title
Lake Powell fisheries investigations : 1982 (segment 11) annual report for Colorado River Drainage and Tailwaters Dingell-Johnson Project F-28-R
author
Array ( [0] => Gustaveson, A. Wayne [1] => Pettengill, Thomas D. [2] => Scott, Steven J. [3] => Johnson, James E. )
abstract
UDWR Publication Number 83-9
date
1983-01-01
organization
Utah. Division of Wildlife Resources
species
Array ( [0] => Not Specified )
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https://grey-lit.s3.wasabisys.com/lake-powell-fisheries-investigations-1982-segment-11-annual-report-for-colorado-river-drainage-and-t.pdf
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N 4650P6.13: Lak/qg~ Lake Powell Fisheries Investigations 1982 (Segment 11) Annual Report for Colorado River Drainage and Tailwaters Dingell-Johnson Project F-28-R Publication Number 83-9 LAKE POWELL FISHERIES INVESTIGATIONS . Annual Performance Report January 1982 - December 1982 A. Wayne Gustaveson, Project Leader Thomas D. Pettengill, Project Biologist Steven J. Scott, Project Biologist James E. Johnson, Fisheries Program Coordinator Publication No. 83-9 Dingell-Johnson Project F- 28-R-ll Utah Department of Natural Resources DIVISION OF WILDLIFE RESOURCES 1596 West North Temple Salt Lake City, Utah 84116 An Equal Opportunity Employer Douglas F. Day Director ABSTRACT Threadfin shad, the major forage species in Lake Powell, declined to the lowest levels since sampling began in 1977. Recruitment was minimal lakewide. Striped bass predation was undoubtedly a contributing factor to the low shad numbers. Angling pressure increased 23% over 1981, indicating more anglers fished at Lake Powell in 1982 than in any other year. The overall catch rate declined slightly from 1981. Black crappie and largemouth bass were creeled most often but walleye and striped bass both reached record harvest levels. Striped bass catch rates averaged .05 fish/angler hour from April through Oc tober. Gill netting during March to monitor game fish population trends showed both walleye and largemouth numbers were down from 1981 figures. This decrease may reflect a late cold spring more than an actual decrease in the number of bass and walleye. Striped bass were caught at all spring netting sites for the first time. Electrofishing surveys indicated crappie were produced at about the same level as 1981 but largemouth bass production was up at all sampling locations . Striped bass successfully spawned for the fourth consecutive year . The 1982 year c l ass was smaller than the dominant 1981 year class. The 1982 striped bass year class was similar to that of 1980 and may represent a more normal spawn . -ii- T ABLE OF CONTENTS LIST OF TABLES • LIST OF FIGURES JOB NUMBER I. THREADFIN SHAD STUDY Methods • • • • • Results and Discussion Recommendations • • • • II . MEASUREMENT OF FISHERY HARVEST, PRESSURE AND SUCCESS Methods • . . . . . Results and Di scussion Recommendations • • • • III. INDEX TO ANNUAL FISH POPULATION TRENDS Annual Netting Methods • • • Results and Discussion Recommendat i ons Elec trof ishi ng Methods • • • Results and Discussion Recommendations • • • • - 111- v vii 1 1 1 7 9 9 9 17 19 19 19 19 22 22 22 24 27 TABLE OF CONTENTS (Continued) JOB NUMBER IV. MONITORING OF STRIPED BASS POPULATION DEVELOPMENT Methods • . . . • • • Striped Bass Spawning Annual Fall Gill Netting Food Habits •• Body Condition Recommendations REFERENCES CITED • • • • • • -iv- Page 29 29 29 31 31 34 37 39 Table LIST OF TABLES 1. Mean number of y- o-y shad collected in meter net tows in Wabweap Bay during 1981 and 1982 •• • ••• • • 2. Mean number of y-o-y shad collected in meter net tows in Bullfrog Bay during 1981 and 1982 • • • •••• • 3. Mean number of y-o-y shad collected in meter net tows in Good Rope Bay during 1981 and 1982 • • • • • • 4. Mean number of y-o-y shad collected in trawl tows in Wahweap Bay during 1981 and 1982 ••••••• 5. Mean number of y-o-y shad collected in trawl tows in the San Juan Arm during 1981 and 1982 • •••• 6. Mean number of y-o-y shad collected in trawl tows in Bullfrog Bay during 1981 and 1982 • • • • • • • • 7. Mean number of y-o-y shad collected in trawl tows in Good Rope Bay during 1981 and 1982 . . . . 8. Species sought (% ) by anglers, Lake Powell, April- June 1982 . . . . . . . . . . . . . . . . 9. Species sought (%) by anglers, Lake Powell, July- October 1982 • •• • •• • •• 10. Sport fishery creel rates (fish/angler hour) by species and access area, Lake Powell, April-october 1982 ..