title
Lake Powell fisheries investigations : 1984 (segment 13) annual report for Colorado River Drainage and Tailwaters Dingell-Johnson Project F-28-R
author
Array ( [0] => Gustaveson, A. Wayne [1] => Bonebrake, Bruce L. [2] => Scott, Steven J. [3] => Johnson, James E. )
abstract
UDWR Publication Number 85-12
date
1985-01-01
organization
Utah. Division of Wildlife Resources
species
Array ( [0] => Not Specified )
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https://grey-lit.s3.wasabisys.com/lake-powell-fisheries-investigations-1984-segment-13-annual-report-for-colorado-river-drainage-and-t.pdf
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N 4650P6 . 13: Lak/ qg'f MAY 5 19 " . UI&1 STA TE LIB Lake Powell Fisheries Investigations Five-Year Completion and 1984 (Segment 13) Annual Performance Report for Colorado River Drainage and Tailwaters Dingell-Johnson Project F-28-R Publication Number 85-12 LAKE POWELL FISHERIES INVESTIGATIONS Completion Report January 1980 - December 1984 Annual Performance Report January 1984 - December 1984 A. Wayne Gustaveson, Project Leader Bruce L. Bonebrake, Project Biologist Steven J. Scott, Project Biologist James E. Johnson, Fisheries Program Coordinator .Publication No. Dingell-Johnson Project F-28-R-13 Utah Department of Natural Resources Division of Wildlife Resources 1596 West North Temple Salt Lake City, UT 84116 William H. Geer Director TABLE OF CONTENTS LIST OF TABLES................................................... v LIST OF FIGURES ••••••.••••••••••••••••••••••••••••••••••••••••••• vii INTRODUCTION. • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 1 JOB NUMBER 1. THREADFIN SHAD STUDy ••••••••• •• ••••••••••••••••••••••• 5 Background.......... •••••••••••••••• •• •• •• ••••• • 5 Methods......................................... 6 Results and Discussion •••••••••••••••••••••••••• 10 Summary and Recommendations ••••••••••••••••••••• 22 II. MEASUREMENT OF FISHERY HARVEST, PRESSURE AND SUCCESS •• 24 Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Methods ••••••••••••••••••••••••••••••••••••••••• 24 Results and Discussion ................•......... 26 Summary and Recommendations..................... 34 III. INDEX TO ANNUAL FISH POPULATION TRENDS •••••••••••••••• 36 Annual Netting................................... 36 Background. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 36 Methods..................................... 36 Results and Discussion ••••••••••••••••••.••• 38 Summary and Recommendations................. 44 Electrofishing •••••••••••••••••••••••••••••••••• 45 Background. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 45 Methods •••••••••••••••••••••••••••••••• ~ . • • . 45 Results and Discussion ••••••••••••••••••••• • 46 Summary and Recommendations ••••••••••••••.•• 50 -iii- TABLE OF CONTENTS (Continued) Page IV. MONITORING OF STRIPED BASS POPULATION DEVELOPMENT. ... . 51 Background. . ••••••••••••• •••••• •• • ••••••• .•• . •• • 51 Methods........ .••• •. ••. ••• • • •••••••• •. ••••• . . •• 52 Results and Discussion •.•••. • •••••••••••••.•.•• 54 Spawning . • • • . • . • • . . . . • • . . . . • • • • • • . . • • . • • • • . • 54 young-Of-The-year ................. .. ........ 56 Recruitment... . .... . .. ... ................... 58 Physical Condition.......................... 58 Food Habits.......... . ........ . .. . . . ........ 62 Tagging Study............................... 64 Age and Growth ... .. .. . . •. ......... • ......... 65 Summary and Recommendations . .. .............. . ... 68 -iv- LIST OF TABLES Table 1. Stocking history of Lake Powell, Utah, 1963-1984.......... 3 2. Mean number of larval thread fin shad collected per ichthyoplankton net tow, Chaol Canyon, Lake Powell, 1983-84. • • • • • . . . . . • . • • • • • • • • • • • • • • • • • • • • • • • • . • • • . • • • • . • • • • 14 3. Mean number of larval threadfin shad collected per ichthyoplankton net tow, mid Lake Powell, 1984 .•. • .• .••• .. 15 4. Mean number of larval thread fin shad collected per ichthyoplankton net tow, San Juan River Arm , Lake Powell, 1982-83.. .. ... .... ........................... 16 5. Monthly inflow (acre-ft) into Lake Powell, 1980-84 ••• • •••• 17 6. Fishing boat use (boat days) by month, Lake Powell, 1975-84. Also given are the average time (hr) fished/trip (H/T) and the mean number of fishermen/boat (F/B) • ••.•••.•.••.•. 27 7. Species sought (%) by anglers, Lake Powell, April-October 1984 .•••.•.••.•..• • •• ••• ••••••.••.•...••.••. 30 8. Sport fishery creel rates (fish/angler hour) by species and access area, Lake Powell, April-October 1984 .•.•.•.... 32 9 . Striped bass creel rates (fish/angler hour) by access area, Lake Powell, 1980-1984.. .... .......... . ....... .... . .. ..... 32 10. Species composition (%) of the total creel, Lake Powell, March-October 1984. . ..... ... .................. .......... .. 33 11. Catch rates (fish/net day) during annual spring gillnetting, Lake Powell, March 1984............ . . .. ....... .. . . ... .. .. . 39 12. Catch rate (fish/net day) by species and year, annual gillnetting, Lake Powell, 1971-84 •..•.•••••••••..••••••••. 40 13 . Mean visceral fat index (VFI) values for walleye collected by gillnetting during 1980-84, Lake PowelL.......... .. ... 44 14 . Mean visceral fat index (VFI) values for largemouth bass collected by gillnetting during 1980-84, Lake Powell .. . .•. 44 -v- LIST OF TABLES (Continued) ~ Page 15. Mean catch rate (fish/hour) of fish collected by e1ectrofishing, Lake Powell, September 1984 •••• •• •. ••••••• 47 16 . Mean catch rate (fish/hour) of fish collected by e1ectrofishing, Lake Powell, 1980-84 • • ••• . •••.•. • ••.••.•.. 48 17. Summary of striped bass caught during fall gi11net sampling, 1981-1984, Lake Powell, expressed in terms of fish caught per 1000 square feet of gi ll net per 12 hour set • • .••••••• 57 18. Food habits of striped bass by season, expressed as percent occurrence, Lake Powell, 1980- 1984 •.••• •• . • •.••••••••••.•• 63 19. Marking, recapture, and movement history of striped bass tagged in Lake Powell , 1981-1984 •••••••••• •••••••• ••.•• • •• 66 20. Backca1cu1ated growth of striped bass at Lake Powell using the method of Monastyrsky. Fish collected be- tween 1980-1984...... . ... ... . . ..... . ...... . . .............. 67 -v~- LIST OF FIGURES Figure 1. Hap of Lake Powell showing trawling and ichthyoplankton netting stations for threadfin shad, 1984................. 7 2. Echograms showing schooling behavior of threadfin shad during the day and random distribution during the night... 9 3. 4. 5. 6. Mean number of larval shad collected per ichthyoplankton tow, lower Lake Powell , 19 81- 1984 •••••••.••••••••••••••••. Mean number of larval shad collec ted per ichthyop lankton tow, mid Lake Powell, 1981-1984 •.•••••••••••••••••••••••.• Mean number tow, upper Mean number 1980-1984. total catch of larval shad collected per ichthyoplankton Lake Powell, 1981-1984 • • ••••••• • ••••••••••• • ••• of shad collected per trawl tow, Lake Powell, (The top of each bar represents the cumulative for July-September for each year.) ••.•.••.•••• 11 12 13 18 7. Mean number of threadfin shad collected per trawl t ow, July-September, Lake Powell, 1977-1984 ... ..... . ... . ....... 20 8. Indices of total recreational boat use and angling pressure, Lake Powell, 1965-1984.................................... 28 9. Residence of anglers using Lake Powell by access area, 1980-84................................................... 29 10. Creel rates (fish/angler hour) for largemouth bass, black crappie and all species combined, Lake Powell, April-June 1965-1984...................................... 