ML050100191
| ML050100191 | |
| Person / Time | |
|---|---|
| Site: | North Anna, 05200008  |
| Issue date: | 04/30/2004 |
| From: | Dominion Nuclear North Anna |
| To: | Office of New Reactors |
| References | |
| +reviewedmls | |
| Download: ML050100191 (61) | |
Text
ENVIRONMENTAL STUDY OF LAKE ANNA AND THE LOWER NORTH ANNA RIVER ANNUAL REPORT FOR 2001 Prepared by:
ENVIRONMENTAL BIOLOGY ELECTRIC ENVIRONMENTAL SERVICES In an effort to conserve our natural resources, this report is being printed on both sides of recycled paper.
TABLE OF CONTENTS PAGE Executive Summary...................................................................................................u...ii List of Figures ............. iv List of Tables ........... . . ...
1.0 Introduction ........... I 2.0 Station Operation ........... . . .... 2 3.0 Lake Anna .... 4 3.1 Temperature ........ .... 4 3.2 Fish Population Studies - Gill Netting Results ............................... 13 3.3 Fish Population Studies Electrofishing Results ................................ 19 3.4 Aquatic Vegetation ............................... 28 3.5 Conclusions ............................... 29 3.6 Recommendations ............................... 30 4.0 North Anna River ........... 31 4.1 Temperature ....... 31 4.2 River Flow ....... 33 4.3 Fish Population Studies -Electrofishing ..............................;;.35 4.4 Fish Population Studies - Direct Observations . 41 4.5 Conclusions ...... 49 5.0 Literature Cited ......... 52 i
Executive Summari Following the successful completion of the North Anna Power Station 316(a) Demonstration in 1986, Dominion (the Company) agreed to continue selected environmental monitoring studies on Lake Anna and the North Anna River. Correspondent with the recommendations in the three-year review of post-316(a) studies for 1989-1991, the Company requested and was granted a reduction in certain of the monitoring programs by the Department of Environmental Quality (DEQ). The revised annual study program was to be continued with a review every three years for possible revisions or changes. This report represents findings from monitoring programs conducted during 2001, the first year of the three year study period 2001 through 2003.
Station generation for 2001 was again outstanding with levels comparable to 1990 and 1991.
Water temperature data for 2001 both in the lake and downstream were similar to historical data.
A record number of fish was collected by electrofishing in 2001, hypothesized to be due primarily to a dramatic drop in lake levels during the fourth quarter sampling. This lake level drop in 2001, as in 1998, concentrated bluegill sunfish Lepomis macrochirus at several sample sites resulting in the relatively large numbers of fish collected during that period. The sampling for the first three quarters of 2001 occurred at or near normal lake level. Gill netting numbers in 2001 were higher than in 2000 but similar to historical data. In 2001, Lake Anna anglers reported 50 citation largemouth bass Micropterus salmoides (greater than 55.9 cm in length or 36 kg in weight) ranking Lake Anna as the second best trophy bass lake in the state. The 2001 hydrilla Hydriula verticillata survey was not conducted due to air space restriction because of the September 11, 2001 incident as well as low lake levels.
In the lower North Anna River below North Anna dam the total number of fish collected by electrofishing in 2001 was greater than the 2000 catch with increases at all four stations. Also, ii
underwater observations of largemouth bass and smallmouth bass in 2001 continued to indicate that largemouth bass are more abundant in the upper reaches of the river below Lake Anna and smallmouth bass more abundant in the lower reaches.
In summary, the 2001 data indicate that both the lake and river downstream of the lake support a diverse and healthy fishery.
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List of Figures Figure Number Title Pare 3.1-1 Approximate location of fixed Endeco and Onset temperature recorders in Lake Anna and WHTF ...................................... 4 3.1-2 Approximate location of thermal plume sampling Stations on Lake Anna............... 8 3.2-1 Location of gill netting stations on Lake Anna and WHTF ...................................................................................................... 13 3.2-2 Gill net data (1990-2001) average number and average weight (kg) .......................... 17 3.3-2 Lake level for Lake Anna measured in feet above sea level for 2001 .............. 22 3.3-3 Lake Anna electrofish data (1990-2001) average number and average weight (kg) .......................... 24 3.3-4 Composition of largemouth bass catch in Lake Anna and WHTF (1999-2001) ............ 27 3.3-5 Composition of bluegill catch in Lake Anna and WHTF (1999-2001) ............... 28 4.1-1 Location of North Anna River temperature recording, electrofishing, and snorkel survey stations .31 4.2-1 North Anna River mean monthly streamflows 1980-2001 ................................. 34 4.4-1 NAR-I smallmouth and largemouth bass median densities, and mean visibilities, 1987-2001. ................................. 45 iv
List of Figures (cont.)
