title
Lake Powell fisheries investigations : annual performance report, May 1, 1989 - April 30, 1990, completion report, May 1985 - April 1990, Dingell-Johnson Project F-46-R
author
Array ( [0] => Gustaveson, A. Wayne [1] => Maddux, Henry R. [2] => Bonebrake, Bruce L. [3] => Christopherson, Kevin )
abstract
UDWR Publication Number 90-9
date
1990-01-01
organization
Utah. Division of Wildlife Resources
species
Array ( [0] => Not Specified )
file_path
https://grey-lit.s3.wasabisys.com/lake-powell-fisheries-investigations-annual-performance-report-may-1-1989-april-30-1990-completion-r.pdf
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https://grey-lit.s3.wasabisys.com/lake-powell-fisheries-investigations-annual-performance-report-may-1-1989-april-30-1990-completion-r-pdf-1-757x1024.jpg
content
N 4650P6.13: Lak/ 9 g''l/q<}O Lake Powell Fisheries Investigations Annual Performance Report May 1, 1989 - April 30, 1990 Completion Report May 1985 - April 1990 Dingell-Johnson Project F-46-R LAKE POWELL FISHERIES INVESTIGATIONS Completion Report May 1985 - April 1990 Annual Performance Report May I, 1989 - April 30, 1990 A. Wayne Gustaveson, Project Leader Henry R. Maddux, Project Biologist Bruce L. Bonebrake, Project Biologist Kevin Christopherson, Special Projects Biologist Dingell-Johnson Project F-46-R Utah Department of Natural Resources Division of Wildlife Resources 1596 West North Temple Salt Lake City , UT 84116 Timothy H. Provan Director An Equal Opportunity Employer TABLE OF CONTENTS LIST OF TABLES LI ST OF FIGURES INTRODUCTION . . . . . . FORAGE CONDITION STUDY BACKGROUND .... METHODS . . . . . . RESULTS . . . . . . . . Ichthyoplankton tows Midwater Trawls . . . DISCUSSION ...... . RECOMMENDATIONS . . . . . . . . . . . . . MEASUREMENT OF FISHERY HARVEST, PRESSURE AND SUCCESS BACKGROUND ... . . . METHODS . . . . . . . . . . RESULTS AND DISCUSSION RECOMMENDATIONS . . . . . . . INDEX TO ANNUAL POPULATION TRENDS ANNUAL NETTING ..... . BACKGROUND .. . . .. . METHODS .... .. .. . RESULTS AND DISCUSSION SUMMARY AND RECOMMENDATIONS ELECTROFISHING ... .. . BACKGROUND ....... . METHODS . . . . . . . . . . RESULTS AND DISCUSSION SUMMARY AND RECOMMENDATION S STRIPED BASS POPULATION DEVELOPMENT BACKGROUND ..... . METHODS . . . . . . . . RESULTS AND DISCUSSION Spawning .... . Recruitment ... . Food Habi ts . . . . Physical Condition Age and Growth RECOMMENDATIONS . . . . . . SMALLMOUTH BASS POPULATION DEVELOPMENT BACKGROUND ..... .. . METHODS . . . . . . . . . . RESULTS AND DISCUSSION SUMMARY AND RECOMMENDATIONS LITERATURE CITED . . . . . . . . . i.i.i iii v I 3 3 4 7 7 II 15 17 19 19 19 20 25 27 27 27 27 28 32 33 33 33 33 35 39 39 43 44 44 45 45 48 49 51 55 55 55 55 52 53 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 . 11. 12. LI ST OF TABLES Monthly mean number and total length (mm) of larval threadfin shad collected during ichthyoplankton tows with corresponding mean temperature (C) and secc hi (m) measurements for uplake stations, Lake Powell, 1985. (SE = Standard Error of the Mean) ......... . Monthly mean number and total length (mm) of larval threadfin shad collected during ichthyoplankton tows with corresponding mean temperature (C) and secchi (m) measurements for San Juan Arm, Lake Powell, 1985-1988 . (SE = Standard Error of the Mean) . . . . . Fishing boat use (boat-days) by month, Lake Powell 1975-1985 and 1988. Also given are the average time (hr) fished / trip (H/T) and the mean number of fishermen/ boat (F/ B) ....... . Change in angler origin by percent from the period 1980-1984, and 1988, Lake Powell ...... . . Species sought (%) by anglers, Lake Powell, April-October, 1985 and 1988. Trace (t) = <1% ..... . Species composition by percent (t = <1%) of the total recorded creel census for Lake Powell, 1964-1985 and 1988 . . . . . . . . . . . . . .... Total creel rate for all species by month and year for lake Powell, 1964-1985 and 1988 .... Striped bass creel rates (fish/ angler hour) by access area, Lake Powell, 1980-1985 and 1988 ....... . Catch rate (fi sh/ net day) by species and year, annual gill netting , Lake Powell , 1971-1988 ..... Percent occurrence of food items in wall eye collected in gill net s and during creel census, Lake Powell, 1985-1989. (Perce ntage based on number of stomachs containing food.) ..... ... .............. . Percent occurrence of food items in largemouth bas s collected in gill nets and during creel census, Lake Powell , 1985-1989. (Percentage based on number of stomachs containing food.) ........ . . Mean catch rate" (fi sh/ h) of fish collected by electrofi shing , Lake Powell, September 1989 ....... .. . . v 8 8 21 22 23 24 25 26 30 31 32 34 Table 13 . 14 . 15. 16 . 17. 18. 19. 20. 21. 22 . LIST OF TABLES (Continued) Mean catch ratea (fish/h) of fish collected by electrofishing, Lake Powell, 1985-1989 .. .. Stocking history of Lake Powell, Utah-Arizona, 1963-1989 . ... ... . ... . .... . Percent occurrence of food items in striped bass collected in gill nets and during creel census, Lake Powell, 1985-1989 . (Percentage based on number of stomachs containing food.) .. . .. .... . Mean back-calculated lengths (mm) of striped bass, captured at Lake for each year class Powe 11 duri ng 1985-1989 . .. ...... . . . Back-calculated growth of striped bass at Lake Powell, 1975-1989. Mean estimated total length (mm) , with age classes not separated ... .... . . ... . .. . Back-calculated lengths (mm) of striped bass captured during November gill netting at Lake Powell. Lengths for each age class are combined and averaged for 1985-1989 and compared among four lake areas. Sample size (n) in parentheses . ...... . ..... . Average catch ratea (fish/h) of young-of-the -year smallmouth bass collected by electrofishing . Lake Powell, 1982-1989. (1+ and older fish denoted by parentheses) .. . . .... . ... . .... . Habitat use (%) by smallmouth bass during nighttime electrofishing surveys, Lake Powell, September 1989 Percent occurrence of food items in smallmouth bass collected from gill netting, electrofishing, and creel census, Lake Powell, 1988 -1989. (Percentage based on number of stomachs containing food.) .. . Mean back-calculated lengths for smallmouth Lake Powell, 1986-1989, with compari son s to and largemouth bass (LMB) from Lake Powell vi bass (SMB) , other waters Page 37 40 48 51 52 53 59 60 61 62 Figure I. 2. 3. 4. 5 . 6. 7. 8. 9. 10 . LIST OF FIGURES Map of Lake Powell showing trawling and ichthyoplankton netting stat ion s for threadfin shad , 1985-1989 .... Mean number of larval shad co llected per ichthyoplankton tow and mean water temperature, Hall 's and Bullfrog creeks mid Lake Powell, 1985-1989 ............... . Mean number of larval shad co llected per ichthyoplankton I tow and mean water temperature, Wahweap and Warm creeks, lower Lake Powell, 1985 -1989 .. ..... ...... . Mean number of larval shad col lected per ichthyoplankton tow and mean water temperature, Navajo Canyon, lower La ke Powell, 1985-1989 . . . . . . . . . .. . ..... Mean number of shad collected per trawl tow by station and month , 1985-1989 (lower figure) and hi stor ic catch threadfin shad collected per trawl tow at Lake Powell, 1977-1989 (upper figure) . . ........... . Catch rates (fish/ net day) for walleye and largemouth bass from annual netting, Lake Powell, 1972-1988 Percent of black bass electrofishing catch represented by largemouth and small mouth bass, all sites combined, Lake Powell, 1980-1989 ........... . Average number of striped bass caught during fall netting (fish/ IOOO ft2 of net/ 12 h), Lake Powell, 1981-1989 . . . . . .. . ......... . Annual condition factor (K) of adult and juvenile striped bass, Lake Powell, 1975-1989 . . .. . . Map showing stock ing s ites (x) (1982 -1989) and 1989 capture locations (z) for small mouth bass, Lake Powell .. ...... . ... ........ . . vii 5 10 12 13 14 29 35 47 50 58 LAKE POWELL FISHERIES INVESTIGATIONS INTRODUCTION Fisheries investigations on La ke Powell began in 1963, shortly after impoundment, and have continued to the present. Initial work included physical and chemical descriptions of the filling reservoir, plankton development, life history studie s of introduced game fish, and an estimation of fishing pressure and success. Th ese studies were funded, in part, by federal monies provided under Section 8 of Public Law 485, the Colorado River Storage Project Act, and were comp l eted in 1971. Investigation s since 1971 have been funded by Federal Aid to Fish and Wildlife Restoration, Project F-28-R, and by the Utah Divi sion of Wildlife Resources. Lake Powell Fisherie s Investigations was redesignated as Project F-46-R in 1985. Studies undertaken since 1971 included game fish food habit s, benthic invertebrate studi es, plankton stud i es, threadfin shad Dorosoma pentenense population dynamics and predator impacts, an annual gillnetting program to determine trends in game fish populations , and small mouth bass Micropterus dolomieui stocki ng and population development studies. The study of fishing pressure and success ha s been continuing since 1963, while the study of the physical and chemical nature of Lake Powell was completed in 1974. Important events that have occurred since the initial introduction of largemouth bass Micropterus salmoides, black crappie Pomoxis nigromaculatus and rainbow trout Oncorhynchus mykiss, include the introduction of threadfin shad in 1968, introduction of striped bass Morone saxatilis in 1974 , introduction of smallmouth bass in 1982 and the expansion of the walleye Stizostedion vitreum population which developed from stock present in the drainage prior to impoundment. The sport fisheries have undergone several changes since impoundment. The initial introductions of largemouth ba ss and black crappie were quite success ful and developed into an exce ll ent fishery that peaked in the early 1970's. As the lake filled in 1980, inundated bru sh decomposed and disappeared caus ing a decline in spawning and nur sery habita t which grea tl y 1 reduced largemouth bass and crappie recruitment. To help alleviate the se population declines and to provide more diversity, striped bass and smallmouth bass have been introduced . Striped bass were found to be naturally reproducing in the Colorado River above Lake Powell in 1979. In 1981, striped bass reproduction was detected within the still water of the reservoir . This double dose of reproduction was more than the threadfin shad forage base could support . Striped bass predation eliminated threadfin shad from the pelagic zone of the reservoir. Striped bass physical condition and average size quickly declined without adequate pelagic forage. A search for a remedy to declining size and physical condition of striped bass has continued throughout the 1980's. Despite the problems of the striped bass population, black bass, particularly sma llmouth bass have flourished . The population of largemouth and smallmouth bass in the aggregate, has increased during the present five year report period due to the success of the smallmouth bass stocking program. Finding s of our research from 1985 to 1989 are given in this report along with detailed results of the 1989 sampling year. More detailed accounts of events occurring in any particular year, 1985 to 1988, can be found in Lake Powell annual progress report s for that year (Gu staveson et al. 1986, 1987, 1988 and 1989). 2 FORAGE CONDITION STUDY JOB I BACKGROUND Threadfin shad have been stocked throughout the Southwestern United States as forage (Kimsey et al . 1957 , LaRivers 1962, Beers and McConnell 1966 , Burns 1966). Shad were introduced into Wahweap Bay, Lake Powell in June 1968 (Miller et al. 1969). Approximately 90 percent of the original plant were young-of-the-year (yoy). Sampling in the winter of 1968-1969 revealed that shad had spawned their first summer in Lake Powell. Heidinger and Imboden (1974) found that yoy shad planted into a shad-free environment matured and spawned the same year. Threadfin shad in Lake Powell had spread to Hall 's Crossing, 161 km uplake, by the summer of 1969 and were found reservoir-wide by the summer of 1970 (Gloss et al. 1971) . Threadfin shad quickly became the predominant food item of all major game species in Lake Powell (May et al. 1975; Hepworth and Gloss 1976; Gustaveson et al. 1980). Striped bass were introduced into Lake Powell in 1974 and utilized the dense pelagic shad population. As threadfin shad numbers have decl ined, crayfish Orconectes virilis, sunfish Lepomis spp, and zooplankton have become the predominant prey for most gamefish. Threadfin shad population data collected from 1976-1979 formed a baseline for comparing impacts the expanding striped bass population exerted on threadfin shad abundance (Gu staveson et al. 1980) . Data collected from 1980-1984 provided information on shad abundance following inten se predatory pressure by striped bass. Data were collected from 1985-1989 to determine if shad populations could recover under intense predation caused by the presence of an establi shed striped bass population with unlimited reproductive potential. 3 L METHODS Threadfin shad spawning was monitored from 1985 through 1989 with ichthyoplankton net collections. Ichthyoplankton sampling began in May and continued through September. Weekly samples were taken in the backs of bays at Wahweap Creek, Warm Creek, Bullfrog Creek and Hall's Creek. Biweekly samples were collected in the back of Navajo Canyon. Samples were also collected at Red and Ticaboo canyons during 1985, Piute Farms Wash (1985- 1987) , and from 1985 through 1988 at Piute Red Wall and the San Juan River inflow (Figure I) . Because of logistic and manpower requirements at these sites, sampling was discontinued after 1988. A 1.0 m diameter ichthyoplankton net with 505 micron mesh was towed just below the water's surface. Three tows, each of a two minute duration sampling an average volume of 102 m3 of water per tow , were made at each station. While towing the ichthyoplankton net, the boat moved forward at approximately 0.7 m/s and covered a distance of 129 m per sample. 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 account for fluctuating water levels. Water temperature (C) and clarity (Secchi disk) were collected at each station when possible . All samples were preserved in the field with 10% buffered formalin. A biological stain, Phloxine B, was mixed with formalin to aid in separating larval fish from sample debris. Larval fish were picked from the debris and when possible identified to species. All threadfin shad were counted and a subsample of up to 25 larvae, juveniles and adults, was measured to the nearest mm. Larval and juvenile shad were differentiated by size after criteria presented by Barnes (1977) . Mean number and total length of larval shad per tow were then calculated for all stations. Midwater trawls to sample shad recruitment to the pelagic areas were conducted us ing a 7.32 m work boat outfitted with two Marco W050 hydraulic winches powered by Vickers hydraulic pump s. With dual controls, it was possible to run both winches in tandem or individually . The trawl wa s 4 c: 0 -'" -(/) Ol c: ~ '" ~ t- l- Figure 1. c: 0 -'" -(/) c: 0 -.>< c: '" a. 0 >-.c -.c -... CD a. o J: " o o <:l < - iii J:~ U ~ > IX I Map of Lake Powell showing trawling and ichthyoplankton netting stations for threadfin shad, 1985-1989. 