Pike and Walleye in the Rocky Lake-Root-Reader Marsh

Manuscript Report No. 04-01

PIKE AND WALLEYE IN THE ROCKY LAKE- ROOT-READER MARSH COMPLEX

by Walt Lysack 2004

Manitoba Water Stewardship Fisheries Branch

TABLE OF CONTENTS DESCRIPTION AND HISTORY OF THE STUDY AREA ...... 4 ROOT – READER PIKE STUDY...... 7 ROCKY LAKE FISH STOCK MONITORING PROGRAM ...... 24 ROCKY LAKE CREEL SURVEY...... 29 DISCUSSION...... 39 ACKNOWLEDGEMENTS ...... 52 REFERENCES...... 53

LIST OF TABLES Table 1. Rocky Lake’s water chemistry during the 1980s...... 19 Table 2. Daily angling duration parameters...... 32 Table 3. Parameters of fishing effort and catches of pike, walleye and bass ...... 33 Table 4. Parameters of CUE, no. fish angler hour ...... 34 Table 5. Parameters of individual pike and walleye weights ...... 35 Table 6. Parameters of kept walleye CUE reported on the creel survey forms...... 36 Table 7. Parameters of walleye abundance and yield...... 50

LIST OF FIGURES Fig. 1. Rocky Lake...... 6 Fig. 2. Root-Reader Marsh...... 7 Fig. 3. Water temperatures at station 1 in 2002...... 8 Fig. 4. Water temperatures at station 3 in 2002...... 9 Fig. 5. Water temperatures at station 5 in 2002...... 10 Fig. 6. Water temperatures at station 7 in 2002...... 11 Fig. 7. Temporal changes in flow velocity through the fishway in 2002...... 12 Fig. 8. Temporal changes in flow velocity through the fishway in 2003...... 13 Fig. 9. The increase in flow velocity from the top to the bottom of the fishway in 2002. 14 Fig. 10. DO and water temperature relationship...... 15 Fig. 11. Temporal changes in DO...... 16 Fig. 12. DO during late autumn and winter of 2002-2003...... 17 Fig. 13. Spatial distribution of DO from May to September 2002...... 18 Fig. 14. Temporal changes of pike ages in 2002...... 20 Fig. 15. Temporal changes in pike sizes passing through the fishway in 2003...... 21 Fig. 16. Variability of CUE among gangs in 2003...... 21 Fig. 17. Growth of pike...... 22 Fig. 18. Seasonal changes in age composition of pike in the Root-Reader marsh...... 22 Fig. 19. Changes in pike prey with increasing pike size...... 23 Fig. 20. Size distribution of Root-Reader pike in 2003...... 24 Fig. 21. Temporal abundance changes in Rocky Lake's fish species...... 25 Fig. 22. Comparative growth of Rocky Lake's fish species...... 26 Fig. 23. Changes in Rocky Lake's walleye age compositions from 1981 to 1999...... 27 Fig. 24. Increase in maturity rate of Rocky Lake's walleye females...... 28 Fig. 25. 1999 size distribution of Rocky Lake's pike and mature frequencies...... 29 Fig. 26. Total numbers of boats and anglers on Rocky Lake...... 31 Fig. 27. Walleye, pike and bass CUE in 2002...... 32

2 Fig. 28. Weight distributions predicted from reported fork lengths...... 35 Fig. 29. Distribution of kept :caught ratios of walleyes and pike from the creel survey.. 37 Fig. 30. Size distributions of walleye and pike angled from Rocky Lake in 2002...... 38 Fig. 31. Comparative growth and maturity of Wekusko Lake fish...... 40 Fig. 32. Frequencies of pike body sizes in Wellman Lake...... 41 Fig. 33. Pike and walleye sizes caught by anglers on Cormorant Lake...... 42 Fig. 34. Pike sizes in Cranberry Lake...... 43 Fig. 35. The change from dominance by large pike on Asean Lake...... 44 Fig. 36. Size distribution of pike caught by anglers on Reed Lake...... 45 Fig. 37. Pike size distribution in Wekusko Lake...... 46 Fig. 38. Length frequency distributions of pike in 8 Minnesota lakes...... 47 Fig. 39. Size frequencies of Cedar Lake pike...... 48 Fig. 40. Size distributions of Southern Indian Lake pike...... 49 Fig. 41. Effect of growing season on walleye fecundity...... 50 Fig. 42. Walleye yield distribution...... 51

3 PIKE AND WALLEYE IN THE ROCKY LAKE - ROOT-READER MARSH COMPLEX

DESCRIPTION AND HISTORY OF THE STUDY AREA

Rocky Lake and the Root-Reader Marsh are located about 30 km. north of The Pas, Manitoba, Canada (Fig. 1). The surface area of Rocky Lake is 10968 ha. Rocky Creek drains from the southern bay of Rocky Lake, flows through the control structure into Root Lake, continues into Reader Lake and eventually reaches the second control structure on Whitefish Creek at its junction with the Saskatchewan River. The Root- Reader Marsh is part of the Saskeram Marsh WMA, Wildlife Management Area, that also includes the Carrot River Triangle. This WMA includes 95,812 ha. of crown land along the Saskatchewan River Delta. It was designated as a Wildlife Management Area in 1963 to mitigate the loss of wildlife habitat due to the Grand Rapids Dam at the end of the Saskatchewan River. The original Rocky Creek water control and fishway were built in 1947 by DUC, Ducks Unlimited Canada. The purpose of this structure was to ensure that Root and Reader Lakes had a consistent water supply. This structure also prevented more than 1,800 acres of wetlands upstream of the dam from drying out in years of low precipitation. The structure was built with the full cooperation of the provincial government that assumed operational responsibility for this and several other water controls built by DUC in The Pas area. These water control structures improved muskrat and waterfowl production. In 1974, DUC replaced the original wooden structure and fishway. The current structure was built in 1991 with the cooperation and approval of the provincial government. Manitoba’s Fisheries Branch and the federal Department of Fisheries and Oceans both approved its design. During the history of water control structures on Rocky Creek, there have been occurrences of fishkills in the winter. Winter fishkills are typically due to insufficient DO, dissolved oxygen. Deoxygenation of water occurs naturally in shallow water wetland systems. The water control structure is situated in the natural outlet channel and regulates the flow of water from Rocky Lake into the Reader and Root Lake marshes. Excess water from the system is released into the Saskatchewan River through the South Reader outlet at Whitefish Creek. If the water control structure were not in place, the natural "spill" elevations of Rocky and Reader Lakes would allow the present water level in Rocky Lake to drop approximately 1.2 meters. This would reduce Root and Reader Lakes to a series of small shallow basins resulting in a loss of more than 11000 ha. (27000 acres) of flooded wetland habitat that is utilized by waterfowl and other local wildlife. The Rocky Creek control structure: 1. maintains the water level of Rocky Lake within a prescribed range based on historical water levels that generally satisfies the needs of various groups including cottage owners, lodge owners and commercial bait fishers. 2. allows DUC to use Rocky Lake as a storage reservoir from which water can be drawn to maintain healthy wetland habitat in Root and Reader Lakes. 3. provides fish passage for pike and other species of fish that move between Rocky Lake and Root and Reader Lakes.

