title
Lake Powell fisheries investigations : 1985 (segment 11) annual report, Dingell-Johnson Project F-46-R-1
author
Array ( [0] => Gustaveson, A. Wayne [1] => Bonebrake, Bruce L. [2] => Scott, Steven J. [3] => Johnson, James E. )
abstract
UDWR Publication Number 86-8
date
1986-01-01
organization
Utah. Division of Wildlife Resources
species
Array ( [0] => Not Specified )
file_path
https://grey-lit.s3.wasabisys.com/lake-powell-fisheries-investigations-1985-segment-11-annual-report-dingell-johnson-project-f-46-r-1.pdf
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content
N 4650P6 .1 3 : Lak/ 9F:; Lake Powell Fisheries Investigations 1985 (Segment 11) Annual Report Dingell-Johnson Project F-46-R-1 Publication Number 86-8 I.FaUTAH ~~W NATURAL RESOURCES . .""" Wildlife Resources • LAKE POWELL FISHERIES INVEST1GATIONS Annual Performance Report January 1985 to Decembe r 1985 A. ~vayne Gus taveson, Pro jec t Leader Bruce L. Boneb rake , Project Biologist Steven J. Scott, Projec t Biologist James E. Johnson, Fisheries Program Coordina t or Publication No. 86-8 Dingell - Johnson Project F- 46- R- l Utah Depar tmen t of Natural Resources Division of Wi l dlife Resources 1596 West North Temple Salt Lake City , UT 84116 William H. Geer Director An Equal Opportunity Employer ABSTRACT Threadfin shad , Lake Powell's major forage species, produced a very small yea r class in 1985. There was virtually no recruitment of young-of-the-year shad into the pelagic zone of Lake Powell . Phys i cal condition of striped bass declined in direct response t o lack of ade- quate forage. Anglers harvested s triped bass and walleye in record high numbers, probably as a result of low forage ava ilability. Measurement of adult game fish population trends s howed numbers of walleye and largemouth bass to be essentially the same as 1984, while striped bass numbers increased dramatically. Young-of-the-year largemouth bass and black crappie experienced a modest production peak while striped bass were captured at the highes t rate rec orded. More than 100,000 smallmouth bass were introduced in Lake Powell at S1X different locations to help establish a l ake-wide population. Natural reproduction of s mallmouth bass was documented for the first time. TABLE OF CONTENTS LIST OF TABLES ..................... ... ........................... iv LIST OF FIGURES .................... . ........................... .. 'Ii JOB NUMBER I. FORAGE CONDITION STUDy ................................. 1 Methods ............................................ 1 Results and Discussion ................. o........... 1 Summary and Recommendatio ns ........................ 10 II. MEASUREMENT OF FISHERY HARVEST, PRESSURE, AND SUCCESS •• 12 Me thods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Resul t s and Discussion ............................. 12 III. INDEX TO ANNUAL FISH POPULATION TRENDS ••••••••••••••••• 18 Annual Netting....................................... 18 M.ethods........... ............... .................. 18 Results and Discussion ............................. 18 Recommendations.................................... 22 Electrofishing....................................... 23 Methods............................................ 23 Results and Discussion ..................•..•....... 23 Recommendations.................................... 28 IV. STRIPED BASS POPULATION DEVELOPMENT.................... 29 Methods............................................ 29 Results and Discussion ...................••........ 