•... • . . . . . . • • • • 11. Species composition (%) of the total recorded creel for anglers interviewed at Bullfrog, Hall's Crossing, and Rite, April-October 1982 • • • • • • •••• - v- 3 3 5 5 5 6 6 12 12 14 15 Table 12. LIST OF TABLES (Continued) Species composition (%) for anglers interviewed 1982 • • . • • . . • • of the total recorded creel at Wahweap, April-October 13 . Catch rate (fish/net day) during annual gill netting, Lake Powell, March 1982 14. Percent of total sample occurring in each category of the visceral fat index for walleye collected by gill netting during March 1982 , Lake Powell . . . . . . . . . . . . . . . 15. Percent of total sample occurring in each category of the visceral fat index for largemouth bass collected by gill netting during March 1982, Lake Powell • • • • • • • • • • • • • • • • • 16. Mean catch rate (fish/hour) of fish collected by electrofishing, Lake Powell, September 1982 17 . Striped bass caught per 1,000 square feet of gill net per 12 hour set during fall sampling on Lake Powell compared to similar netting results obtained in 1981 18 . Average total length of young-of-the-year bass collected during annual fall netting and 1982 on Lake Powell • • • • • • • • • striped in 1981 19. Seasonal occurrence of food items in striped bass stomachs collected during 1982. Percent occurrence of food items based on number of stomachs containing 20. food Condition factors · of yearling taken during annual fall gill Lake Powell • • • • • • • • • -vi- and adult striped bass netting, November 1982, Page 15 20 23 23 25 32 32 33 35 LIST OF FIGURES Figure 1. Map of Lake Powell showing trawling locations, annual netting sites and electrofishing stations • • • • • 2. Indices of total recreational boat use and angling pressure, 1965-1982, Lake Powell •••••• 3. Catch rates (fish/angler hour) for largemouth bass, black crappie and all species during the months of April-June 1965-1982, Lake Powell • • • • • • • • • 4. Catch rates (fish/net day) for walleye and largemouth bass from annual netting, 1971-1982, Lake Powell 5. Mean number of young-of-the-year largemouth bass and black crappie collected/hour of electrofishing during August-September, 1978-1982, Lake Powell •••••• -vi i- 2 10 13 21 26 Methods THREADFIN SHAD STUDY JOB I Threadfin shad (Dorosoma petenense) spawning was monitored with meter net collections. Monthly meter net samples were taken in side canyons or the backs of bays near each trawling location. The standard meter net tow was 2 minutes in length with the net towed just under the surface. Four tows were made at each station. Monthly mid-water trawl collections were taken from July through September in Wahweap, Bullfrog, Good Hope and the San Juan (Figure 1). Sampling methods used were reported in Gustaveson et al. 1980. Shad were divided into one of three life history stages; larvae « 25 mm), juveniles (26-50 mm), and adults ( > 50 mm). Results and Discussion Meter netting began in late May and continued until mid-August when shad spawni ng ended. Threadfin shad spawning success varied from an increase from that of 1981 in the upper end of the reservoir to almost zero at Wahweap. No young-of-the-year (y-o-y) shad were collected in meter net tows in Wahweap Bay (Table 1) or on the lower end of the San Juan Arm. Meter netting in Bullfrog Bay revealed an extended spawning season from late May through mid-August 1982 (Table 2). However, only -1- ~ ! M i ~ s I i o 5 m • E le ct ro fi sh in g S ta ti o n o An n u al N et ti n g S it e T T ra w lin g S ta ti o n G o o d H o p e B ay F ig u re 1 . M ap o f L ak e P o w el l sh ow in g tr a w li n g lo c a ti o n s, an n u al n e tt in g s it e s an d e le c tr o f is h in g s ta ti o n s . I N I -3- Table 1. Mean number of y-o-y shad collected in meter net tows in Wahweap Bay during 1981 and 1982. Sample Date May 27 June 11 June 16 July 23 August 12 August 21 Ta b1e 2. Sample Date June 1 June 9 June 17 June 24 July 2 July 8 July 14 July 20 July 27 August 3 August 12 1981 Mean number of shad per tow o 14 2 66 1 1 Sample Date June 15 June 23 July 2 July 9 1982 Mean number of shad per tow o o o o Mean number of y-o-y shad collected in meter net tows in Bullfrog Bay during 1981 and 1982. 