5 designed after that described by von Geldren (1972). It measured 3.05 m x 3.05 m at the mouth, 15 .24 m long with 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 cables (0.48 cm in diameter) running from each winch were used in deploying and retrieving the trawl. A standard tow was developed and used to permit consistent sampling 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 retrieved . The average volume of water sampled, calculated using a T.S .K. flowmeter, was 8,178.44 m3 and the maximum depth fished was approximately 10.7 m, as measured by a Bendix T-l bathykimegraph. The oblique tow allowed sampling of the water column from the surface to maximum depth, rather than sampling shad from anyone depth. For consistency, sampling was done at night when shad were uniformly distributed instead of grouped in schools as found during the day (Houser and Dunn 1967, Netsch et al. 1971, Gustaveson et al. 1985). Sample nights were selected between new moon and first quarter to eliminate variability caused by moonlit nights. Once the net was retrieved, all fish were immediately removed from the net. All shad collected were preserved in the stained, buffered formalin solution. Mean shad number and total length were determined for each haul . Trawling locations were selected to midway uplake and near the Colorado River Good Hope bays, re spectively (Figure 1). sample lake areas near the dam, inflow in Wahweap, Bullfrog, and Each trawling location was sampled one night a month from July through September. The three areas of the lake were sampled on consecutive nights to allow comparison under approximately similar times and conditions. Three tows were made each sample night. Actual trawling tran sec t s were selected at random within each bay but they were in clo se proximity to previous tran sec t s ites. Each night before trawl samp l es were taken, an 8-minute sonar tran sec t was run over the trawling course using a Lowrance Model ISIOC recorder with a LPT-IOI transducer. The boat wa s operated at 800 rpm's during the sonar run. Echograms generated from these runs were used to supplement the trawl data. 6 RESULTS Ichthyoplankton tow s Catches of shad peaked in June 1985 at both uplake sites, but neither reflected large numbers (Table 1) . Shad reproduction at these s ites declined in July as water temperatures exceeded 27 C. Increases in numbers to 6.3 shad/tow and a decrease in mean length to 10.3 mm in Red Canyon during August suggests resumption of spawning as temperatures declined . Secchi mea surement s in Red Canyon were consistently less than 1.0 m throughout the sampling period. Samples were collected from the San Juan arm of the re servoir from 1985- 1988 (Table 2). Catches at Piute Farms Wash and Piute Redwall generally peaked in June with very little reproduction from July through September (Table 2) . The greatest catch at Piute Farms Wash (150 . 7 shad/tow) occurred in June 1987 . Catches at Piute Redwall were greater than any other site sampled in the San Juan arm . During June of 1986 and 1987, catches averaged 227.3 and 472.9 shad/tow, respectively . Large numbers of shad were never collected from the San Juan River inflow site, suggesting either low reproduction or drift of newly hatched shad from the collection si te. Water temperatures at these sites peaked during July and August corresponding to months of low reproduction, but unlike other lake sites reproduction showed little increase as temperatures cooled in September. Secchi mea surements never exceeded 1.8 m throughout the sampling period and appeared not to be a limiting factor for shad reproduction in these areas. The midlake s ites, Bullfrog and Hall 's creeks, have showed di ss imilar patterns in shad catches from 1985-1989 . Bullfrog Creek peaks in shad reproduction have shown a steady dec line from 364.7 shad/ tow in 1985 to 8.9 shad/ tow in 1989 (Figure 2). Peaks in shad/tow occurred in May and June when water temperatures were increasi ng but still l ess than 27 C. Reproduction and catches declined as t emperatures exceeded 27 C. Secchi mea surements were cons i st en tly l ess than 2.0 m and did not appear to affect the magnitude of reproduction. Pea k cat che s of shad in Hall 's Creek remain ed fairly co nstant from 1985-1988 , howeve r , like Bullfrog Creek, peak catc he s in 1989 were the 7 Table 1. Monthly mean number and total length (mm) of larval threadfin shad collected during ichthyoplankton tows with corresponding mean temperature (C) and secchi (m) mea surement s for uplake stat ion s, Lake Powell, 1985. (SE = Standard Error of the Mean) Station Year Month Shad/Tow SE Length SE Temp Secchi Red Canyon 1985 May 4.0 • 9.3 • 20.0 0.8 Jun 26.5 1. 56 9. 5 0. 18 24.7 0.6 Jul 0.3 0.24 14.5 27 .2 0.7 Aug 6.3 3.66 10 .3 1.44 25.9 0.5 Sep 0.2 0.12 13.0 21.4 0. 5 Ticaboo Canyon 1985 May 5.0 7.3 19 .4 1.2 Jun 8. 5 5.80 9.4 3. 11 24.7 1.9 Jul 0.0 0.00 27 .8 2.8 Aug 0.4 0.24 9.5 3. 18 26.1 1.7 Sep 0.2 0. 11 9.0 21.7 1.0 a Blank indicates single sample with no SE. Table 2. Monthly mean number and total length (mm) of larval threadfin shad collected during ichthyoplankton tows with corresponding mean temperature (C) and secc hi (m) mea surements for San Juan Arm, Lake Powell, 1985-1988. (SE = Standard Error of the Mean) Stat ion Yea r Month Shad/Tow SEa Length SEa Temp Secchi Piute Farms Wash 1985 May 17.3 10.3 22.8 0.5 Jun 6.0 8.8 23.9 0.5 Jul 1.3 9.0 28.9 0.7 Aug 0.0 26.7 0.6 Sep 0.0 21.1 0.3 1986 May 5.0 10.8 17 .2 0.5 Jun 128.9 65 .87 8 . 7 1.17 25.0 0.5 Jul 6.3 3. 20 10 .9 1.71 25.9 0.8 Aug 0.0 27.2 0.5 1987 May 3.3 9.3 18.9 0.5 Jun 150 . 7 57.74 10.9 0.67 22.2 1.1 Jul 0.0 0.00 28.1 1.4 Aug 0.2 0.12 13 .0 27.2 1.0 Pi ute Redwall 1985 May 68.7 8.4 23.3 0.5 Jun 31.3 8.7 26. 1 1.0 Jul 0. 7 11.5 27 .8 0.6 Aug 0.3 13.0 27 .2 1.1 Sep 4.7 7.8 21. 1 0. 5 8 Table 2. (Continued) Station Year Month Shad/Tow SE Length SE Temp Secchi Piute Redwall 1986 May 28.3 a 9.8 a 19.4 0.3 (Continued) Jun 227.3 69.30 11.4 0.32 23.3 0.3 Jul 23.0 6.80 13.3 1. 28 26.5 0.5 Aug 1.3 13.5 27.2 0.5 1987 May 16.0 7.2 17.8 0.3 Jun 472.9 48.19 11.3 0.25 21.1 0.8 Jul 36.7 12.98 12.5 0.46 28.1 0.9 Aug 5.9 1. 31 13.1 0.74 26.1 0.5 1988 May 3.7 10.0 23.9 0.9 Jun 155.7 12.2 24.4 0.5 Jul 23.5 16.62 5.5 3.89 28.1 0.8 Aug 14.3 11.1 28.3 1.2 Sep 5.7 17.6 21.7 0.2 San Juan River 1985 May 0.3 9.0 17.8 0.1 Jun 1.0 4.0 17.2 1.8 Jul 0.0 25.0 0.6 Aug 0.0 26.7 0.3 Sep 0.3 8.0 18.9 0.1 1986 May 0.3 5.0 18.9 0.2 Jun 0.9 0.11 4.2 2.02 20.8 0.2 Jul 30.9 25.23 12.4 23.4 0.2 Aug 0.7 10.0 28.9 0.2 1987 May 0.0 15.6 0.3 Jun 6.5 1.06 7.7 0.46 21.4 0.5 Jul 3.0 1. 91 8.3 1. 63 26.9 0.7 Aug 0.7 0.25 14.7 5.41 27.2 0.5 1988 May 0.7 6.3 23.3 0.5 Jun 0.0 22.2 0.5 Jul 2.7 0.25 11.6 2.30 27.8 0.5 Aug 24.7 17.0 27.5 0.3 Sep 1.3 19.3 19.2 0.6 \ a Blank indicates single sample with no SE. lowest (15.7 shad/tow) of any recorded period (Figure 2). Because of the close proximity of Hall's and Bullfrog creeks, temperatures varied little between the two sites. However, in 1989 secchi measurements differed at the two sites, although the difference was probably related to changes in accessibility caused by the drastic drop in reservoir level. Sand bars and trees which had been submerged but were above the water level in August and 9 HALLS CREEK 250 , 35 30 200 -I ", , -' ~ . , , , u , , .' , 25 ~ , . , ~ , ' . • W , " , , . , -' - a: 0 150 • • '.' 20 :::::> t: · • f- 0 « « 15 a: I 100 W 0.. (j) ~ 0 10 ~ W 50 l Kli tsli Kli ts!I Kli C)11 1 f- 5 0 ' ! (",!l ! j?l' ,?T"'" 1 ?!' ~II!i'" 'F ! t' ~ til !?l1 'F7~vl t ~ y 'F 'F 72<"1 k'7' ,?" r ' a 5678956789567895678956789 1985 1986 1987 1988 1989 MONTH BULLFROG CREEK _ , 35 300 I I.?\l j ~.: , . , . ..... -, , , ',. # ...... . -. - , , , ~ 30 ,- - - .... -j 25 0-~ '. 2i 200 '. ~ w a: 20 :::::> ~ « I (j) Figure 2. 100 - a: 15 W 0.. ~ -. 10 W f- ~ 5 o I ~~ ~-?o/~-~jo 5 6 7 895 6 7 8 9 5 6 789 5 6 7 895 6 7 8 9 1985 1986 1987 MONTH 1988 1989 Mean number of larval shad col l ect ed per ichthyop l ankto n tow and mea n water temperature , Hall 's and Bullfrog creeks, mid Lake Powell, 1985 -1989 . 