29 Summary and Recommendat ions. . . . . . . . . . . . . . . . . . . . . . .. 33 V. SMALUfOUTH BASS POPULATI ON DEVELOPMENT ................. 35 Methods ............................................ 35 Results and Di sc ussion .. . ...•............... .. .. . .. 36 Summary and Recommendations ........................ 38 REFERENCES CITED.... ............ .. ............................... 39 -iii- Tab le LIST OF TABLES 1. Mean number of larval thread fin shad collected per ichthyop1ankton net tow, Chaol Canyon, Lake Powell, 1983- 85. .•.•• ..•......••. .•.••.•.•.••••••. .•.•.•.••. .•. 6 2. Mean number of larval thread fin shad collected per ichthyoplankton net tow, San Juan River Arm, Lake Powe 11, 1984-85................................... 7 3. Species sought (%) by ang lers, Lake Powell, April-October 1985..................................... 14 4. Sport fishery creel rates (fish/angler hour) by species and aCCeSS area, Lake Powell, April-October 1985 ....... 16 5. Species composit i on (%) of the t ota l creel, Lake Powell, April-October 1985 ........................ 17 6 . Catch rates (fish/net day) during annual gillnetting, Lake Powell, March 1985...... .......................... 20 7. Percent occurrence of food items in largemouth bass and walleye stomachs collected in gill net s and during creel census, Lake Powell, 1985. (Percentage based onl y on number of stomachs containing food).................... 22 8. Mean catch rate (fish/hour) of fish collected by e lectrofishing, Lake Powell, Sep t ember 1985 ............ 24 9 . Percent occu rrence of food items in striped bass stomachs, Lake Powell, 1985. (Percentage based on number of stomachs containing food.) ................ 32 10. Summar y of striped bass caught duri ng fall gillnet sampl ing exp res sed in terms of fish caught per 1000 square feet of gi ll net per 12 hour set , Lake Pm,ell, 1981-85................................... 33 11. Smallmouth bass stocking history, Lake Powell , 1982-85 .. 36 12. Mean catch rate (fish/hour) of young-of-the-year sma llmouth bass collected by e l ectrof i shing, Lake Powell, 1982- 85... ................................ 37 -iv- LIST OF FIGURES Figure 1. Map of Lake Powe ll showing t rawl ing and ichthyoplankton netting stations for thread fin shad , 1985 .................. 2 2 . Mea n number of l a r val shad co lle c t ed per ichthyop lankton net tow, lower Lake Powe ll, 1984-85 ••••••••••••.•••••.••.•• 3 3 . Mea n number of larval shad co llected per i chthyoplankton net tow , mid Lake Powell, 1984-85 •.•..••.••.•.•.••..••.••. • 4 4 . Mean numbe r of larval shad co ll ec t e d pe r i chthyoplankton net tow, upper Lake Powell , 1984-85 •..•.•••••.•••••••.••... 5 5 . Mea n numbe r of s had co ll ec t ed pe r trawl tow, Lake Powell 1980-1 985 . (The top of each bar represe nts the cumulative total ca tch for Ju l y-September fo r each year . ) •••••••.•...• 8 6. Mean numbe r of thread f in shad collected per trawl tow, Ju l y- Septembe r, Lake Powe l l, 1977-85 •.••••.••.•.•.•••.• •••• 9 7 . Indi ces of total r ec r ea tiona l boat use and angl ing pr essure, Lake Powell, 1965-85 ..••...•.•.....•....•..••..•• 13 8 . Cree l rates (fish/angle r hour) for largemouth bass , black crappie a nd all species comb ined, Lake Powell, Apri l-Ju ne 1965-85 ••••.•••••.•••.•••••••••.•••••..•.•..•... 15 9 . Map of Lake Powe ll, Utah-Arizona, s howing annual netting sites (circ l es) and e l ec trof i shing transects (dots) ••.••.•. 19 10. Catch rates (fish/net day) fo r wa ll eye and l argemouth bass from annua l net ting , Lake Powell , 1971-85 •.