1981 1982 Mean number Mean number of shad Sample of shad per tow Date per tow 41 May 28 187 317 June 11 389 221 June 25 49 586 July 1 26 110 July 9 41 4 July 14 5 19 July 21 1 113 July 27 0 11 August 10 3 3 1 -4- two weeks during that period produced meter net catches averaging over 100 y-o-y shad/tow. By comparison, in 1981 there were five weeks when over 100 y-o-y shad were collected per tow. Limited meter netting in Good Hope Bay indicated shad production was up in 1982 (Table 3). Mid-water trawl catches of y- o-y shad were at the lowest levels since 1akewide trawling began in 1977. In the lower half of Lake Powell trawling results reflected meter net catches. At Wahweap no y-o-y shad were collected in meter net tows and none were caught in trawl tows with the exception of August sampling when an aver.age of one fish/tow was collected (Table 4). Trawling on the San Juan indicated very little shad recruitment (Table 5) . Bullfrog Bay had an extended spawn but recrui t- ment was low (Table 6). Meter netting in the upper end of Lake Powell showed increased spawning success in the canyons but recruitment into the open water trawling sites was severely limited (Table 7) . Moczygemba and Morris (1977) reported that the open water zone is inhabited by surplus shad that are forced into open water by competition. Lack of shad i n the open water area is an indication of a predation impacted shad population . The disparity between meter net and trawl catches probably re sulted from striped bass predation. Members of the unusually large 1981 year class of striped bass were present in most locations where shad spawning occurred . Unlike the adult striped bass that had to retreat to deeper, cooler water during the heat of the summer (Job IV), the yearlings stayed in the shallows with the shad and fed heavily on both adults and y-o- y shad. -5- Table 3. Mean number of y-o-y shad collected in meter net tows in Good Hope Bay during 1981 and 1982. Sample Month June July Red Canyon 1981 1982 102 o 378 o Ticaboo Canyon 1981 1982 7 o 1,420 o Table 4. Mean number of y-o-y shad collected in trawl tows in Wahweap Bay during 1981 and 1982. Sample Mean number of shad per tow Month 1981 1982 June 0 0 July 170 0 August 68 1 September 3 0 Table 5. Mean number of y-o-y shad collected in trawl tows in the San Juan Arm during 1981 and 1982 . Sample Mean number of shad eer tow Month 1981 1982 June 238 0 July 105 1 August 67 16 September 33 1 -6- Table 6. Mean number of y-o-y shad collected in trawl tows in Bullfrog Bay during 1981 and 1982. Sample Mean number of shad Eer tow Month 1981 1982 June 55 0 July 971 1 August 224 II September 92 0 Table 7. Mean number of y-o-y shad collected in trawl tows in Good Hope Bay during 1981 and 1982. Sample Mean number of shad 2er tow Month 1981 1982 June 1,511 0 July 426 4 August ll8 8 September 38 0 -7- In Lake E. V. Spence striped bass reduced the standing crop of gizzard shad and eliminated threadfin shad from the population (Morris 1978). Young gizzard shad that escaped predation grew rapidly, and after exceeding the desired forage size preferred by striped bass (76-178 mm), they matured and spawned. Threadfin shad because of their smaller size did not grow larger than preferred prey size and were eliminated . Threadfin shad are the only schooling bait fish in Lake Powell and they support the striped bass population. Not only was shad recruitment reduced, shad population levels were at the lowest point since sampling began in 1977. Recommendations Continue meter netting and trawling. The meter netting has proven important in monitoring larval shad production and the duration of the spawn. Discontinue the June trawling . Most years the y-o-y shad have not moved from the canyons out to the trawling sites until July . Discontinue meter netting and trawling on the San Juan. No larval shad have been collected in two years of meter netting on the San Juan. The trawling results have not contributed anything unique to the understanding of the shad population of the lake and only reflect the findings at Wahweap, Bullfrog, and Good Hope Bays. Start biweekly meter netting at Good Hope Bay. Good Hope Bay is an important station in our shad studies and monthly meter netting the last two years has been insufficient to fully assess shad spawning in the upper reservoir. This is an area which will see increased striped bass predation in the years to come. Methods MEASUREMENT OF FISHERY HARVEST, PRESSURE AND SUCCESS JOB II A scheduled creel census was conducted from April through October 1982, at the four major access areas on the lake - Wahweap, Bullfrog, Hall's Crossing and Hite. Anglers were interviewed as they returned to launching ramps. Catch rates (fish/angler hour) were estimated from data reported by anglers for their previous day of fishing, as well as for the census day. Estimates of angling pressure were based on recreational use data collected by National Park Service personnel at access point s. Results and Discussion A total of 4,944 boating parties was checked by creel clerks during the seven month census period. Of these, 1,945 (39%) reported angling activi ty. The mean number of anglers per fishing boat was 2.5 while each angler spent an average of 3.9 hours fishing per day. While