4 4. maintains wetland habitat immediately upstream of the water control structure and provides a consistent water supply to the three lakes (Bignell, Watseskwatipi and Keaskeskak) south of Rocky Lake. 5. provides flood and drought protection to Rocky, Root and Reader Lakes during periods of extreme high and low precipitation. During years of normal to above normal precipitation, water is released through the water control structure in the spring and flows into Root and Reader Lakes. Excess water is released into the Saskatchewan River through the South Reader control. The control is closed when water levels in Rocky Lake are within the historical range. Provided water levels remain well within the historical range, fall releases through the dam supply water to Root and Reader Lakes to enhance winter conditions for muskrat. During years of low precipitation, and when the water levels in Rocky Lake are at the low end of the historical range, minimal or no amounts of water flow through the dam. The fish ladder remains constantly open to provide for fish passage. On December 17, 2001, Manitoba Conservation and Ducks Unlimited Canada were advised of a fish kill at the Rocky Creek fishway and water control structure downstream of Rocky Lake. Ducks Unlimited Canada and Manitoba Conservation staff observed a large number of dead and dying juvenile northern pike at the site. The fish were concentrated downstream of the water control structure. The cause of the mortality was unknown at that time although oxygen depletion was considered the likely cause. Winter fish kills are typically a result of insufficient dissolved oxygen. These kills are a natural event that periodically occurs in shallow water wetlands systems. Manitoba Conservation staff collected water samples to determine if the cause was a result of factors other than oxygen depletion. On December 18, 2001 Manitoba Conservation and Ducks Unlimited Canada staff returned to the site to conduct dissolved oxygen sampling in Rocky Creek upstream and downstream of the water control structure. The samples revealed that low levels of dissolved oxygen were present approximately 1.5 km upstream of the control structure. Extremely low levels were detected approximately 500 meters upstream. There was no oxygen detected immediately upstream of the control structure and near zero levels immediately below where the dead and dying pike were concentrated. A sample collected approximately 800 meters downstream of the control structure revealed no dissolved oxygen. It appears that the fish were on their way upstream from the Reader and Root Lake marshes and were prevented from moving further upstream to Rocky Lake due to the anoxic conditions. A late fall, lower than normal water levels and the presence of large floating mats of decaying vegetation contributed to this event.

Fig. 1. Rocky Lake.

6 The three studies that pertain to this report are: 1. Root – Reader pike study 2. Rocky Lake fish stock monitoring 3. Rocky Lake creel survey

ROOT – READER PIKE STUDY Staff from Ducks Unlimited Canada and Manitoba Fisheries Branch completed an initial survey of fish passing through the Rocky Creek fishway in the spring of 2002 and continued monitoring dissolved oxygen at seven sampling stations in the Root- Reader marsh (Fig. 2).

Fig. 2. Root-Reader Marsh. Four automated water temperature recorders that collected temperature four times a day (6 a.m., 12 noon, 6 p.m. and 12 midnight) each day from June 27 to October 3 were set at stations 1, 3, 5 and 7. DO, dissolved oxygen, data were collected with a YSI meter. The fishway was converted into a fish sampling trap by inserting a screen barrier at either the upstream or downstream end (depending on the fish movement to be monitored). Pike passing through the fishway were counted and their fork lengths were measured. Anal fin rays were collected to determine the fishes’ ages. Anal fins were clipped as a marker before fish were released. Signs posted at the Rocky Lake lodges and cottage areas invited anglers to submit information if they caught a fin-clipped pike. Water temperatures were coolest in Rocky Lake (Fig. 3) and generally became progressively warmer downstream (Figs. 4-6). The upper lethal temperature for pike,

7 30°C, was most exceeded at station 5 in Root Lake (Fig. 5). During a typical day, water temperatures were warmest at 6 p.m. and coolest at 6 a.m.

40 midnight 35 6 a.m. 12 noon 30

) 6 p.m. C 25 E (° R U

T 20 A

15 MPER E T 10

n l l l l g g g g g p t u u u u u u u u u u e ep ep ep c J J J J J O - - - - A A -A -A -A S -S -S -S 4- 1- 8- 5- 3- 27 11 18 25 15 22 29 12 19 26 TIME (date)

Fig. 3. Water temperatures at station 1 in 2002.

8 40 midnight 35 6 a.m. 12 noon 30

) 6 p.m. C 25 E (° R U

T 20 A

15 MPER E T 10

n l l l l g g g g g p t u u u u u u u u u u e ep ep ep c J J J J J O - - - - A A -A -A -A S -S -S -S 4- 1- 8- 5- 3- 27 11 18 25 15 22 29 12 19 26 TIME (date)

Fig. 4. Water temperatures at station 3 in 2002.

9 40 midnight 35 6 a.m. 12 noon 30 6 p.m. C) ° ( 25 E UR 20 RAT E

P 15 M E T 10

n l l l l g g g g g p t u u u u u u u u u u e ep ep ep c J J J J J O - - - - A A -A -A -A S -S -S -S 4- 1- 8- 5- 3- 27 11 18 25 15 22 29 12 19 26 TIME (date)

Fig. 5. Water temperatures at station 5 in 2002.

10 40 midnight 35 6 a.m. 12 noon 30 6 p.m. C) ° ( 25 E UR 20 RAT E

P 15 M E T 10

n l l l l g g g g g p t u u u u u u u u u u e ep ep ep c J J J J J O - - - - A A -A -A -A S -S -S -S 4- 1- 8- 5- 3- 27 11 18 25 15 22 29 12 19 26 TIME (date)

Fig. 6. Water temperatures at station 7 in 2002.

11 The velocity of water flows through the fishway in 2002 increased through the summer and were relatively high in autumn (Fig. 7).

110 MEAN ± 95% CI MEDIAN, QUARTILES, MIN.&MAX. ) 100 -1 sec.

m. 90 c ( Y T I 80 C O L E 70 V W O L

F 60

50 27/6/2002 7/8/2002 21/8/2002 25/9/2002 3/10/2002 DATE (d/m/y) Fig. 7. Temporal changes in flow velocity through the fishway in 2002. CI – confidence interval. The first and third quartiles are plotted.

12 Flow rates through the fishway during 2003 were relatively high in spring, decreased during the summer and increased during the fall (Fig. 8).

1.9

1.8

1.7 ) -1 1.6 sec. .

m 1.5 ( E T

A 1.4 R W

O 1.3 L F 1.2

1.1

1 r y y n n n n l l l l g g g g g p t p a a ay ay ay u u u u u u u u u u u e ep ep ep c ct A Ju J J J Ju -J -J -J O O - M M -M -M -M - - - 4- A A -A -A -A S -S -S -S - 2- 9- 6- 11 18 25 1- 8- 5- 3- 25 16 23 30 13 20 27 15 22 29 12 19 26 10 TIME (date)

Fig. 8. Temporal changes in flow velocity through the fishway in 2003.