10 September limited access to the back of Hall 's Creek. Trends in shad catches in downlake sites at Wahweap and Warm creeks and Navajo Canyon varied by site. Peaks in shad/tow at Wahweap Creek have generally declined from 1985-1989 (Figure 3). The highest peak (131 .2 shad/ tow) was observed in 1985 with a peak of only 27.4 shad/tow in 1989 . Similar to most other stations, mean fish length at Wahweap Creek increased through the summer and declined again in September. Water temperature patterns varied little from year to year, generally warming to highs between July and August and cooling in September. Secchi measurement s have remained fairly constant, ranging from 0.4 -0.9 m. Warm Creek is the only site lakewide which has shown an increase in larval shad abundance from 1985 -1989 (Figure 3). Peaks in abundance generally occurred in May and/ or June, however, in 1989 a early summer peak was not observed. Rather, abundance peaked in September at 309.9 shad/ tow . Shad reproduction appeared to decrease as summer water temperatures approached their apex. Except for an unu sual secc hi reading of 1.5 m in August of 1985 , secchi measurements were always <1.0 m. Navajo Canyon has also shown a decline in catch rates of larval shad from 1986-1989 (Figure 4). In 1989 there were peaks of 102.0 and 117.2 shad/tow in June and August, re spectively . Although these peaks were less than most years for Navajo Canyon, they were well above peaks at most other Lake Powell sites during 1989 . Midwater trawls Midwater trawl catches of t hreadfin shad in Lake Powell ha ve stead ily declined. Catches in 1989 were at their lowe st level since monitoring began in 1977 (Figure 5) . In 1989 pelagic shad were not captured from Wahweap or Good Hope bays and only a single adult shad wa s co llected in 9 trawl hauls from Bullfrog Bay. Catches of shad in 1988 were only slightly better. The highest catches from 1985 -1989 were just over 9 shad/ trawl in Wahweap Bay in 1987 and 11 shad/ trawl in Good Hope Bay during 1985 (Figure 5) . Th ese catches are well below those of previou s years in which catches averaged nea r 131 shad/ trawl in 1984 and over 1,250 shad/ trawl prior to 1980 . 11 140 ,20 ,oa. $ o 80 t: 0 « 60 I (J) 40 20 0 500 400 $300 g o « I 200 (J) ,00 o WAHWEAP CREEK , , , , , , ,. , , , , . , • , • , . • , , , , , , , , , , , , , , " " . .' , " , 567 8 9 5 6 7 8 956 789 5 6 7 8 9 5 6 7 8 9 1985 , , . · • , · , " 1986 ,- -, 1987 MONTH WARMCREEK . -. . . . .: 1988 1989 , . , • . --. • , . , , , - 5 6 8 9 5 6 7 8 9 5 6 7 895 6 789 567 8 9 1985 1986 1987 MONTH 1988 1989 30 25 Q: 20 W a: :::J I- 15 « a: w a.. 10 :2 w I- 5 o 35 30 25 Q: w a: 20 :::J I-« 15 a: W a.. :2 10 W I- 5 o Figure 3. Mean number of larval shad collected per i chthyoplankton tow and mean water temperature, Wahweap and Warm creeks, lower Lake Powell, 1985 -1989. 12 800 600 ~ 0 ~ 400 « I en 200 0 5 Figure 4. NAVAJO CANYON 30 , , , , , --. , , , , ' , , , , 25 , , , , , , , , , , , , , , , ' . , , " ~ 0 20 ~ w CC ::J 15 I-« CC W a... 10 ~ W l- S I I I 0 6 7 8 9 5 6 7 8 9 5 6 7 8 9 5 6 7 8 9 7 8 9 1985 1986 1987 1988 1989 MONTH Mean number of larval shad collected per ichthyop lankto n tow and mean water temperature, Nava jo Canyon, lower Lake Powell, 1985-1989. 13 4~ ,-------------------------------------------------------, 3000 2000 1~ 3: 800 o r-SOO -l 3: 400 « 0:200 t: 0100 « I 80 (f) 80 40 .......................... ..... . ... ... . ..... fci ITI;L ,, '. WAI-I'NEAP BULLFROG GOODHOPE , ,', .. ,' ....... '\ .. . , \ -- ---, ., ... . / . .... ··· ····· ···:·c , , ~. I ~ , "' H' i '\ '- \ I ... ... , .. • ·· f . ~ , ," I • .. ! .... ~ I • 20 o ~ ') ~;/~i~:~~~~ 3: o 40 30 ~ 2O « I (f) 10 o Figure 5, 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 YEAR Shad trawls 1985-1989 • JULY SAMPLE El AUGUST SAMPLE [J SEPTEMBER SAMPLE 85 86 87 88 89 85 86 87 88 89 85 86 87 88 89 WAHWEAP BULLFROG GOODHOPE STATION Mean number of shad collected per trawl tow by station and month, 1985 -1989 (lower figure) and hi stori c catch of threadfin shad coll ec t ed per trawl tow at Lake Powell , 1977 - 1989 (upper figure), 14 DISCUSSION In Lake Powell, shad generally spawn when water temperature at dawn is between 16 and 27 C. Spawning begins in early or mid-May, peaks during June and sometimes pers ists into September. Threadfin shad reproduction in the backs of canyons and yoy recruitment to the pelagic zone have been monitored with ichthyoplankton tows and midwater trawl sampling. Reproduction in the backs of Lake Powell's canyons has been verified and monitored since 1976 (Gustaveson et al. 1980, 1985). As yoy shad grow and densities increa se, they become more pelagic and move to the open waters of the reservoir becoming less vulnerable to 1.0 m nets and more vulnerable to midwater trawls (Hou se r and Dunn 1967, Houser and Netsch 1971) . Those recruited to the pelagic zone become available forage for striped bas s and other open water predators (Morris and Follis 1978, Mosher 1984). Decrea s ing pelagic shad populations were first observed in Lake Powell in 1982-1983 and immediately resulted in reduced condition factors in striped bass (Gustaveson et al. 1985) . The larval shad peaks observed in September in Wahweap and Warm creeks may have resulted from yoy spawning which has been observed in other lakes (Johnson 1971; Heidinger and Imboden 1974; McHugh 1983). Yoy spawning may have been triggered by low population numbers reflected by low larval abundance in May and June . This perhaps serves as a mechanism for the population to maintain a level sufficient for survival. Anderson (1973) found spawning was affected by density dependent factors, including crowding and nutritional conditions. Shad abundance in ichthyoplankton tows in 1989 were the lowest since monitoring began. Indications are that threadfin shad will not recover to their previous abundance and will probably provide little if any forage to striped bass in the pelagic zone. The shad that do migrate out of turbid waters are probably consumed before reaching open bays. Greater visibility in some canyons may contribute to low numbers of shad. Shad tend to spawn in shallow, turbid water along shorel ines and in the backs of canyons and bays (Gustaveson et al. 1985) . Turbidity also reduces predatory effectiveness and probably permits development of smal l populations within turbid zones. 15 Striped bass have been shown to be effective predators, eliminating or impacting shad in other systems (Combes 1978, Morris and Follis 1978). In lakes and reservoirs with sufficient productivity and ample prey species diversity, shad have suffered little or no impact from striped bass predation (Nash et al. 1987) . Lake Powell, with a single pelagic prey species, offers little prey diversity to striped bass predation . It is likely that the threadfin shad population in Lake Powell will continue to exist in the turbid waters of the backs of canyons but will not provide enough forage under the intense predatory pressure of the existing striped bass population. Although shad reproduction was confirmed in the backs of canyons, results from midwater trawls indicated that few if any of these fish recruited to the pelagic zone during the summer. 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. Pelagic shad were virtually absent at all trawl stations in Lake Powell since 1987. Gustaveson et al. (1985) proposed that shad populations in Lake Powell were cyclic because peaks in trawl catches were observed in 1978, 1981, and 1984. If a 3-year cycle still existed on Lake Powell, 1987 would have been the next population peak. Wahweap Bay, the furthest site downlake had a slight peak in 1987 but no peaks were evident further uplake. However, decreases in the amplitude of each successive peak from 1978-1984 were noted by Gustaveson et al. (1985). It has been shown that density dependent factors, including crowding and food, affect shad spawning. The cycling observed in the shad population could be density related, whereas, the overall long-term decline in the population is probably predator related. The near absence of pelagic shad in 1988 and 1989 suggests that shad numbers may be suppressed by predators to a level where the population cannot rebound under current condition s. In lake E. V. Spence, striped bas s reduced the standing crop of gizzard shad and completely eliminated threadfin shad (Morris and Folli s 1978). Young gizzard shad that escaped predation grew rapidly. After exceeding the desired forage size preferred by striped bass (76-178 mm) they matured and spawned. Threadfin shad, because of their smaller size, were unable to outgrow the preferred prey size and thus were eliminated. Threadfin