Figure Number Title Pate 4.4-2 NAR-2 smallmouth and largemouth bass median densities and mean visibilities, 1987-2001 ................... ............. 45 4.4-3 NAR-4 smallmouth and largemouth bass median densities, and mean visibilities, 1987-2001 ..................... ........... 46 4.4-4 NAR-5 smallmouth and largemouth bass median densities, and mean visibilities, 1987-2001 .................... ............ 46 V
List of Tables Table Number Title Page 2.0-1 Seasonal summary of North Anna Power Station operation (percent of total station load) 1978-2001 ................................. 3 3.1-1 Summary of North Anna fixed recorder temperature data during 2001 ...... ;.5 3.1-2 North Anna Lake Survey showing temperatures (in Celsius degrees) measured at one meter interval depths for stations in Lake Anna ...................... 9 3.2-1 Surface water temperature (C), conductivity (umhos),
pH (standard units) and dissolved oxygen (mg/I) recorded at time of sampling during 2001 .......................... 14 3.2-2 Fishes collected in Lake Anna by gill netting in 2001 ............. 15 3.2-3 Number and weight (g) of fishes by station collected by gill netting at Lake Anna during 2001 ................................. 16 3.2-4 Gill Net Summary 2001 .................. 18 3.3-1 Fishes collected in Lake Anna and the WHTF by electrofishing during 2001 .20 3.3-2 Number and weight (g) of fishes by station collected by electrofishing at Lake Anna during 2001 .................................... ;.23 3.3-3 Electrofish Summary 2001 .26 4.1-1 Mean, maximum, and minimum hourly water temperatures (C) recorded in the North Anna River, at station NAR-I by month, during 2001.
Sample size (n) equals the number of hourly Observations recorded each month .32 vi
1.0 Introduction In 1972, the North Anna River was impounded to create Lake Anna, a 3885 hectare (9600 acres) reservoir (lake) that provides condenser cooling water for the North Anna Power Station (NAPS). Adjacent to Lake Anna is a 1376 hectare (3400 acre) Waste Heat Treatment Facility (WHIT) that receives the cooling water and transfers excess heat from the water to the atmosphere before discharging into the lake.
Aquatic monitoring studies have been conducted on Lake Anna since its inception.
In January, 1984, the Company initiated an extensive Section 316(a) demonstration study (P.L.95-500) to determine if proposed effluent limitations on thermal discharges from the power station were more stringent than necessary to assure the protection and propagation of a balanced, indigenous community of shellfish, fish and wildlife in Lake Anna and the lower North Anna River. The final report (Virginia Power 316(a) Report 1986) successfully demonstrated that the operation of the power station had not resulted in appreciable harm to the biological community. The Virginia Water Control Board (VWCB) accepted the study as a successful demonstration in September, 1986.
Subsequent to the 316(a) study, the Company committed with the VWCB to continue environmental monitoring on Lake Anna and the lower North Anna River as part of a post 316(a) agreement. Also, following each three year period of data collection, a summary report is provided with recommendations for future studies. This report presents the findings for calendar year 2001, the first year of the three year period 2001-2003.
1
2.0 Station Operation North Anna Power Station (NAPS) operated at an average of 81% of capacity for 2001. The station operated at 84% and 94% of capacity for the first quarter and second quarter respectively and 80% for the third and 67.8% in the fourth quarter. The Station's Unit 1 was shutdown in September for a scheduled refueling outage. This outage resulted in the lower capacity during the third quarter. Unit 2 was out from 10/28 through 12115 for repair to the reactor head. This combined with a short outage on 12/23 resulted in the fourth quarter percentage of 67%. The yearly average of 81% for 2001 was comparable. to generation capacity in 1990, 1991 and 1996 thereby placing North Anna Power Station as an industry leader in low cost generation (Table 2.0-1).
2
TABLE 2.0-1 Seasonal summary of North Anna Power Station operation (percent of total station load) 1978-2001.
Quarterly Year Wintf Spring Summer Fall Average 1978 0 23 42 45 27.5 1979 43 ' 31 44 0 29.5 1980 31 37 53 65 46.5 1981 46 80 67 82 68.8 1982 78 26 19 48 42.8 1983 53 58 96 84 72.8 1984 76 64 16 66 55.5 1985 87 96 82 62 81.8 1986 75 88 62 80 76.3 1987 92 45 23 47 51.8 1988 75 99 94 97 91.3 1989 47 26 87 65 56.3 1990 98 98 69 61 81.5 1991 63 89 84 92 82 1992 35 80 92 71 69.5 1993 49 83 79 82 73.3 1994 96 91 75 91 88.5 1995 87 64 98 97 86.5 1996 76 98 83 66 80.8 1997 98 80 97 97 93 1998 96 81 85 94 89 1999 97 90 87 93 92 2000 84 91 100 100 .94 2001 84 94 80 67 81 Quarters at 75-100% 15 15 14 12 cjqbnatable2.G-1hds 3
3.0 LDke Anna 3.1 Temperature Methods Lake water temperature data in 2001 were collected using continuous monitors (fixed temperature recorders) and instantaneous field surveys. Continuous temperatures were measured using Onset Optical Stowaway temperature recorders which measure and record the water temperature at one hour intervals at seven (7) stations in the lake and three (3) stations in the WHITF. These instruments were located one meter below the lake surface at the stations depicted in Figure 3.1-1, the lone exception being Station NALST1O. The instrument at this station was located at a depth of three meters to account for the turbulence associated with mixing. A summary of the data recorded by these instruments for 2001 is presented in Table 3.1-1 as daily high, mean and low temperatures.
ORANGE CO. N LAKE ANNA t NAUL19NT.