Flow rates increase from the top to the bottom of the fishway (Fig. 9).

120

MEAN ± 95% CI

) 110 1 - . MEDIAN, QUARTILES, MIN.& MAX. sec . 100 m c (

Y T I 90 C O VEL

FLOW 70

60 12356789exit FISHWAY BAY

Fig. 9. The increase in flow velocity from the top to the bottom of the fishway in 2002. CI – confidence interval. The first and third quartiles are plotted.

14 DO is expected to increase as water temperature decreases but this relationship varies because several other factors modify it (Fig. 10). Oxygen is consumed by aquatic animals, produced by aquatic phytoplankton and plants and consumed by decaying organic matter. 15 )

-1 13 . l . g

(m 11 EN

XYG 9 O

VED 7 L MEAN ± 95% CI SSO I

D 5 MEDIAN, QUARTILES, MIN.& MAX. 3 4 6 8 101214161820222426

WATER TEMPERATURE (°C) Fig. 10. DO and water temperature relationship. CI – confidence interval. The first and third quartiles are plotted.

15 DO decreased slightly from May until August 2002 and increased as autumn approached (Fig. 11). 15 ) -1 . l

. 13 g

(m 11 EN YG

X 9 O

7 VED L MEAN ± 95% CI O S

S 5 I MEDIAN, QUARTILES, D MIN.& MAX. 3

02 02 02 02 02 02 02 02 /20 /20 /20 /20 /20 /20 /20 /20 5 6 7 8 8 9 9 0 /0 /0 /0 /0 /0 /0 /0 /1 30 27 16 07 21 11 25 03

TIME (date) Fig. 11. Temporal changes in DO. Variability about each mean or median is due to spatial differences among stations. CI – confidence interval. The first and third quartiles are plotted.

16 DO decreased rapidly in November and remained low at all stations except those in or adjacent to Rocky Lake. The fishway improved DO amounts during the winter (Fig. 12). 16 station 1 station 2 14 ) station 3 -1 .

l fishway US .

g 12 fishway DS station 4 (m 10 station 5 EN station 6

XYG 8 O

6 VED L

O 4 S S I D 2

0 ...... t v v v n c o o o ec ec ec a O J - -N -N -N -D -D -D - 22 21 25 28 02 06 17 03 STATION Fig. 12. DO during late autumn and winter of 2002-2003. US – upstream, DS – downstream.

17 DO amounts were relatively constant from station 1 – 5, increased slightly in Root Lake and tended to be relatively low in the downstream reach of Rocky Creek ( Fig. 13).

15 )

-1 13 . l . g

(m 11 EN YG

X 9 O

VED 7 L O

S MEAN ± 95% CI S I

D 5 MEDIAN, QUARTILES, MIN.& MAX. 3 1234567 STATION

Fig. 13. Spatial distribution of DO from May to September 2002. Variability about each mean or median is due to temporal changes. CI – confidence interval. The first and third quartiles are plotted.

In 2002, records of Rocky Lake’s water chemistry in the 1980s were retrieved. Rocky Lake’s pH tended towards being basic. Water transparency was relatively deep for Manitoban lakes and turbidity was correspondingly low. Temperatures measured at the top and bottom of the water column during the early 1980s revealed that Rocky Lake does not stratify. Phosphorus, nitrogen and chlorophyll A were relatively low (Table 1).

18 Table 1. Rocky Lake’s water chemistry during the 1980s.

Sample Date Temperature pH Conductivity Turbidity Secchi Total Total Particulate Dissolved Chlorophyll transparency N P P P A (°C) (uS/cm) (NTU) (m.) (mg./l.) (mg./l.) (mg./l.) (mg./l.) (ug./l.)

WQ1981TOP JUN16 18 8.61 428 1.9 2.90 .40 .017 .009 .008 <1 WQ1981BOT JUN16 17 8.61 428 1.5 .40 .020 .012 .008 <1 WQ1982TOP JUN16 18 8.63 428 1.5 3.40 .40 .016 .009 .007 <1 WQ1982BOT JUN16 17 8.63 426 2.0 .40 .021 .013 .008 <1 WQ1983TOP JUN16 17 8.65 417 1.8 2.70 .50 .019 .011 .008 <1 WQ1983BOT JUN16 18 8.68 412 1.8 .50 .022 .013 .009 1 WQ1984TOP JUN16 17 8.76 373 3.6 1.60 .60 .020 .014 .006 1 WQ1984BOT JUN16 17 8.76 374 3.6 1.60 .70 .021 .013 .008 1 WQ1981 JUL5 18 8.65 425 1.4 1.60 .60 .014 .007 1 WQ1982 JUL5 18 8.64 423 1.6 1.60 .80 .020 .009 2 WQ1983 JUL5 18 8.73 416 1.4 1.90 .70 .013 .008 2 WQ1984 JUL5 19 8.90 369 3.0 1.25 .80 .021 .008 2 WQ1981 JUL18 20 8.62 427 1.8 2.50 .80 .022 .015 .007 2 WQ1982 JUL18 20 8.62 426 1.7 2.50 .70 .021 .013 .008 2 WQ1983 JUL18 20 8.66 422 1.7 2.25 1.00 .018 .011 .007 2 WQ1984 JUL18 20 8.86 372 5.5 1.75 1.00 .021 .014 .007 2 WQ1981 JUL28 8.65 424 3.4 .70 .024 .015 .009 3 WQ1982 JUL28 8.67 423 3.0 .70 .023 .014 .009 6 WQ1983 JUL28 8.73 418 2.7 .90 .023 .014 .009 2 WQ1984 JUL28 8.74 365 13.0 1.10 .036 .029 .007 10 WQ1981 AUG16 20 8.68 429 2.0 2.00 .70 .023 .013 .010 WQ1982 AUG16 18 8.67 426 2.6 1.90 .80 .030 .023 .007 WQ1983 AUG16 20 8.72 423 3.5 1.80 .80 .032 .024 .008 WQ1984 AUG16 20 8.80 374 4.8 1.20 .90 .028 .021 .007 WQ1981 AUG29 18 8.69 422 4.0 2.00 .80 .029 .019 .010 4 WQ1982 AUG29 18 8.66 426 6.2 1.50 .80 .031 .020 .011 4 WQ1983 AUG29 19 8.70 424 4.2 1.50 .80 .023 .014 .009 4 WQ1984 AUG29 17 8.62 384 14.0 .50 1.10 .040 .027 .013 7 WQ1981 SEP15 15 8.70 426 5.1 1.00 .90 .032 .020 .012 <1 WQ1982 SEP15 15 8.71 427 4.7 1.00 1.00 .029 .018 .011 1 WQ1983 SEP15 15 8.73 425 5.3 1.00 1.00 .031 .020 .011 1 WQ1984 SEP15 12 8.70 391 21.0 .50 1.50 .047 .030 .017 2

19 The ages of some pike passing through the fishway were determined by sectioning the anterior 2 or 3 spines of the anal fin. Ages of pike were relatively high in the spring and decreased as the season progressed (Fig. 14).

