title
Lake Powell fisheries investigations : 1975-1979 five-year completion and 1979 (segment 8) annual performance report for Colorado River Drainage and Tailwaters Dingell-Johnson project F-28-R
author
Array ( [0] => Gustaveson, A. Wayne [1] => Pettengill, Thomas D. [2] => Ottenbacher, Michael J. [3] => Johnson, James E. )
abstract
UDWR Publication Number 80-11
date
1980-01-01
organization
Utah. Division of Wildlife Resources
species
Array ( [0] => Not Specified )
file_path
https://grey-lit.s3.wasabisys.com/lake-powell-fisheries-investigations-1975-1979-five-year-completion-and-1979-segment-8-annual-perfor.pdf
thumb
https://grey-lit.s3.wasabisys.com/lake-powell-fisheries-investigations-1975-1979-five-year-completion-and-1979-segment-8-annual-perfor-pdf-1-757x1024.jpg
content
N 4650P6. 13: Lak/ 9'7Q 1IY AH OEPOSnOldl SYSTEM Lake Powell Fisheries OEC2 1980 I nvestigations UTAH SlATE u~ 1975-1979 Five-year Completion and 1979 (Segment 8) Annual Performance Report for Colorado River Drainage and Tailwaters Dingell-Johnson project F-28-R Utah Division of Wildlife Resources Publication Number 80-11 LAKE POWELL POSTIHPOUNDHENT INVESTIGATIONS Completion Report January 1975- December 1979 Annual Performance Repo r t January 1979- December 1979 A. Wayne Gustaveson, Project Leader Thomas D. Pettengill , Project Biologist Hi chael J . Ottenbacher , Project Biologist James E. Johnson, Superv isor Fisheries Research Publication No. 80-11 Dingell- Johnson Project No . F- 28- R-8 Copyright @ 1980 Utah State Division of \Hldlife Resources An Equal Opportunity Bnployer Douglas F. Day Director TABLE OF CONTENTS LIST OF TABLES . LIST OF FIG UR ES INTRODUCTION JOB NUMBER 1. THREADFIN SHAD STUDY Background Methods . . Results and Discussion Recommendations References II . MEASUREt1ENT OF FISHER I ES HARVSST . PRESSURE AND SUCCESS III. IV . Background 11e thods . . Results and Discussion Recorrunendations Re f erences I NDEX TO ANNUAL FISH POPULATION TRENDS Background Methods Results and Discussion Annual Netting Electrofish i ng Recorrunendations References STRIPED BASS CULTURE Background 11ethods . . ii iv vi 3 3 4 8 15 16 18 18 18 19 32 33 35 35 35 38 38 44 48 49 5 1 51 52 V. naLE OF CONTENTS ( continued ) Preseason Trea~~ent Fertil iza tion Filling .. . .. . Oxyg en and Plankton Development Supplemental Fertilization Stocking of Fry Insect Control .. Veg etation Control Fry Food Hab i cs Supplemental Feeding Harvest . . . . . Results and Discussion Recommend a t ions References EVP.LUATION OF STRIPED BASS INTRODUCTIOIIS Background Methods . . Re sults and Discuss ion Recommendations References iii Page 52 52 52 53 53 53 55 55 56 56 56 57 62 64 65 65 65 66 74 75 Table 1. 2 . 3 . 4 . 5 . 6. 7 . 8. 9. 10. LIST OF TABLES Monthly water temperatures, measured from the surface to the bottom, during the winters of 1977- 78 and 1978-79, at the three trawling locations . . . . . . Estimated fishing pressure (angler days) by access area and month, Lake Powell, Ma r ch- September 1979 .... Fishing boat use by month and year at Lake Powell, 1975- 79. Numbers represent total fishing boats using lake/month. Also given are the average time (hr) fished/trip (H/T) and the mean number of fishermen / boat (F/B) . Catch rates (fish/angler hr) by species and access area, Lake Powell, March-September 1979 . . . . . . . . .. . ... . Catch rates ( fish/angler month, Lake Powell , 1979 . . . . . . hr) by species and t1arch-September Species composition by percent of the total recorded creel, Lake Powell, 1975- 79 Numbe r of fish caught in gi ll nets (30 net- days/station), Lake Powell , March 1979 Catch rate (fish/net-day) of fish caught in gill nets, Lake Powell-, March 1979 . . . . . . . . . • . . . . Catch rate by species and year, annual gill netting, Lake Powell, 1971-79 .. Mean catch rate (f ish/hr) of fish caught by electrofishing, Lake Powell , August- September 1979 . .......... . iv 14 21 23 26 27 3 1 39 40 43 45 Table 11. 12. 13. 14. 15. 16. 17 . 18. LIST OF TABLES (continued ) Fingerling survi val and total producti on of culture ponds, 1974-79 ..... . Production/ha during 1979 culture season Food habits of 13-day- old fry during 1978 , the most productive culture season Striped bass stocking history of Lake Powell Average catch/seine haul of young-of-the- year striped bass introduced into Wahweap Bay, 1975- 1979 .. . .•. . ......... Back calculated gr owth in total len~th (mm) of Lake Powell striped bass from 1975-79 Comparison of gr owth ra tes of striped bass fr om various studies. All data converted to total length (mm ) ......... . Food habits, by season, of striped bass collected in Lake Powell from 1975-79 ........ . v Page 58 58 61 67 69 70 71 73 Figure 1. 2. 3. 4. 5. 6. 7. LIST OF FIGURES Echograms sho"ing random distribution of thread fin shad at night and schooling behavior during the day ...... . Lake Powell, · showing trawl ing locations (dots) [1ean number of young- of- the - year shad captured/ trawl haul at Bullfrog . . . . . . . . Mean number of young- of-the- year shad captured/ trawl haul at Hite ........... . i~ean number of young- of- the-year shad captured/ trawl haul at Hahweap . . •.. . . . Residence of anglers using Lake Powell, 1975- 79 Indices of total recreat i onal boat use and angling pressure, Lake PO\,ell, 1965-79 8 . Catch rates (fish/angler hr) for largemouth 9 . 10. 11 . 12 . bass , blac~ c r appie and all species d uring the months of April - June , 1965- 79 , Lake Powell Hap of Lake Powell , Utah- Arizona , showing annual netting sites (dots) and electro fishing transects (c ircles) ••.. .. .. Catch rates ( fish/net- day) of largemouth bass and walleye from annual neeting , 1971 - 79, Lake Powell . . . . . . . . • • . . . . i1ean number of young - of- the - year largemouth bass and black crappie collec ted/hr o f electr ofishing during August -Septembe r 1977-79, Lake Powell ..... . Timing of fry introductions in relation to relative abundance of small plankters in the most productive ponds from culture seasons , 1975- 79 . Fingerling production/ha is listed in brackets . . . . . . . . . . . vi 5 7 10 11 12 22 24 28 36 41 46 60 INTRODUCTION Fisheries investigations on Lake Po"ell began in 1963 . sho r tly after impoundment and have continued to the pr esent . Tile initial work included physical and chemical descr i ptions of the filling reservo i r . plankton development, life history studies of intr oduced game fish. and an estimation of fishing pressure and s uccess. These studies were funded. in part . by federal monies provided under Section 8 of Public Law 485 , the Colorado River Storage Pr oject Act , and were completed in 1971. Important events that have occurr ed since th8 initial introduction of largemouth bass (M icropterus salmoides) , black crappie (Pomox is nigromaculatus) and rainbow trout (Sa lmo ~ai rdneri ) , include the intr oduct i on of thr ead fin shad (Dorosoma petenense) in 1968 . and the steadily increasing walleye (S tizostedion vit r eum vitreum) population which developed from stock present in the drainage before impoundment. Threadfin shad "ere introduced to provide for age for all game fish and to allow introduction of striped bass (Mo rone saxat ilis ) . Striped bass were introduced in 1974 after shad were permanently established. New studies und ertaken since 1971 , included an annual netting program to determine trends in game fish population dynamics; fish food supplies and utilization; thread fin shad population dynamics and predator impact; striped bass culture and evaluation of striped bass introductions. The study of fishing pressure and success has been on going since 1963 . while the study of the physical and chemical nature of Lake Powell was completed in 1974 . 2 Findings of our research from January 1975 to Dece~ber 1979, are given in this report along '.ith detailed results of the 1979 sampling year . More detailed accounts of events occurring in any particular year, 1975 to 1978, can be found in Lake Powell annual pr ogress reports f or that year (Hepworth et al. 1976; Hepworth et al. 1977 ; Hepworth et al. 1978; and Gustaveson et al. 1979). Lake Powell investigations since 1971 have been funded, in part , by Federal Aid to Fish and Wildlife Restoration , Project F-28- R, and by the Utah Division of \hldlife Resources. 3 THREADFIN SHAD STUDY JOB I Background Threadfin shad were first introduced into Lake Powell in 1968 . Shad are the predominant food item of all maj or game species (Hepwortn and Gloss 1976; and i~ay et a1. 1975). They are typically pelag ic and not readily sampled with conventional entrapment gear. The major objec tive of this study wa s to develop, through midwater trawling, an adequate system for sampling threadfin shad . The development of a midwater trawling system was completed in 1976. Data collected from 1976-79 were used to determine shad population indices and monitor monthly and annual population fluctuations. Information was also obtained on shad spawning periodicity. Striped bass, a pelagic predator, \lere i ntroduced into Lake Po\- ~ 1 8 0 ~ 1 6 0 o III 1 4 0 u. 0 1 2 0 (/ ) 0 1 0 0 z ~ 8 0 ::: I o 6 0 :I : t- 4 0 2 0 T O T A L B O A T S - - - F IS H IN G B O A T S . - ~ --- -- .. -- .. -- - ~~ _. ... .. ---- _... . ~~ .... ~ .