2 K~M 2 M.ws SPOTSYLVANIA CO.
LOUISA CO. C4reek STANLTHIST
- N~~ADISCI ALRT 2PiWastington. D.C. a; Lake Anna I RscteHnond, VA Waste Heat Treatment FacitityNAS1 NAWHTF2' FIGURE 3.1-1 Approximate location of fixed Endeco and Onset temperature recorders in Lake Anna and WIH{T 4
TABLE 3.1-1. SUlMARY OF NORTH ANNA FIXED RECORDER TEMPERATURE DATA DURSNG 2001. ALL RESULTS ARE CALCULATED FROM HOURLY TEMPERATURES (IN DEGREES CELSIUS). ALL ARE SURFACE INSTRUMENTS EXCEPT FOR NALST10 WHICH IS AT MID-DEPTH.
A *- INDICATES DATA MISSING DUE TO INSTRUMENT MALFUNCTION OR DAMAGE.
YEAR-200 MONTU-JAANUARY STATISTIC! NAL719ST NAL719NT NAL2OST NALINT NALTmIST NALsRPTT NALSTIO NADISCI NAWIT2 NAWIr3 NARIV60I STATION 6 5 4 2 1 3 1o 7 a 9 11 HOURLY mHGH 5.t 3. _t .S 7.7 10.0 102 1720.9 14.1 114. .
HOURLY HIMAN3 2 .9 5.6 S 13.3 7.7 1 2 10.1 4.11 14.1 1.7 HOURLY LOW 3.5 2. 3.5 4.7 6.9 8.0 1311 10.2 10.2 so YEAR=2001 MONTH-FEBRUARY STATISTIr NAL719ST NAL719NT NAL208T NALINT NALnnST NALBRP7Tr NALSTIO NADISCI NAWITM NAWnTF3 NARIV6O1 STA1ION 5 4 2 . 3 10 7 S 9 i HOURLY lIGH 8.S 780 1 9.2 101 116 19.7 16.2 14.d 11.3 HOURLY MEAN 6.4 S_6 5 1.9 7A 9.5 16. 1.2 144 12.d 9.4 HOURLY LOW 5.0_ 4J3____ 4.3 5.8 8.0 9.1 16.9 12. 11.3 S YEAR=20t1 MONTUMARCH STATISM NAL717 NAL719sT NLtT NALINT l NALTHIST NALBRmTT NALSTlO NADISCI NAWITIn2 NAWHTF3 NARIV641 STATION 6 5 2 1 3 1 7 8 9 1 HOURLY IlGH 11.3 10.2 a 9.s 10. 11.6 12.3 2@A I1" 14.8 12.
HOURLY MEAN 8.6 7.7 90 9.7.61 10A 11.5 19.1 14.2 13A 10.51 HOURLY LOW C.C 5.4 6.1 7.3 9.5 1.2r 14.8 12.3 12.3 S YEAR-2041 MONTH=APRIL STATIsTnC! [NAL7195T l NAL719NT NAL20ST NALINT NALTnIST NALBRmr NALSTl$ NADISCI NAWIrTF2 NAWIITF3 NAR2V601 STATION l 6 J 5 4 2 1 3 10 7 S 9 11 lHOURLY HIGH 1 21.1 2t
- 19.0 19A 20.I 4 1 21A 25J7 241.9 21.5 HOURLY H21AN l 1.1 20s8
- 1. A 194 15.-.0 2 021 18.2 22.6 2 2" I1s HOURLY LOW 9.9l 8J
- 84 9.5 10l4 1.1 14.1 14.5 13A 16.2 5
TABLE 3.1-1(CONT.).
SUMMARY
OF NORTH ANNA FIXED RECORDER TEMPERATURE DATA DURING 2001. ALL RESULTS ARE CALCULATED FROM HOURLY TEMPERATURES (IN DEGREES CELSIUS). ALL ARE SURFACE INSTRUMENTS EXCEPT FOR hALSTIO WHICH IS AT KID-DEPTH.
A INDICATES DATA MISSING DUE TO INSTRUMENT MALFUNCTION OR DAMAGE.
STATION NO. 6 5 4 2 1 3 10 7 8 9 YEAR=2001 MONTH=MAY STATISTIC/ NAL719ST NAL719NT NAL20ST NALNT NALTmIST NALBRPTE NALSTte NADISCI NAWHTZ NAWHTF3 NARIV601 STATION 5 4 2 1 10 8 9 11 nOuRLY HIGH 25.3 25.3 243 23.9 23.5 23.9 22.8 315 29.7 275 24.7 HOURLY MEA&N 2131 21J 21. 21.7 21.7 22.1 20.1 29.9 271 25.6 21J HOURLY LOW 19.3 1.7 18.3 18.7 17 19.0 169 275 24.6 22.5 18A YEAR=2001 MONTH-JVNE STAT=STCf NAL719ST NAL719NT NAL20ST NALENT NALTIMT NALBRPTT NALSTIO NADISCI NAW rTM 2 NAWITF3 NARI6lO STrAnON C 5 4 2 1 3 10 8 9 11 HOURLY HIGH 31.5 31.5 31.1 31.1 30.8 31.1 2S3 37.3 3C.1 3J.2 31.5 HOURLY MEAN 27.0 273 26.9 26.7 26.6 26.9 2S.2 33.9 31.6 30.1 26.6 HOURLY LOW 21.8 21.5 22.1 22.1 22.1 2218 21.7 301 27.1 25.7 22.1 YEAR-2"1 MONTI-JULY STATSTIC/ NAL719ST NAL719NT NAL20ST NALINT NALTHIST NALBKrTf NALSTIO NADISCI NAWHTF2 l NAWHITF3 NARIV"I STATION 6 5 4 2 t1 3 10 7 8 9 11 HOURLY HIGH 30.8 3e3 36A 30.0 30.0J 30A 30.3 37.3 35.01 33.1 305 HOURLY MEAN 23.1 28.2 28A 2S.4 2871 29.1 2.81 35.8 33.2 3tA 283 HOURLY LOW 25.7 25.7 24A 2U1 27.11 27.8 27.1 34.2 293 2.