N=25 MEAN 6 MINIMUM MEDIAN 5 MAXIMUM ) s r a e 4

E (y N=1 N=23 G

A 3 E K PI 2 N=2 1

0 27/06/2002 16/07/2002 07/08/2002 11/09/2002 DATE (d/m/y)

Fig. 14. Temporal changes of pike ages in 2002. In 2003, Derek Kroeker, a University of Manitoba Natural Resources Institute student, began a more intensive and extensive sampling program on the Root – Reader system. As in 2002, sizes of pike passing through the fishway decreased as the season progressed (Fig. 15). CUE, catch per unit of effort, is an index of abundance. Each gangs of gillnets was composed of four 25 yard long by 1 yard deep nets. Mesh sizes were 2 inch, 3 inch, 3.75 inch and 4.25 inch (stretched measure). Gang were set in various locations in Root and Reader Lakes but were not set in Rocky Lake. CUE (no./gang/night or weight/gang/night) was highly variable in 2003 (Fig. 16). High variability was also associated with age-specific mean and median fork lengths of pike sampled in 2003. The single pike aged 11 was probably an erroneously aged 5 year old fish (Fig. 17). As in 2002, older spawning pike were present in the marsh in May but returned to Rocky Lake after spawning. Younger fish remained in the marsh throughout the season presumably to feed and grow (Fig. 18).

20 1000 900 D

S 800 1 ±

) 700 .

m 600 m ( 500 TH G

N 400 LE 300 K 200 FOR 100 0 l l l r y y y y y n n n n u u u p a a u u u u J J J A - - J J J J M M - - - - -Ma -Ma -Ma 4- 6- 2- 9- 6 3 0 11 18 25 13 20 27 1 2 3 SAMPLING DATE (d/m)

Fig. 15. Temporal changes in pike sizes passing through the fishway in 2003.

60 50 WEIGHT (kg.) 45 NO. 50 40 ) ) t 35 t

40 gh i nigh 30 g/n ng/ n 30 25 a /ga g./g k no. 20 ( ( E E 20 U U 15 C C 10 10 5

0 0 1 2 3 4 5 6 7 8 9 10111213141516171819202122 GANG

Fig. 16. Variability of CUE among gangs in 2003. 21 800 QUARTILES 1-3 MEAN ± 95% C.I. 700 MEDIAN, MIN. & MAX. ) .

m 600 m ( H T 500 NG LE

RK 400 O F

300

200 012345678911

AGE (years) Fig. 17. Growth of pike. CI – confidence interval.

50 Y y 40 C Ma 30 June EQUEN y 20 FR Jul

TIME gust 10 r u A be 0 em t

ber 01234567891011 p o t e c S AGE (years) O

Fig. 18. Seasonal changes in age composition of pike in the Root-Reader marsh. 22

The stomach contents of 104 pike sampled in 2003 were identifiable. Other stomachs were either empty or contained chyme. Smaller pike consumed invertebrates and minnows. One small pike had ingested a smaller pike. As pike sizes increase, they become more piscivorous and cannibalistic (Fig. 19).

550 QUARTILES 1-3 ) . 500 95% CONFIDENCE INTERVAL m N=1 m MEAN ( 450 MEDIAN TH G N 400 LE K N=2 N=33 350 FOR

E K I 300 N=1 P N=2 N=65 250

s s s e h e e e er k s t t t fi ra ra ra ck pi b u e eb eb s rt rt rt e v ve ve in n in , i e ow, ik PREY p inn m

Fig. 19. Changes in pike prey with increasing pike size.

23 The size distribution of 508 pike captured in the Root-Reader marsh during 2003 indicates that most of them are shorter than 60 cm. (Fig. 20). 60

FREQUENCY (no.) 50 FREQUENCY (%)

40 NCY

UE 30 Q E R F 20

0 0 100 200 300 400 500 600 700 800

FORK LENGTH CLASS (mm.) Fig. 20. Size distribution of Root-Reader pike in 2003. On August 18, 2003, one walleye was caught in the marsh complex. No other walleyes were observed during 2002 or 2003. Fatheads, spottail shiners, emerald shiners and blacknose shiners were observed at various times below the fishway.

ROCKY LAKE FISH STOCK MONITORING PROGRAM Manitoba Fisheries Branch conducted fish stock surveys on Rocky Lake in 1962, 1981, 1991 and 1999. Samples and data are obtained by setting gangs of gillnets for an overnight period. Each gang is composed of 25 yard long nets of the following mesh sizes (in., stretched measure): 2, 3, 3.75, 4.25, 4.75 and 5.25. Temporal changes in CUE of Rocky Lake’s fish species indicate that pike, walleyes and cisco have declined while suckers have increased since the 1960s (Fig. 20). Pike grow faster than other species in Rocky Lake and attain a maximum body size of about 60 cm. Walleyes take much longer to attain their maximum body size. Suckers grow at about the same rate as do walleyes for the first 6 years (Fig. 21).

24 40 Walleye 35 Pike

RT Whitefish

O 30 F ) Cisco F E

White Sucker

F 25 /night

. Perch O s T

d Burbot

y 20 0 UNI 0 R E o./1 P 15 N ( CH 10 CAT 5

0 1962 1981 1991 1999 TIME (year)

Fig. 21. Temporal abundance changes in Rocky Lake's fish species.

650

600

) 550

mm. 500 ( H T 450 NG E 400

RK L 350 O WALLEYE 300 AN F PIKE E

M WHITEFISH 250 SUCKER 200 CISCO

150 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 AGE (years)

Fig. 22. Comparative growth of Rocky Lake's fish species. Long term changes in the age composition of Rocky Lake’s walleye stock reveal that recruitment of various year-classes or cohorts is highly variable (Fig. 23). In 1999, the 1993 cohort was small while the 1991 cohort was relatively large. The maturity rate of walleye females increased and the mean age at 50% mature decreased from 1981 to 1999. Male walleyes mature slightly faster than do female walleyes (Fig. 24). The majority of Rocky Lake’s pike are shorter than 60 cm. All female and male pike gillnetted during the 1999 monitoring program were mature (Fig. 25).

26 30

25 1981 ) 1999

% 20 (

NCY 15 UE Q E R

F 10

0 1234567891011121314 AGE (years)

Fig. 23. Changes in Rocky Lake's walleye age compositions from 1981 to 1999.

27 100 ) %

( 80 NCY

UE 60 Q E R F 40 URE T

A 1999 MATURE MALES M 20 1999 MATURE FEMALES 1981 MATURE FEMALES

0 12345678910 AGE (years)

Fig. 24. Increase in maturity rate of Rocky Lake's walleye females. In the course of dissecting gillnetted walleyes and pike to determine sex and state of maturity, it was noted that almost all of the walleyes had ingested small (100- 200 gm.) suckers or cisco. Several pike stomachs were full of chyme. Cisco and suckers were the most common prey consumed by pike.