•.••..•••.••• • .. 21 11. Mean catch ra t es (fish/hour ) for largmouth bass, black crappie and str iped bass col lected by elect rofishing, August-Sep t ember, 1978- 85 , Lake Powell •.•..••.•.•.....•.... 26 12. Relations hip be twe en largemouth bass pr oduction (lakewide e l ect roEishing average) and thread fi n shad recru i tment (Bullfrog and Wahweap trawling average) , Lake Powell, 1977-85 •......•..•....•.•..••••..••..•..•.........••.••.... 27 13 . Year end (November) average condition factor (K) of adult a nd juvenile st riped bass, Lake Powell, 1975- 85 ...• •• ..•.•• 31 -vi - FORAGE CONDITION STUDY JOB I METHODS Threadfin shad (Dorosoma petenense) spa\vning was monitored with ichthyoplankton net co l lec t ions, beg inning in May and con tinuing into October . Weekly samp l es were taken in the backs of bays at \,ahweap Creek, Warm Creek, Bullfrog Cr eek and Halls Creek. Biweekly samp l es ,,,ere collec ted at Red , Ticaboo and Chaol Can yo ns, whi l e monthly mon- i t o r ing was conducted at Piute Fa rms \,ash, Pi ute Farms Red Wall and the San J uan Rive r Inflow (F i gure 1 ) . A one -mete r, 505 mlcron net t-las towed just below the water's surface. Three tows, two minutes in dura - tion, were taken a t each station, samp ling an ave r age volume of 102 m3 of water per t ow. Previous findings have demonstra t ed that shad in Lake Powell prefer to spawn in turbid waters (Gustaveson et a le 1982), therefore , th e shallow, turbid water areas at the backs of can- yo ns and bays were c hos en for sampling. Sampl e locations were adj u sted periodically to compensate fo r fluctuating water levels . Recruitment of youn g- of-the-yea r (y-o-y) thread fin shad into pela- g1C areas of Lake Powell was monitored by mo nthly midwater trawl col- lections and e i gh t-minut e sonar transects. Sampl ing was conducted from July throu gh Sep t e mb e r at Wahweap, Bullfro g and Good Hope Bays (Figure 1). A complete description of i chthyoplankton a nd trawl sam- pling methods can be found in Gus t a veson et al. 1985 . RESULTS AND DISCUSSION Ichthyoplankton netting bega n in May a nd co ntinue d until Oc tober when shad spawnin g e nded. Compared to 1984, thread fin shad spawning decreased at all lake locations (Figures 2 , 3 a nd 4) . Spawning in the • I N I T • I M ile s I o 5 10 T ra w li n g S ta ti o n Ic h th yo p la n kt o n S ta ti o n H al ls C re ek ~ A r/ z o n; - - _ _ C h ao l C an yo n T lc a b o o C an yo n F ig u re 1 . ~ a p o f L ak e P o w el l sh o w in g tr a w li n g an d ic h th y o p la n k to n n e tt in g st a ti o n s fo r th re a d fi n sh ad , 19 85 • I W I 2 0 0 0 1 0 0 0 - 3 0 0 2 0 0 1 0 0 M a y • 0 ' • o • 0 0 • o • 0 0 • o • •• * ~ o • 0 0 • o • ... .. • • o • · . · . • • • • • • • • · ' • • • • · ' • • · . • • • • · . • · . • • • • • • • : • • • • • i ____ ____ e _ o ~ J u n e Ju ly W ah w ea p C re ek A u g u st 2 0 0 0 1 0 0 0 3 0 0 2 0 0 1 0 0 S ep t. ° :-.. • • . '. '. '. ••• •• '. '. • • ... ' . • '. • '. 1 9 8 5 - - - - 19 84 .