recreational boat use decreased on Lake Powell during 1982, angling pressure continued to increase (Figure 2). Proportionally more boats reported angling activity than in 1981 at all access points except at Rite. The index of angling pressure was 110,556 fishing boat days, an increase of 23% over 1981. The index of total recreational boat use -9- In >- tV 0 .... tV 0 III (J) Il . z 0- 0 In 't I C tV In ~ 0 .J: : I- 3 2 0 2 8 0 2 4 0 2 0 0 1 6 0 1 2 0 8 0 4 0 - - - T o ta l B o a t D a y s - - - F is h in g B o a 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 82 Y e a r F ig u re 2 . In d ic e s o f to ta l re c re a ti o n a l b o at u se an d an g li n g p re ss u re , 1 9 6 5 -1 9 8 2 , L ak e P o w el l. I ..... ? - - - - ~ = = 1111 - 11- (including nonfishing boats) was 278,838 boat days, compared to 290,689 boat days in 1981. As in 1981, the Bullfrog access area accounted for the highest angler use of the four major access points, while Hall's Crossing, Wahweap, and Hite accounted for 29%, 24% and 10% of angler use respectively . Most angling pressure during the spring (April- June) was directed at largemouth bass (Micropterus salmoides) and black crappie (Pomoxis nigromaculatus) , except for Wahweap where striped bass (Morone saxatilis) was the most sought after species (Table 8). During the summer and early fall (July-Oc tober), striped bass gained considerable importance at Bullfrog and interest in striped bass remained high at Wahweap (Table 9) . Creel rates (fish/angler hour) for largemouth bass (0.093), black crappie (0 . 091) and all species combined (0.283) were down slightly from 1981 (Figure 3) . The best fishing for largemouth bass and black crappie in 1982 was in the upper reservoir (Rite), while striped bass fishing was better on the lower end of the reservoir (Wahweap) (Table 10). Those fishing for walleye had highest success in the middle of the reservoir (Bullfrog and Hall's Crossing) . The bulk of the fishery in the upper reservoir was supported by largemouth bass (Table 11). Crappie contributed a large portion of the fishery in the spring and fall, while walleye were important only in June and July . The fishery in the lower reservoir was dominated by striped bass (Table 12 ); largemouth, crappie and walleye were important here only in the spring. -12- Table 8. Species sought (%) by anglers, Lake Powell, April- June 1982 . Species Wahweap Bullfrog Hall's Rite Total Any 11.5 18. 2 20.2 15.0 16 . 2 Largemouth bass 29.4 50. 3 44. 1 51.3 43 . 8 Black crappie 7.4 18.8 13 . 6 31.3 17. 8 Striped bass 42.8 6.2 8. 4 1. 2 14 . 7 Walleye 7.6 6. 2 12. 3 0. 8 6.7 Channel catfish 1.0 0 . 3 1.3 0 . 4 0 . 7 Rainbow trout 0.2 0. 0 0. 0 0. 0 0 . 1 Bluegill 0.2 0 . 0 0.0 0 . 0 0.1 Table 9. Species sought (%) by anglers, Lake Powell, July- October 1982. Species Wahweap Bullfrog Hall's Rite Total Any 11.6 30.1 41.3 29.2 28.0 Largemouth bass 13.9 25 . 2 31. 5 46.2 29. 2 Black crappie 0.7 1.2 1.1 4 . 1 1.8 Striped bass 66 . 9 34.6 18.5 7.6 31. 9 Walleye 2.4 5.7 4 . 3 4.7 4.3 Channel catfish 4.5 3. 3 2. 2 8.2 4.5 Rainbow trout 0.0 0.0 0.0 0.0 0. 0 Bluegill 0.0 0.0 1.1 0.0 0.3 ~ ::J 0 :r ~ G I O l c - <'II Q -CD Z -.. .t:. III u.. 5 4 3 2 1 6 5 4 3 2 1 -21- Walleye /.---., ,I • • 1\ I' , I' \ .. , /' ., /' , /' , , , ~ \ I' • / "\. ,I r·.....i ':.~ ,I .......... ,/ / '." • 71 72 73 74 75 76 77 78 79 80 81 82 Year • • Largemouth Bass ."/.,, . . ....... .--. \. 71 72 7 3 74 7 5 7 6 7 7 7 8 7 9 8 0 8 1 82 Ye a r Figure 4. Catch rates (fish/net day) for walleye and largemouth bass from annual netting, 1971-1982, Lake Powell. year class. collections . - 22- Other species collected showed no major changes from past Vi sceral fat index values indicated that walleye collected were in good to excellent condition- (Table 14). The previous trend of slightly lower VFI values for walleye captured in the lower reservoir continued to exist in 1982. Largemouth bass were in fair condition and showed no major differences in fat index between lake areas (Table 15). Recommendations Continue the annual netting program during the month of March for fish population trend data . Evaluate specific net sites so that net locations (habitat type and depth) remain as consistent as possible between all lake areas . Monitor fish condition at the time of annual netting with the visceral fat index . Electrofishing Methods Electrofishing procedures were similar to those described by Gustaveson e t aL 1980, with the exception of a new electroshocking unit. The Coffelt Model RF-IO was replaced with a Coffelt Model VVP-15 d .c. pulsator . The output to the positive array was 12-15 a. and 220- 240 v . d . c., with a pulse rate of 80 