YEAR=2041 MONTH-AUGUST rSTATSTI STATION 1NAL719sl l 6 NAL719NT S 4 l 2 l NALTIIET I NALBRPTT l NALSTll NAD1 CI NALIT lINAL20sT 1 3 l 103. 7 NAWITFZ 8
a NAw1T3 9
NARIY6I 11 1
HOURLY HIGH 3231 32.5 32.3 31.5 330. 30 43l 322 HOURLY MEAN l 2.31 2921 2 .51 29.61 2931 l 2951 Al 35 1 335 1 32.0 29 31 l IHOURLY LOW l 26A l 2,6.11 26.8 l 27.11 27.5 27A l 23J l 3421 312 1 29.l 26.3]
6
TABLE 3.1.1(CONT.).
SUMMARY
OF NORTH ANNA FIXED RECORDER TEMPERATUREDATA DURING 2001. ALL RESULTS ARE CALCULATED FROM HOURLY TEMPERATURES (IN DEGREES CELSIUS). ALL ARE SURFACE INSTRUMENTS EXCEPT FOR hALST1O WHICH IS AT MID-DEPTH.
A *- INDICATES DATA MISSING DUE TO INSTRUMENT MALFUNCTION OR DAMAGE.
YEAR=2001 MONmTHsE~rElSBER STATISTIC/ NAL719SST NAL719NT NAL20ST NALcr'% NALVHIST NALBRMT NALSTIO NADLSCI NAWHnT2 NAWHTF3 NARiV6O1 STATIO.N 6 5 4 2 1 3 10 7 S 9 it HOURLY HIGH 28.9 29J 293 30. 29.1 29.7 29.9 36.0 33.7 31.7 29.9 HOURLY MEA. 25.6 255 265 272 26A 26.8 27.2 33A 29.9 2J.2 26.1 HOURLY LOW 21.1 21.1 22.5 232 22.2 22I 22.9 30.1 25.1 232 21.3 YEAR.2"1 MONTn=OCTOBER STATISnTCI NAL719ST NAL719NT NAL2IST NALINT NALTHIST NALBRrTE NAIST1 NADISCI NAWHTF2 NAWHTF3 NARIV601 STATION 6 5 4 2 1 3 to 7 t 9 11 HOURLY HIGH 223 23.3 2sA 24.3 23.2 2D.0 23.2 302 27.3 24.7 234 HOURLY MEAN ItJ 19.1 20. 20.2 20A 205 215 273 24.7 22.8 20.2 HOURLY LOW 144 15.2 164 17.A 175 9.1 19.0 22.S 20A 20.1 16.3 YEARl.20H MO.NTU-NOVENOER YEAR-el I UONTH-DECEMBER STATISTIC NAL719ST NAL719NT NAL2e8T NALINT NALTEMST NALBRPTl NALSI'S NADrSCI NAWINT2 l NAWHTFJ l NARIV6U1 STATION 6 5 4 12 1 3 I l 7 3 9 l 11 HOURLY15JG ISA 15.4 16.11 1.0 16.5 I" 164 23.3 234 10.3 16.3 HOURLYMEAN 10.7 11.1 12. 1229 13.3 14.1 l1. 2L7 174 15S31 135 HOURLY LOW 5.7 6.3 7.91 9.0 1 9.6 110.6 l 12.l 13.11 15.2 127 l 93 1 7
The instantaneous temperatures were measured using a Yellow Springs Model 3000 T-IC field temperature instrument. Temperatures were measured at one (1) meter intervals, surface to bottom, at the stations shown in Figure 3.1-2. The results of these surveys are shown in Table 3.1-2.
FIGURE 3.1-2 Approximate location of thermal plume N sampling stations on Lake Anna. i I
K
-I H
G
- F E
C a
8
TABLE 3.1-2. NORTH ANNA LAKE SURVEY SHOWING TEMPERATURES (IN CELSIUS DEGREES ) MEASURED AT ONE METER INTERVAL DEPTHS FOR STATIONS IN LAKE ANNA.