• •• •• •• •• •• •• •• ~ : .... . . · -'. o ~ . ~ o •• o : 0 '0 '0 · ~ M a y · ~ . · '. · ~ • 0 0 • o. J 0__ _ .. o 0 • • o 0' J u n e J u ly W a rm C re e k A u g u st S ep t. F ig u re 2 , M ea n nu m be r o f la rv a l sh ad c o ll e c te d p e r ic h th y o p la n k to n n e t to w , lo w er L ak e P o w el l, 1 9 8 4 -8 5 , 2 0 0 0 1 0 0 0 -1 3 0 0 " I 2 0 0 J ~ I 1 0 0 -1 , " .. • • • • • • • • • • • • · • • • • • • • · • ,. • ~ • • · · · • · • • , "' • , • · • • • • , :'. , , , , I : ' , • , , • • • • • • • • • • • • • , • • • , • · • , • • • • • • • , • , • • , • • • • • • • • • •• • • " • " • " • " • • • f : M ay Ju ne Ju ly B u ll fr o g C re e k 2 0 0 0 1 0 0 0 3 0 0 2 0 0 1 0 0 " " '" I' A ug us t S ep t. M ay , " · . , . • • • • · . • • • • • • · , • • • • • • · , , , · , · ' · ' · ' · ' • • · . · ' • • , . · ~ · , • • · , • • • • · . · , · , • • · , • • • • i/ '\ \. Ju ne • • • • , " , Ju ly " " H a ll s C re e k 1 9 8 5 - - - - 19 84 ·· ·· ·· ·· ·· ·· ·· ·· , " •• •• " , , A ug us t S ep t. F ig u re 3 . H ea n nu m b e r o f la rv a l sh ad co ll e c te d p e r i ch th y o p la n k to n ne t to w , m id L ak e Po w e l l , 19 84 - 85 . I en I 2 0 0 0 1 0 0 0 3 0 0 2 0 0 10 0 2 0 0 0 1 9 8 5 1 9 8 4 . .. .. .. .. .. .. . . o " · . · . • • · . • • • • • • · . • • • • • • • • • • • • • • • • · . • • • • • • · . • • • • • • • • • • · . • • · . • • · . o • • • • • • • , . • • • • : , · ' · ' · ' · ~ · ' · ' · ~ · ' : ~. · ~ . ~ . . ~ ---. ..... ..... . ... M a y Ju n e J u ly A ug us t R e d C a n y o n S e p t. 1 0 0 0 3 0 0 2 0 0 1 0 0 M a y o " .. • • · . • • • • , . • • • • • • • • • • • • · ' • • • • • • · . • • • • • • • • , . • • • • · . • • · . • • • • • • • • · . • • · ' • • , . · ' • • · . · . · ' • 0 : ... , " . " o " 0 - - '" " Ju n e J u ly T ic a b o o A u g u st C a n yo n F ig u re 4 . M ea n nu m be r o f la rv a l sh ad c o ll e c te d p e r ic h th y o p la n k to n n e t to w , u p p er L ak e P o w el l, 1 9 8 4 -8 5 . S e p t. • • lower r eserVOH began earlie r 1n 1985 than normally recorded and ex- tended into Septembe r ) wi th a few larvae even be ing co l lee t ed during Octobe r. Spawning intensity ) however , was somewhat reduced f r om 1984 (Figure 2). Peak spawnin g ) which normall y occu r s In Mayor June at other sampling locations, occurred during August a t Wahweap Creek . \,ahweap Creek was the coldes t spawning a r ea sampled and took the long- est time to atta in optimum temperature fo r shad spawn1. ng , which ex - plai ned late r spawning . Chao l Canyon , also located in the lower lake, expe rienced an unusual spawn i -ng year in 1985. The r e was no distinct spawning peak as seen in 1983 and 1984, a lthough fair numbers of shad were collec t ed throughout the spawning season ( Tabl e 1 ) . Tab l e 1. Mea n number of larval thread fin sh ad collec t ed per ichthyo- plankton net tow, Chaol Ca nyon, Lake Powe ll, 1983- 85 . Sample Month 1985 1984 1983 May 48 791 a June 40 47 335 July 24 4 1 August 65 2 1 Sep t ember 10 a 1 a Not sampled . Spawning at midlake was le ss 1n 1985 with peak numbers of larval shad collecte d a t Bul lfrog Creek on 29 May ( 1111 fish/tow) . activity a t midlake continued into the fall , but very few larvae \ve r e collec t ed af t e r June (Figure 3) . The grea t est r educt i on in spawning was observe d at uppe r lake sta- t ions . Samples collected dur ing 1985 revealed almost no spawning - 6- activity at Red and Ticaboo canyons, which are normally productive, as evidenced by the 1984 samples (F i gure 4). Samples collected in the San Juan Arm were also low durin g 1985 (Table 2) . The highest numbers of shad co llected were 69 f ish/tow at Piute Red Wall and 17 fish/tow a t Piute Farms I-Iash, compa red to 252 fish/tow and 1200 fish / t ow, re Spec- tively, co llected during 1984. Table 2. Mea n number of larval thread fin shad collected per ich th yo- plankton net tow, San Juan River Arm, Lake Powell, 1984-85 . Sample Piut e Red Wall Piute Farms Wash San Juan