per second. Sampling stations were similar to t hose in 1981 with one exception. Hall's Creek Bay was replaced by a transect in Warm Creek Bay to monitor the smallmouth bass introduction program. Five stations were sampled for one night each, approximately one hour of electrofishing per station. The index of 11' -23- Table 14. Percent of total sample occurring in each category of the visceral fat indexa for walleye collected by gill netting during March 1982, Lake Powell. Visceral Fat Index Cate~ory Location 0 1 2 3 4 Good Hope Bay 0 8 16 48 28 (n = Rincon 0 9 20 58 13 (n = San Juan 0 11 33 39 17 (n = Padre Bay 1 33 44 19 3 (n = aInternal body fat present: o - None. 1 - Little, less than 50% of each caecum is covered. 2 - Approximately 50% of the caecum is covered. 3 - More than 50% of each caecum is covered. 4 - Pyloric caeca are completely covered with fat. Table 15. Percent of total sample occurring in each category of the visceral fat index for largemouth bass collected by gill netting during March 1982, Lake Powell. Visceral Fat Index Categorl Location 0 1 2 3 4 Good Hope Bay 5 73 22 0 0 (n = Rincon 0 46 46 8 0 (n = San Juan Arm 7 64 29 0 0 (n = Padre Bay 14 72 14 0 0 (n 50) 55) 18) 79) 22) 24) 14) 7) -24- abundance for the species collected at each location was mean catch rate (fish/hour of electrofishing) for each night of sampling . Results and Discussion A total of 1,419 fish was collected during the 5 nights of electro- fishing. Mean catch rates for all specJes were highest at Stanton Creek, followed by Good Hope Bay, Warm Creek, Rincon and San Juan (Table 16). All stations showed little deviation from last year's catch rate for all species except Good Hope Bay where the catch rate nearly doubled. This was primarily due to the increased catch of y-o-y largemouth bass. While bluegill (Lepomis macrochirus) and green sunfish (Lepomis cyanellus) accounted for a large portion (83%) of the tot al catch in 1981, these two species accounted for only 36% in 1982 . Young- of-the-year l argemouth bass comprised over 51% of the total catch, a considerable increase over 1981 (6 . 3%) . While largemouth bass had high catch rates, comparable with 1980, those of black crappie remained low (Figure 5). The high catch rate of y-o- y largemouth bass suggests a strong 1982 year class and should dampen the effect the low 1981 production might have on the future sport fishery harvest . Striped bass made up 1. 2% of the total catch and occurred most frequently at the Good Hope Bay station. This represents a slight decrease from 1981 (5.4%) and suggests a smaller year class in 1982. A limited number of adult threadf in shad were encountered at all stations , but were not quantitatively sampled . -25- Table 16. Mean catch ratea (fish/hour) of fish collected by electro- fishing, Lake Powell, September 1982. Good % of Hope Stanton San Warm Total Species Bay Creek Rincon Juan Creek Catch Young-of-the-year largemouth bass 228 194 151 29 165 51.1 Age I and older largemouth bass 11 24 2 5 4 3.1 Young-of-the-year black crappie 4 34 13 3 10 4.3 Young-of-the-year striped bass 16 0 2 0 0 1.2 Channel catfish 30 5 0 2 6 2.9 Green sunfish 30 100 39 153 13 22.3 Bluegill 37 101 22 33 13 13.7 Young-of-the-year smallmouth bass 0 0 0 0 22 1.5 All speciesa 356 458 229 225 233 aTotal fish divided by total hours of electrofishing. 300 ~200 0 :: II: w a. :z: en ~ 100 300 ~ 200 0 :: II: w a. :z: en ~ 100 -26- • ___ _ • Y- O - y BLACK CRAPPIE _____ y - O- y LARGEMOUTH BASS RINCON • " I I I • I I I I .~. , • 78 79 80 • "\ ,," \ STANTON CREEK " . \ // /\ / '-1- / / / I --. • 78 79 80 • ~i _____ • i i 81 82 • ~ \ -. \ ___ -e \ --.- 81 82 Figure 5. Mean number of young-of - the-year largemouth bass and black crappie collected/hour of e1ectrofishing during August- September, 1978-1982, Lake Powell. ~ • -27- Recommendations Continue annual electrofishing during August-September 1983 . Main- tain 1982 sampling stations, which coincided with the spring annual netting sites. Conduct electrofishing in the spring , during black crappie spawning , to explore possibilities of obtaining more information on spawning habitat and size of spawning population. Methods MONITORING OF STRIPED BASS POPULATION DEVELOPMENT JOB IV Biological data were obtained from striped bass taken in gill nets, by angling, elec trofishing and during regular creel census interviews. Data necessary to determine age and growth, food habits, stage of maturity, and condition factor (based on fork length) were routinely taken from all fish sampled. Duri ng November, an annual survey of striped bass abundance was conducted by fishing 10 experimental gill nets for 42 consecutive hours (two nights and one day) at each of four previously established stations. Nets were set in similar habitat at each station. Experimental gill nets were 30 . 