-- -- " ~ 1 9 6 5 1 9 6 6 1 9 6 7 1 9 6 8 1 9 6 9 1 9 7 0 19 71 1 9 7 2 1 9 7 3 1 9 7 4 1 9 7 5 1 9 7 6 1 9 7 7 1 9 7 8 1 9 7 9 Y E A R F ig u re 7 . In d ic e s o f to ta l re c re a ti o n a l b o a t u se an d a n ~ l i n g p re s s u re , L ak e P ow e l l , 1 9 6 5 -7 9 . N -'" 25 0.45 fish/angler hr. Success rate was highest for anglers censused at Wahweap (Table 4), followed by Hite ~nd successively lower at Bullfrog and Hall's Crossing. Success rates also varied by month (Table 5). Fishing was best during April and May when anglers (all areas combined) cree led fish at a rate of 0.54 fish/angler hr. Largemouth bass were caught more often than other species in 1979, comprising 48.4% of the catch. Black crappie accounted for 35 . 5% of the total harvest. Catch rates (all areas combined ) for largemouth bass and black crappie for the 1979 census period were 0 . 22 and 0.16 fish/angler hr, respectively. Catch rates for these two species showed an improvement for the first time since 1975 (Figure 8). For the three months of most intensive angling (April -June ) , the catch rates for largemouth bass and black crappie were about double the rates for the same months in 1978. Channel catfish made up 6.1% of the har vest in 1979, being creeled at rates up to 0 . 10 fish/angler hr during the warmer summer months. Striped bass we r e caught at an overall rate of 0 . 02 fish /angler hr and comprised 3.4% of the harvest . Many factors influence angling success rates, including the absolute numbers of catchable-sized game fish available and the vulnerability of the available fish to anglers. The former category includes spawning success and recruitment (year-class strength), and interactions (competition, predation, etc.) among sympatric species. Factors affecting the vulnerability of available fish to anglers include weather conditions, fish behavior, and angler techniques and skill . Indices of abundance (see Job III) for catchable-sized largemouth bass have shown no correlation with angler success at Lake Powell in the past . The same 26 Table 4 . Catch rates (fish/angler hr) by species and access area, Lake Po\o/ell , March- September 1979 . Species dahweap Bullfrog Hall ' s Hi te rlean a Largemouth bass 0.28 0 . 09 o. 15 0 . 30 0 .22 Black crappie 0 . 18 0. 23 0 . 05 0. 07 0 . 16 Channel catfish 0 . 03 t b 0 . 04 0 . 04 0 . 03 Bl ueg ill 0 . 02 0 . 01 0.01 0.02 0 . 02 Ra in bow trout t 0.00 0 . 00 0 . 00 t Ha lleye t 0.01 t t t St r iped bass 0. 03 t t 0 . 00 0 . 02 Total 0 . 55 0 . 35 0 . 26 0 . 43 0 . 45 aTotal catch divided by sum of angler hr . b Less than 0.01 fish/angler hr. 27 Table 5. Catch rates (fish/angler hr ) by species and mon th, La ke Powell , ~arch-Saptember 1979 . Spec i es flar. Apr . May Jun . July Aug . Sept . Mean a Largemouth bass 0 . 35 0 . 25 0 . 19 o. 18 0 . 02 0 . 09 0.08 0.22 Black crappie 0.06 0 . 28 0.26 0.06 0.02 0.02 t 0.16 Channel catfish t b t 0 . 04 0 . 07 0 . 07 O. 10 0.04 0.03 Bluegill 0 . 00 0. 01 0 . 04 0 . 03 0 . 03 0 . 03 0 . 05 0 . 02 Rainbow trout t t t 0 . 00 0 . 00 t 0 . 00 t lia lleye t t t 0 . 05 0 . 02 0.01 0 . 01 t Striped bass 0 . 00 t 0 . 01 0 . 04 0 . 05 0 . 06 0 . 05 0 . 02 Total 0 . 41 0 . 54 0 .54 0 . 43 0 . 20 0 . 31 0 . 24 0 . 45 aTotal catch d ivided by s um of angler hr . bLess than 0 . 01 fish /angler hr . 1. 3 a: ::::> 0 :: t 0. 8 a: w 0 .7 ' - I 29 phenomenon continued in 1979 when the angler success rate for bass more than doubled from 1978, while the numbers of largemouth bass caught during the annual gill netting decreased by about 301 . Factors besides those which affect only the absolute numbers of largemouth bass are apparently influencing angler success rates at Lake Powell . One such factor during 1978-79 may have been the decrease in the numbers of forage fish available to game fish ( see Job I) and resulting changes in feeding behavior. Since game fish in Lake Powell feed almost exclusively on thread fin shad (Hepworth and Gloss 1976 ; and May et al. 1975), the dramatic change in shad density and biomass may have been reflected in an increased vulnerability of game fish to angling. This hypothesis is supported by the data for anglers at vlahweap. In recent years, anglers gaining access there usually had the lowest success rate of the four access areas. In 1979, however, anglers at V/ahweap had the highest success rate on the reservoir. At the same time, the numbers and biomass of threadfin shad at Wah>leap showed the most dramatic decreilse among the areas sampled by trawling. Anderson and Heman (1969) reported differences in vulnerability to angling related to differences in forage