67.5%, and 100% of the fish in the small, medium, and large size categories, respectively. Growth of northern pike in Minto Flats is faster than that of any of the other three lakes for which large sample sizes are available. For example, a 5 year old male northern pike in Minto Flats averaged 560 mm, whereas, average length of five year old males were 496, 505, and 448 mm for George, Volkmar, and T Lakes, respectively. Five year old female northern pike in Minto Flats averaged 587 mm, while average length of five year old females was 531, 541, and 527 mm in George, Volkmar, and T Lakes, respectively. These high growth rates for northern pike in Minto Flats probably indicate the existence of a 26

33 / 0 0 [iiq ) Figure 11. Percent of radio tagged northern pike that remained stationary or moved to a different area of Hinto Flats between time of tagging and 4 December 1987.

34 more abundant food source than is available in the lake systems of interior Alaska. Maximum age of northern pike in Minto Flats was slightly above that of northern pike in George, Volkmar and T Lakes. In Minto Flats, the oldest male northern pike sampled was 14 and the oldest females were 16. For males, maximum ages were 11, 12, and 13 at T, George, and Volkmar Lakes, respectively. For females, maximum ages were 12, 14, and 16 at George, Volkmar, and T Lakes, respectively. The older age structure of northern pike in Minto Flats relative to other lakes in interior Alaska could indicate that overharvest has not occurred there. However, in 1968, out of a sample of 177 fish from Minto Flats, 54% were older than age 10 and the oldest fish sampled was age 23 (Alt 1969). These values are well above those seen in 1988 and indicate that recent increases in harvest may have contributed to declines in northern pike stock structure. Declines in the quality of the sport fishery also support the conclusion that declines in northern pike abundance have occurred. Catch rates of anglers interviewed in 1987 ranged form 0.1 to 0.4 northern pike per hour (Appendix 3). This is well below the catch rates of from 0.8 to 1.7 fish per hour reported by Alt (1970). To accurately assess the relative magnitude of current harvests (exploitation rate), an estimate of population abundance is necessary. Therefore, estimating abundance of northern pike in Minto Flats is a recommended research priority. Stock identification of northern pike in Minto Flats was not completed during the first year of the study. The question of whether more than one population exists in Minto Flats will be answered through tag recoveries in future years as well as through continued monitoring of the movements of the radio tagged fish. However, results to date indicate that the northern pike of Minto Flats represent only one population. These results include: (1) the similarity of the length-weight relationships for northern pike in Areas I and II sampled during the spring; and (2) the lack of consistent movements of radio tagged northern pike to separate overwintering areas. For example, about half of the fish that were tagged in Area II moved to Area I and half to Area III to overwinter. However, if separate over-wintering groups spawn in discrete areas, separate spawning populations do occur. High catch rates and larger size of fish sampled during May and June in Area I indicate that sampling there was targeting on a spawning concentration. Since there is also a major overwintering group in Area I (as documented though radio telemetry and past winter fisheries), separation of this group from other spawning groups may occur. However, even if discrete spawning units exist, for management purposes, one stock must be assumed because of significant mixing that appears to occur at other times of the year. ACKNOWLEDGEMENTS The authors are grateful for assistance with field work in 1987 from Fred DeCicco (who was the field project supervisor), Bob Murphy, Joe Klein, John Usian, Bob Clark, Al Mathews, Jared Baker, and Gary Pearse. We also thank L. Saree Gregory who determined ages from all scale samples, assisted with data entry and analysis, and prepared some tables and figures. Dave Bernard and John Clark assisted with all aspects of the project from planning to editing 28