5 m long by 1.8 m deep, with four panels of 1.9, 2.5, 3.8 and 5.1 cm square mesh. Catch was quantified by striped bass caught per 1000 square feet of gill net per 12 hour set. This enumeration is a standard method developed by the AFS Striped Bass Committee (McCloskey 1980) . Striped Bass Spawning Mature adult striped bass were found congregated in the Colorado River near Gypsum Canyon, and in Wahweap and Warm Creek Bays near Glen Canyon Dam. Striped bass tend to congregate in large schools near preferred spawning areas apparently awaiting environmental conditions -29- - 30- that trigger spawning . These · staging areas· a t Lake Powell were occupied for at least one month prior to spawning during 1982. The staging areas were in the same locations that had been used in previous years. Evidence of spawning, usually in the form of dead floating eggs, was usually found near a staging area, indicating the fish probably di d not move long distances between staging and spawning. was delayed somewhat by unseasonably cold spring Spawning in 1982 temperatures . The first ripe males were collected on 25 April 1982 near the dam . The first spent female was collected mid-lake on 15 May 1982. The spawning peak was during the last two weeks of May in 1982, compared to the first two weeks in previous years . Spawning apparently occurred in the Colorado River above Lake Powell . The mouth of the San Juan River , on the other hand, was guarded by a silt barrier that had been deposited by the river during seasonal lake level fluctuations. Striped bass were therefore not ascending the San Juan River for spawning purposes . Subsequent collection of y-o-y striped bass in the San Juan Arm indicated that spawning had occurred during 1982, probably in the reservoired portion of the San Juan. Striped bass were observed spawning in Warm Creek Bay, near Glen Canyon Dam, on 22 May 1982. Confirmed angler reports indicated spawning occurred from 2230 hours until dawn on 23 May 1982 . Dead striped bass eggs were observed on the water surface for approximately one week following spawning. In-reservoir reproduction also may have occurred in many other canyons, as evidenced by collection of y-o-y striped bass throughout the - 31 - length of the reservoir (see fall netting results). It has been previously shown that the overflow density current cannot distribute y-o-y from the tributaries throughout the expanse of the entire reservoir (Gustaveson et al. 1982) . Annual Fall Gill Netting Gill netting results during November 1982 confirmed that y-o-y striped bass production was well below the record year class spawned in 1981. The 1981 year class was well represented at all four stations sampled, while y-o-y were found at abundance levels similar to those of 1980 (Table 17). A slight drop in catch/unit effort at Wahweap corresponded with an increase of yearling striped bass caught at the San Juan station, indicating some migration from the southern end of the reservoir may have occurred . The total number of striped bass caught was essentially the same in 1981 and 1982 . The bulk of the catch was yearlings in 1982 instead of y- o-y, indicating an increase in total striped bass biomass. The delayed spawn, the large 1981 year class and intense competition for the small shad crop may explain the inhibited growth of the 1982 striped bass year class . Average total length of 1982 y- o-y was 40 . 8 mm shorter than the average total length of y- o- y caught in 1981 (Table 18) . Food Habits Investigation of striped bass food habits (Table 19) showed marked changes from the 1980 food habits survey (Gustaveson et a1. 1981) . The number of empty stomachs doubled from 24% in 1980 to 56% in 1982. Threadfin shad were still the most frequently occurring food item but -32- Table 17. Striped bass caught per 1,000 square feet of gill net per 12 hour seta during fall sampling on Lake Powell compared to similar netting results obtained in 1981. 1981 1982 Location y-o-y 1+ All SB Y-O-Y 1+ All SB Good Hope 4.11 0.58 4.95 0.47 4.91 6. 81 Rincon 0.58 0.26 1.74 0. 14 0.52 0.76 San Juan 0.31 0.05 0 . 79 1.00 1.52 2.71 Wahweap 6.53 0.63 7.84 0.14 3.24 4.00 Average 2.88 0.38 3 . 83 0.45 2.55 3.57 aStandard method after McCloskey, 1980. Table 18. Average total length of young-of-the-year striped bass col- lected during annual fall netting in 1981 and 1982 on Lake Powell. 1981 1982 Location Mean Total Length (n) Mean Total Length (n) Good Hope 288.16 (77) 208.60 (10) Rincon 239.27 (11) 247 . 