R. Inflow Month 1985 1984 1985 1984 1985 1984 May 69 252 17 1200 1 36 June 31 3 6 1 1 1 July 1 0 1 1 0 1 Augus t 1 0 0 0 0 0 September 5 a 0 a 1 a a No t sampled . Midwater trawl catches of y-o- y shad Were also low during 1985. A few y-o-y were cap tured during August at Bu llfrog and during July at Good Hope Bay, but almost no fish were col lected in any o ther s amples (Figure 5) . Echograms run during each s amp l e period also reflected the lack of shad in the pelagic zone o f the lake. Sume evidence ind icates thrli!adfin shad popu latiuns at Lake Powel l may be cyclic (Gustaveson e t al . 1985) . Since 1977, trawl ca tcheS have exhibited three distinct, but decreasing , pli!aks occurring a t th ree year inte rval s , 1978 , 198 1 and 1984 (Figur e 6) . Years between peaks have been c haracterized by l ow s had rec ruitment in most areas of the lake . - 7- 2000 1000 80 81 82 83 84 85 Wahweap 0 ffi¥! I~ I 60 81 82 83 84 85 Bullfrog July Sample August Sample September Sample "0 % 80 81 82 83 84 85 Good Hope Figure 5. ~Iean number of shad collected per trawl tow, Lake Powell, 1980-85. (The top of each bar represents the cumulative total catch fo r July- September fo r each year.) -8- 6 0 0 0 5 0 0 0 '0 0 0 3 0 0 0 2 0 0 0 10 0 0 5 0 0 I '"' I '0 0 3 0 0 2 0 0 - 10 0 · • ° 0 • ... :\ . . . \. G l ! \ • G • • . - . . ~ ~ : ~ • A • • • 0 ' . ~ ~ : ~ ... i ... ... I ... . ' . . ' . .. : .. · . . · . . · . . · . . · . . · . . · . . · . . \ ! \ \ V i . ~\ " . \ f \ . . . . . . ... ; ... . . . . . . .. ! .. • - - -: '! . ... ... ... ... . ;.-. .. / \ . : °0 : 0. . . . . : 0. . . . . .: \. . . . . .f" ...... ./ \. : .. / \.. .: --- .-- -- .. 77 7 8 7 9 8 0 81 8 2 8 3 8 4 8 5 F ig u re 6 . M ea n nu m be r o f th r ea d fi n sh ad co ll e c te d p e r tr a w l to w , Ju ly - S ep te m b er , L ak e P o w el l, 19 77 - 19 85 . • Extremely low numbers of shad collected during 1985 represent a contin- uation of this three year cycle and could project another low shad year in 1986 if the pattern con tinues. Moczygemba and Morris (1977) reported that the open water zones ar. inhab ited by surplus shad forced into off-shore areas by intraspecific compe tition. Lack of shad in the pelagic zone is an indication of a preda tor-impacted shad population. Large year classes of striped bass (Maro ne saxatilis) have been produced since 1981 (Job IV) and may be causing the decreasing trend seen in numbers of shad collected from the population peak years of 1978, 1981 and 1984 (Figure 6). Striped bass reduced the standing crop of gizzard shad (Dorosoma cepedianum) 1n Lake E . V. Spence and eliminated threadfin shad from the population (Morris and Fo lli s 1978). Young gizza rd shad escap ing predation g rew rapidly . Afte r exceeding the forage s i zes preferred by s triped bass 06-17 8 mm) gizza rd shad ma tured and spawned . Thread fin s had, because of smaller size, were unable to outgrow predation and were e liminated. Threadfin shad are the only schooling forage fish in Lake Powell that supply suitable prey for the striped bass populat i on. Striped bass have pr o- duced large year classes since 19 8 1 and are now present in greater num- bers than the shad population can support (Job IV) . Hi gh striped bass r eproduction has exerted a negative impact upon shad recruitment and may also be impacting the available brood stock in years of 1o,,,, shad production. SUMMARY AND RECOMMENDATIONS In summary, 1985 was a poor year for both shad reproduction and recruitment at Lake Powell. Together, the