I-------------------------------------------------- STATION ---------------------------------------------- I DEPTH DATE (M) A B C D E F G H I J K L H N 02/07/2001 a 10.3 10.5 10.1 10.1 10.1 9.5 8.7 8.1 7.9 7.3 6.2 5.2 5.6 5.5 1 10.0 10.5 10.0 10.0 10.0 9.2 8.5 7.9 7.7 7.1 5.8 5.0 5.3 5.3 2 10.0 10.4 9.7 9.8 9.8 8.9 8.4 7.7 7.4 7.0 5.7 4.8 5.3 5.3 3 9.9 10.4 9.0 9.2 9.2 8.8 8.3 7.6 7.3 7.0 5.6 4.8 5.3 5.2 4 9.8 10.3 8.9 8.9 9.1 8.8 8.3 7.5 7.3 6.9 5.5 4.8 5.3 5.2 5 9.8 10.2 8.8 8.9 9.0 8.7 8.3 7.4 7.2 6.9 5.3 4.8 5.3 5.2 6 9.6 10.0 8.8 8.8 9.0 8.7 8.2 7.4 7.2 6.9 5.2 4.8 5.3 5.2 7 9.5 9.8 8.8 8.8 8.9 8.7 8.2 7.3 7.2 6.8 5.1 4.8 5.3 5.2 8 9.3 9.5 8.8 8.8 8.9 8.6 8.1 7.1 7.1 6.7 5.1 5.3 9 9.1 9.2 8.8 8.7 8.8 8.5 8.1 7.0 7.0 6.6 5.1 10 8.8 8.9 8.7 8.7 8.7 8.4. 7.9 6.8 6.9 6.5 5.1 11 8.7 8.9 8.7 8.7 8.5 8.3 7.8 6.6 6.8 6.2 5.1 12 8.6 8.8 8.7 8.7 8.5 8.2 7.6 6.3 6.5 5.9 5.1 13 8.6 8.8 8.7 8.7 8.5 8.0 7.4 6.1 6.2 5.9 .5.1 14 8.6 8.8 8.6 8.6 8.5 8.0 7.3 6.1 5.9 15 8.5 8.8 8.6 8.6 8.5 7.8 7.2 6.1 16 8.5 8.8 8.5 8.5 8.5 7.8 7.1 17 8.5 8.3 8.4 8.5 7.8 7.1 18 8.5 8.3 8.4 8.5 7.8 6.9 19 8.4 8.3 8.4 7.8 6.9 20 8.4 7.8 21 8.4 CD
TABLE 3.1-2(CONT.). NORTH ANNA LAKE SURVEY SHOWING TEMPERATURES (IN CELSIUS DEGREES) MEASURED AT ONE METER INTERVAL DEPTHS FOR STATIONS IN LAKE ANNA.
STATION ---------------------------------------------- I DEPTH DATE (M) A B C D E F C H I J K L M N 06/06/2001 0 24.8 24.3 24.6 24.6 24.6 25.2 25.0 24.8 24.7 24.8 24.4 24.1 25.0 24.7 1 24.6 24.3 24.3 24.3 24.3 24.4 24.4 24.2 23.9 23.9 23.8 23.5 23.7 23.5 2 24.4 24.1 24.2 24.0 24.2 24.2 24.3 23.8 23.6 23.7 23.1 23.1 22.9 22.8 3 24.3 24.0 23.8 23.7 24.0 23.9 24.0 23.1 23.0 23.2 22.6 22.5 22.4 22.2 4 24.2 23.6 23.5 23.5 23.7 23.7 23.6 22.8 22.8 22.9 22.4 22.3 22.1 21.9 5 24.1 22.9 23.3 23.3 23.4 23.6 23.2 22.6 22.7 22.8 22.2 22.1 21.8 21.7 6 23.9 22.4 23.1 23.1 23.1 23.3 22.9 22.5 22.5 22.5 22.0 22.0 21.4 21.5 7 23.8 21.9 23.0 22.9 22.9 22.9 22.6 22.3 22.3 22.2 21.9 22.0 21.2 21.4 8 23.3 21.4 22.8 22.8 22.8 22.6 22.3 22.0 22.1 22.0 21.6 21.1 9 22.6 21.2 22.5 22.6 22.5 22.4 21.8 21.7 21.8 21.9 21.3 10 22.1 20.9 22.3 22.2 22.2 22.0 21.5 21.5 21.6 21.4 20.9 11 21.4 20.5 21.7 21.7 21.6 21.4 20.9 21.1 21.3 20.5 20.4 12 20.6 19.6 21.0 21.0 21.0 20.6 20.2 20.6 20.9 20.4 20.3 13 19.6 19.0 20.2 20.2 20.0 19.9 19.8 20.4 20.5 20.3 20.5 14 18.9 18.9 19.3 19.4 19.6 19.5 19.5 20.1 20.0 15 18.4 19.0 18.8 18.9 19.1 19.0 19.3 20.0 16 17.6 19.2 18.3 18.2 18.3 18.5 19.0 17 16.5 16.9 17.3 17.6 17.9 18.1 18 15.4 16.0 15.7 17.4 16.7 17.1 19 14.8 16.3 15.5 15.5 16.1 20 14.5 15.7 21 14.5 0
TABLE 3.1-Z(CONT.). NORTH ANNA LAKE SURVEY SHOWING TEMPERATURES (IN CELSIUS DEGREES) MEASURED AT ONE METER INTERVAL DEPTHS FOR STATIONS IN LAKE ANNA.