31 11. Map of Lake Powell, Utah-Arizona, showing annual netting sites (dots) and electrofishing transects (circles) •••..•. 37 12. Catch rates (fish/net day) for walleye and largemouth bass from annual netting, Lake Powell, 1971-1984 •• ••••.••• .••.• 41 13. Relationship of gi llnetting catch rates (solid lines) and creel rates (dashed lines) of walleye and largemouth bass collected at Lake Powell, 1972-1984 •.••..•..•••• •• .......• 43 -vii- LIST OF FIGURES (Continued) Figure 14 . Mean catch rates (fish/hour) for largemouth bass, b lack crappie and striped bass collected by electro fi shing, Page Lake Powell, August-September, 1978-1984 • • •••• • .•..••••••• 49 15. Yearly average condition factor (K) of adult and juvenile striped bass, Lake Powell, 1975-1984 •.•.•••••••..•...•••.. 60 -viii- LAKE POWELL FISHERIES INVESTIGATIONS INTRODUCTION Fisheries investigations on Lake Powell began ln 1963, shortly after impoundment, and have continued to the present. The ini tial work included physical and chemical descriptions of the filling res- ervoir, plankton development, life history studies of introduced game fish, and an estimation of fishing pressure and success. These studies were funded, in part, by federal monies provided under Section 8 of Public Law 485, the Colorado River Storage Project Act, and were completed in 1971. Lake Powell investigations since 1971 have been funded by Federal Aid to Fish and Wildlife Restoration, Project F-28-R, and by the Utah Division of Wildlife Resources. New studies undertaken since 1971 include game fish food habits, benthic studies, plankton studies, thread fin shad population dynam- ics and predator impac t) an annual net ting program to determine trends ln game fish populations, and smallmouth bass culture and stocking. The study of fishing pressure and success has been on- going since 1963, while the study of the physical and chemical na- ture of Lake Powell was completed in 1974. Important events that have occurred Slnce the initial intro- duction of largemouth bass (Micropterus salmonides), black crappie (Pomoxis nigromaculatus) and rainbow trout (Salmo gairdneri), in- clude the introduction of thread fin shad (Dorosoma petenense) in 1968, introduction of striped bass (Morone saxatilis) in 1974, in- troduction of smallmouth bass (Micropterus dolomieui) in 1982 (Table 1), and the expansion of the walleye (Stizostedion vitreum vitreum) population which developed from stock present ln the drainage before impoundment. The sport fisheries have undergone several changes since im- poundment. The initial introductions of largemouth bass and black crappie were quite successful and developed into an excellent fish- ery that peaked in the early 1970's. As the lake level approached full pool in 1980, however, a decline in spawning and nursery hab i tat great ly reduced largemouth bass and black crappie recruitment. To help alleviate this situation and provide more diversity, (Table 1). striped bass and Striped bass smallmou th bas s are presently have well been introduced established 1n Lake Powell and are providing an excellent fishery. Smallmouth bass, which were first introduced in good numbers in 1984 (Tab le 1), appear well suited to Lake Powell's steep, rocky shoreline habitats and will hopefully provide a good fishery for black bass fishermen in the future. Findings of our research from January 1980 to December 1984 are given in this report along with detailed results of the 1984 sam- pling year. Mo re detailed accounts of events occurring in any par- ticular year, 1980 to 1984, can be found in Lake Powell annual prog- ress reports for that year (Gustaveson et a1. 1981, 1982, 1983 and 1984). -2- Table I. Stocking history of Lake Powel I, Utah, 1963-1984 . Year Species 1963 Largemouth bass Rainbow trout Ra 1 nbow trout Rainbow trout Kokanee salmon 1964 Largemouth bass Largemouth bass Largemouth bass Largemouth bass Rainbow trout Rainbow trout Rainbow trout Kokanee sa lmon Black crappie Black crappie 1965 Rainbow trout Rainbow trout Black crappie Black crappie 1966 Rainbow trout 1967 Rainbow trout Rainbow trouT Rainbow trout 1968 Rainbow trout Threadf i n shad 1969 Rainbow trout Number 924,000 3,000,000 800,000 35,000 600,000 1,000,000 250,000 250,000 500,000 3,000,000 325,650 365,730 35,000 350 9,000 4,383,525 40,000 30,000 4,700 2,140,000 344,049 103,205 102,590 20 1,364 1,500 251,238 Size 2-3 " 2 " 2-4 " 4 " 1-2 " 2-3 " 2-3 " 2-3 If 2-3 " 2-3 " 5-8 " 5-8 II 2-3 " 6 3 " " 2-3 " 5 " I " 4 " 2-3 " 4-5 " 4-5 " 4-5 It 3-5 11 1-4 " 5 " Area Warm Creek - Aztec Reservoir Wide Wahweap Creek Hal l's Crossing Ka ne Creek Warm Creek-Last Chance Mouth Escalante Rincon Su II frog Creek Dam-Bu l I frog Creek Hlte Wahweap Creek Wahweap Creek Wahweap Creek Wahweap Creek Reservoir Wide Wahweap Creek Wahweap Creek Wahweap Creek Reservoir Wide Wahweap-Warm Creek Hal I 's CrOSSing-Sui Ifrog Red Canyon Wahweap Creek Wahweap Creek Wahweap Creek Method Aer ia l Aeria l TrUCk Truck Truck Aerial Aeria l Aerial Aerial Aer ial Truck Truck Truck Truck Truck Aerial Truck Truck Truck Aeria l Aerial Barge Barge Sarge Truck Barge Threadfin shad 200,000 Egg-Fry Wahweap Creek Spawning mats 1970 -------------------------NO STOCKING------------------------------------ 1971 Rainbow trout Rainbow trout Rainbow trout 281,000 527,000 40 , 000 4-5 II 4-5 It 4-6 " 8ullfrog Wahweap Creek Warm Creek Barge Barge Barge 1972 ------------------------NO STOCKING----------------------------------- 1973 Rainbow trout 1974 Striped bass 1975 Striped bass 1976 Rainbow trout Striped bass Str i ped bass 233,400 49,885 94,878 50,000 35,752 19,305 5 n 2-3 " 2-3 " 3-6 " 2-3 " 2-3 " Wahweap Creek Wahweap Creek Wahweap Creek Wahweap Creek Wahweap Creek Bull frog -----continued next page -3- Truck Truck Truck Truck TrUCk Aerial Table I . Stocking history of Lake Powell, Utah, 1963-1984 (continued) . Year S~ecles Number Size Area I~ethod 1977 Rainbow trout 18,600 5 .. Wahweap Creek Truck Striped bass 86,003 2-3 " Wahweap Creek Truck Str I ped bass 52,650 2- 3 " Bullfrog Aerial 1978 Striped bass 169,469 2- 3 " Wahweap Creek Truck Striped bass 84 , 821 2- 3 " Bullfrog Aer I a 1- Truck 1979 Str i ped bass 222,550 2-3 " Wahweap Creek Truck 1980 Rainbow trout 13,210 6 .. Wahweap Creek Truck 1981 ------------------------NO STOCKING----------------------------------- 1982 Sma I I mouth bass 3,100 2-4 " Warm Creek Truck Sma I I mouth bass 59 10-15" Warm Creek Truck 1983 ------------------------NO STOCKING----------------------------------- 1984 Smal lmouth bass 26,600 2-4 " Wahweap-Warm Creek Truck Sma I I mouth bass 4,000 2-4 " Stanton Creek Aer ia l -4- THREADFIN SHAD STUDY JOB I BACKGROUND Threadfin shad have been stocked throughout the Southwestern United States as forage (Burns 1966; LaRivers 1962; Kimsey et al. 1957; and Beers and McConnell 1966). Shad were introduced into Wahweap Bay, Lake Powell 1n June 1968 (Miller et al. 1969). Approx- imately 90 percent of the original plant were young-of-the-year (y-o-y). Sampling in the winter of 1968-69 revealed the shad had spawned their first summer in Lake Powell. Heidinger and Imboden (1974) found that y-o-y shad planted into a shad-free environment matured and spawned the same year. Threadfin shad 1n Lake Powell had spread to Hall's Crossing, 161 km uplake, by the summer of 1969 and were found reservoir-wide by summer of 1970 (Gloss et al. 1971). Threadfin shad tend to spawn in shallow, turbid water along shorelines and in the backs of canyons and bays. As y-o-y shad mature, however, they become more pelagic and are not readily sam- pled with conventional entrapment gear (Van Den Avyle and Fox 1980, Edwards et al. 1977). The major objective of this study was to dev- elop, through ichthyoplankton netting and midwater trawling, a method for assessing annual reproduction and recruitment of y-o-y thread fin shad into the pelagic zones of Lake Powell. The develop- ment of a midwater trawling system was completed in 1976 and a stan- dard ichthyoplankton netting system was developed 1n 1981. Data collected from 1980-84 were used to determine shad population in- dices, monitor annual reproduction and reflect monthly and annual population fluctuations. -5- Threadfin shad are presently the predominant food item of all major game species in Lake Powell (Hepworth and Gloss 1976; May et a1. 