00 (3) San Juan 202 . 67 ( 6) 179. 81 ( 21) Wahweap 199.78 (124) 170. 30 (3) Average 233.07 192. 27 -33- Table 19. Seasonal occurrence of food items in striped bass stomachs collected during 1982. Percent occurrence of food items based on number of stomachs containing food. Spring Summer Fall Mar-May June-Aug Sep- Nov Sample size 42 41 73 Empty stomachs 22 19 46 Food Item Fish Threadfin shad 35 18 33 Carp 10 4 Red shiner 4 Unidentified 11 Bait Anchovy 5 45 26 Waterdog 5 Crayfish 15 27 15 Debris 5 14 Zooplankton 30 5 19 - 34- low shad availability apparently caused the s t riped bass to utilize food items such as crayfish, carp, and plankton. Lake Powell carp are a pelagic schooling fish, due to the reservoir's relative sc arcity of littoral zone and may , therefore, be more available to striped bass than they would be in many other waters. No game fish were observed in the 156 stomachs examined in 1982. Even though forage was limited, no evidence was found that striped bass utilized shore bound game fish a s a food item. The effectiveness of dead anchovies as a bait was documented by the occurrence of the bait fish in 45% of the stomachs during the summer months. This is obviously an overestimate of anchovy ingestion, caused by the collection of stomachs from angler caught striped bass. Striped bass continued to be very selective in their food requirements . If the sought after food item was not available, striped bass went without eating instead of turning to a new unfamiliar forage item. Body Condition Following spawning, striped bass usually begin regaining weight lost to spawni ng ac t i vity • During 1982 it became apparent that shad forage was low (Job I) and adult striped bass were not rebuilding body mass, but declining in body condition t hroughout the summer. By November adult striped bass in the southern half of the reservoir had an average condition factor (K factor) of less than 1.0 (Table 20), while yearling fish still exhibited a normal K factor of near 1. 3 (Table 20). The difference in K factor between adults and subadu1ts can be ex plained by thermal preference. Subadult striped bass seek water that is 20-24 C, but they can utilize warmer water. As they grow and mature they prefer -35- Table 20 . Condition factors of yearling and adult striped bass taken during annual fall gill netting, November 1982, Lake Powell. Location Yearling K factor (n) Adult K factor (n) Good Hope 1.43 (30) 1. 25 (11) San Juan 1.31 (10) 0.85 ( 5) Rincon 1. 29 (9) 1. 07 (3) Wahweap 1.10 (10) 0 . 89 ( 9) water that is 16-20 C (Schaich 1979). Adult striped bass avoid water warmer than 25 C (Schaich 1979) and were repeatedly caught by anglers and charted by sonar at depths near or below the metalimnion in the summer months . This change in temperature preference serves to separate year classes and reduce competition. Lake Powell is a warmwater impoundment typified by a high degree of thermal stratification. Stratification is greatly affected by the amount of spring overflow density current. Years with a large spring flood are characterized by a deeper , more diffused metalimnion than years when runoff is low (Merritt and Johnson 1977) . The epilimnion is wedge shaped, being thicker near the inflow than at the dam (Johnson and Merritt 1979). The cooler water of the metalimnion which adult striped bass prefer is often at depths of 15- 30 m. As Lake Powell's stratification intensifies during the summer a distinct oxygen minimum layer develops in the upper reaches of the metalimnion . The oxygen depletion is probably the result of organic -36- matter collecting on the denser water of the metalimnion and being oxidized at that point (Johnson and Merritt 1979) . Threadfin shad typically inhabit the epilimnion in a stratified reservoir. Following the establishment of the striped bass population in Lake Powell, shad also sought the security of turbid water near shore and shunned the formerly safe, pelagic sanctuary they occupied when only shorebound predators adult striped bass existed. Consequently, and threadfin shad has a thermal separation of occurred annually . The vertical separation may be as much as 30 m depending on the width of the epilimnion and lake location. The boundary between the predator and prey was fenced by the oxygen depletion zone. An additional, horizontal, separation occurred in some cases when shad occupied the shallow, turbid water at the back of a long, gradually deepening canyon. It has been reported that a separation of "a few meters" was enough to prevent striped bass from foraging on shad in Cherokee Reservoir, TN during a severe low oxygen-high temperature situation (Schaich 1979). Adult