cyclic nature of the lake's shad popu l ations and he avy predation by striped bass have produced an unstable si tuation. During peak years , thread fin shad provide exeel- lent forage for the lake's game fish populations, however, during 10w cye le years game fish suffer . The adrlition 0f another f0ra~e species could help remedy this situation by providing not only better diversi t y -1 0- to the system , but also stability to the highly cycl ic populations of s had by buffering predatory pressure . Ichthyoplankton netting and mi dwater trawling should be continued as estab lished . Ichthyoplankton netting has proven useful in monitor - ing seasonal and annual l a rval shad pr oduction. Midwa ter trawling has been useful ,n evaluating y- o- y shad recruitment into the pelagic zo ne of the lake as well as determining available forage for striped bass . Use of echosounding to supp l ement trawling data shou ld also be contin- ued . Echosounding has proven a valuable tool when equipment br eakdotvns have prevented trawl sampling . In addition, echosounding is presently the on ly effective technique for monitoring adult populations of thread fin s had in the winter. - 11- MEASUREMENT OF FISHERY HARVEST, PRESSURE AND SUCCESS JOB II METHODS Creel census was conducted from April through October 1985, at four major access areas on Lake Powell: Wahweap, Bullfrog, Hall's Crossing and Hite. Anglers were int erviewed as they returned to launch ramps. Ca tch rates (fish/angler hour) were estimated from data reported by anglers for the census day and previous day of fishing. Estimates of angling pressure were based on recreational use data collected by National Park Service (NPS) at access points. Food habits of striped bass, walleye (Stizostedion vitreum) and largemouth bass (Mic ropte rus salrnoides) were observed and record'ed by percent occurrence and pres- e nted in Jobs III a nd IV of thi s report. A computer program was util- ized to summarize data collected from the cree l survey . RESULTS AND DISCUSSION In 1985, a total of 2,403 boating parties was checked by cree l c lerks during seven months of census. A total of 994 parties (41 per- cent) had fis hed. Mean number of anglers per fishing boat was 2.5 a nd each angler spent an average of 4.3 hours fishing per day . Both angling pressure and recreational boat use increased during 1985 (Figure 7). Ang ling pressure was 128,186 fishing boat days, a n increase of 32 percent from 19 84 . Total r ec r eational boat u se (includ- ing fishing and nonfishing boats) was 342,887 boat days in 1985. Bul lfrog/Ha ll's Crossin g produce d the hi ghest a ng l e r us e (58 percent) of the three access zones, while angler use at Wahwe ap and Hite mad e up the rema in i ng pressure , 29 and 13 percent, respec tivel y . -1 2- " >- .. c -.. 0 III U) Q. Z I ~ W I 0 " .., c .. .. ~ 0 .l: .... 3 4 0 - 3 2 0 2 8 0 2 4 0 2 0 0 1 6 0 1 2 0 8 0 4 0 - - - - T o t a l B o a t D a y s - - - F is h in g B 0 8 t D a y s "- - - " , ' ~r -- -- -.... - ........ - ........ " -- ~- - -- - ~ / / , / ~ , / .' - / .. .. - 6 5 6 6 6 7 6 8 6 9 7 0 7 1 7 2 7 3 7 4 7 5 7 6 7 7 7 8 7 9 8 0 8 1 8 2 8 3 8 4 8 5 Y e a r F ig u r e 7 . In d ic es o f to ta l r ec re a ti n a l bo a t u s e an d a ng li n g p re ss u re , L ak e P ow el l , 19 6 5- 1 9 8 5 . Most ang ling pr essure was directed spec ifical ly a t striped bass and largemouth bass (Table 3). not target a single species . Many anglers were indis c r im inate a nd did Table 3 . Species sought e%) by anglers, Lake Powell , April-October 1985 Species Hite Bullfrog/Hall' s Wahweap Total Largemou t h bass 28 12 12 14 Black Crappie 5 1 2 2 Striped bass 20 47 40 41 Walleye 2 3 3 3 Channe 1 ca tfish 1 t a 2 1 Bluegill 0 t 1 t Any 44 37 40 39 a le ss than 1% Cree l rate (fish/angle r hour) for largemouth bass (0 .044) decreased again ~n 1985 , cont inuing a slow dec l in ing trend ove r the past six years (Figu r e 8) . Cree l rates fo r str iped bass, walleye, and all species combined increased in 1985 (Table 4) . Best fishing for striped bass was mid-reservoir (Bul lfrog and Ha ll' s Crossing) where cree l rateS during August exceeded 0.91 fish/hour. Lakewide c r eel rates for black crappie (Pomoxis nigromaculatus) remained similar t o 1984, with fishe r- men in the upper reservoir (Hite) having the grea t est success . -14- ~ " 0 :x: ~ ~ '" c ... - '" ~ I Q . .t= .. IL 1. 3 1. 2 - - - - ·A II S p e c ie s 1. 1 - - - - - - - B la c k C ra p p ie 1 .0 - - - - L a r g e m o u th B a ss 0 .9 0 .8 0 .7 0. 6~ _ _ \ 0 .5 , 0 .4 0 .3 0 .2 • 0 .1 -1 , / \ , , .... .... ... , I ' I , I ' , I ,.. ... I ' I " I ' I . A ..... - J " / ' " 6 5 6 6 6 7 6 8 6 g 7 0 7 1 7 2 7 3 7 4 7 5 7 6 7 7 7 8 7 9 8 0 8 1 8 2 8 3 8 4 8 5 Y e a r F ig u re 8 . C re e l ra te s (f is h /a n g le r h o u r) fo r la rg em o u th b a ss , b la c k c ra p p ie an d a ll sp e c ie s , L ak e P o w el l, A p ri l- Ju n e 19 65 - 19 8 5 . Table 4 . Spo rt fishery creel rates (f i sh /angler hour) by spec 1es a nd access area , Lake Powell, Apri l-Oc t obe r 1985. Bullfrog Lakewide Avera~e Hall ' s N . f ' 1 onspecl Ie Specific Species Hite Crossing \,ahweap Angling Angling Largemouth bass 0 . 069 0 . 034 0 . 053 O. 044 0 .1 69 Black crappie 0 . 083 0 . 015 0 . 033 0 . 029 0 . 684 Striped bass 0 .118 0 . 320 0 . 219 0 . 265 0 . 511 \,alleye 0 . 020 0 .043 0.049 0.042 0 . 263 Channel cat fish 0 . 02 7 0 . 017 0 . 030 0 . 022 0 . 260 Bluegill 0 . 014 0 . 008 0 . 012 0 . 010 0 . 053 Smallmou th bass 0 . 000 0 . 000 0 . 002 0 . 001 0 . 000 Other 0 . 001 0 . 001 0 . 001 0 . 001 0 . 002 All spec i es 0.333 0.438 0 . 400 0 . 414 lC r eel rat es fo r all a ngle r s combined. 2 Cr ee l rates using onl y data of ang l er s targe ting spec i f i c speC Ies . 2 The bu l k of the fishe r y i n 1985 was suppor t ed by striped bass (63.9 percent) , wh il e l a r gemouth bass 0 0 . 6 percent) and walleye (10 . 2 per- ce nt ) were also seasonally i mportant (Tab le 5) . Black c rappie were poorl y r ep r esent ed i n 1985 compri sing onl y 6.9 percent of total harvest . - 16- Table 5. Species compos ition (%) of the t otal creel, Lake Powell, Ap ril-Oc tober 1985. Species Apr May Jun Jul Aug Sep Oc t Largemouth bass 37.4 15.1 9 . 9 8 . 8 1.4 8 . 0 B. 4 Black crappie 23 .0 17.2 1.4 0 . 0 1.5 6 . 5 3 . 8 Striped bass 13.9 24.9 50 .4 69.1 90 . 3 75 . 6 79.6 IVall eye 19.0 28.4 25.7 8 .7 1.3 3 . 2 2.4 Channel ca t fish 2 .5 9 .9 6.4 10.3 4 .1 6 . 4 3 . 0 Bluegill 3.8 3.4 6.1 2 . 8 1.2 0.0 2.5 Smallmou th bass 0 .3 0.1 0.0 0 . 0 0.0 0.5 0.0 Other 0 .1 1.0 0.1 0.4 0 .1 0 .1 0 .3 l1ean 10 . 6 6 .9 63 . 9 10 . 2 5 . 4 2 . 4 0 .1 0 . 