1975; Gustaveson et al. 1980) . Striped bass, a pelagic predator, were introduced into Lake Powell in 1974 and utilized the dense shad population in the open water areas of the reservoir . Previously established game species were usually confined to the littoral zones o f Lake Fowell. Threadfin shad population da ta collected from 1976-79 formed a baseline for comparing the impacts the expanding striped bass population has exerted on threadfin shad abundance (Gustaveson et a1. 1980). Data collected from 1980-84 provides information on shad abundance following intense predatory pressure by striped bass. METHODS Threadfin shad spawning was monitored with ichthyoplankton net collections, which began when lake temperatures approached l4C in May, and continued until September. Weekly samples were taken in the backs of bays at Wahweap Creek, Warm Creek, Bullfrog Creek and Hall's Creek. Bi-weekly samples were collected at Red, Ticaboo, Hoki and Chaol canyons, while monthly monitoring was conducted at Piute Red Wall, Piute Farms Wash and the San Juan River Inflow (Figure 1l. A 5.4 m aluminum Jon boat "ith a 40 hp outboard motor towed a one-meter, 505 micron ichthyoplankton net just below the water's surface. Three each station, sampling tows, two minutes in duration, were taken at 3 an average volume of 102 m of water per tow. While towing the ichthyoplankton net, the boat moved forward at approximately 0.7 mls and covered a distance of 129 m per sam- ple. Shallow, turbid water sites at the backs of canyons and bays were chosen for sampling because previous findings have demonstrated that shad in Lake Powell tend to spawn in turbid waters (Gustaveson et al. 1982) . Sample locations were adjusted periodically to ac- count for fluctuating water levels . -6- I " I .. T T ra w li n g S ta ti o n • Ic h th y o p la n k to n S ta ti o n M il e s I , o 5 10 C h ao , C an yo n ~ Ar j~ on i- -- _ H ai ls C re ek T ic ab o o C an yo n F ig u re 1 . M ap o f L ak e P o w e ll sh o w in g tr a w li n g an d ic h th y o p la n k to n n e tt in g s ta ti o n s fo r th re a d fi n sh a d , 1 9 8 4 . All samples were preserved in the field with 5.0 percent for- malin. A solution of biological stain , Phloxine B, was mixed with the preserving formalin to aid in separating larval fish from sample debris. Larval fish were picked from the debris and identified to specles. All larval thread fin shad ( 25 mm TL) were counted and an average number of shad per tow was computed for each station. A monthly average of shad per tow was then calculated for all stations. An 8.53 m steel hulled work boat was used for trawling. Two Marco W050 hydraulic winches powered by Vickers hydraulic pumps were run directly from the boat's inboard engines. With dual controls, it was possible to run both winches ln tandem or individually. The t r awl was designed after that described by von Geldern (1972). It measured 3.05 m x 3.05 m square at the mouth, 15.24 m long wi th bar mesh net tapering from 20.4 cm in the throat to 0.32 cm at the cod end. The trawl was held open by a pair of depressors and hydrofoils attached at the corners of the mouth. Galvanized wire rope cables (0.48 cm diameter) running from each winch were used in deploying and retrieving the trawl. A standard t ow was developed and used to permit consistent sam- pling and replication. During each tow, the boat was operated at 1,100 rpm's (1.6 m/s) while 45.72 m of cable were played out and immediately 3 8,178.44 m retrieved. and the The average volume of water sampled was maximum depth fished was approximately 10.7 m. The oblique t ow allowed equal sampling of the water column from the surface to maximum depth, rather than sampling shad from anyone depth. For consistency, sampling was done at ni ght when shad were distributed in a dense and uniform layer instead of grouped in schools as found during the day (Figure 2) (Houser and Dunn 1967; Netsch et a1. 1971). Sample nights were during the per- iod between new moon and first quarter to ensure dark nights and el iminate variability caused by moonlit nights . Trawling locations were selec t ed t o sample lake areas near the dam, midwa y uplake and near the Colorado River inflow at Wahweap, Bullfrog and Good Hope Bay, respectively (Figure 1). Each trawling -8- I '" I DA Y ~ fI - -- - . - - ~ - - ~ - SU RF A CE D EN SE SC H O O LS O F SH AD BO TT OM N IG H T SU RF A CE U N IF O RM LA YE R OF SH AD BO TT OM F ig u re 2 . E ch o g ra m s sh o w in g s c h o o li n g b e h a v io r o f th re a d f in sh a d d u ri n g th e d ay a n d ra n d o m d is tr ib u ti o n d u ri n g th e n ig h t. location was sampled one night a month from July through September. Wahweap, Bullfrog and Good Hope were sampled on consecutive nights to allow comparison under approximately si~ilar times and conditions . Three standard tows were made each sample night. Floating buoys, permanently fixed in position, were used to mark trawl transects . Each night before trawl samples were taken, an 8-minute sonar transect was run over the trawling course. The sonar units, which were also used to generate the echograms of Figure 1, were Lowrance Model 1510 Band C recorders using LPT-lOl transducers. The boat was operated on one engine at 800 rpm's during the sonar run. The echograms generated from these runs were used as "back-up" data to the trawl tow information. The trawl selectively captured larval and juvenile shad. Adults were taken infrequently. Larval and juvenile shad were differen- tiated by total length after criteria presented by Barnes (1977). Larval shad were designated as shad smaller than 25 mm total length while juveniles were considered to be between 25 mm and 50 mm. All shad collected were immediately preserved in a 10 percent formalin solution. Number of shad, average total length and range, and average weight per catch were determined for each haul. RESULTS AND DISCUSSION In Lake Powell, shad generally begin to spawn in early or mid-May at the upper lake locations and by late May at lower lake areas. This is similar to the progressive spawning pattern reported by Ne tsch e t a1. (1971) in Beaver Reservoi r, Arkansas. Mos t years , spawn~ng continues at Lake Powell throughout the summer and extends into August at upper lake, and August or September at mid lake and lower lake (Figures 3, 4 and 5). Many studies have revealed shad spawnlng more than once a year, and thread fin shad are known to spawn as y-o-y (Heidinger 1983). Two spawning peaks were observed -10- , ~ ~ I 2 0 0 0 1 0 0 0 3 0 0 2 0 0 1 0 ) /0 / \ / \ / \ / / \ / \ ;" \ I \ I \ I \ I \ 1 0 \ I \ I \ I \ I ' ,. ' - \ I ° 1_ -- -, / ° -- -- \ Ju n e ..... ..... ... "" Ie. .. ..• .. .. .. .. . ... ... ... • . Ju ly - A u g u st W a h w e a p C re e k 2 0 0 0 1 0 0 0 1 0 0 o S e p t. r ~ ~ ~ ~ ~ ~ ~ ~ " " o ~ \ \ \ \ \ \ \ o ~ •.. ... ... . ~ ... . 0 , " " ·0 1 9 8 4 - - - - - 1 9 8 3 - - - - 1 9 8 2 • •• .• .. •. .• .. .. .. . 