striped bass do eat shad in the summertime despite the thermal separation. To do so they must leave their preferred temperature zone, cross the oxygen depletion layer, quickly forage in the warm water layer, and then retrace their path. The warm water layer was thick and shad numbers were low in 1982. Striped bass probably expended more energy foraging than they gained from shad consumption. The result was a general decline in body condition. As condition declined, the ability to effectively perform the exhaustive foraging journey diminished. A decline in condition can also cause the fish to seek even cooler water - 37- where less energy is required for body maintenance (Schaich 1979) , resulting in a wider separation of predator and prey . Subadult striped bass were able to live in the same temperature zone (20-28 C) as the shad . The large striped bass year class produced in 1981 was never separated from the 1982 shad forage crop. Predation by these yearling striped bass probably contributed to the paucity of shad recruiting to the adult population in 1982. Body condition of these yearlings remained high (Table 20) although growth was slower than found in 1981 (Table 18). Recommendations 1. Monitor the spawning population to determine overwinter survival, gonadal development, and possible impact of poor body condition on fecundity in 1983 . 2. Determine mechanism responsible for in- reservoir reproduction in Lake Powell . To successfully complete this objective a spawning school must be found and the eggs followed until hatching occurs. 3 . Quantify spawning success and recruitment with the fall gill net survey . Discontinue seining as an index of striped bass a bundance because of limitations created by Lake Powell's steep rocky shoreline habitat . 4 . Continue tagging striped bass to determine long range movement and distribution throughout the reservoir . Tag fish taken by different angling techniques to determine survivability of fish under catch and release conditions . REFERENCES CITED Gustaveson, A. W., T. D. Pettengill, M. J. Ottenbacher, and J. E. Johnson. 1980. Lake Powell fisheries investigations. 5-year Completion and 1979 Annual Performance Report. Federal Aid in Fish Restoration F-28-R-8. Publication Number 80-11. Salt Lake City, UT: Division of Wildlife Resources. 75 pp. Gustaveson, A. W., T. D. Pettengill, M. J. Ottenbacher, and J. E. Johnson. 1981. Lake Powell fisheries investigation. 1980 (Segment 9) Annual Report for Colorado River Drainage and Tailwaters Dingell-Johnson Project F-28-R. Publication Number 81-9. Salt Lake City, UT: Division of Wildlife Resources. 35 pp. Gustaveson, A. W., T. D. Pettengill, J. R. Wahl, and J. E. Johnson. 1982. Lake Powell fisheries investigation. 1981 (Segment 10) Annual Report for Colorado River Drainage and Tailwaters Dingell-Johnson Project F-28-R. Publication Number 82-6. Salt Lake City, UT: Division of Wildlife Resources. 41 pp. Johnson, N. M. and D. H. Merritt. 1979. Convective and advective circulations on Lake Powell, Utah-Arizona, during 1972-1975. Water Resources Research 15: 873-884. McCloskey, K. 1980. Striped bass investigations. Federal Aid in Fish Restoration F-15-R-12-l5. Study No. 050. Pratt, KS: Fish and Game Commission. 74 pp. Merritt, D. H. and N. M. Johnson. 1977. Advective circulation in Lake Powell, Utah-Arizona. Lake Powell research project bulletin number 61. Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire. 72 pp. Moczygemba, J. H. and D. J. Morris. 1977. Statewide striped bass study, Texas Parks & Wildlife Department. Federal Aid Project F-31-R-3. Final Report. 30 pp. Morris, D. J. and B. J. Follis. 1978. Effects of striped bass preda- tion upon shad in Lake E. V. Spence, Texas. Proceedings, Annual Conference of the Southeast Association of Fish and Wildlife Agencies. 32: 697-702. -39- - 40- Schaich , B. A. 1979. A biotelemetry study of spring and summer habitat selection by striped bass in Cherokee Reservoi r, Tennessee , 1978 . M. S . Thesis. University of Tennessee, Knoxville , Tennessee . 206 pp . Archives Number P830l78 APpropriations Number 015926 The Utah Division of Wildlife I1esources receives federal aid funds . Under Title IV of the 1964 Civil Rights Act, The O. S. Department of the Interior prohibits dlscrl.tnatlon on the basia of race, color, or national origin. If you believe that you have been discriminated against in any program, activity or facility , or If you desire further infamation regarding Title VI, please write to 'ft1e Office for Equal Opportunity, U.S . Department of .the- Interior, Office of the Secretary, Washington, D. C. 20040 .
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