densities . They observed that largemouth bass from areas with low forage densities were more vulnerable to angling than fish from areas with hi 3her forage densities. Rose (1949) observed the same phenomenon for walleye at Spirit Lake , Iowa. High catch rates of walleye were usually associated with years featuring weak year classes of yellow perch, the main forage for walleye . For the first time since impoundment, the catch rates of walleye and striped bass exceeded 0.01 fish/angler hr for more than half of the months of creel census. Striped bass made up approximately 301 of the 30 catch during July , August and September for anglers gaining access at \;ahweap . The increased catch rates for both striped bass and walleye were likely a function of increases in absolute numbers of both species and the above-mentioned change in their forage base. In addition , the introduction of striped bass has resulted in a change in angler attitudes and techniques. More anglers became aware of the presence of striped bass and began using techniques that were conducive to taking these pelagic predators. Trolling open water areas became more common as anglers were rewarded with limit catches of striped bass . As more anglers used this technique in pursuit of striped bass, the catch of walleye also increased because walleye are more susceptible to anglers who troll deeper strata than to anglers who fish shallow structure near shore in search of largemouth bass. Other than the incr eased number of walleye and striped bass creeled , the species composition of the average angler ' s catch has not appreciably changed in the past five years (Table 6) . The logistics involved in obtaining a precise estimate of fishing pressure have presented a problem since creel census work began on the reservoir. Methods employed in the past have included attempts at complete counts of all boats launched over a 24-hr period and counts made from aircraft . More recently, pressure estimates have been made by adjusting counts of empty boat trailers at access areas as recorded by NPS personnel. The primary objective of estimating pressure at Lake Powell is to detect and descr ibe changes in angler use over a given time period, especially in relation ,to changes in the reservoir fishery or managemen t programs. Cons,equently, methods of estimating pressure 31 Table 6 . Species compos ition by percent of the total recorded creel, Lake Powell , 1915- 19. Largemouth Black Channel Striped Year Bass Crappie Catfish Bluegill \falleye Bass Other 1915 48 44 3 4 t t t 1916 42 41 2 1 t t t 1911 32 49 10 1 t t 1918 38 40 12 1 t t 1919 48 36 6 4 2 3 t Mean 41. 6 43.2 6.6 5.8 t t t t Less than H of total . 32 should be consistent from year to year. Although the NPS total boat use figures are subject to a number of valid criticisms ( counts are made at a high use time , the length of their "boat day" is not defined), they do provide consistent indices for purposes of describing relative changes in angler use . Adjus~~ent factors have not proved to be statistically reliable enough to justify their use and, in fact , have tended to compound the probl em. Recommendations It is recommended that the NPS data for total boating use , along ,.ith information obtained from angler interviews , continue to be used to estimate fishing boat days ( NPS boat days x percentage of boats reporting angling activity) and angler days (fishing boa t days x mean number of anglers per fishi~6 boat). In addition , it is recommended that an intensive creel census be conducted every other year rather than annually. On years of intensive study (1981 and 1983), the census would be conducted during April through September . During 1980, 1982 and 19 84, a census conducted during the three months of greatest angling activity--April, May and June--would still provide a means of detecting changes in angling success and pressure. References Anderson , R. 0 ., and M. L. Heman. 1969 . Angling as a factor influencing catchability of largemouth bass. Trans. Am . Fish . Soc. 98 (2) :317- 320. 33 Gloss , S., B. E. May, and R. Stone. 1973. Colorado River drainage reservoirs and tailwaters fisheries management investigation and surveys . Annual Prog . Rept. , Fed . Aid in Fish Restoration, F- 28-R-2. Utah Div. of Wildl . Resour ., Publ. No . 74-1 1. 10 pp . Gustaveson, A. \/., T. D. Pettengill, and M. J. Ottenbacher. 1979. Lake Powell postL~poundment investigations , Annual Perf. Rept ., Fed. Aid in Fish Restoration , F- 28- R- 7. Utah Div. of Wildl . Resour., Publ . No. 79- 8. 57 pp. Gustaveson, A. W. , F. M. Stowell, and D. K. Hepworth . 