19 81 - - - - - - - - - - - " " " " " ... .. Ju n e Ju ly A u g u st S e p t. W ar m C re e k F i g u re 3 . M ea n n u m b e r o f l a rv a l s h a d c o l l e c te d p e r i ch th y o p l a n k to n to w , lo w e r L ak e P o w el l , 19 8 1 -1 98 4 . 2 0 0 0 .. 2 0 0 0 1 0 0 0 . 3 0 0 " ~ 2 0 0 1 1 0 0 . 0 0 ' \ 1 9 8 4 - - - - - . " 1\ , \ 1 9 8 3 I \ 1 0 0 0 I 1 9 8 2 •• •• •• •• •• •• •. .• •• • I \ I \ 19 81 - - - - - - I \ '\ \ I \ I 0 · ', \ I \ I \ \ \ I \ 3 0 0 I \\ .\ 0 I ' \ I \\ \ I \\ I , , I \.. , o ' \ , (" " , \ 2 0 0 I ' , \\ I \' . .... I I \\ \ I .... \ ..... \ I \ ••• •• I I \ \( ... I .. '\ , " ' , \ ," . , " '\ 1 0 0 " " , I -. ..... .. I " ~ ~/ ~. ", \: - ..... ., !/O _ .. . " , , .. .... ~ ..... . - , , ... •. ... ... ... ~ I · . • • i , , .... .. , , Ju n e J u ly A u g u st S e p t. Ju n e Ju ly A u g u st S e p t. B u llf ro g C re e k H a lls C re e k F ig u re 4 . M ea n n u m b er o f la rv a l sh a d c o ll e c te d p e r ic h th y o p la n k to n to w , m i d L ak e P o w e ll , 19 8 1 - 19 84 . ~ w I 2 0 0 0 1 0 0 0 3 0 0 2 0 0 1 0 0 • • 1\ /. \ I \\ / \ ~ I \ ~ I \ I \ I \ I \ I \ ~ I .~ . . • • ~ .\ \ \ • • • • · • • • • • · • • • • , , · \ \ , ..... ..... . \ . ~ ~ , -" ,\ ~ • Ju n e Ju ly R ed C an yo n A ug us t 2 0 0 0 1 0 0 0 3 0 0 2 0 0 1 0 0 S ep t. • • · • · • • • · • • · • ~ • · • • • r, \ I \ \ I \ \ I \ \ I H I \\ I \\ I ~ I \. I \ I ~ I \ • I \ I \ I W ...... .... 19 84 - - - - - 19 83 1 9 8 2 .. .. .. .. .. .. .. .• .. 19 81 - - - - - - I \ . ~ .... . I ! ~ . - - - - - - - . Ju n e • J u ly A ug us t S ep t. T ic ab o o C an yo n F ig u re .5 . M ea n n u m b er o f la rv a l sh a d c o ll e c te d p e r i c h th y o p la n k to n to w , u p p e r L ak e P o w e ll , 1 9 8 1 -1 9 8 4 . in California ponds in 1955, and Lake Havasu, California-Arizona ~n 1956 (Kimsey 1958; Kimsey et a1. 1957). Threadfin shad stocked ~n Hawaii spawned from June through September (Hida and Thompson 1962). Threadfin shad normally spawn at water temperatures between l4C and 28C. Heidinger (1983) found a thermal cut-off of spawning activity at approximately 30C. He felt that the duration of shad spawning was longer in Illinois study lakes than ~s typical of more southern states because surface temperature did not often exceed 30C. He found higher shad recruitment where optimum water temperatures for shad spawning occurred for longer periods of time without exceeding the thermal cutoff temperature. Surface water temperatures at Lake Powell seldom exceed 30C for more than a few days in August. The extended spawning season revealed in the ichthyoplankton sampling is, therefore , most likely the result of water temperatures remaining at the preferred temperature range for threadfin shad spawning, without exceeding the 30C cutoff. Shad spawning, indicated by the number of shad collected per tow, was higher in 1984 than has been recorded since the standard ichthyoplankton netting began in 1981 (Figures 3, 4 and 5). In lower Lake Powell this high point represents two years of high pro- duction at Warm Creek, and exceptional production during 1984 at Wahweap, with an average of 415 fish/tow collected in the July sam- ples (Figure 3). levels in 1982. Both sample sites exhibited lowest reproduction Limited ichthyoplankton netting in Chaol Canyon indicated good shad production, but for only one month during 1983 (June) and 1984 (May) in that portion of the lake (Table 2). Table 2. Mean number of larval threadfin shad collected per ichthyo- plankton net tow, Chaol Canyon, Lake Powell, 1983-84. Sam.E.le Month 1984 1983 May 791 a June 47 335 July 4 1 August 2 1 September a 1 a Not sampled. -14- Spawning success at mid lake peaked in June 1984 with record monthly averages of 1314 fish/tow and 1443 fish/tow collected at Bullfrog Creek and Hall's Creek, respectively (Figure 4). Since 1981, the only year that low production has been recorded at midlake was 1983. During 1983, all other lake locations recorded good shad spawning, but highs of only 51 fish/tow and 66 fish/tow, respect- ively, were recorded for June at Bullfrog Creek and Hall's Creek (Figures 4). Ichthyoplankton netting was also conducted in Moki Canyon during 1984 to assess how well the results from the Bullfrog and Hall's samples reflect mid lake trends. Numbers of larval shad collected were very close among the three sites and production trends were essentially the same (Table 3). Table 3. Mean number of larval thread fin shad collected per ichthyoplankton net tow, mid Lake Powell, 1984. Sample Month Bullfrog Creek Halls Creek Moki Canyon May 42 16 4 June 1314 1443 1046 July 70 90 46 August 8 46 Shad production in the upper lake was quite high during 1984 and reflected trends observed in 1982 and 1983. June 1984 samples contained 758 fish/tow and 365 fish/tow, respectively, at Red and Ticaboo canyons (Figure 5). The only low production year that has been observed up lake was 1981 when 54 fish/tow and 4 fish/tow were found at Red and Ticaboo canyons, respectively, during June. Limited netting conducted in the upper end of the San Juan Arm revealed a good shad spawn in May of 1984 at Piute Red Wall (252 fish/tow) and Piute Farms Wash (1200 fish/tow, Table 4). Spawning also appeared good during June . of 1983 at Piute Farms with 665 fish/tow being collected at the Piute Red Wall. Some shad spawn- ing did occur in the San Juan River Inflow during May of 1984 (36 -15- 0 fish/tow) but this area was relatively unimportant during the rest of 1984 and all of 1983 (Table 4). Although thread fin shad did not use the San Juan River heavily for spawning in 1983 and 1984, the interface at Piute Farms where the turbid, nutrient rich waters of the San Juan River mix with the lake waters was obv ious- l y preferred spawning habitat (Piute Red Wall and Piute Farms Wash samples). Because this area of mixing is quite large at Piute Farms, substantial shad production undoubtedly occurs in this area each year. A similar occurrence probably results in the upper end of Lake Powell where the waters of the Colorado River enter the lake. Table 4. Mean number of larval thread fin shad col l ected per ichthyo- plankton net tow, San Juan River Arm, Lake Powell, 1982-83. Sample Piute Red Wall Piute Farms Was h San Juan River Flow Month 1984 1983 1984 1983 1984 1983 May 252 a 1200 a 36 a June 3 665 1 a 1 0 July 0 67 1 a 1 0 August 0 0 0 a 0 0 a Not sampled. No primary production studies have been conducted at Lake Powell over the past 5 years. It may be possible, however, to gain some idea of primary production leve ls through examination of the water records for the lake. Thi s could give some idea of the annual influx of nutrients which could in turn effect primary production and shad produc ti vi ty. The annual inflows were, in fact, exce pt- ional1y high during 1983 and 1984 which coincides with two high pro- duction years in most portions of the lake (Table 5). The lowest inflow year (1981) was characterized by low production in upper Lake Powell, but did not appear to exe rt much effect on shad reproduction in the mid and l ower lake areas (Figure s 3, 4 and 5). Thus, the -16- amount of nutrient inflow may have direct impact on shad product- ivity in the inflow areas of Lake Powell but a somewhat diluted effect in lower lake areas as sediments settle out. Table 5. Monthly inflow (acre-ft) into Lake Powell, 1980-84.a Month 1980 1981 1982 1983 1984 January 661,970 500,269 368,780 701,100 821,040 February 802,208 410,826 472,010 662,210 874,810 March 790,180 389,175 686,150 1,126,190 1,046,460 April 1,146,340 389,916 891,960 1 , 094,750 1 , 500,680 May 2,951,360 652,725 2,005,040 2,789,960 4,474,440 June 2,951,038 1,087,500 2,340,720 5,530,560 4,805,880 July 942,365 528,900 1,315,800 3,587,490 2,417,770 August 338,291 331,173 