28 30 100

25 SIZE FREQUENCY MATURE MALE 80 ) % ) (

% MATURE FEMALE ( 20 NCY

NCY 60 UE Q UE

15 E Q R E F R 40 F

E 10 URE Z I T S A

20 M 5

0 0 421 441 461 481 501 521 541 561 581 601 621 641 FORK LENGTH CLASS (mm.)

Fig. 25. 1999 size distribution of Rocky Lake's pike and size-specific mature frequencies.

ROCKY LAKE CREEL SURVEY In 2002, a voluntary creel survey was conducted on Rocky Lake. Large signs with containers for blank and completed creel survey forms were erected at Wanless, the cottage area on the eastern shore and at each of the lodges on the northern shore. All anglers were encouraged to record their angling data on the following form:

29 SUMMER 2002 ROCKY LAKE CREEL SURVEY

DATE NUMBER OF ANGLERS IN YOUR GROUP

HOW MANY HOURS DID YOU SPEND FISHING?

HOW MANY FISH DID YOU CATCH? HOW MANY FISH DID YOU KEEP? PIKE (JACKFISH) PIKE (JACKFISH) WALLEYE (PICKEREL) WALLEYE (PICKEREL) WHITEFISH WHITEFISH CISCO (TULLIBEE) CISCO (TULLIBEE) BASS BASS

IF YOU WOULD LIKE, PLEASE RECORD THE FORK LENGTH OF EACH FISH: PIKE WALLEYE WHITEFISH CISCO BASS 1. 1. 1. 1. 1. 2. 2. 2. 2. 2. 3. 3. 3. 3. 3. 4. 4. 4. 4. 4. 5. 5. 5. 5. 5. 6. 6. 6. 6. 6. 7. 7. 7. 7. 7. 8. 8. 8. 8. 8. 9. 9. 9. 9. 9. 10. 10. 10. 10. 10. 11. 11. 11. 11. 11. 12. 12. 12. 12. 12. 13. 13. 13. 13. 13. 14. 14. 14. 14. 14. 15. 15. 15. 15. 15. 16. 16. 16. 16. 16.

FORK LENGTH FROM TIP OF SNOUT TO FORK IN TAIL:

NAME: ADDRESS: PHONE:

30 107 forms were completed. 8 of these forms were cumulative reports that included several days of angling by an angling group. Total lake counts of boats and anglers were made on June 16, July 7, July 21, August 4 and August 18 (Fig. 26). Three of these counts were completed by aerial surveys and two counts were made by boat. 70

boats 50 anglers

R 40 BE

30 NUM

0 0 7 14 21 28 35 42 49 56 63 ABSOLUTE TIME (days) Fig. 26. Total numbers of boats and anglers on Rocky Lake. The curves on Fig. 26 were integrated to yield 691.5 boat-days and 2298 angler- days. Since the daily count of anglers included both boat and shore anglers, the integral of the boat count curve is included in the integral of the daily angler count curve. Parameters of the daily angling duration were estimated from 99 of the returned creel survey forms since the remainder were summaries of several days of angling. The mean and median daily angling duration were 5.12 and 4 hours, respectively (Table 2). The 2298 angler-days from Fig. 24 translate to 11768.5176 angler-hours using the mean angling duration or 9192 angler-hours using the median angling duration from Table 2. CUE in terms of no. fish angler hour was highly variable for walleye, pike and bass throughout the period (Fig. 27). Parameters of fishing effort and catches of pike, walleye and bass calculated from the returned survey forms are listed in Table 3. The parameters of species CUE (Table 4) were combined with estimates of total angling effort to yield estimates of total catches from June 16, 2004 to August 18, 2004. Using mean CUE and 11768.5176 angler-hours, total catches were 19159.15 pike, 6510.34 walleye and 3611.76 bass. Using mean CUE and 9192 angler-hours, total catches were 14964.58 pike, 5085.01 walleye and 2821.02 bass. These total catches are estimated for a duration of 63 days.

31 Table 2. Daily angling duration parameters.

Parameter Hours

Number of samples 99 * Lower 95% confidence interval 4.3882 Mean 5.1212 Upper 95% confidence interval 5.8542 Standard deviation 3.6750 Variance 13.506 Mean standard error 0.3694 Coefficient of variation 71.760 Minimum 1 First quartile 3 Median 4 Third quartile 7 Maximum 24

* excludes 8 cumulative reports

6 WALLEYE 5 PIKE -1 BASS UR 4 HO -1 R E

L 3 ANG

H 2 C

CAT 1

0 l l l l g g g n n g n n n p p p p p u u u ay e e e e e u u u u u u u J J J Ju - - - J J J Ju Ju S S S S S M A A A A ------7- 2- 9- 1- 8- 4- 14 21 28 16 23 30 15 22 29 26 11 18 25 TIME (date)

Fig. 27. Walleye, pike and bass CUE in 2002.

32 Table 3. Parameters of fishing effort and catches of pike, walleye and bass calculated from the returned survey forms.

Parameter Effort No. Pike Pike Walleye Walleye Bass* anglers caught kept caught kept (angler-hours)

No. observations 107 ** 107 106 89 68 51 17 Sum 2036 284 2902 343 501 155 34 Lower 95% confidence interval 14.742 2.4451 20.619 2.9944 5.3117 1.972 1.1474 Mean 19.028 2.6542 27.377 3.8539 7.3676 3.0392 2 Upper 95% confidence interval 23.314 2.8633 34.136 4.7135 9.4236 4.1064 2.8526 Standard deviation 22.364 1.0912 35.093 4.0803 8.4939 3.7945 1.6583 Variance 500.16 1.1906 1231.5 16.649 72.146 14.398 2.75 Standard error mean 2.162 0.1055 3.4085 0.4325 1.03 0.5313 0.4022 Coefficient of variation 117.53 41.11 128.18 105.87 115.29 124.85 82.916 Minimum 1.5 1 0 0 0 0 1 First quartile 6 2 7.75 1 1 1 1 Median 12 2 15 2 5.5 1 1 Third quartile 21 3 30.25 6.5 11 4 2.5 Maximum 120 6 185 20 53 22 6

* Incidental catches of 3 cisco, 3 whitefish and 1 sucker were also reported. ** Includes 8 cumulative reports that include several days of angling.