1979. A of fishing success and pressure on Lake Powell, 1954-1976. Div. of Wildl. Resour . , Publ. No. 79- 4 . 24 pp. rev iew Utah Hepworth, D., and S. P. Gloss. 1976. Food habits and age-growth of walleye in Lake Powell, Utah- Arizona, , .. i th reference to introduct ion of thr eadf in shad . Utah Div. of Wildl. Resour .. Publ. No. 76- 15. 13 pp. Hepworth , D. K. , A. W. Gustaveson, and R. Biggins . 1976 . Lake Powell post impoundment investiga tions. Annual Perf . Rept ., Fed. Aid in Fish Restorat ion, F- 28- R- 4 . Utah Div . of I-JildL Resour., Publ. No. 76- 21. 37 pp. Hepworth , D. K., A. W. Gustaveson, and F. M. Stowell . 1977. Lake Powel l postL~poundment investigations . Annual Perf . Rept . , Fed . Ud in Fish Restoration, F- 28- R- 5. Utah Div. of ',o/ildl. Resour. , PubL No . 77 - 13 . 61 pp. 1978. Lake Powell postimpoundment invest i gat i ons. Annual Perf . Rept ., Fed. Aid in Fish Restoration. Utah Div. of Wildl. Resour . 60 pp. May , B. E. , and D. Hepworth . investigations. Annual F- 28- R- 3. Utah Div . of 1976. Lake Powell postimpoundment Prog. Rapt., Fed. Aid in Fish Resto ra tion, Wildl . Resour ., Publ. No. 76- 3. 42 pp. Hay , B. E. , C. Thompson , and S. P. Gloss . 1975. Impact of threadfin shad (Dor osoma petenense) introduction on food habits of four centrarchids. Utah Div. of Wildl . Resour., Publ . No . 75- 4. 22 pp . 34 Rathbun, N. L. 1970 . Glen Canyon Unit-Colorado River storage project, Lake Powell fisheries investigations, creel census studies. February 1, 1969- January 31, 1970. Ariz . Game and Fish Dept. 66 pp . Rose , E. T. 1949 . The population of yellow pike perch (Stizostedion v . vitreum) in Spirit Lake , Iowa . Trans. Am. Fish. Soc. (77):32 - 41. Stone , J . L. 1965 . Glen Canyon Unit-Colorado River storage project, reservoir fisheries investigation , creel census and plankton studies, July 1, 1964- January 31 , 1965. Ariz. Game and Fish Dept . 60 pp. 1966. Glen Canyon Unit- Colorado River storage project, reservoir fisheries investigations, creel census and plankton studies, February 1, 1965-January 31, 1966 . Ariz. Game and Fish Dept. 40 pp . 1967. Glen Canyon Unit- Colorado River storage project , reservoir fisheries investigations, creel census and plankton studies , February 1, 1966- January 31 , 1967. Ariz. Game and Fish Dept . 41 pp . 1971. Glen Canyon Unit- Colorado River stor age project , Lake Powell fisheries investigations , February 1, 1970- January 31, 1971 . Ariz. Game and Fish Dept . 50 pp. 1972 . Glen Canyon Unit- Colorado River storage project , Lake Powell fisheries investigations , February 1, 1971-January 31, 1972 . Ariz . Game and Fish Dept. 52 pp. Stone , J . L. , and N. L. Rathbun. 1968. Glen Canyon Unit- Colorado River storage project, Lake Powell fisheries investigations, February 1, 1967- January 31, 1968. Ariz. Game and Fish Dept . 56 pp. 1969 . Glen Canyon Unit-Colorado River storage project, Lake Powell fisheries investigations , creel census and plankton studies, February 1, 1968-January 31,1969 . Ariz. Game and Fish Dept . 61 pp. 35 INDEX TO ANNUAL FISH POPULATION TRENDS JOB III Background Logistical problems preclude estimates of absolute numbers of fish in large reservoirs . Indices of relat ive abundance , however , may be used in such instances to desc ribe gross cha nges in fish population densities and species composition. Catches from standardized gill- net sampling Oloyle 1950; and G<.loch 1977) and electrofishing (von Geldern 1971) have been used as measures of relative abundance . A program of annual standardized gill netting has been conducted at Lake Powell since 1971 (Gloss et a1. 1974; 11ay and Hepworth 1976; Hepworth et a1. 1976, 1977, 1978; and Gustaveson et al. 1979) . In general, past gill-net catches have been dominated by largemouth bass and walleye , with the numbers of walleye increasing since the early 1970s. An annual pr ogram of electrofishing was initiated in 1977 to obtain information on the relative abundance of fishes which were inadequately sampled by gill nets , e.g ., young- of-the-year largemouth bass and black crappie. Methods Gill -net sampling was conducted during March 1975- 79 , at Padre Bay, the San Juan arm between Cha and Trail canyons, Rincon and Good Hope Bay ( Figure 9). Gangs of ten 30.5 m diving experimental gill nets (mesh s izes 25, 38, 51 and 76 mm) were fished for three consecutive days at M ile s I I i o 5 10 K n o w le s C an yo n F ig u re 9 . M ap o f L ak e P o w el l, U ta h -A ri zo n a, sh o w in g a n n u al 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 se c ts (c ir c le s ). w a> 37 sizes 25 , 38 , 51 and 76 mm) were fished for