730,140 1,481,710 1,382,150 September 528,231 447,374 815,420 751,090 875,470 October 487,270 605,847 964,150 898,190 1,004,630 November 568,556 456,445 833,380 783,350 925,260 December 548,079 432,247 790,450 809,230 824,870 Total 12,717,888 6,232,396 12,214,000 20,215,830 20,953,460 a Unpublished data, U.S. Bureau of Reclamation, Reservoir status re- port, Salt Lake City, Utah. Midwater trawl catches of y-o-y have varied greatly from year to year, but do show similar trends within years throughout the lake. Since 1980, good numbers of shad were only collected during 1981 and 1984 in trawl samples (Figure 6). Trawl catches in 1981 were 241 fish/tow, 1287 fish/tow and 582 fish/tow at Wahweap, Bullfrog and Good Hope, respectively. This compares with high catches observed i n 1984 of 45 fish/tow, 595 fish/tow and 536 fish/tow, respectively. The poorest recruitment years have been 1982 and 1983 when almost no y-o-y shad were collected in trawl tows from all locations (Figure 6). There is some evidence that the threadfin shad population In Lake Powell may be cyclic. Since 1977, trawl catches have exhibited -17- 1000 o July Sample August Sample September Sample " .! Co E .. (/) o z 80 81 82 83 84 Wahweap 80 8 1 82 83 84 Bu l!frog 80 81 82 83 84 Good Hope Figure 6. Mean number of shad collec ted per trawl tow, Lake Powell , 1980- 1984. (The top of each bar r epresents the total c at ch for Jul y- Sep t ember for each year.) -18- three distinct peaks occurring at three year intervals; 19 78, 1981 and 1984 (Figure 7). The two years between each peak have been characterized by very low shad recruitment in most areas of the lake. The high points and low points of the graph in Figure 7 do not, however, coincide with high and low production years revealed by the ichthyoplankton sampling (Figures 3, 4 (1973) found spawning was affected by density including crowding and nutritional conditions. and 5). Anderson dependent factors, It is possible that the cycling in numbers of y-o-y shad found 1n the pelagic zone of Lake Powell would have occurred regardless of the impact of pred- atory game fish. (1979 and 1980) Certainly during the first pelagic predators (i.e., low point 1n Figure 7 striped bass) were not present in large numbers and would have had a negligible effect on shad populations (Job IV). Thus, density dependent factors may have caused the first observed crash (1979-80) 1n the shad cycle 1n Lake Powell but subsequent low points were probably exacerbated, at least in part, by predation. Moczygemba and Morris (1977) reported that the open water zone is inhabited by surplus shad that are forced into the open water by intraspecific competition. Lack of shad in the pelagic zone is an indication of a predator-impacted shad population. The disparity between relatively high thread fin shad reproduction and subsequently low recruitment into the pelagic zones of Lake Powell probably resulted from striped bass predation. Large year classes of striped bass have been produced since 1981 (Job IV) and may be causing the decreasing trend seen in the numbers of shad collected from the population peak years of 1978, 1981 and 1984 (Figure 7). Members of the large 1981-83 year classes of striped bass were also present in most locations where shad spawning occurred. Unlike the adult striped bass that must retreat to deeper, cooler water during the heat of summer (Job I V), the year- lings stayed in shallow water with the shad and fed heavily on both adults and y-o-y shad. -19- 6 0 0 0 5 0 0 0 4 0 0 0 3 0 0 0 2 0 0 0 1 0 0 0 5 0 0 I 4 0 0 N 0 I 3 0 0 2 0 0 1 0 0 • • • . . • • • • . . . . . . • • . . . . . . . . •• * • • •• . . • • • • • • • • • • • • • • . . • • . . • • . . • • • • S s • • s. _ . • • •• . . . . : ~ . . . •• O l • • .. < =- : .. · ...... . . · ..... . . · ... . . · "" . . • 0 • • ".,g . : .. · ' . · ' . · ' . · ' . · ' . · ' . · ' . · ' . • • • • • • • • • .. . .. · . . • • • • • • · . . • • • · . . • • • ' . . ' . . ' . . ' . . • • • • ' . . ' . . ' . . ' . . ' . . •. . .. · . . • • • · . . • • • • • • • • • • • • • • • · . . • • • · . . .... . ... .. .. .. .. .. .. .. . ~ 77 78 7 9 8 0 81 8 2 • ." • : : • • • • : • • • • • : • • • • • : : • • : . : • • • :' • • • • : . ~ . 8 3 8 4 F ig u re 7 · M ea n nu m b e r o f th re a d f in sh ad c o ll e c te d p e r tr a w l to w , Ju ly -S ep te m b er , L ak e P o w el l, 1 9 7 7 -1 9 3 4 . In lake E. V. Spence, striped bass reduced the standing crop of gizzard shad and eliminated threadfin shad from the population (Morris & Follis 1978). Young gizzard shad that escaped predation grew rapidly. After exceeding the desired forage size preferred by striped bass 06-178 mm) they matured and spawned. Threadfin shad, because of their smaller size, were unable to outgrow the preferred prey size and were eliminated. Threadfin shad are the only school- ing forage fish in Lake Powell and they support the striped bass population. Striped bass in Lake Powell presently have unlimited reproductive potential (Job IV). This has exerted a negative impact upon shad recruitment and may also be impacting the available brood stock in years of low shad populations. Threadfin shad are very susceptible to low water temperatures and winter mortality. Parson and Kimsey (1954) observed high mor- talities at 7.2C. Griffith (1978) tested thermal tolerances of threadfin shad in the laboratory and found a feeding reduction at 10C, and a lack of response to movements and vibrations around them at 6.1-6. 7C. Temperature related mortality began at 8. 9C. Strawn (1965) observed a 50 percent loss at 6.1C and Hubbs (1951) found shad dying at 11.7-13.9C after a sudden cold period. Gustaveson et a1. (1980) reported a winter shad die-off of un- known magnitude at Lake Powell during the winter of 1978-79. Water temperatures throughout the reservoir were near or below the criti- cal 7.2C temperature for most of the winter. At that time it was felt that winter die-offs of shad could present a major problem to Lake Powell's shad population. Since 1979, there have been no reports of large numbers of dead shad found during the winter. A small number of dead shad were reportedly seen around the docks at Hite, Bullfrog and Hall's mar1nas by marina employees 1n February 1984, but it was never confirmed. There have been few times since 1979 that lake temperatures have fallen below 7C for extended periods. -21- SUMMARY AND RECOMMENDATIONS Water t empera tures at Lake Powell are probably optimum for maximum annual production of thread fin shad. In most years shad are able to begin spawning in May and continue into September. This fact alone could account for the ability of Lake Powell's shad popu- lation to rebound quickly 0-2 years) from population low points, whether they be caused by density dependent factors, predation or other causes. What factorCs) are responsible for the cycles ob- served in the lake's pelagic shad populations are somewhat unclear. It appears, however, that striped bass predation has been respon- sible for an overall reduction of shad numbers in the open water areas of Lake Powell. Threadfin shad reproduction has been quite high in both 1983 and 1984 . This allowed y-o-y shad to once again inhabit the pelagic zone of the lake in good will continue in 1985 or numbers in 1984. Whether this condition the shad population will again crash will be the subject of shad studies in 1985. It is thus recommended to continue ichthyoplankton netting and midwater trawling as established during this reporting period. The ichthyoplankton netting has proven useful in monitoring seasonal and annual larval shad production, and the duration of the spawn. Midwater trawling