I- -------------------------------------- STATION ---------------------------------------------- I DEPTH DATE (M) A B C D E F G H I J K L H N 11/27/2001 0 16.0 16.1 16.0 15.8 15.9 15.8 15.5 15.4 15.1 15.0 14.6 13.9 13.2 13.4 1 15.9 16.1 15.8 15.7 15.8 15.0 15.5 15.2 15.0 15.0 14.3 13.9 13.1 13.3 2 15.9 16.0 15.6 15.6 15.7 15.6 15.4 15.1 14.9 14.9 14.3 13.3 13.0 13.2 3 15.8 16.0 1s.s 15.5 15.6 15.6 15.3 15.0 14.7 14.8 14.1 13.1 12.9 12.7 4 15.8 15.9 15.4 15.3 15.1 15.5 15.2 14.7 14.5 14.7 14.2 13.0 12.4 11.9 5 15.7 15.8 15.3 15.2 15.3 15.5 15.1 14.5 14.4 14.5 13.1 12.9 11.7 11.8 6 15.6 15.7 15.2 15.2 15.3 15.4 14.9 14.4 14.3 14.3 13.0 12.8 11.4 11.7 7 15.4 15.6 15.2 15.2 15.2 15.2 14.7 14.3 14.3 14.0 12.8 12.8 11.4 11.7 8 15.1 15.6 15.1 15.1 15.2 15.1 14.5 14.2 14.1 13.4 12.6 9 15.0 15.5 15.1 15.1 15.1 15.0 14.3 14.0 13.8 13.2 12.6 10 15.0 15.4 15.1 15.1 15.1 14.8 14.2 13.9 13.4 13.0 12.5 11 15.0 15.5 15.1 15.0 15.0 14.6 14.1 13.6 13.2 12.9 12.4 12 15.0 15.2 15.0 14.9 15.1 14.4 13.9 13.5 13.1 12.9 12.3 13 15.0 15.2 15.0 14.9 15.1 14.1 13.8 13.4 13.1 12.9 12.3 14 14.9 15.2 .15.0 14.9 15.1 14.0 13.7 13.1 12.9 12.2 15 14.9 15.2 14.9 14.8 15.1 14.0 13.7 13.4 12.2 16 14.9 15.2 14.9 14.8 14.0 13.6 17 14.9 14.8 14.8 14.0 13.6 18 14.9 14.8 14.9 14.0 13.7 19 14.9 14.8 14.9 14.0 13.8 20 14.9 14.0 21 14.9
Results The maximum high temperature recorded for the lake in 2001 by continuous monitors was 32.5 0 C in August at Station NA7I9NT which is located on the Pamunkey Arm of the upper lake (Table 3.1-1). The lowest monthly temperature recorded was 2.8 0C in January again at Station NAL719NT. The 2001 monthly temperature data in Table 3.1-1 are within the ranges of data reported in previous years..
The instantaneous temperature surveys were conducted in February, June and November to provide temperature data to assess seasonal thermal stratification patterns in the lake (Table 3.1-2). The February survey shows a consistent change of approximately 20 C from surface to bottom in the deeper portion of the lake.
The June survey results show a thermocline at the 12 to 15 meter depth in the lower lake which disappears in the upper, shallow portion of the lake. The November survey again shows little stratification with surface to bottom temperature of approximately 20 C from the lower lake and continuing in the upper lake. This stratification pattern in the lake is not unusual and is similar to previously reported patterns (Virginia Power 1986-2000).
12
3.2 Fish Population Studies - Gill Netting Methods The monitoring of fish assemblage abundance and species composition for Lake Anna and the WHTF continued in 2001 using the same basic sampling technologies applied since 1972. Experimental gill netting was used to capture fishes which normally inhabit the deeper strata of the lake, or exhibit a diel movement to and from the shoreline. Similar to previous years, 2001 gill net surveys were conducted during February, May, August, and December at the stations shown in Figure 3.2-1. Experimental gill nets were set near littoral drop-off areas with procedures remaining unchanged since 1972. Fish collected by gill netting were returned to the laboratory where all individuals were measured to the nearest millimeter total length and weighed to the nearest 0.1 gram. Surface water temperature (0 C), dissolved oxygen (mgfl), pH and conductivity (4rmhos) were recorded at the time of each sample collection (Table 3.2-1).
iORANGE CO.'
-LAKE ANNA 2 KM 2 M.ies North Ana Arm t.
SPOTSYLVANIA Co.