three consecutive days at each stat i on . On occasion , fewer nets were used due to equipment loss . Nets were set on the bottom and perpendicular to the shore in rock and rubble habitat with one end anchored at the shoreline. Fish were removed at 24-hr intervals, measured to the nearest millimeter (TL) and weighed to the nearest 5 g . Scales were taken from selected samples of all game fish for age and growth analysis. The electr of ishing boat was an 8 .5 m Yukon Delta with fiberglass hull. An Dnan 7.5 kw generator provided electrical power for the lighting system and a Coffelt Model RF -1 0 electroshocker. In 1977 and 1978, five 1.8 m long sect i ons of 13 mm diameter cable, which hung from a bow-mounted boom, served as the positive electrodes. The negative electrode consisted of two 4.6 m long cables which trailed along both sides of the boat . Output of the electroshocker was 150- 200 v dc , which was sequenced to the five positive electrodes so that each electrode was pulsed one time/second. In 1979, an electrode system similar to that described by Novotny and Priegel (1974) was used. The positive array cons isted of two 1.0 m diameter hoops of EWr electrical conduit , each with seven to ten dropper electrodes. The negative electrode was increased to five 2.0 m long sections of cable on each side of the boat. The output to the entire positive array was 10-15 a and 150-200 v dc with a pulse rate of five/second. \-later conductivities at the five transects ranged from 400- 600 micromhos/cm . The sampling crew consisted of a boat driver and two netters . Sampl ing began after dusk and continued until the transect was covered, usually 2-6 hr . Five shoreline transects were sampled ( Figure 9), including areas along the 38 midchannel of the lake, bays, and large and small side canyons. Each transect, except the Stanton Creek transect in Bullfrog Bay , was sampled twice in August-September 1977. All stations were sampled three times each at approximately one-week intervals in August-September dur ing 1978 and 1979 . Slinilar shoreline habitat was electro fished at each transect. All captured fish were measured to the nearest millimeter TL and released in the area of capture . The time of electroshocker operation was recorded and a catch rate was calculated for each species collected. The index of abundance for a given species and area was the mean of the catch rates for the three samples. Largemouth bass less than 175 mm TL and black crappie less than 125 mm TL were considered youn5-of-the-year. Results and Discussion Annual netting. In 1979, 733 fish were caught in 116 net-days (Tables 7 and 8). The highest catch rate was in Good Hope Bay, followed by Rincon, Padre Bay and the San Juan. The majority of the catch at each station consisted of largemouth bass and walleye. When catches from all stations were combined, largemouth bass accounted for 28.9% of the total and walleye for 51.4%. The combined catch rate o f largemouth bass during 1979 was 31% lower than that recorded during the annual netting in 1978 (Figure 10). A decrease of about one bass/net-day occurred at Rincon, San Juan and Good Hope Bay. The catch rate of largemouth bass at Padre Bay remained about the same, one fish/two net- days. The overall catch rate for largemouth bass in 1979 was the lowest recorded since 1971. Walleye, on the other hand , were caught at the highest rate recorded since the annual netting program was initiated 39 Tabl e 7 . Numbe r of f i sh caught i n gi l l nets (30 ne t - days/station) , Lake Powell , Ma r ch 1979. Good Percent Padre San Hope of Spec i es Bay Juan Rincon Bay Total Catch Largemouth bass 18 110 30 54 212 28.9 Walle ye 109 6 142 120 377 51. 4 Black crappie 0 15 8 24 3. 3 Bl ueg il l 0 3 0 4 0 . 5 Green sunfish 0 3 6 3 12 1. 6 Channel catfish 15 22 6 44 6. 0 Ca r p 20 10 6 37 5. 0 Fl annelmouth sucker 3 0 5 0 . 7 Rainbow trout 3 0 5 0.7 St r i ped bass 9 0 0 10 1. 4 Yellow bullhead 0 0 0 3 3 0.4 Al l spec i es 175 143 220 195 733 40 Table 8. Catch r ate (fish/net-day ) of fish caught in gill nets, Lake Powell, ~larch 1979. Good Percent Padre San Hope of Species Bay Juan Rincon Bay Total a Catch Largemouth :,ass 0 .6 3 . 7 1 . a 2. 1 1.8 28 . 9 Walleye 3.6 0 . 2 4 . 7 4 . 6 3.3 51.4 Black crappie' 0.0 0.5 0 . 3 t b 0.2 3.3 Bluegill 0.0 O. 1 0 . 0 t t 0.5 Green sunfish 0 . 0 O. 1 0 . 2 O. 1 O. 1 1. 6 Channel catfish 0.5 t 0.7 0 .2 0 .4 6 . 0 Carp 0. 7 t 0.3 0 .2 0.3 5 . 0 Flannelmouth sucker t O. 1 t 0.0 t 0 .7 Rainbow trout 0.1 t 0.0 t t 0.7 Striped bass 0.3 0 . 0 t 0 . 0 t 1.4 Yellow bullhead 0 . 0 0 . 0 0.0 O. 1 t 0.4 All species 5. 8 4 . 