has been useful in evaluating y-o-y shad recruit- ment into the pelagic zone of the lake as well as for monitoring trends of available forage for striped bass. The use of echosound- ing to add support to trawling data should also be continued. Echo- sounding has proven a valuable tool when equipment breakdowns have prevented trawl sampling. In addition, echosounding is presently the only effec tive technique for monitoring adult populations of thread fin shad in the winter. Ichthyoplankton netting at Moki Canyon will be discontinued. The samples collected at Moki Canyon during 1984 do not add anything -22- unique to our understanding of shad reproduction in mid Lake Powell and only reflect the findings at Bullfrog and Hall's Creek. Water temperatures should continue to be monitored winter months to assess any problems with shad die-offs. during the Al though no major problem was observed during this reporting period, winter- time shad die-off has occurred previously at Lake Powell. -23- MEASUREMENT OF FISHERY HARVEST, PRESSURE AND SUCCESS JOB II BACKGROUND Angler use and success rates have been estimated annually at Lake Powell, beginning soon after impoundment (Gustaveson et al. 1979, 1980, 1981, 1982, 1983). In general, both total r ec reational boat use and angling pressure have increased steadily since 1965. Angler s uc cess has varied over the history of the reservoir with the highest catch rates occurring in the early 1970' s. Black crapp,e and largemouth bass consistently comprised over 70 percent of the annual catch from 1970-1979. Since 1980, the striped bass fishery has gradually improved as the population increased. A scheduled creel September in 1981 and During 1980, the census METHODS census was conducted from April through from April through October in 1982-1984. was conducted during the three months of most intensive angler use - April through June. In 1984, a March cree l census was conducted at Wahweap to obtain biological data and harvest information on striped bass from pres pawning staging areas near the dam. Anglers were interviewed as they returned to launching ramps at the four major access areas - Hite, Hall's Crossing, Bullfrog, and Wahweap. Due to the isolated nature of the reservoir and limited access, most anglers gained access at one of these four points. Historically, the Wahweap access area was censused an average of 10 days/month, while a total of 8-14 days/month were spent censusing anglers at Hite, Hall's Crossing, and Bullfrog. As angling pressure equalized between areas, the Wahweap cens us was reduced to 5 -24- 11 days/month while Bullfrog and Hall's Crossing were combined into one mid-reservoir area and surveyed a total of 6 days/month (3 days at each station). The Hite survey remained at 4 days / month. In 1984, all creel survey days were reduced from 8 hours to 4 hours. Census days for each access area were divided equally between weekdays and holidays/weekends. Data obtained during interviews of anglers in- cluded number and species of fish caught, time spent fishing, the number of anglers/boat, residence of anglers, location fished, and preferred species sought. Creel rates presented in this report were deri ved from all fishermen collec ti ve l y. Since many Lake Powe 11 anglers often camp out overnight and fish for several days at a time, data was collected from the fishermen for the census day, as well as for their previous day of fishing. Total length measure- ments, scales, and stomach samples were obtained from selected samples of game fish. In 1983 a computer program was designed to summarize data col- lected from the creel survey and was used in 1983 and 1984. Pres- sure estimates used in the program were based on the total number (fishing and non fishing) of boat days and the percentage of total boat days which included angling activity. The total number of boat days was provided by the National Park Service and was calculated from (1) daily boat trailer counts at launch ramp and marina parking lots; (2) number of rental boats used each day; and (3) number of boats being used from local boat storage lots. The percentage of fishing boats was estimated for each month and access area from creel census November-March interview represents data. only a Since fishing pressure from small portion (13 percent) of annual pressure (Gustaveson et al. 1979), creel survey s were not conducted during these months. Limited, random interviews during this time revealed that approximately 75 percent of all boats were involved 1n fishing activity. This arbitrary figure was subse- quently used to calculate fishing pressure from November-March. -25- RESULTS AND DISCUSSION In 1984, a total of 3,098 boating parties was checked by creel c lerks during the eight month census period. Of these, 1,058 (34 percent ) reported angling activity. The mean number of anglers per fishing boat was 2.5 and each angler spent an average of 4.0 hours fishing per day (Table 6). While angling pressure decreased on Lake Powell in 1984, recreational boat use increased (Figure 8). Angling pressure was 96,859 fishing boat days in 1984, a decrease of 2 percent from 1983. Total recreational boat use (including fishing and nonfishing boats) was 318,554 compared to 266,364 boat days in 1983. Bullfrog access area acc ounted for the highest angler use (42 percent) of the four major access points, while angler use at Wahweap, Hall's Crossing, and Hite access points was 36 percent , 14 percent, and 8 percent , respectively . This use trend has prevailed throughout the 1980-1984 period. Prior to 1980, Wahweap access area accounted for the highest angler use at Lake Powell. The majority of anglers fishing at Lake Powell during the 1980-1984 census period "ere from Utah, Arizona, and Colorado. Al- most all of the anglers censused at Bullfrog and Hite were from Utah and Colorado (Figure 9). More than 75 percent of the anglers at Hall's Crossing were from Colorado and New Mexico, while most o f the anglers interviewed at Wahweap were from Arizona. Most specific angling pressure in 1984 was directed at large- mouth bass and striped bass (Table 7) . The majority of the fisher- men, however, were indiscriminate anglers or those willing to creel any fish that was captured. The percentage of anglers choosing to fish specifically for black crappie has steadily declined during the past 5 years to the current low point of 2.4 percent. -26- I N " I T a b le 6 . F is h in g b o a t u se (b o a t- d a y s ) by m o n th . L ak e P o w e ll , 1 9 7 5 -8 4 . A ls o g iv e n a re t h e a v e ra g e ti m e (h r) fl s h e d lt rl p (H IT ) an d th e m ea n nu m be r o f fi s h e rm e n /b o a t (F IB ). Y e a r 19 75 19 76 19 77 19 78 19 79 19 80 19 81 19 82 19 83 19 84 A ve . % Ja n . 44 3 59 3 25 1 29 0 34 0 23 8 81 7 40 8 66 8 25 4 43 0 0 .5 F eb . 1, 23 7 1 ,3 0 0 1, 60 2 66 9 40 7 60 6 1, 27 9 65 6 76 8 63 6 91 6 1 .2 M a r. A pr . M a y 4 ,3 6 4 9 ,7 7 0 I 1, 2 6 5 4 ,5 7 2 12 ,7 76 15 ,1 37 3 ,3 2 7 12 ,7 72 15 ,5 01 3 ,1 1 8 12 ,8 7 7 10 ,5 97 3 ,8 4 9 12 ,2 57 14 ,3 90 3 ,6 4 7 10 ,6 88 19 ,8 32 4, 68 1 9 ,4 9 5 14 ,0 33 3 ,0 9 4 16 ,8 94 19 ,7 14 3 ,9 9 6 12 ,6 55 23 ,0 08 2 ,6 7 5 14 ,7 68 12 ,8 65 3 ,7 3 2 12 ,4 95 15 ,6 34 4 .8 1 5 .9 1 9 .9 Ju ne 7 ,3 2 2 8 ,6 4 2 10 ,1 68 8 ,4 9 9 8 ,7 8 4 15 ,0 14 13 ,7 72 15 ,0 97 13 ,4 75 17 ,4 63 I 1, 82 4 15 . I Ju ly 3 ,1 0 0 5 ,3 5 4 4 ,9 5 7 4 ,9 8 6 6 ,9 1 4 5 ,7 4 3 1 1 ,8 8 6 8 ,7 1 9 8 ,9 9 9 8 ,1 3 6 6 ,8 7 9 8 .8 A ug . 2 ,5 0 3 5 ,6 5 5 4 ,6 4 0 4 ,6 4 0 8 ,0 8 5 6 ,1 1 6 1 1 ,0 9 2 8 ,9 5 5 8 ,3 8 3 10 ,1 85 7 ,0 2 5 9 .0 S ep t. 3 ,4 3 2 4 ,4 6 0 6 ,7 0 0 5, 1 74 8 ,2 4 2 7 ,4 6 9 12 ,4 40 I 1, 12 8 10 ,0 76 1 1 ,0 8 6 8, 02 1 10 .2 O ct . 