33 Table 4. Parameters of CUE, no. fish angler hour .

Parameter Pike CUE Walleye CUE Bass CUE

N 98 61 14 Lower 95% C.I. 1.4049 0.3804 0.0114 Mean 1.6280 0.5532 0.3069 Upper 95% C.I. 1.8511 0.7260 0.6023 Standard deviation 1.1128 0.6748 0.5117 Variance 1.2383 0.4553 0.2618 Mean standard error 0.1124 0.0864 0.1367 Coefficient of variation 68.352 121.98 166.73 Minimum 0 0 0.0125 First quartile 0.6563 0.1056 0.0506 Median 1.5000 0.3333 0.1429 Third quartile 2.3452 0.8167 0.3333 Maximum 5.5357 4.0000 2.0000

Using data from the 1999 Rocky Lake fisheries survey, the geometric mean regression equations developed to predict fish weight from fish fork length are: (-12.96014 + 3.173806 · log fork length) Pike weight = exp n (-12.63065 + 3.207787 · log fork length) Walleye weight = exp Each walleye and pike fork length reported on the creel survey forms was converted to weight using the above equations. Various parameters associated with these predicted weights are listed on Table 5. The predicted weight distribution (Fig. 28) reveals that most angled pike weighed 2 kg. or less and most angled walleyes weighed 1.5 kg. or less. Using 11768.5176 angler-hours and mean weights from Table 5, total estimated catches are: Pike Walleye number 19159.15 6510.34 weight 28386.20 kg. 6682.86 kg. Using 9192 angler-hours and mean weights from Table 5, total estimated catches are: Pike Walleye number 14964.58 5085.01 weight 22171.52 kg. 5219.76 kg. Using 11768.5176 angler-hours and median weights from Table 5, total estimated catches are: Pike Walleye number 19159.15 6510.34 weight 23611.74 kg. 5967.38 kg. Using 9192 angler-hours and median weights from Table 5, total estimated catches are: Pike Walleye number 14964.58 5085.01 weight 18442.35 kg. 4660.92 kg.

34 Table 5. Parameters of individual pike and walleye weights predicted from fork lengths recorded on creel survey forms. Parameter Predicted Predicted pike weight (kg.) walleye weight (kg.)

N 403 85 Lower 95% confidence interval 1.3778 0.8722 Mean 1.4816 1.0265 Upper 95% confidence interval 1.5854 1.1809 Standard deviation 1.0600 0.7157 Variance 1.1235 0.5122 Mean standard error 0.0528 0.0776 Coefficient of variation 71.544 69.719 Minimum 0.0199 0.0329 First quartile 0.7739 0.4860 Median 1.2324 0.9166 Third quartile 1.8490 1.5258 Maximum 7.5837 2.8081

100 90 80 pike walleye 70 60 NCY Pike Walleye UE 50 mean 1.4816 1.0265 Q

E median 1.2324 0.9166

R 40 F 30 20 10 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

WEIGHT CLASS (kg.) Fig. 28. Weight distributions predicted from reported fork lengths.

35 Rocky Lake has a surface area of 10968 ha. The MSY (maximum sustainable yield) of walleyes ranges from 10448 kg. to 10968 kg. (Baccante and Colby 1996; Colby, personal communication). From June 16, 2002 to August 18, 2002, the total catch of walleyes ranged from 4661 to 6683 kg. For the remainder of the year, the walleye MSY “balance” ranges from 3765 to 5787 kg. Using the mean CUE parameter (Table 6), the walleye MSY “balance” would provide an additional 18538 to 28493 angler-hours before walleye MSY was removed from Rocky Lake. This translates to about 3619 to 5563 additional angler-days.

Table 6. Parameters of kept walleye CUE reported on the creel survey forms.

Parameter Kept walleye CUE

N 51 Lower 95% confidence interval 0.1148 Mean 0.2031 Upper 95% confidence interval 0.2914 Standard deviation 0.3139 Variance 0.0985 Mean standard error 0.0440 Coefficient of variation 154.55 Minimum 0 First quartile 0.0476 Median 0.1000 Third quartile 0.2500 Maximum 2.0000

36 3 pike that were fin-clipped at the Rocky Creek fishway on May 30, 2002 were angled in Rocky Lake from June 9-16, 2002. One lodge angler provided this information. Anglers either tended to release most pike or keep all the pike they caught. Fewer walleyes were released (Fig. 29). 25

walleye 20 pike

15 NCY UE Q E

R 10 F

0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 KEPT : CAUGHT RATIO

Fig. 29. Distribution of kept :caught ratios of walleyes and pike from the creel survey. Walleyes caught by Rocky Lake’s anglers in 2002 ranged from 20 – 65 cm. 40 - 60 cm. walleyes were caught most frequently. Pike caught by anglers in 2002 ranged from 20 – 100 cm. 50 – 65 cm. pike were caught most frequently. Pike > 65 cm. were infrequently caught (Fig. 30).

37 90

80 pike walleye 70

NCY 60 UE Q

E 50 R

F 40 NG I L 30

ANG 20

0 10 20 30 40 50 60 70 80 90 100 FORK LENGTH CLASS (cm.)

Fig. 30. Size distributions of walleye and pike angled from Rocky Lake in 2002.

38 DISCUSSION The water control structure on Rocky Creek was constructed to maintain water levels on Rocky Lake because cottage owners and lodges did not want their boat docks far out of the water during low water periods. The water control structure also allows DUC to maintain downstream wetlands for waterfowl by drawing water from Rocky Lake. The water control structure also maintains wetland habitat immediately upstream and provides a consistent water supply to three lakes (Bignell, Watseskwatipi and Keaskeskak) south of Rocky Lake. The Root –Reader study that is being completed by Derek Kroeker demonstrates that mature pike from Rocky Lake migrate downstream in spring to use Root and Reader marshes and the surrounding areas as spawning sites and as “nursery” areas for the juvenile pike produced from spawning. The larger pike that have completed spawning leave the Root – Reader marshes through the fishway and return to Rocky Lake. This was demonstrated by the fin-clipped pike caught by a lodge angler on Rocky Lake and by the temporal changes in age distributions (Figs. 14,18). Presumably, pike also use Bignell Lake and inlets upstream of the Rocky Lake control structure as spawning areas. Only one walleye was observed at the fishway in 2003 and no walleyes were observed in 2002. Water temperatures exceeded 30°C, the upper lethal limit for pike, in 2002 at the downstream stations (Figs. 5, 6). Water temperatures were lower in 2003 and none exceeded 30°C. No reports of summer fishkills were received. Upper lethal temperature for northern pike was reported to be 29° C (84° F), optimal growth occurs from 19-25° C (66-77° F) (Casselman 1978, Bevelhimer et al. 1985). Northern pike were reported to be susceptible to winter kill in small shallow lakes (Margenau et al. 1998). Juvenile northern pike that were 10 mm. to 12.5 mm. long feed on zooplankton and aquatic insects. As they grow, juvenile pike feed on aquatic insects and increase the proportion of fish prey as their size increases. Adult pike are primarily piscivorous but will include a variety of items in their diet including frogs, crayfish and ducklings (Lawler 1965, Lux and Smith 1960). In 2003, smaller pike captured in the Root – Reader marshes did not have any fish in their stomach contents. As they grew larger, these pike began feeding on some fish and continued consuming invertebrates. They also began preying on each other. As they grew even larger, they switched to consuming primarily fish. Since the marsh did not contain enough fish of other species, pike became very cannibalistic (Fig. 19). Many anglers were searching for large pike. They tended to release smaller pike while searching for larger ones. Fewer anglers kept all the pike they caught (Fig. 29). Releases of caught walleyes were less frequent. Anglers tended to retain all the walleyes they caught (Fig. 29). 45 -65 cm. long pike were caught most frequently. The frequency of pike > 65 cm. caught by anglers was relatively low (Fig. 30). The frequency of pike >65 cm. was also low in the 1999 monitoring program (Fig. 25). The abundance of walleyes and pike in Rocky Lake has declined since the 1960s while the abundance of suckers has increased (Fig. 21).