2 Most striped bass harvested in 1985 were three and four year old f ish with some of two year old fi s h. Mean lengths of largemouth bas s, black crapp1e, and striped bass 1n 1985 were 348 mm, 239 mm, and 555 mm, respectively. At all locations, creel rates for striped bass in 1985 exceeded previous highs. Anglers discovered a large , striped bass population in mid-reservoir and harvested over 100 ,000 fish during August. Low num- bers of pelagic thread fin shad (Job I) may have increased catchability of stripe d bass. Game species tend to be more catchable in the absence of suitable forage fish (Anderson and Heman 1969). Anglers with a f ull creel limit (10 fi s h per angler) were common. Ang lers a ls o harvested walleye in rec ord numbers in 1985 . Walleye in Lake Powel l tend to be le ss dependent on thread fin s had a nd di splay mo r e diverse feeding habits than striped bass . However, the reduction in s had number s in 1985 may have helped increase catchability of wall eye and sub sequentl y contributed to the rec ord harves t. -17- INDEX TO ANNUAL FISH POPULATION TRENDS JOB II I ANNUAL NETTING METHODS Methods for standardized gillnetting were described 1n Gustaveson et al. 1985. Fou r stations were sampled ,n 1985 (Figure 9) during the last three weeks in March, using 20 net-days per station . Sampling was reduced from 30 net-days in 1984. Samples of largemouth bass , walleye and striped bass were used to quantify food habits by percent occurrence. RESULTS AND DISCUSSION A total of 493 fish was collected ,n 80 net-days. Ca tch ra t e was highest at the Rincon followed by the San Juan, Padre Bay, and Good Hope Bay, respectively (Table 6). Overall catch for 1985 doubled at the Rincon and substantially increased at the San Juan and Padre Ray sta tions, while catch ra t es at Good Hope Bay were less than 1984. Total catch rate for all species and s tations comb ined (6.16 fish/net day) was appreciably highe r than 1984 (4.35 fish/net day). -[ 8- ~ -0 I W a h w e a p I M ile s i o 5 10 • E le c tr o fl s h in g S ta ti o n o A nn ua l N o lt in g S it e G o o d H o p e B a y . . - ' ~ R i v . r F ig u re 9 . M ap o f L a k e P o w e ll , U ta h -A ri zo n a , sh o w in g an n u a l n e tt in g s it e s (c ir c le s ) a n d e le c tr o f i s h in g tr a n s e c ts (d o ts ). Table 6 . Ca tch rates (fish/ne t day) during annual g illnetting, Lake Powell, March 1985. Good Hope San Padre Species Bay Rinc on Juan Bay Total a Striped bass 1.45 7.90 2 . 75 0 . 20 3 . 07 Wa ll eye 1.15 2 . 20 1.10 3 . 75 2 . 05 Largemou th bass 0 . 25 0 . 30 0 . 55 0 . 25 0 . 34 Black c rappie 0 . 25 0 .00 0 . 00 0 . 00 0 . 06 Carp 0 . 65 0 . 40 0 .30 0 . 05 0 . 35 Channe 1 catfish 0 . 00 0 . 20 0.45 0.05 0 .17 Blu~gill 0 .1 5 0 . 05 0 . 00 0 . 05 0 . 06 Green sunfish 0 . 00 0 . 05 0 .10 0 . 00 0 . 04 Ye 110w bu llhead 0 . 05 0.00 0 . 00 0 . 00 0 . 12 Total 3.95 11. 1 5.25 4.35 6 . 16 a Total total number of fish divided by t otal net days. % of Catch 49 . 8 33 . 3 5 . 5 1. 0 5 . 7 2 . 8 1.1 0.6 0 . 2 Mean catch rat e for both largemouth bass and walleye decreased 1n 1985 (F i gure 10). Whil e the largemouth bass ca t ch rate decreased for the past seven years, th e reduction has s l owed and the population seems to be stabilizing . Following a peak in 1981, walleye appeared to be stabilizing at a lower level . Reductions in catches of largemouth bass and walleye were offset by large increases in st riped bass a t o th er samp l i ng locations (Table 6) . Striped bass have historically been sampled 1n low numbers during spr ing gillne ttin g . However, the extremely abundant 1983 yea r-class was captur ed in high numbers at the Rincon 1n 1985 . Quan tifying food habits of walleye was difficult because 92 percent of the s t omachs exam ined were emp t y (Tab le n. con t en t s suggt:!s ted oppo rtuni st i c feeding behavior. - 20- Anal ysis of stomac h Shad t
geography
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