shad are the only schooling forage fish in Lake Powell 16 to support the striped bass population. Striped bass in Lake Powell seemingly have unlimited reproductive potential (Gustaveson et al. 1985). Although larval shad collected from the backs of canyons are evidence of reproduction and a susta ined population, predatory impact appears too great to allow reestablishment of a pelagic population. When threadfin shad were first introduced into Lake Powell, a lakewide population developed in just over one year. However, that took place in the absence of striped bass which had not yet been introduced into the reservoir . Spawning in Lake Powell wa s directly related to water temperature. Threadfin shad at Lake Powell appear to spawn at water temperature s from 16-28 C. Heidinger (1983) found a thermal cut-off of spawning activity at approximately 30 C. He also found higher shad recruitment where optimum water temperatures for shad spawning occurred for longer periods of time without exceeding the thermal cut-off temperature. Sample temperatures never exceeded 30 C, however, these measurements were probably not taken when temperatures were at their daily apex. When sample temperatures exceeded 27 C larval shad catches declined to near zero. Water temperatures from May through September remained near optimum and accounted for the extended spawning season. Shad winter die-offs which occur in temperate lakes (Par~ons and Kimsey 1954) are a rare occurrence at Lake Powell (Gustaveson et al . 1985) and do not appear to be a limiting factor on population numbers . RECOMMENDATIONS Monitoring since 1979 ha s documented continued shad existence even under extreme predatory pres sure. Turbid water in the backs of some canyons provides rufugium for shad. Enough shad survive in these areas each year to spawn. However , successful reproduction does not mean recruitment to the pelagic zone or to the forage ba se for striped bass . From 1985 to the present, few shad have been co ll ected from the pelagic zone . Because continued monitoring of shad at the present level of inten sity will probably not reveal any further information under present predatory pressures it is, therefore, recommended that ichthyoplankton netting be reduced or discontinued and midwater trawling in Lake Powell be reduced to a one-month period. Larval 17 shad samples indicated peak spawning generally occurred from mid-May through June and yoy shad historically recruited to the pelagic areas in July and August. Sampling of the pelagic zone in July would maximize chances for capturing recruited shad. Sampling intensity can be increased if shad recruitment to the pelagic zone reoccurs . Striped bass condition (Kll ) has been an immediate proxy for shad availability (Gu staveson et al. 1985) . In addition, st riped bass stomach contents have reflected when shad were present; shad being their preferred food. When shad are absent striped bass switch to plankton, crayfish, and sunfish. These indicators should allow for continued feedback on shad population level s. 18 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 (Gu staveson et al . 1980, 1985; Scott and Gustaveson 1989) . In general, both total recreational boat use and angling pressure have increased steadily since 1965 . However, a sharp reduction in angling pressure was observed in 1988. Angler success has varied over the history of the reservoir with the highest catch rate s occurring in the early 1970 's. Black crappie and largemouth bass consistently comprised over 70 percent of the annual catch from 1970-1979 (Scott and Gustaveson 1989). Since 1984, striped bas s have been a major component of angler success and harvest. METHODS A scheduled creel census was conducted from April through October in 1985 and 1988. In 1985 angler s 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 re se rvoir and limited access, most anglers gained access at one of the se four points. However , in 1988 a new marina was opened at Piute Farms Wa sh and this new access area wa s added to the creel survey. During 1985 each station was surveyed 4 random days /mo nth . In 1988 Wahweap was surveyed 5 days/mont h while Bullfrog and Hall 's Crossing were combin ed into one mid-reservo ir area and surveyed a total of 6 days/ month (3 days at each station). The Hite survey remained at 4 day s/month and a 2 days/month survey wa s added at Piute Farms. All cree l survey days were 6 hours; generally 1400 -2000 h. Data obtained during angler interviews included number and spec i es of fi sh caug ht , time spent fishing, the number of 19 anglers/boat, residence of anglers, location fished, and preferred species sought. Creel rates presented in this report were derived from all fishermen collectively. Since many Lake Powell 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 measurements, scales, stomach samples were obtained from selected samples of game fish. Pressure estimates 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 launching ramps 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 interview data. Since fishing pressure from November-March represents only a small portion (13 percent) of annual pressure (Gustaveson et al. 1980), creel surveys were not conducted during these months. However, / pressure estimates were provided by the National Park Service for the entire year. Creel survey data presented in this report are based only on those months when a census actually occurred (April-October). RESULTS AND DISCUSSION Fishing pressure on Lake Powell increased from 1975-1982 . Fishing pressure decreased in 1983-1984 when gas prices dramatically increased nationwide. Decreased fishing pressure during this period were observed elsewhere (Osburn et al. 1988). Fishing pressure increased in 1985 to 128,186 fishing boat-days but dropped again in 1988 to 104,482 fishing boat-days (Table 3). This drop corresponds to decreases in striped bass average size and condition (see Job IV) . Average time fished/trip and mean number of fishermen/boat have remained fairly constant from 1975-1988. 20 T ab le 3 . Fi sh in g bo at us e (b oa t- d ay s) by m on th , L ak e Po w eL L , 19 75 -1 98 5 an d 19 88 _ A ls o gi ve n a re th e av er ag e ti m e (h r) fi sh ed /t ri p ( H /T ) an d th e m ea n nu m be r of fi sh er m en /b oa t (F /B ). Y ea r Ja n. Fe b . Ma r . A 2r . Ma l:: Ju n. Ju l. A ug _ Se 2 · O ct . No v . D ec . T ot al H[ T Fi B 19 75 44 3 1, 23 7 4, 36 4 9, 77 0 11 ,2 65 7, 32 2 3, 10 0 2, 50 3 3, 43 2 3, 40 4 1, 54 6 34 4 48 ,7 30 4. 5 3 .0 19 76 59 3 1, 3 00 4, 57 2 12 ,7 76 15 ,1 37 8, 64 2 5, 35 4 5, 65 5 4, 46 0 4, 02 1 1, 85 3 38 4 64 ,7 47 3 .8 2 .8 19 77 25 1 1, 60 2 3 , 3 27 12 ,7 72 15 ,5 01 10 ,1 68 4 ,9 5 7 4, 64 0 6, 70 0 4, 96 0 1, 63 4 32 6 66 ,8 38 3 .3 2 .9 19 78 29 0 66 9 3, 11 8 12 ,8 77 10 ,5 97 8, 49 9 4, 98 6 4, 64 0 5, 17 4 4, 69 3 2, 33 2 96 5 58 ,8 40 3. 1 2. 4 19 79 34 0 40 7 3, 84 9 12 ,2 57 14 ,3 90 8, 78 4 6, 91 4 8, 08 5 8, 24 2 5, 70 9 1, 81 1 68 4 71 ,4 72 4. 5 2. 4 19 80 23 8 60 6 3, 64 7 10 ,6 88 19 ,8 32 15 ,0 14 5, 74 3 6, 11 6 7, 46 9 5, 71 7 2, 59 3 74 2 78 ,4 05 4 .0 2 .6 19 81 81 7 1, 27 9 4, 68 1 9, 49 5 14 ,0 33 13 ,7 72 11 ,8 86 11 ,0 92 12 ,4 40 6, 16 6 3, 54 5 83 3 90 ,0 39 4 .0 2. 5 19 82 40 8 65 6 3 ,0 94 16 ,8 94 19 ,7 14 15 ,0 97 8, 71 9 8, 95 5 11 ,1 28 17 ,5 14 6, 97 0 1, 40 7 11 0, 55 6 3 .9 2. 5 1 9 83 66 8 76 8 3, 99 6 12 ,6 55 23 ,0 08 13 ,4 75 8 ,9 9 9 8, 38 3 10 ,0 76 7, 52 2 7, 52 2 1, 29 2 98 ,5 50 4 .9 2 .6 N .... 19 84 25 4 63 6 2, 67 5 14 ,7 68 12 ,8 65 17 ,4 63 8, 13 6 10 ,1 85 11 ,0 86 8, 95 6 8, 07 7 1, 75 8 96 ,8 59 4 .0 2. 5 19 85 99 7 1 ,2 08 3, 38 2 17 ,2 17 14 ,8 73 18 ,3 89 8, 79 8 18 ,8 58 18 ,1 84 17 ,4 67 6, 63 1 2, 18 2 12 8, 18 6 4 .3 2. 5 19 88 1, 51 1 1, 49 2 2, 80 8 14 ,3 86 16 ,6 77 12 ,6 53 6, 53 7 9, 28 3 16 ,8 15 16 ,6 45 4, 03 1 1, 81 2 10 4, 48 2 3 .9 2. 4 Av er ag e 56 7 98 8 3, 62 6 13 ,0 46 15 ,6 58 12 ,4 40 7, 01 0 8, 19 9 9, 60 1 8, 56 4 4, 03 1 1, 06 1 X 0 .7 1 .2 4. 