35 of reports and their help is appreciated. Thanks also to the U.S. Fish and Wildlife Service for providing partial funding though the Federal Aid in Sport Fish Restoration Act (16 U.S.C k) under Project F-10-3, Job Number N- 8-3). LITERATURE CITED Alt, K.T Sheefish and pike investigations of the upper Yukon and Kuskokwim drainages with emphasis on Minto Flats drainages. Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Report of Progress, , Project F-9-1, 10: Sheefish and pike investigations of the upper Yukon and Kuskokwim drainages with emphasis on Minto Flats drainages. Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Report of Progress, , Project F-9-2, 11: Andrews, E. (in preparation). Use of fish and wildlife in Minto, Alaska. Alaska Department of Fish and Game Technical Paper No Carlander, K.D Handbook of freshwater fishery biology, Volume I, Iowa State University Press, Ames, Iowa. 752 p. Casselman, J.M External sex determination of northern pike, Esox Lucius Linnaeus. Transactions of the American Fisheries Society 103(2): Clark, J.H Abundance and life history features of the T Lake northern pike population during 1986 and Alaska Department of Fish and Game. Fishery Data Series (In Press). Clark, J.H. and L.S. Gregory Abundance estimates of the Volkmar Lake northern pike population with estimates of age, sex, and length composition, 1985 through Alaska Department of Fish and Game. Fishery Data Series (In Press). Clark, J.H., D.R. Bernard, and G.A. Pearse Abundance of the George Lake northern pike population in 1987 and various life history features of the population since Alaska Department of Fish and Game Fishery Data Series (In Press). Cochran, W.G Sampling techniques, 3rd ed. John Wiley & Sons, Inc. New York. 428 p. Holmes, R.A Research and regulatory summary report. Alaska Department of Fish and Game Report to the Alaska Board of Fisheries. Memo. 34 p. Holmes, R.A. and G.A. Pearse Northern pike stock status and regulatory concerns in the Arctic Yukon Kuskokwim Region. Alaska Department of Fish and Game Report to the Alaska Board of Fisheries. Memo. 12 p. 29

36 LITERATURE CITED (Continued) Mills, M. J Alaska statewide sport fish harvest studies. Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, Project F-9-11, 20 (SW-I-A). 122 pp Alaska statewide sport fish harvest studies. Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, , Project F-9-12, 21 (SW-I-A). 65 pp a. Alaska statewide sport fish harvest studies (1979). Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, , Project F-9-13, 22 (SW-I-A). 77 PP b. Alaska statewide sport fish harvest studies (1980). Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, , Project F-9-13, 22 (SW-I-A). 107 pp Alaska statewide sport fish harvest studies (1981). Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, , Project F-9-14, 23 (SW-I-A). 115 pp Alaska statewide sport fish harvest studies (1982). Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, , Project F-9-15, 24 (SW-I-A). 118 pp Alaska statewide sport fish harvest studies (1983). Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, , Project F-9-16, 25 (SW-I-A). 123 pp Alaska statewide sport fish harvest studies (1984). Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, , Project F-9-17, 26 (SW-I-A). 137 pp Alaska statewide sport fish harvest studies (1984). Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Performance Report, , Project F-9-17, 26 (SW-I-A). 137 pp Alaska statewide sport fish harvest studies. Alaska Department of Fish and Game. Federal Aid in Fish Restoration, Annual Report of Progress, , Project F-10-1, 27(RT): 137 pp Alaska statewide sport fisheries harvest report. Alaska Department of Fish and Game. Fishery Data Series No. 2:140 pp. Peckham, R.D. and D.R. Bernard Northern pike abundance and composition study. Alaska Department of Fish and Game. Fishery Data Series No p. Ross, M.J Shielded-needle technique for surgically implanting radiofrequency transmitters in fish. Progressive Fish Culturist 44(1):

37 APPENDICES 31

38 Appendix Table 1. Length frequency distribution of northern pike sampled from sport and subsistance harvests in Minto Flats. sport Subsistance Winter (1986 and 1987) Sumner (1987) Winter (1987) Males Females Combined' Males Females Combined Combined Length (nxn) n x l-8 x n x n x n x n x n x Total Combined includes northern pike of undetermined sex.

39 Appendix Table 2. Mean lengths of northern pike sampled from subsistance and sport harvests in Minto Flats. Sport Subsistance Summer 1987 Winter 1986 and 1987 Winter 1987 Parameter Male Female Combined Male Female Combined1 Combined Mean length SE n ' Combined includes northern pike of undetermined sex. 33

40 Appendix Table 3. Minto Flats northern pike sport fishing statistics. Date Catch CPUE Anglers Hours Interviewed Fished Kept Released Total Kept Total 3/30/ /17/ /4-31/ /4-23/ Total