8 7.3 7.5 6.3 aTotal fish divided by total nets . bLess than 0. 1 fish/net-day. >- ~ c , r- w z a: w Q . J : C /) IL . 6 5 4 3 2 1 - - L A R G E M O U T H B A S S - - - W A L L E Y E ," -- - , -, ,.... . " ... " " , ,,, ..... . " ... ... " ... , ,, ' . 19 71 1 9 7 2 1 9 7 6 1 9 7 4 1 9 7 5 Y E A R 1 9 7 3 1 9 7 7 1 9 7 8 1 9 7 9 F ig u re 10 . C at c h ra te s (f is h /n e t- d a y ) o f la rg em ou th b a ss an d w al le y e fr om an n u a l n e tt in g , 19 71 - 7 9 , L ak e Po w el l. -<= 42 (Figure 10) . The Rincon accounted for most of the increase in the over all catch rate of walleye in 1979 . Numbers of walleye caught there were up over 50% . There was a sign ificant correlation (5~ level) bet\ieen the catch rate of walleye for the nine years of annual netting and the age of the reservoir according to Spearman's rank correlation coefficient (Snedecor and Cochran 1971) . The catch rates for largemouth bass did not show a correlation with reservoir age as determined by the same test. According to the netting indices, however, densities of bass have decreased annually since 1975, except for 1978 . It is possible that the number of largemouth bass has been affected by the expanding walleye population . \~alleyes are competitors of largemouth bass (N iemuth et al . 1962) as well as predators on small bass . Several stomach samples taken from walleye in 1979 contained remains of small largemouth bass . The adverse effects of an expanding walleye population on sympatric species would tend to be accentuated in years when the usual forage base ( threadfin shad) was low, as in 1979. Black crapp ie, carp and channel catfish were also occasionally caught and together comprised 14.3% of the total gill-net catch . These species have sho,," no apparent changes in density over the past five years (Table 9). Striped bass were first collected during the annual net sampling in 1977, and have made up about 5~ of the catch at Padre Bay in 1978 and 1979 . The expanding range of striped bass was also documented in 1979. For the first time since their introduction , a striped bass was collected during the annual netting at an area outside T ab le 9 . C at ch ra te b y sp ec ie s an d y ea r , an n u al g il l ne tt in g , L ak e Po we ll , 19 7 1 -7 9 . C at ch R at e S p ec ie s 19 71 19 72 19 73 19 '7 4 19 75 19 76 19 77 19 78 19 79 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. 83 V /a ll ey e 0 .2 9 1. 1 2 0 .4 1 1. 09 2 . 1 5 2 . 11 1. 17 2 .8 4 3 .2 5 B la ck c ra p p ie 0 . 12 0 .6 7 O . 1 2 0 .2 7 0 .3 6 0 .2 7 0 .2 6 0 .3 3 0 .2 1 B lu e g il l 0 .1 2 0 .5 2 0 .0 6 0 .0 5 0 .0 4 0 . 10 0 .0 9 0 .0 4 0 .0 3 G re en su n f is h 0 .1 0 O . 1 6 0 .0 9 o. 13 0 .0 6 0 .0 4 0 .0 9 0 .1 0 0 .1 0 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 O . 16 0 .2 0 0 .2 9 0 .3 8 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 F la n n el m o u th su ck e r O . 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 1 1 R ai nb ow tr o u t 0 .2 4 0 .3 1 0 . 10 0 .0 8 o. 19 0 .2 5 0 .2 6 O . 11 0 .0 4 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 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 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 .0 1 0 .0 4 0 .0 3 A ll sp ec ie s 3. 98 10 . 1 0 4. 24 6 .3 1 8 .0 2 6 . 15 4 .4 4 6 .8 2 6 .3 2 -'= w 44 Bay is the station nearest the stocking po int for iped bass) . In Ha r ch 1979 , a 51 0 nun TL striped bas s tinean. :. A total of 3 ,305 fish w3s cOllected durin ,; 15 shing for an overall catch rate of 400 fish/hr Youn~-of- tI1e -yea r Jlack crappie w,=re cau3ht most lcts , making up 42.9% of the total. Green sunfish and .argemouth bass each made up over 17% of the total IS t he only other species collected in si,n ificant ~he total . Limited numbers o f channel catf ish t red I older largemouth bass and one you ng- of- the - year Ilso caught during sampling at the five transects . 1 rate of young- of- the - year lar3emouth bass in 1979 It recorded for the previous years at Rincon , Hall's Les Canyon ( Fig ure 11) . The elect ro fishing indices, a weaker year class compared to tha t of 1978 at the oansects--Crappie Cove and Stan ton Creek . El ectro- young- of- the - year black cra ppie demonstrated a very in 1979. The mean catch rates at the five transects ~s hi~her than those reco r ded in 1978 . The strong black crappie was also suggested by the midwater thread fin shad . Substantial numbers of young - of-the- were found in ea rl y sum,ner tr awl sa'l1ples . In !N small crappie were collec ted whi le traHling . T ab le 10 . M ea n c a tc h r a te (f is h /h r) o f fi sh ca u g h t by e le c tr o fi sh in g , L ak e Po w e ll , A ug us t- S ep te m b er 19 79 . H a ll 's C re e k S ta n to n C ra p p ie K no w le s % o f T o ta l S pe c ie s R in co n B ay C re ek C ov e C an yo n C at ch Yo u n g -o f- th e - y ea r la rg em o u th b as s 72 84 44 72 87 17 .7 Ag e I an d o ld e r la rg em ou th b as s 2 'I 6 0 .5 Y ou ng -o f- th e -y ea r b la c k c ra p p ie 21 7 23 8 16 6 86 14 1 42 .9 G re en su n fi sh 65 85 33 32 14 5 17 . 