LOUISA CO. Creek Thurman Island i' PWPOWER Lagoon 1 ; , }_Lsy re LeyCreek
._WasNngton. D.C. BDm Lake ra to R X~~nd, VA WasHo W 1- olS Treatment Facility aon rge k FIGURE 3.2-1 Location of Gill Netting stations on Lake Anna and WHTF 13
TABLE 3.2- 1 Surface water temperature (C), conductivity (umhos),pH (standard units) and dissolved oxygen (mg/I) recorded at time of sampling during 2001 FEBRUARY MAY Electrofish Stations Electroflsh Stations Temperature Conducivity pH Dissolved Oxygen Temperature Conductivity pH Dissolved Oxygen 88 7 11.2 Dike 1 WHTF 29.4 41 7.5 9.3 Dike 1 WHTF 18.9 Dike 3 WHTF 13 74 7.1 10.3 Dike 3 WHTF 25.6 43 7.4 8.3 Lagoon 1 18.9 68 7 11.5 Lagoon 1 28.4 37 7 8.6 Lagoon 3 12.9 76 7.2 10.6 Lagoon 3 25.3 42 7.5 8.7 North Anna Arm 7.6 86 7.8 14.6 North Anna Arm 20.8 64 7.3 8.9 Thurman Island 9.8 86 7.1 12.4 Thurman Island 20.5 7.2 8.7 Dike 1 Lake 8.3 67 6.8 13 Dike 1 Lake 20.8 43 7.5 9.5 Dike 3 Lake 11.4 69 6.8 11 Dike 3 Lake 22.5 61 7.5 9.2 Lower Lake Cove 11.4 88 7.1 10.9 Lower Lake Cove Gillneting Stations Gillneting Stations Lagoon 1 19.2 82 7.2 11.5 Lagoon I 29.7 40 6.9 8.5 Lagoon 3 13.5 88 7.2 9.7 Lagoon 3 26.4 59 7.8 8.4 North Anna Arm 7.6 78 7.3 13.6 North Anna Arm 21.3 39 7.7 10.8 Thurman Island 9.2 75 7 13.3 Thurman Island 21.4 44 . 7.5 10.7 Levy Creek 10.8 70 6.9 12.2 Levy Creek 22.4 61 7.1 9.1 LowerLake 11.8 71 6.8 11.2 Lower Lake 22.5 61 7.5 9.2 AUGUST DECEMBER Electrofish Stations Electrofish Stations Conductivity pH Dissolved Oxygen Temperature Conductivity pH Dissolved Oxygen Temperature Dike 1 WHTF 35.6 63 6.7 6.7 Dike I WHTF 20.9 53 7.8 8.5 Dike 3 WHTF 32.3 63 6.8 6.7 Dike 3 WHTF 17.9 54 7.8 8.3 Lagoon 1 35.4 64 6.6 7.2 Lagoon i 20.9 54 7.8 8.1 Lagoon 3 32.8 62 6.8 6.9 Lagoon 3 17.7 56 7.8 7.8 63 8.2 8.8 North Anna Ain 12.5 52 7.9 7.9 North Anna Arm 30.2 8.7 62 6.8 7.2 Thurman Island 14.3 51 7.9 Thurman Island 30 8.4 8.8 29.9 64 6.7 7.3 Dike 1 Lake 14.5 52 Dike I Lake 7.7 7.7 Dike 3 Lake 29.6 63 6.7 Dike 3 Lake 16.2 52 6.8 6.7 Lower Lake Cove 16.3 52 7.9 8.3 Lower Lake Cove 30.6 63 Glilneting Stations Gillneting Stations 21.4 54 7.7 8.4 Lagoon 1 35.7 64 6.8 6.9 Lagoon 1 6.9 Lagoon 3 17.9 54 7.7 8.7 Lagoon 3 32 64 6.7 North Anna Arm 12.9 51 7.8 9.8 North Anna Arm 30.1 64 8.2 10.2 Thurman Island 14.8 51 7.8 8.9 Thurman Island 29.5 62 6.6 7.9 Levy Creek 16.1 52 8.5 9.1 Levy Creek 31.2 62 7.1 7.5 Lower Lake 16.7 52 7.8 9.8 Lower Lake 31.3 63 6.8 7.5
Results Seventeen (17) species of fish representing seven (7) families were collected in Lake Anna and the WHTF by quarterly gill netting in 2001 (Table 3.2-2). In 2001, a total of 926 fish weighing 288.0 kg was collected from four stations in the lake and two stations in the WHTF (Table 3.2-3). The 2001 total number of fish (926) was higher than 2000 (710) and 1999 (670), while gill net biomass in 2001 (288.0 kg) was the same as biomass totals in 2000 and lower than 1999 (296.5 kg). Of the 926 fish collected, 764 (214.8 kg) were collected in the lake and 162 (73.1 kg) were collected in the WHTF. The February survey yielded the greatest total weight of fish collected (83.5kg) representing approximately 30°/0 of the total weight of all fish collected from all stations and surveys combined. Striped bass and common carp accounted for approximately 50%/o of the biomass taken in February (Table 3.2-4). The August survey yielded the greatest total numbers of fish collected from the 2001 gill netting representing 46% of the total of all fish collected (44% of the August collection were threadfin shad Dorosoma petense).
Table 3.2-2. Fishes collected In Lake Anna by gIll netting during 2001.
FAMILY SPECIES LAKE WHTF Clupeidae Dorosoma cepedianum X X Dorosoma petenense X Cyprinidae Ctenopharyngodon idella X Cyprinus carpio X X Notropis hudsonius X Catostomidae Carpoldes cyprinus X Ictaluridae Arneiurus catus X X Ameiurus nebulosus X Ictalurus punctatus X X Moronidae Morone americana X X Morone saxatilis X X Centrarchidae Lepomis gulosus X Lepomis macrochirus X X Lepomis microlophus X Micropterus. salmoides X X Pomoxis nigromaculatus X X Percidae Stizostedion vitreum X X 15
I Table 3.2-3 also includes the average number and weight of fish collected per net set for each station for comparison of catch per unit effort by number (CPUE-N) and weight (CPUE-W). CPUE-N for all stations combined in 2001 was 38.6 fish per net while CPUE-W was 12.0 kg per net.