39 Despite the decline in their abundance, walleye and pike are still angled at a higher CUE (pike CUE: 1.5-1.63 angler hour , walleye CUE: 0.33-0.55 angler hour ) than they are in some other Manitoban lakes:

1995 Dauphin L. all species 0.46 fish angler hour 1993 Assiniboine R. all species 0.475 fish angler hour 1995 L. of the Prairies all species 0.271 fish angler hour 1984 Athapapuskow L. all species 0.32 fish angler hour 1988 Clearwater L. all species 0.25 fish angler hour 1995 Reed L. all species 0.7 fish angler hour 1995 Iskwasum L. all species 1.16 fish angler hour 1995 Cranberry Lakes all species 0.62 fish angler hour 1993 Wellman L. all species 0.151 fish angler hour

The same effects are evident in other lakes where continuous, long-term removal of larger pike has created a stock of 40-60 cm. long pike that can maintain themselves. Pike grow rapidly and mature at an early age (about 2 years) and relatively small body size (about 40 cm. fork length). Compare this with walleyes which mature in about 5.5 years (50% mature) at a body size of about 46 cm. fork length (Fig. 31).

700

600 )

mm. 500 ( H T 400 NG white sucker E pike 300 RK L longnose sucker O walleye 200

AN F whitefish E

M 50% of females ciscoe 100 mature perch

0 123456789101112131415161718 AGE (years)

Fig. 31. Comparative growth and maturity of Wekusko Lake fish. During the 1960s, many lakes contained relatively large pike and walleyes. Walleyes tended to be more numerous. These two species were the top predators in many lakes and controlled forage species such as suckers, cisco (tullibee) and perch by eating

40 them. As fishing pressure increased, the largest pike and walleyes were removed. Pike change their prey at a fork length of about 60 cm. (24 inches). Pike shorter than 60 cm. eat many of the same prey that walleyes eat (small perch, cisco and suckers). Once they are bigger than 60 cm., pike begin to eat larger fish including their own species. In other words, large pike eat small pike. Pike from 40 – 60 cm. long are well adapted to sustaining themselves. They produce eggs at a body size of 40 cm. and grow rapidly. If large, trophy sized pike are continually removed from a lake, smaller pike will continue to prosper especially if the walleyes are also continually harvested. Removal of the top predators allows forage fish to increase and these provide food for the small pike. Notice how many small pike exist in Wellman Lake compared to large (> 60 cm.) pike (Fig. 32). Pike greater than 60 cm. are continually removed by fishing. This allows smaller (< 60 cm.) pike to flourish because they begin producing eggs at 40 cm. and there are a lot of forage fish that provide them their food.

8 NCY

UE 6 Q E R F 4

0 80 140 200 260 320 380 440 500 560 620 680 740 800 860 920 FORK LENGTH CLASS (mm.)

Fig. 32. Frequencies of pike body sizes in Wellman Lake. On Wellman Lake, local anglers attempted to remove small pike during 3 fishing derbies. However, small pike continue to prosper.

A different situation with pike exists on Cormorant Lake (Fig. 33). Here, most of the pike are longer than 60 cm. and they suppress the development of many smaller pike.

35 WALLEYE n = 115 30 PIKE n = 248

25 Y C

N 20 E U Q

E 15 FR 10

0 330 370 410 450 490 530 570 610 650 690 730 770 810 850 890 FORK LENGTH CLASS (mm.)

Fig. 33. Pike and walleye sizes caught by anglers on Cormorant Lake. Numbers of commercial gillnet fishers on Cormorant Lake have declined from 17 to 2. This has removed the gillnet selectivity for larger pike but if anglers continue to remove the larger pike, smaller pike will become dominant. This will also affect walleye abundance in the future.

42 Similarly, on Cranberry Lake, the maintenance of pike > 60 cm. suppresses the development of many small pike (Fig. 34). 18

NCY 10 UE

Q 8 E R F 6

0 80 140 200 260 320 380 440 500 560 620 680 740 800 860 920 FORK LENGTH CLASS (mm.)

Fig. 34. Pike sizes in Cranberry Lake.

43 In the mid 1990s, Asean Lake pike were changing from being dominated by large pike to dominance by small pike (Fig. 35). 16

10 NCY

UE 8 Q E R

F 6

0 80 140 200 260 320 380 440 500 560 620 680 740 800 860 920 FORK LENGTH CLASS (mm.)

Fig. 35. The change from dominance by large pike on Asean Lake.

44 The angling size regulation on Reed Lake helped to maintain higher frequencies of relatively large pike in Reed Lake (Fig. 36). 100

60 NCY

UE 50 Q E

R 40 F 30

0 80 140 200 260 320 380 440 500 560 620 680 740 800 860 920 FORK LENGTH CLASS (mm.)

Fig. 36. Size distribution of pike caught by anglers on Reed Lake.

45 The continual removal of larger pike on Wekusko Lake allows small pike to flourish (Fig. 37).

20 ) %

( 15 NCY UE Q

E 10 R F

0 140 180 220 260 300 340 380 420 460 500 540 580 620 660 700 740 780 820 FORK LENGTH CLASS (mm.)

Fig. 37. Pike size distribution in Wekusko Lake. This effect was documented on 8 lakes in Minnesota (Goeman et al. 1993). Total lengths less than 60 cm. were most frequent in all lakes (Fig. 38) because anglers continually removed any pike that managed to grow larger than 60 cm.

Fig. 38. Length frequency distributions of pike in 8 Minnesota lakes sampled by trap nets(t, bars) and creel surveys (c, lines) from Goeman et al. 1993.

This effect also occurs in commercial gillnet fisheries in Manitoba. In the Cedar Lake fishery, annual gillnetting has selectively removed larger pike. In spite of relatively high

fishing effort, smaller (40-60 cm. long) pike continue to prosper (Fig. 39).

1993 n=50

16 1995 n=201

1998 n=131

1999 n=53

)

12 2000 n=260

Y (%

C 10 N

F 6

0 281 321 361 401 441 481 521 561 601 641 681 721 761 801 841 881 921 FORK LENGTH CLASS (mm.)

Fig. 39. Size frequencies of Cedar Lake pike.

The Southern Indian Lake commercial gillnet fishery also selectively removes larger pike allowing smaller pike to flourish (Fig. 40).

Fig. 40. Size distributions of Southern Indian Lake pike (Bodaly and Lesack 1984). Attempts to selectively remove small pike are unsuccessful. Altering angling regulations to protect large pike are proving to be successful in many Minnesotan pike fisheries (D. Schupp, personal communication). The presence of abundant cisco also assists maintenance of large pike by providing a preferred prey.