3 15 .4 18 .5 14 .7 8 .3 9 .7 11 .3 10 .1 4 .8 1 .3 Angler orlgln was different in 1988 than during previous creel years. Gustaveson et al. (1985) reported little change in angler origin from 1980- 1984 . Resident states (Utah and Arizona) showed slight gains in percent of angler representation (Table 4) . The greatest changes in angler representation were in western non-resident states. Colorado anglers , who gained access to Lake Powell at Hite, Hall's Crossing, and Bullfrog marinas, declined 7.2%. New Mexico anglers, who normally come to Hall's Crossing, declined 1.9%. The largest increase was from California anglers who increased from 5.5% to 12 . 6% of total anglers . Table 4. Change in angler orlgln by percent from the period 1980-1984 and 1988, Lake Powell . ORIGIN 1980 -1984 1988 % CHANGE Utah 29.8 30 .9 + 1.1 Colorado 28.6 21.4 - 7. 2 Arizona 26 .8 27.5 + 0.7 New Mexico 5.6 3.7 - I. 9 Cal ifornia 5. 5 12.6 + 7.1 Other 3. 7 3.9 + 0.2 Changes in angler fish preference were observed between 1985 and 1988. In general, anglers on Lake Powell were less discriminating and not targeting specific species (Table 5). In a national survey (U S Fish Wildlife Service 1988), 20% of the anglers responded that they fished for any species of fish available. This is well below the 45% of Lake Powell anglers responding that they fished for any fish. Declines in the largemouth bass and black crappie fisheries, and the reduction in size and condition of the striped bass fishery may have discouraged some anglers (see Jobs III and IV) . Wahweap was the only area where fishermen were more discriminating in 1988 than 1985 . This was primarily due to an increase in anglers targeting juvenile striped bass . Anglers who normally seek a specific game fish (i.e. trophy striped bass or black crappie) may travel elsewhere to fish when these fish were not available at Lake Powell. Thi s may account, in part, for the decline in total fishing pressure at Lake Powell witne ssed during 1988. 22 Table 5. Species sought (%) by anglers, Lake Powell, April-October, 1985 and 1988 . Trace (t) = < 1%. Hite Bull frog/Ha 11' s Wahweap Total Species 1985 1988 1985 1988 1985 1988 1985 1988 Largemouth Bass 28 13 12 13 12 13 14 13 Black Crappie 5 0 1 t 2 0 2 t Striped Bass 20 24 47 42 40 45 41 37 Wa 11 eye 2 2 3 2 3 2 3 2 Channel Catfish 1 3 t t 2 2 1 3 Bluegill 0 1 t t 1 t t 1 Small mouth Bass 0 t 0 t t 1 t 1 Any 44 56 37 41 40 36 39 45 Striped bass have become a major component of the Lake Powell fishery in the 1980's. Striped bass accounted for 64% and 60% of all fish creeled in 1985 and 1988, respectively (Table 6). Largemouth bass and black crappie which once combined for over 90% of all fish harvested now account for only 10%. Smallmouth bass were first observed in the creel in 1988 but represented only 1% of all fish creeled. The total creel rate in 1988 remained the same as it was in 1985 . Although changes in species composition of the creel have occurred, total creel rate was 0.41 fish/h (Table 7). Increases in total creel rate above 1984 levels could have been influenced by a peak in striped bass population size and a change in striped bass daily creel limits from 4 to 10 fish. Creel rates of striped bass increased to near 0.20 fish/h in 1985 and 1988 (Table 8). This represents a substantial increase from <0.04 fish/h at all sites in 1984. 23 T ab le 6. S pe ci es c om po si ti on by pe rc en t (t = < 1% ) of t he t o ta l re co rd ed c re el ce ns us fo r La ke P ow el l, 19 64 -1 98 5 an d 19 88 . L ar ge m ou th B la ck R ai nb ow S tr ip ed C ha nn e 1 Sm al l m ou th Ye ar B as s C ra Q Q ie T ro ut B as s W a 1 1 e ~ e C at fi sh B lu eg il l B as s O th er 19 64 60 25 9 6 19 65 61 27 7 5 19 66 62 27 8 3 19 67 69 1 5 20 3 2 19 68 47 9 1 21 17 5 19 69 42 16 10 11 19 2 19 70 37 34 4 8 14 3 19 71 34 50 1 4 10 1 19 72 -7 3 29 50 2 8 10 1 19 74 37 '- 48 1 5 8 1 19 75 48 44 t 3 4 t 19 76 42 47 t 2 7 t 19 77 32 49 t t t 10 7 1 to. > 19 78 38 40 1 t 12 7 t ~ t 19 79 48 36 t 3 2 6 4 t 19 80 29 24 t 15 10 12 10 t 19 81 39 18 t 12 10 13 8 t 19 82 26 16 t 33 9 13 2 t 19 83 19 23 30 7 10 10 1 19 84 34 18 15 8 11 12 2 19 85 10 7 64 10 5 2 t 19 88 9 1 60 3 11 13 1 2 T ab le 7. T ot a 1 c re el ra te f or a ll sp ec ie s by m on th an d ye ar f or L ak e P ow el l, 19 64 -1 98 5 an d 19 88 . Y ea r Ja n fe b M a r A (;! r M al :: Ju n J u t Au g Se Q O ct N ov O ec M O lA ve a \J tl A ve b 19 64 .7 3 .4 8 .6 2 .5 6 .7 5 .8 1 .6 6 .6 1 19 65 .5 1 .6 6 .5 9 .6 9 .6 1 .4 7 .5 2 .5 7 .5 2 .6 9 .7 4 .6 7 .6 0 .5 9 19 66 .6 9 .4 3 .6 1 .5 8 .5 1 .7 2 .8 2 .8 6 .5 1 .4 9 1. 1 6 .7 1 .6 7 .6 1 19 67 .4 0 .2 9 .4 5 .4 2 .4 0 .4 6 .5 7 .3 8 .3 8 .4 0 .3 6 .5 1 .4 2 .4 2 19 68 .0 4 .1 7 .3 4 .4 2 .5 2 .3 5 .3 2 .4 7 .6 5 .4 6 .2 7 .2 8 .3 3 .4 1 19 69 .2 5 .0 8 .3 4 .5 2 .7 1 .4 4 .4 1 .6 0 .5 4 .7 1 .7 5 .3 6 .4 8 .5 4 19 70 .1 7 .3 7 .5 3 .6 9 .6 8 .5 9 .5 3 .6 2 .5 6 .2 9 .4 3 1 . 1 9 .5 5 .6 0 19 71 .5 0 .6 4 1 .5 8 1 .2 8 1. 1 4 1 .2 8 .7 6 .8 1 .4 8 .4 5 .6 3 .2 8 .8 2 1. 0 5 19 72 .3 9 1 .4 7 .9 0 .6 7 .4 9 .3 9 .3 4 .4 7 .4 0 .6 1 .5 3 19 73 .5 6 .6 2 .6 8 .4 7 .2 9 .2 1 .1 8 .4 3 .4 3 19 74 .8 4 .5 9 .4 3 .3 7 .1 7 .4 1 .3 1 .4 5 .4 5 19 75 .3 5 .5 8 .6 7 .5 3 .5 2 .2 2 .1 5 .3 0 .5 5 19 76 .5 8 .5 4 .3 8 .5 0 .5 1 19 77 .4 7 .3 4 .3 1 .1 7 .2 9 .1 7 .2 9 .3 7 19 78 .1 4 .2 8 .2 1 .2 3 .3 4 .1 9 .1 9 .2 3 .2 3 19 79 .4 1 .5 4 .5 4 .4 3 .2 0 .3 1 .2 4 .3 8 .4 5 19 80 .5 4 .4 3 .3 4 .4 4 .4 7 N 19 81 .5 0 .3 4 .2 6 .3 0 .4 8 .2 9 .3 6 .3 4 '"' 19 82 .3 1 .3 8 .2 6 .3 0 .5 2 .3 5 .3 1 .3 5 .2 8 19 83 .2 5 .2 3 .2 1 .1 6 .1 4 .1 1 .4 4 .2 2 .2 1 19 84 .1 5 .2 0 .1 9 .2 3 .1 1 .1 8 .2 2 .1 8 .1 8 19 85 .2 4 .4 0 .3 1 .3 0 .8 4 .4 2 .4 2 .4 2 .4 1 19 88 .2 9 .4 2 .4 5 .3 5 .3 5 .3 8 .3 8 .3 7 .4 1 ~A Ve ra ge o f m on th ly c re el ra te s. T ot al fi sh ca ug ht d iv id ed b y to ta l ho u rs . Table 8. Striped bass creel rates (fish/ angler hour) by access area, Lake Powell, 1980-1985 and 1988 . Location 1980 1981 1982 1983 1984 1985 1988 Hite 0.002 0. 005 0. 015 0.023 0. 024 0.118 0. 180 Bullfrog/Hall's 0. 004 0. 008 0. 026 0.031 0.032 0.320 0.320 Wahweap 0.007 0. 034 0.083 0. 154 0.023 0.219 0. 240 RECOMMENDATI ONS The creel survey should continue every third year to assess changes in Lake Powell's sport fishery . The survey will follow the same methods so that the data will be comparable between years and so trends can be readily identified. The 1991 creel census should document the expanding smallmouth bass fishery and predict how important that fishery will be to the future of Lake Powell. " 26 / INDEX TO ANNUAL POPULATION TRENDS JOB III ANNUAL NETTING BACKGROUND Standardized spring gill net sampling has been used to describe gross changes in fish population densities and species composition at Lake Powell since 1971 (Gloss et al. 1974; May and Hepworth 1976; Gustaveson et al. 1980, 1985). The gill net sampling has been most effective in describing changing trends in the largemouth bass and walleye populations. 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; however, trout stocking was discontinued when striped bass were introduced in 1974. The survey depicted the decline of trout abundance and the subsequent increase in striped bass numbers (Gustaveson et al. 1980). METHODS Gill net sampling was conducted during March 1985-1988 at Padre Bay, San Juan Arm, Rincon, and Good Hope Bay (Figure 1). Spring netting was not conducted in 1989 due to personnel changes and time constraints. Gangs of ten 30.5 m diving experimental gill nets with four 7.62 m panels (mesh sizes 25, 38, 51, and 76 mm) were fished for two consecutive days at each station. On rare occasions , 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 each morning, weighed and measured, scales taken for age and growth analysis, and stomach contents classified. 