5 B lu e g il l 44 19 31 48 16 5 15 .1 Re d sh in e r 38 25 5 4. 1 C na nn el c a tf is h 6 12 13 10 4 2 .2 A ll sp ec ie s 40 6a '17 7 31 6 25 5 54 8 aT o ta l fi sh d iv id ed by to ta l hr o f e le c tr o fi sh in g . .0 = en I 200 .,1 I I You ng-of-the-year RINCON I largemouth bass 150-1 I I ___ Young- of-the-year 100-1 I black crappie I • I-SO I // 250 1977 1978 1979 I t!l 200 200 HALLS CREEK I BAY I z I ~ 150 STANTON I I CREEK I 150 I LI. I 0 I I c: 100 100 I ~ I () I I w -' 50 -I- 50 I w I - / I LI. _--.,I 0 c: ::J 1977 1978 1979 1977 1978 1979 0 : 200] 200 ~ CRAPPIE COVE 150J KNO WLES 150 CANYON J: en LI. 100-111 100 50-1 ~ .... / ......... 50 I i i 1977 1978 1979 1977 1978 1979 Figure 11. Hean number of young- of- t he - year larger.1outh bass and black crappie collected/hr of electrofi shing during August - September 19 77 - 79 , Lake Pm,elL 46 47 Year- class strength of largemouth bass and black crappie is 60verned by a number of factors, including water level fluctuations during spawning season (von Geldern 1971), wind conditions (Miller and Kramer 1971) , and competition and predation by other fishes (Kramer and Smith 1960) . \Iater levels at Lake Powell usually are rising during the spring spawning season . In 1979, water levels reached a new record hi3h level. Such conditions are usually associated with strong year classes · of centrarchids . The low density of threadfin shad in 1979 may also have been a facto r in the production of a strong year class of crappie . von Geldern (1971) described an inverse relationship between the abundance of adult thread fin shad and numbers of fingerling lar3emouth bass in Lake Nacimiento, California. He concluded that an abundance of adult threadfin shad was detr i mental to spawning success or fingerling survival of bass. Black crappie may be similarly affected . Young-of- the - year centrarchids and adult thread fin shad were often found together in littoral zones during electrofishing and may have been competing for food . Factors other than those affecting relative abundance may influence catch rates obtained by electro fishing and gill netting . Some of these include fish behavior , shape and structure of fish , weather conditions during sampling and operator skill and experience . The modification of the electrode system on the electrofishing boat may have also influenced sa~pling efficiency and catch rate. In tests of the new system , however , the modifications did not visibly alter the effective range of the electroshocker. The dramatic increase in catch rates of only certain species s~npled also suggests a real change in population 48 densities of those species rather than a change in overall effectiveness of the sampling gear. Recommendations The annual netting has traditionally been conducted during the month of :~arch, cOinciding with the spawning season of walleye . Halleye utilize the rock and rubble hab i tat found at all netting stations for spawning . Consequently , their vulnerability to gil l netting may chanae sianificantly dependinil upon the t iming of sampl in3 and the initiation of spawning activity for a given year. It is rec omm ended that limited netting be conducted during the fall to determine if any bias is resulting from the timing of the annual g ill- net sampling. It is also recommended that the cond ition of fish at the time of annual netting be monitored. An ind e x similar to the visceral fat method used in the Utah Division of Wildlife autopsy classificaLion should provide a means of quantifying fish cond ition . HIlen Lake POl
geography
Array ( [0] => Array ( [state] => Utah [province] => ) )
batch_date
Tue, 05 May 2020 19:04:31 +0000
original_file_path
https://digitallibrary.utah.gov/awweb/awarchive?type=download&item=68500
group__id
5eb1b9d052a847.63901505
document_format
1.1.7
disabled
-1
processing_date
1609350612
year
1980
hash
Array ( [document] => 697b1743ae61676a04a9a4975e4e6a81783d85da [content] => c0bc5d66f669b15541367a5c8046780d126ffcaf [dedupe] => 4382ced3b6b3db43132cea280b5cafdd5a6ad1fd )
id
doc-5eb1b9d082ecd3e58b026289
__hash__
Content: c0bc5d66f669b15541367a5c8046780d126ffcaf | Abstract: d7d0f59b30e4c85e1576c9bebe6a517241e30dc5