49 Baccante and Colby (1996) developed the equation that estimates sustainable angling walleye yield as a function of lake surface area: angling yield of walleye (kg.) = 1.81 · surface area (ha.) (n=168, r = 0.59) This equation estimates that Rocky Lake can produce 10448 kg. (23034 lbs.) of walleye per year. However, this estimate is also subject to several constraints discussed by the authors. These constraints include walleye fecundity as affected by growing degree- days >5°C (Fig. 41), adult walleye density and angling exploitation rate (Table 7).

142000 ) . -1 g

k 122000 Lake of the Woods L.Winnipeg s

g north & south g e o.

n 102000 (

Y T I D

N 82000 U C FE

E 62000 V TI LA

E 42000 R

22000

00 00 87 87 87 87 87 19 62 00 64 00 00 00 78 12 12 12 12 12 12 12 14 16 18 18 20 23 26 40 GROWING SEASON (GDD>5°C)

Fig. 41. Effect of growing season on walleye fecundity. Table 7. Parameters of walleye abundance and yield (from Baccante and Colby 1996).

Quartiles n range

25 50 75

exploitation rate (%) 14 21 25 46 3-55.6 adult density (no. ha. ) 7.8 14.8 23.9 85 0.1-168 harvest weight (kg. ) 0.48 0.58 0.67 113 0.26-1.18 yield (kg. ha. ) 0.50 1.24 2.95 168 0.01-49.6

50 The majority of the 168 North American lakes analyzed by Baccante and Colby (1996) produced less than 1 kg. ha. of walleyes (Fig. 42). 45

35 )

% 30 ( 25 NCY

UE 20 Q E R

F 15

0 0-.99 1-1.9 2-2.9 3-3.9 4-4.9 5-5.9 6-6.9 7-7.9 8-8.9 9-9.9 10+

-1 YIELD (kg. ha. ) Fig. 42. Walleye yield distribution (Baccante and Colby 1996).

Using mean CUE and 11768.5176 angler-hours, total walleye catch was 6510.34 walleye. This translates to 0.59 walleye ha. which is lower than the first quartile of adult density on Table 7. This lower density estimate is supported by the fact that the index of walleye abundance in Rocky Lake has declined since the 1960s, sucker abundance has increased (Fig. 21) and walleye maturity rate has increased (Fig. 24). The creel survey estimated a walleye harvest that ranged from 4661 to 6683 kg. for a period of 63 days. Angling on Rocky Lake continues through the autumn and winter months. If we assume that the total harvest of walleye remains constant and that an additional 200 days of angling occur, 14796 to 21216 additional kg. of walleye are removed. Even if the estimate of additional walleye harvest is reduced in half, 7398 to 10608 additional kg. of walleye are removed and walleye MSY is exceeded. As in any other Manitoban lake, each year the standing stock of walleye in Rocky Lake produces new walleye biomass by growth and by reproduction. The newly hatched walleyes have to survive the first 2 to 3 years before they are recruited to the angling fishery. Thus walleye productivity varies from year to year. If the angling fishery removes more than the new walleye biomass each year, angling yields will decline since all the “interest” and some of the “principal” of the walleye “bank account” are removed. Small pike are waiting to fill the void created by excessively fishing walleyes. Allowing more small pike to recruit to the Rocky Lake fishery by allowing passage through the Rocky Creek fishway exacerbates the “over-recruitment” problem with small pike. Operating the fishway to attempt to prevent winterkill of pike is both unrealistic and 51 counterproductive. The winter anoxia that caused the winterkill in 2001 was due to decaying vegetation above and below the fishway. Changing the fall and winter flows through the fishway will not prevent decaying vegetation upstream and downstream of the fishway. The fishway provided a small, temporary refuge because it increased DO concentrations at a time when other marsh areas were anoxic. Even if the fishway could be operated to eliminate winterkill, the increase in recruitment of small pike to the Rocky Lake fishery would be detrimental to the restoration of large pike and to an increase in walleye abundance. Complete closure of the fishway during the open water period would reduce the small pike “over recruitment” problem but it would not eliminate it because pike use other inlets upstream of the fishway and other marshes connected to the south end of Rocky Lake for spawning. To restore some semblance of the former fishery, some of the larger pike (>60 cm. fork length) that are angled have to be released so that they can grow and begin to consume smaller pike as well as some of the larger suckers whose abundance is increasing. This will allow the development of a “catch and release” trophy fishery for pike. Anglers are encouraged to catch and retain smaller pike. As this occurs, competition between small pike and walleye for the same prey will decrease and walleye abundance will increase. The notion that Rocky Lake can provide a continual supply of walleyes for harvest by an unlimited number of anglers each year is old and false. This was true when there was a large standing stock during the 1940s-1960s but continual removal of the “interest” and part of the “principal” has decreased the size of the walleye “bank account”. Catch and release must become the norm if the walleye stock is to recover. The Rocky Lake fishery should not be expected to provide “freezer fulls” of fish for an unlimited number of anglers.

ACKNOWLEDGEMENTS Sincere thanks are expressed to the anglers who submitted creel survey forms in 2002. The Rocky Lake fishing lodges and Dan Davies and the Wanless citizens provided valuable support. Robin Reader and Chris Smith from Ducks Unlimited Canada and Sean Sexsmith from the Kelsey Conservation District provided a huge amount of support. Jeff Stepaniuk from the Keewatin Community College arranged to build the creel survey sign boards. Derek Kroeker continues to work on the Root- Reader fish data. Doug Leroux and Jeff Moyer and the Manitoba Conservation staff in The Pas provided invaluable assistance with the fishery monitoring program. All these contributions are greatly appreciated.

52 REFERENCES

Bevelhimer, M.S., R. A. Stein, and R. F. Carline. 1985. Assessing significance of physiological differences among three esocids with a bioenergetics model. Can. J. Fish. Aquat. Sci. 42:57-69.

Baccante, D.A. and P. J. Colby. 1996. Harvest, density and reproductive characteristics of North American walleye populations. Ann. Zool. Fennici 33:601-615.

Bodaly, R. A. and L. F. W. Lesack. 1984. Response of a northern boreal pike population to lake impoundment: Wupaw Bay, Southern Indian Lake, Manitoba. Can. J. Fish. Aquat. Sci. 41:706-714.

Casselman, J. M. 1978. Effects of environmental factors on growth, survival, activity, and exploitation of northern pike. Pages 114-128 in R. L. Kendall, editor. Selected coolwater fishes of North America. American Fisheries Society, Spec. Pub. 11, Bethesda, MD.

Goeman, T. J., P. D. Spencer, and R. B. Pierce. 1993. Effectiveness of liberalized bag limits as management tools for altering northern pike population size structure. North American Journal of Fisheries Management 13:621-624.

Lawler, G. H. 1965. The food of pike, Esox lucius, in Heming Lake Manitoba. J. Fish. Res. Bd. Canada 22:1357-1377.

Lux, F. E. and L. L. Smith. 1960. Some factors influencing seasonal changes in angler catches in a Minnesota lake. Trans. Am. Fish. Soc. 89:67-79.

Margenau, T. L., P. W. Rasmussen, and J. M. Kampa. 1998. Factors affecting growth of northern pike in small northern Wisconsin lakes. North American Journal of Fisheries Management 18:625-639.