27 I RESULTS AND DISCUSSION The 1988 total spring gillnetting catch rate (1.62 fish/net day) was the lowest since netting began in 1971 (Table 9). The catch rates for individual species have the fishery. varied over time corresponding to changes in the reservoir and The highest catch rates were in 1972 and 1975 corresponding to peaks in largemouth bass abundance. However, largemouth bass catch has remained at a stable, though relatively low level since 1983. As largemouth bass abundance declined after 1975, walleye abundance increased (Figure 6). Walleye abundance peaked in 1981 at 4.99 fish/net-day (Table 9). Walleye catches have also stabilized at a low level near 0.70 fish/net-day since 1986. Striped bass numbers increased in the gill net catch, peaking in 1985 at 3.07 fish/net-day and then declining to 0. 18 fish/net-day in 1988. The decrease in overall catch from 2.18 fish/net-day in 1987 to 1.62 fish/net day in 1988 was primarily caused by a decrease in striped bass catch. Some species which were represented in early gill net catches have disappeared from Lake Powell. Flannelmouth sucker Catastomus 7atipinnis, the one Colorado River system native species which was once abundant in Lake Powell, has not been collected since 1984. Rainbow and brown trout Sa7mo trutta, sport fish once common in areas of Lake Powell, have also disappeared . Channel catfish Icta7urus punctatus and common carp Cyprinus carpio catches have remained fairly constant from 1971-1988. Smallmouth bass were collected in the 1988 gill netting and should become more abundant as this population develops. Smallmouth bass harvest has surpassed largemouth bass harvest in other reservoirs dominated by rocky substrate (Rideout and Oates 1975) . Despite low threadfin shad abundance in Lake Powell (Job J) shad remain the predominant food item for walleye (Table 10) . Crayfish appear infrequently in walleye stomach samples although they are the most common food item in largemouth bass (Table 11). Some dietary overlap exists between walleye and largemouth bass, but analysis of stomach contents suggested that interspecific competition for food may be low. Low sample size in 1989 made comparisons to previous years unreliable. 28 6 5 4 >- '" q 0;3 ~ . !!1 u.. 2 o 7 6 5 2 o Figure 6. WALLEYE i l I i i /\ I . \ i \ \ i \ \ i . \ \,- / ,- ""'. ,,/ ' . , \. , \. \. '-'- ._-_._._._ .- 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 \ i \ i i \ \ I i \ / " i i Year LARGEMOUTH BASS --_ ._---- - "- ,- - ,- _ ._ -- 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 Year Catch rate s (fi sh/ net day) for walleye and largemouth ba ss from annual nett ing, Lake Powell, 1972-1988. 29 w o T ab le 9 . C at ch ra te (f is h /n et d ay ) by sp ec ie s an d ye ar , an nu aL gi L L n et ti n g , L ak e P ow el l, 19 71 -1 98 8. C at ch R at e Sp ec i es 19 71 1 9 n 1 9 ~ 1 = 1 9 ~ 1 m l m l ~ l m l B ln l 1 m 1 ~ 1 . lr u 1 _ 1 _ 1 _ L ar ge m ou th ba ss 1 .6 5 5 .8 2 2. 71 4 .0 1 4 .4 9 2 .7 2 1 .8 5 2. 61 1 .8 3 1 .5 7 1. 41 0 .6 3 0 .4 7 0 .4 6 0 .3 4 0 .3 0 0 .4 0 0 .3 9 Sm al lm ou th b as s 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0. 01 IJ al le ye 0 .2 9 1 .1 2 0. 41 1 .0 9 2 .1 5 2. 11 1 .1 7 2 .8 4 3 .2 5 3 .6 6 4 .9 9 2 .1 7 1 . ~ 2 .2 6 2 .0 5 0 .7 0 0 .6 9 0 .6 3 S tr ip ed 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 3 .0 7 0 .7 0 0 .4 9 0 .1 8 BL ac k cr ap 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. 21 0 .0 3 0 .1 6 0 .0 8 0 .0 4 0. 01 0 .0 6 0 .0 0 0 .0 0 0 .0 0 B L ue gi I I 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. 01 0 .0 5 0 .0 2 0. 01 0 .0 5 0 .0 6 0. 01 0. 11 0 .0 4 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 0 .0 4 0. 01 0 .0 5 0 .0 4 C ha nn e L c at fi sh 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 0 .1 7 0 .1 6 0 .1 3 0 .1 3 Co nm on 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 0 .3 5 0 .2 2 0. 31 0. 21 F la nn el m ou th su ck er 0 .1 8 0 .2 8 0. 21 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. 01 0 .0 2 0 .0 0 0 .0 0 0 .0 0 0 .0 0 R ai nb ow tr ou t 0 .2 4 0. 31 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. 01 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 Br ow n tr ou t 0 .0 2 0 .0 0 0. 01 0 .0 3 0 .0 4 0 .0 4 0 .0 2 0 .0 1 0 .0 0 0 .0 0 0. 01 0 .0 0 0 .0 0 0. 01 0 .0 0 0 .0 0 0 .0 0 0 .0 0 Y el lo w b u ll h ea d 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0 .0 0 0. 01 0 .0 4 0 .0 3 0 .0 3 0 .0 3 0 .0 2 0 .0 2 0 .0 0 0. 01 0 .0 5 0 .0 0 0. 01 A ll sp ec 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 . ~ 3 .6 2 3 .6 8 4 .3 5 6 .1 6 2 .1 6 2 .1 8 1 .6 2 Table 10. Percent occurrence of food items in walleye co ll ected in gill nets and during creel cens us, Lake Powell, 1985-1989. (Percentage based on number of stomachs containing food.) YEAR 1985 1986 1987 1988 1989 Sample size (n) 218 56 55 50 11 Empty stomach s 201 (92%) 36 (64%) 36 (65%) 21 (42%) 6 (55%) Stomachs w/ food 17 20 19 29 5 Food item Crayfi sh 1 (6%) 0 0 0 0 Pl ankton 0 0 0 0 0 Fish Threadfi n shad 5 (29%) 5 (25%) 12 (63%) 22 (76%) 1 ( 20%) Bluegill 0 0 0 0 0 Green sunfish 2 (12%) 1 ( 5%) 4 ( 21%) 1 ( 3%) 0 Centrarchids 1 ( 6%) 0 0 4 (14%) 2 (40%) Other fish 1 (6%) 0 1 ( 5%) 0 0 Unknown fish 7 ( 41%) 14 (70%) 4 ( 21%) 3 (10%) 2 (40%) 31 Table II. Percent occurrence of food items in largemouth bass collected in gill nets and during creel census, Lake Powell, 1985-1989 . (Percentage based on number of stomachs containing food.) YEAR 1985 1986 1987 1988 1989 Sample size (n) 49 24 32 31 7 Empty stomachs 26 (53%) 3 (13%) 11 (34%) 8 (26%) 3 (43%) Stomach s wi food 23 21 21 23 4 Food item Crayfish 18 (79%) 14 (67%) 19 (90%) 22 (96%) 1 (25%) Pl ankton 0 0 0 0 0 Fish Threadfin shad 0 1 (5%) 1 (5%) 2 (9%) 1 (25%) Bluegill 1 (4%) 1 (5%) 1 (5%) 0 0 Green sunfish 2 (9%) 1 (5%) 3 (14%) 3 (13%) 0 Centrarchids 1 (4%) 0 0 2 (9%) 2 (50%) Other fish 0 0 0 0 0 Unknown fish 1 (4%) 5 (24%) 0 0 0 SUMMARY AND RECOMMENDATIONS Largemouth bass and walleye catches have stabilized at low levels . Striped bass have reached their lowest level since they peaked in 1985. Only channel catfish and carp catches have remained constant since 1971. Smallmouth bass were sampled for the first time during spring gill netting in 1988 and should increase in the future. Annual gill netting catch rates have corresponded with fishermen creel rates for largemouth bass and walleye. Netting should continue to determine if a relationship between smallmouth bass relative abundance and sport fishery catch rate exists . Monitoring of other fish species comprising the Lake Powell fishery with gill nets should also continue . 32 ELECTROFISHING BACKGROUND An annual program of electrofishing was initiated in 1977 to obtain information on the relative abundance of yoy largemouth bass and black crappie which were inadequately sampled by gill nets . More recently, this survey has been used to assess smallmouth bass population development . METHODS A 5. 5 m specially fabricated aluminum boat was used for electrofishing . An Onan 7. 5 kw generator provided electrical power for the lighting system and a Coffelt Model VVP-15 electroshocker. The positive array consisted of two dropper electrodes. The negative electrodes were 2.0 m long sections of 13 mm cable, one on each side of the boat. The output to the entire positive array was 5-8 a and 150-200 v dc with a pulse rate of 80/second and a pulse width of 60 percent. Five shoreline transects (Warm Creek, San Juan, Rincon, Stanton Creek, and Good Hope Bay) were sampled each year (Figure I). Similar shoreline habitat was electrofished at each transect . Electrofishing time included only that time in which the shocking system was engaged and the time was measured with a stopwatch. Four 15 minute timed transects were conducted at each station. Following each 15 minute session, captured fish were measured to the nearest mm and released at the capture site. Fish per hour totals were summations of all fi sh captured during the four 15 minute sessions at each station. RESULTS AND DISCUSSION Electrofishing catch rates by site in 1989 appeared similar to previous ye ars . Stanton Creek had the highest mean catch rate (107 fish / h) whereas , the San Juan arm had the lowest (28 fish/h) (Table 12) . This ranking also occ urred during the 1988 electrofishing survey (Gustaveson et al . 