3 ,4 0 4 4, 02 1 4 ,9 6 0 4 ,6 9 3 5 ,7 0 9 5 ,7 1 7 6 ,1 6 6 17 ,5 14 7 ,5 2 2 8 ,9 5 6 6 ,8 6 6 8 .7 N o v. 1, 5 4 6 I, B 53 1, 6 3 4 2 ,3 3 2 1, 81 1 2 ,5 9 3 3 ,5 4 5 6 ,9 7 0 7 ,5 2 2 8 ,0 7 7 3 ,7 8 8 4 .8 D ec . 34 4 3B 4 32 6 96 5 68 4 74 2 83 3 1, 40 7 1, 29 2 1, 75 8 87 4 1 .1 T ot a l 4 8 ,7 3 0 6 4 ,7 4 7 6 6 ,8 3 8 5 8 ,8 4 0 7 1 ,4 7 2 7 8 ,4 0 5 9 0 ,0 3 9 11 0, 55 6 9 8 ,5 5 0 9 6 ,8 5 9 H IT FI B 4 .5 3 .0 3 .8 2 .8 3 .3 2 .9 3. 1 2 .4 4 .5 2 .4 4 .0 2 .6 4 .0 2 .5 3 .9 2 .5 4 .9 2 .6 4 .0 2 .5 3 2 0 2 8 0 II I >- 2 4 0 0 :I : ~ Q ) - CI c:: < ~ Ql I Q . w ~ I s: ; III LL 1. 3 1. 2 1. 1 1 .0 0 .9 0 .8 0 .7 .. 1\ i \ I \ I \ I \ I \ I \ I \ I \ I \ - - - - · A I I S p e c ie s - - - - - - B la c k C r a p p ie -- -- -- -- L a r g e m o u th B a ss 0 . 6 1 - - , , I~ \ . ( " I , ,/ " \ \ I " I'" ~ / . \ . ' , , , 0 .5 0 .4 0 .3 0 .2 0 .1 ' / I , . ' , '- , ' / . \ " , " ~-~ J '- _ '. ' ," "\ . '- ,_ . I J __ __ _ " /" '- .. .. _ / • I / ,,' " ~ 6 5 6 6 6 7 6 8 6 g 7 0 7 1 7 2 7 3 7 4 7 5 7 6 7 7 7 8 7 9 8 0 8 1 8 2 8 3 8 4 V a a r F ig u re 10 . C re e l ra te s (f is h /a n g le r h ou r) fo r la rg em o u th b a ss , b la ck c ra p p ie an d a ll sp e c ie s, L ak e P o w el l, A p ri l- Ju n e 19 65 -1 9 84 . Table 8. Sport fishery creel r a tes (fish/angler hour) by species and access area, Lake Powell, April-October 1984. Lakewide Species Hite Bullfrog / Hall's Wahweap Average Largemouth bass 0 . 062 0.044 0.070 0.052 Black crappie 0.032 0.027 0.032 0.029 Striped bass O. 024 0.032 0.023 0.029 Walleye 0.007 0.033 0.009 O. 022 Channel catfish 0.020 0.019 0.025 0.020 Bluegill 0.008 0.030 0.036 0.023 Other species 0.002 0.003 0.002 0.002 All species 0.155 0.187 0.196 0.176 Table 9. Striped bass creel rates (fish/angler hour) by access area Lake Powell, 1980-1984 Location Hite Eullfrog/Hall's Wahweap 1980 0.002 0.004 0.007 1981 0. 005 0.008 0.034 1982 0.015 0.026 0.083 1983 0.023 0.031 0.154 1984 0.024 0.032 0.023 of the fishery throughout most of the season. Walleye made up the largest portion of the catch in June (36.2 %) and a substantial por- tion (9.7 %) of the harvest in May (Table 10). -32- Table 10. Species composltlon (%) of the total creel, Lake Powell, March-October 1984. Species Mara Apr May Jun Jul Aug Sep Oct Mean Largemouth bass 5], 7 34.0 31.7 15.4 58.4 16.5 29.8 31.3 34.3 Black crappie 35.9 47.6 18.3 3.6 18.1 9.1 1.0 10.1 18.0 Striped bass 3.8 6.1 12.9 23.9 3.5 25.9 19.4 23.6 14.9 Walleye 1.3 2.9 9.7 36.2 8.3 3.4 0.2 5.2 8.4 Channel catfish 0.0 2.4 6.1 16.8 8.8 25.1 20.9 6.4 10.8 Bluegill 0.0 6.1 19.2 3.6 1.9 20.0 27.7 20.8 12.4 Other 1.3 0.9 2.1 0.5 1.0 0.0 1.0 2.6 1.2 a March creel conducted at Wahweap only. The first confirmed occurrence of lake trout (Salvelinus namaycush) in Lake Powell was recorded during creel census in May 1983. Another was netted by a Bureau of Reclamation biologist in April 1984 and a third was caught from Bullfrog Bay in December 1984. All three fish probably migrated downstream from either Flaming Gorge Reservoir, Utah, or Blue Mesa Reservoir, Colorado. In spite of the growing sophistication of the Lake Powell bass anglers, catch rates of largemouth bass have continued to decline over the pas t five years. Many bas s anglers now use complex and expenSlve equipment, including electric trolling motors, depth sounders and fish finders, electronic temperature and pH gauges, and other gadgets. While use of this gear does not guarantee fishing success, the anglers versed in operation and application of this equipment generally catch more fish than those without it. The reduced catch rates reported at Lake Powell over the past few years are mainly the result of decreasing populations of largemouth bass. Indices of abundance for catchable-size largemouth bass have shown -33- substantial correlation with angler success at Lake Powell, espe- cially since 1979 (Job III). It appears that the once booming largemouth bass fishery that existed shortly after impoundment has dec 1 ined to ales s succes sful fishery, a pat tern common to many aging reservoirs (Hashagen 1973, and Jenkins 1968). The striped bass creel limit was increased from 4 to 10 fish in 1984, yet harvest of striped bass declined substantially from 1983, especially in the Wahweap area. Following striped bass spawning in May 1983, a buoy-line was installed by the U.S. Bureau of Recla- mation to exclude boats from approaching the dam. In 1984, there- fore, fishermen were barred from congregations of prespawning striped bass which staged at the dam and were quite vulnerable to angling. This has effectively eliminated a highly successful spring fishery and probably contributed to the decrease in harvest of striped bass in 1984. Additionally , the relative abundance of adult striped bass was probably less in 1984 than in 1983 (Job IV). Prior to 1980, the bulk of the striped bass fishery in Lake Powell was in the lower portion of the reservoir. Since then, striped bass have become established lakewide. Subsequently the creel rate and harvest of this species has increased substantially 1n the middle and upper reservoir. Many anglers are now versed in the techniques necessary to effectively harvest striped bass, and in 1983 an exceptional striped bass harvest exceeded that of all other species in Lake Powell. The striped bass fishery is well accepted by most anglers and provides a trophy fishery as well as an abundant fishery that less experienced anglers can enjoy. SUMMARY AND RECOMMENDATIONS While angler creel rates for largemouth bass and black crappie have decreased annually over the past five years, striped bass c reel rat e s have increased. As a result, a large portion of anglers -34- have become opportunists and fish for whatever they can catch. Some fishermen still primarily pursue largemouth bass. Striped bass have been highly accepted by anglers and have become an important component of the Lake Powell fishery. Future creel surveys should continue to closely monitor the dynamic striped bass fishery as well as the other Lake Powell sport fisheries. Recent introductions of smallmouth bass will also be monitored with the creel survey. As the smallmouth bass fishery expands 1n Lake Powell, the creel census should be a useful method of obtaining the biological data needed to make correct management decisions. In recent years, the mid-reservoir access areas have had the highest use by fishermen. The addition of a Bullfrog-Hall' s Cros- s1ng car ferry in the summer of 1985, as well as future plans to pave the Burr Trail road should further increase visitation rates and fishing pressure at the mid-reservoir access areas. -35- INDEX TO ANNUAL POPULATION TRENDS JOB III ANNUAL NETTING BACKGROUND Standardized gillnet sampling has been used to describe gross changes 1n fish population densities and species composition at Lake Powell. Standardized gillnet sampling has been conducted annu- ally since 1971 (Gloss et al. 1974; May and Hepworth 1976; Gustaveson et al. 1980, 1981, 1982, 1983, 1984). The gillnet sam- pling has been most effective in describing changing trends in the largemouth bass and walleye populations . The largemouth bass popu- lation was most abundant during the early 1970's and has generally declined since that time. During the same period walleye abundance has generally increased. The survey has been quite sensitive in detecting the presence of new species and illustrating the decline of others. Rainbow trout were an important sport fish in the 1960' s and early 1970' s; how- ever, trout stocking was discontinued when striped bass were intro- duced in 1974. The survey depicted the decline of trout abundance and the subsequent increase in striped bass numbers (Gustaveson, et al. 1980). METHODS Gillnet sampling was conducted during March 1980-84 at Padre Bay, the San Juan Arm, the Rincon, and Good Hope Bay (Figure 11). Gangs of ten 30.5 m diving experimental gillnets with four 7.62 m -36- .., I w ...., I • E le c tr o fi s h in g S ta ti o n o S p ri n g N et ti n g S it e 9- t M ile s I o 5 10 G o o d H o p e B a y ~- -- - A r/ o l O ll a - - W ah w ea p F ig u re 1 1 . M ap o f L ak e P o w e l, U ta h - A ri z o n a , s h o w in g a n n u a l n e tt in g s it e s (d o ts ) an d e le c tr o fi s h in g tr a n s e c ts (c ir c le s ). pane Is (mesh sizes 25, 38, 51, and 76 mm) were fished for three consecutive days at each station. On occasion, fewer nets were used due to net loss or damage while sampling. Nets were set perpendicular to the shore with one end anchored to the shoreline. The nets were set on the bottom, in similar talus rock and rubble habitat. Fish were removed at 24-hour intervals, we i ghed and measured, and scales were taken for age and growth analysis. A selected sample of walleye and largemouth bass was used to quantify fish condition according to the UDWR Visceral Fat Index (VFI) (Ronald Goede, Fish Pathologist, UDWR Experiment Station, Logan, Utah, personal communication, 1980). Fish were assigned cat- egorles depending on the amount of visceral fat found on the pyloric caeca. The ca tegories were as follows: O=no fat; 1 =less than 50% of the caecum covered with fat; 2=approximately 50% of the caecum covered wi th fa t; 3=more than 50% of each caecum covered wi th fat; 4=pyloric caeca completely covered with fat. RESULTS AND DISCUSSION A total of 522 fish was collec ted in 120 net days during the 1984 annual netting. The highest catch rate (6.17 fish/net day) was recorded at Good Hope Bay, followed by the Rincon, Padre Bay, and the San Juan, respectively (Table 11) . The overall catch for 1984 was slightly higher than 1983 at all stations except Padre Bay where a small reduction occurred. The total catch rate for all species and stations combined (4.35 fish/net day) increased slightly from 1983 (3.68 fish/net day) (Table 12) . The catch rate of largemouth bass continued to decrease in 1984 as it has for the past six years (Figure 12) . However, the rate of decrease has slowed and the largemouth bass population seems to be stabiliz i ng at a lower relative abundance than seen historically. -38- Table 11. Catch rates (fish/net day) during annual spring gill- netting, Lake Powell, March 1984. Padre San Good Hope Species Bay Juan Rincon Bay Totala Largemouth bass 0 . 33 0.67 0.33 0.50 0.46 Walleye 2.53 1.03 1.53 3.97 2.26 Striped bass 0.07 0 . 30 2 . 53 0.67 0.89 Black crappie 0 . 00 0.03 0 . 00 0.00 0.01 Carp 0.13 0.30 0 . 53 0 . 50 0.37 Channel catfish 0.03 o .l3 0 . 30 0 . 30 0.19 Green sunfish 0.00 0.07 0.13 0 . 17 0.09 Bluegill 0.l3 0.00 0.00 0.10 0.05 Brown trout 0 . 00 0 . 03 0 . 00 0.00 0.01 Flannelmouth sucker 0.00 0 . 00 0 . 07 0.00 0.02 Total 3.23 2.57 5.43 6.17 4.35 a Total = total number of fish divided by total net days. -39- % of Catch 10.6 52.0 20.5 0.2 8.5 4.4 2.1 1.1 0.2 0.5 T ab le 1 2 . C a tc h ra te (f is h /n e t d ay ) by sp e c ie s an d y e a r, an n u al g il ln e tt in g , L ak e P o w el l, 1 9 7 1 -8 4 . C at ch R at e S p ec ie s 19 71 19 72 19 73 19 74 19 75 19 76 19 77 19 78 19 79 19 80 19 81 19 82 19 83 19 84 L ar ge m ou th b as s 1 . 6 5 5 .8 2 2 .7 1 4 .0 1 4 .4 9 2 .7 2 1 .8 5 2 .6 1 1 .8 3 1 .5 7 1 .4 1 0 .6 3 0 .4 7 0 .4 6 W al le y e 0 .2 9 1 .1 2 0 .4 1 1 .0 9 2 .1 5 2 .1 1 1 .1 7 2 .8 4 3 .2 5 3 .6 6 4 .9 9 2 .1 7 1 . 7 3 2 .2 6 S tr ip e d b as s 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 2 0 .0 8 0 .0 9 0 .0 2 0 .2 4 0 .1 3 0 .3 2 0 .8 9 B la ck c ra p p ie 0 .1 2 0 .6 7 0 .1 2 0 .2 7 0 .3 6 0 .2 7 0 .2 6 0 .3 3 0 .2 1 0 .0 3 0 .1 6 0 .0 8 0 .0 4 0 .0 1 I B lu e g il l 0 .1 2 0 .5 2 0 .0 6 0 .0 5 0 .0 4 0 .1 0 0 .0 9 0 .0 4 0 .0 3 0 .0 1 0 .0 5 0 .0 2 0 .0 1 0 .0 5 ~ 0 I G re en su n fi sh 0 .1 0 0 .1 6 0 .0 9 0 .1 3 0 .0 6 0 .0 4 0 .0 9 0 .1 0 0 .1 0 0 .0 2 0 .0 7 0 .0 5 0 .0 2 0 .0 9 C h an n el c a tf is h 0 .1 2 0 .4 3 0 .2 1 0 .1 4 0 .2 5 0 .1 6 0 .2 0 0 .2 9 0 .3 8 0 .3 6 0 .1 7 0 .0 4 0 .2 7 0 .1 9 C ar p 1 .1 4 0 .7 9 0 .3 2 0 .3 4 0 .3 6 0 .3 8 0 .4 4 0 .3 4 0 .3 2 0 .3 2 0 .5 5 0 .4 9 0 .7 9 0 .3 7 F 1a n ne 1m ou th su ck er 0 .1 8 0 .2 8 0 .2 1 0 .1 7 0 .0 8 0 .0 8 0 .0 3 0 .0 3 0 .0 4 0 .0 6 0 .0 4 0 .0 0 0 .0 1 0 .0 2 R ai n b ow tr o u t 0 .2 4 0 .3 1 0 .1 0 0 .0 8 0 .1 9 0 .2 5 0 .2 6 0 .1 1 0 .0 4 0 .0 2 0 .0 1 0 .0 0 0 .0 0 0 .0 0 B ro w n tr o u t 0 .0 2 0 .0 0 0 .0 1 0 .0 3 0 .0 4 0 .0 4 0 .0 2 0 .0 1 0 .0 0 0 .0 0 0 .0 1 0 .0 0 0 .0 0 0 .0 1 Y el lo w b u ll h e a d 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 1 0 .0 4 0 .0 3 0 .0 3 0 .0 3 0 .0 2 0 .0 2 0 .0 0 A ll sp e c ie s 3 .9 8 1 0 .1 0 4 .2 4 6 .3 1 8 .0 2 6 .1 5 4 .4 4 6 .8 2 6 .3 2 6 .1 2 7 .7 3 3 .6 2 3 .6 8 4 .3 5 5 4 3 -Q) z 2 ---.c UI u.. 1 6 5 4 >- 01 C 3 -Q) z --- 2 .c UI u.. 1 • Walleye .--. I , 1 1 ,I 1 " • • " . " ~ ./ / / , I 1 • 1\ 1 \ 1 \ ;.' \ . ; \ •• ,,/ \ • , /' './ • 71 72 73 74 75 76 77 78 79 80 81 82 83 84 Year • Largemouth Bass ;/\ • • "/',, • . . ...... '--. " • '-. 71 72 73 74 75 76 77 78 79 80 81 82 83 84 Year Figure 12. Ca t ch rates (fish/net day) for walleye a nd largemouth bass f rom a nnual ne tting, Lake Powell, 19 71-1984 . - 41- The catch rates for both walleye and striped bass increased slightly in 1984. Between 1971 and 1981, walleye catch rates gener- ally increased suggesting that the population expanded during that period (Figure 12). Substantial reductions in catch rates of walleye occurred in 1982-83, however , the walleye gillnet catch again increased in 1984. Striped bass catch rates have generally increased since they were first recorded in the survey in 1977 (Table 12). Striped bass catch rates in 1984 were second only to walleye. Black crappie, carp, and channel catfish were occasionally caught and collectively comprised 13.1 percent of the total gillnet catch in 1984. These species have density over the past five years and this survey in large enough numbers their relative abundance. shown no apparent are probably not to make inferences changes ~n sampled by concerning Trends of abundance in the gillnet survey appear to follow the annual trends in creel rates for both walleye and largemouth bass (Figure 13). Both surveys appear equally effective in des c ribing population trends for these two species and complement one another. Visceral Fat Index (VFI) values indicated that walleye normally exhibit a value of around 2.9 (Table 13). A trend of slightly lower VFI values for walleye captured in the lower reservoir persisted throughout the sampling. Largemouth bass normally exhib it a VFI value of about 1.5, which is considerably lower than VFI values for walleye. VFI values for largemouth bass dropped over a full "point" between 1981 and 1982 and have remained low for the past three years (Table 14). VFI appeared to be influenced by thread fin shad abun- dance. VFI values for both walleye and largemouth bass were quite high at the beginning of 1981, but following a decrease in shad abun- dance in 1981 (Job I), VFI values dropped considerably (Tables 13 and 14) . Correlations between VFI and condition factors (K) were statis - tically analyzed for both walleye and largemouth bass. While some correlation existed, linear regression values for both walleye (0.22) and largemouth bass (0.13) were low in 1984. -42- >-co C 6 5 4 ~ 3
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Content: 3e88a0a828c7caf268552190c03c9d7b02d3c04d | Abstract: 38e396633c2f193ed2ca2413c0015f932fbc567f