1989) . Converting catch rates to percent of catch allowed annual comparisons of 33 largemouth and small mouth bass relative abundance (Figure 7) . Prior to smallmouth bass introduction into Lake Powell in 1982, largemouth bass were the only black bass (Gustaveson et al. 1985) . Since their introduction, smallmouth bass have represented an increasing portion (97% in 1989) of the electrofishing black bass catch (Figure 7) . Table 12 . Mean catch rate" (fish/h) of fish co llected by electrofishing , Lake Powell, September 1989. SJl.ecies Young-of-the-year largemouth bass Age I and older 1 argemouth bass Young-of-the-year small mouth bass Age I and older sma 11 mouth bass Young-of-the-year black crappie Young-of-the -year striped bass Age I and older striped bass Channel catfish Green sunfi sh Bluegill Total b Good Hope Bay 15 17 4 50 9 95 Stanton Creek Rincon 1 11 69 2 21 3 107 1 1 2 7 4 29 2 46 San Juan 5 12 28 5 6 Warm Creek 3 14 27 14 58 " Total fish divided by total hour s of electrofishing b Due to rounding total will not always equal sums of all species 34 % of Tota 1 Catch 0.3 0.6 10 .8 31.4 0.0 1.2 0 . 6 6 . 9 39.8 8 . 4 100 I U 80 f-« u (f) (f) « []) 60 - :::c u :s []) LL 40 0 f- Z W U a: 20 W 0.... 0 Figure 7. _ .. _ .. _ .. _ .. _ .. - .- .. _ .. _ .. _ .. - .. , 80 . --- - Largemouth Bass , , , - ", , , -- " --- , , , , , , , , , , , , \J' ,\ , \ , \ , \ , , , , \ \ \ \ --' Small mouth Bass \ \ --- ------. ._ .. _ .. - .. - 81 82 83 84 85 86 87 88 89 YEAR Percent of black ba ss el ectrofi shing catch represented by largemouth and sma llmouth bas s, all s ite s combined, Lake Powell, 1980 - 1989 . 35 Current electrofishing sites, however, are also the locations of smallmouth bass stockings. Thus, the data presented on changing largemouth bass abundance may represent a phenomenon occurring in the stocking areas rather than a lakewide population decline. Current electrofishing sites of talus and rubble shoreline habitat are preferred by smallmouth bass but not necessarily by largemouth bass (Carlander 1977) . In a Massachusetts reservoir with predominantly rocky habitat and a developing smallmouth bass fishery, smallmouth harvest exceeded that of largemouth bass and eventually increased to 5 times the historic largemouth bass harvest. However, at the same time largemouth bass harvest was unaffected and remained constant (Rideout and Oatis 1975). It is unclear what effect the expanding smallmouth bass population will have on the existing largemouth bass population. SUMMARY AND RECOMMENDATIONS Sampling sites may need to be added or changed as present sites represent smallmouth bass stocking sites. Past electrofishing proved valuable in monitoring smallmouth bass population development but may not meet our needs to monitor other species including largemouth bass. Habitat preference and use by smallmouth and largemouth bass at Lake Powell need to be determined. These data can then be used to select sampling sites more representative of each or both species. Electrofishing gear can be variable from year to year. Methods of reducing variation between years needs to be examined. Alternative gears and methods should also be examined to obtain less biased data than currently collected through electrofishing. 36 Table 13 . Mean catch rate" (fi sh/ h) of fi sh collected by electrofishing, Lake Powell, 1985 -1989. Spec ies 1985 1986 1987 1988 1989 Young-of-the-year largemouth bass 127 99 27 2 <1 Age I and older largemouth bass 6 3 2 1 <1 Young-of-the-year small mouth bass 13 23 73 154 9 Age I and older small mouth bass <1 5 19 30 26 Young-of-the-year black crappie 22 3 11 2 0 Young-of-the-year striped bass 150 1 26 11 1 Age I and older striped bass <1 0 0 0 <1 Channel catfi sh 26 12 14 23 7 Green sunfish 208 180 281 140 33 81 uegi 11 203 165 104 26 7 Total b 754 491 555 390 84 " Total fi sh divided by total hour s of electrofishing b Due to rounding total will not always equal sums of all species 37 38 STRIPED BASS POPULATION DEVELOPMENT Job IV BACKGROUND Striped bass fingerlings were stocked into Lake Powell annually from 1974 -1979 (Table 14). Natural reproduction wa s detected in 1979 at which time stocking was curtailed so that impact of that reproduction could be fully evaluated. Yoy striped bass were found only in the upper re servo ir in 1979 and 1980 and were presumed to be the result of spawning in the Colorado River above Lake Powell . However, spawning congregations of mature str iped bass were present in the lower reservoir during thi s same time. Collection of yoy st riped bass near Glen Canyon Dam annually s ince 1981 indicated st riped ba ss had successfully spawned within the reservoir de spite the absence of current to suspend the eggs during incubation . It was determined that the oligotrophic nature of the re servoir allowed the fertilized eggs to set tle on highly oxyge nated sa ndy substrate where they hatched in stead of being smothered by an oxygen poor environment as occurs in mo st eutrophic lakes. (Gustaveson et al. 1984). Striped bass introduced in the 1970 's readily adapted to their new environment. Growth was rapid with little intraspecific competition and an abundant pelagic threadfin shad forage base . An excellent sport fi shery emerged in 1979 and peaked in 1982 -1983 when the large population of mature striped bass and low shad number s combined to produce exce llent angling for hungry striped bass. Unlimited st riped bass natural reproduction placed ext reme predatory pre ss ure on the s ingle pelagi c forage fish, threadfin shad , in Lake Powell. In 1982-1983, the progeny of the fir st generation of stoc ked st riped bass declined in phys i ca l condition as forage became scarce. Adult st riped ba ss were most affected beca use they were forced into deep, coo l water st r ata by ontogenetic thermal requirements (Sc hai ch 1979) where forage was absent. Adult fish (> 500 mm) declined in abundance due to l ack of shad forage, angling harvest and natural mortality . Old adults, originally stocked in the 1970 's, survived by foraging on carp in the pelagic zone . New adults, spawned in the 1980's, could not thrive without a pelagic shad population. Small er juvenile fish were present in the warm surface layers and subs i sted by ea ting the annual shad crop and then reverting to a pelagic plankton diet. 39 Table 14 . Stocking history of Lake Powell, Utah-Arizona, 1963 -1988. Year 1963 1964 1965 1966 1967 1968 1969 Species Largemouth Bass Rainbow Trout Rainbow Trout Rainbow Trout Kokanee Salmon Largemouth Bass Largemouth Bass Largemouth Bass Largemouth Bass Rainbow Trout Rainbow Trout Rainbow Trout Kokanee Salmon Black Crappie Black Crappie Rainbow Trout Rainbow Trout Black Crappie Black Crappie Rainbow Trout Rainbow Trout Rainbow Trout Rainbow Trout Rainbow Trout Threadfin Shad Rainbow Trout Threadfin Shad 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 2,140,000 344,049 103,205 102,590 201,364 1,500 251,238 Size 2-3" 2" 2-4" 4" 1-2" 2-3" 2-3" 2-3" 2-3" 2-3" 5-8" 5-8" 2-3" 6" 3" 2-3" 5" I" 4" 2-3" 4-5" 4-5" 4-5" 3-5" 1-4" 5" Area Warm Creek-Aztec Reservoir Wide Wahweap Creek Hall's Crossing Kane Creek Warm Creek-Last Chance Mouth Escalante Rincon Bullfrog Creek Dam-Bullfrog Creek Hite Wahweap Creek Wahweap Creek Wahweap Creek Wahweap Creek Reservoir Wide Wahweap Creek Wahweap Creek Wahweap Creek Reservoir Wide Wahweap-Warm Creek Hall's Crsng-Bullfrog Red Canyon Wahweap Creek Wahweap Creek Wahweap Creek Method Aeri a 1 Aeri a 1 Truck Truck Truck Aerial Aeri a 1 Aerial Aerial Aerial Truck Truck Truck Truck Truck Aerial Truck Truck Truck Aeri a 1 Aerial Barge Barge Barge Truck Barge 200,000 Egg-fry Wahweap Creek Spawning mats 1970 -------------- - -- ------ -----NO STOCKING------------------------------- 40 Table 14. Continued. Year Species Number Size Area Method 1971 Rainbow Trout 281,000 4-5" Bullfrog Barge Ra
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Content: bb698a66ed62b97ac7110e3fd2e6d2c7c27b60ad | Abstract: 72242b09314edfc8f0a7529118d76ec2a1a86157