TABLE 3.2-3 NUMBER AND WEIGHT (g)OF FISHES BY STATION COLLECTED BY GILL NETTING AT LAKE ANNA DURING 2001 STATION FEBRUARY' MAY AUGUST
- DECEMBER' TOTAL
- CPUE LAGOON 1 *
- NUMBER* 30* 35* 4* 23* 92' 23 WEIGHT 16072.8'
- 1332i 3947.5* 8105 41446.3 10361.575 LAGOON 3
- NUMBER' 25' 16* 18'* Ill 70* 17.5 WEIGHT
- 16883.6 4774.7
- 3772 6222.5
- 31652.8 7913.2 LEVY CREEK *
- NUMBER
- 5 28' 22' 7' 62' 15.5 WEIGHT' 4145 7658.5
- 3515.5
- 2369.7
- 17688.7
- 4422.175 LOWER LAKE * *
- NUMBER' 9' 47' 17' 18' 91' 22.75 WEIGHT
- 8859.1 15431.5' 4380.5 12767 41438.1
- 10359.525 NORTH ANNA ARM*
- 41 NUMBER
- 51' 41 352* 71* 515' 128.75 WEIGHT' 30533.9 21294.5 49175.6
- 22981.5* 123985.5 30996.375 THURMAN ISLAND' * * '
NUMBER' 9' 39' 15' 33- 96' 24 WEIGHT' 7009.7 10287.5
- 6745 - 7e94 31736.2 7934.05 TOTALS * * '
NUMBER
- 129* 206
- 428' 163* 926
- 38.6 WEIGHT
- 83504.1
- 72767.7 71536.1
- 60139.7 287947.6 11997.8 These values are compared to CPUE in previous years in Figure 3.2-2. Over the last 10 years, CPUE-N has ranged from 42 to 28 with a mean of 30, while CPUIE-W has ranged from 16 kg to 12 kg with a mean of 14 kg. Figure 3.2-2 also indicates that the size of fish collected by gill net has decreased in recent years (1999-2001) because CPUE-N has increased during this period while CPUE-W has remained steady. As mentioned above, relatively high 16
numbers of threadfin shad (188) were collected in August yet these small fish represented only 2.2% of the biomass that survey.
FIGURE 3.2-2 Gill Net data (1990-2001) average number and average weight (Kg) 50 . 20 40-30 -C -- NUNUER 10 10 z~
90 91 92 93 94 95 96 97 98 99 00 01 When the catch per unit effort is compared among stations in 2001, CPUE-N ranged from a low of 15.5 fish per net at the Levy Creek Station to a high of 128.8 fish per net at the North Anna Arm Station (Table 3.2-3). CPUE-W ranged from a low of 7.9 kg per net at the Lagoon 3 Station to a high of 30.9 kg at the North Anna Arm Station. This is consistent with past data.
The numerically dominant species collected by gill netting in the lake were gizzard shad Dorosoma cepedianum (32%), and threadfin shad (26%, Table 3.24). These results are similar to data collected in 2000 and 1999 and are also consistent with other years. The dominant species in the lake relative to biomass was striped bass Morone saxatilis (23%), followed by gizzard shad (20%) and common carp (19%).
17
TABLE 3.2-4 GILL NET
SUMMARY
2001 GILL NET- LAKE STATION ALL STATIONS FEBRUARY MAY AUGUST DECEMBER TOTALS % OF TOTAL SPECIES NUMBER WEIGHT
- NUMBER WEIGHT
- NUMBER WEIGHT
- NUMBER WEIGHT
- NUMBER WEIGHT NUMBER WEIGHT D.cepedienum 24 3785 a8 15925* 11e 15711
- 31 0oo4 241 43424 32 20-
- 0. petenense
- 188 1577 ' 9 a* 197 18386 20 1 P.nlgromaculatus
- 9 1299
- 5 279
- 41 2929
- 17 1523
- 72 6029
- 9 3 -
M. amerkcana
- 2 100
- 25 2151
- 16 1297
- 20 677
- 63 4224
- 8 2 1.pundntus
- 7 4872
- 17 e78s
- 18 4928
- 10 2842
- 50 19224
- 7 9 M.saxatli
- 18 20921
- 12 14987
- 4 67e2
- 17 7792
- 49 50481
- 6 23-A. catu
- 7 2542 12 1767 3 2845 8 4524 30 114768 4 5 S.vitreum
- e 7539
- a 4350
- 2 3645
- 5. 6802
- 19 22135
- 2 10 C.carplo
- 2 7190
- 2 5899
- 8 17758
- 4 97s8
- 14 40413
- 2 19 M.silmoldes
- 3 1713 6 2017 3 390S 12 763e 2 4 A.nebulosus
- 4 1007 4 .1007 I 0 L maetchlrus
- 2 51* 2 83 4 134 1 0 N.hudsonlus
- 1 13
- 3 37 4 50 1 0 C.cyprlnus 3 4494*
- 3 4494 0 2 C.idea
- 1 2500*
- 1 2500 0 1' Lgulosus I* 8 1 8a 0 0
- > Total No.
- 74 155 408
- 129 784
- 100 Total W.
- 0548
- 54872
- 83817
- 45812
- 214849
- 100 GILL NET TOTALS-.WHTF *- *. -----
- ---........... ... .................. ....... ... ........................ t.. . .
STATION:ALL STATIONS FEBRUARY MAY AUGUST DECEMBER TOTALS % OF TOTAL SPECIES
- NUMBER WEIGHT NUMBER WEIGHT
- NUMBER WEIGHT
- NUMBER WEIGHT
- NUMBER WEIGHT
- NUMBER WEIGHT 1.punctatus
- 23 8458
- 25 6932
- a 1505
- 18 3483
- 70 20355
- 43 28 D. capedianum
- 17 8177
- 22 7891
- 4 1740
- 6 2580
- 49 20388
- 30 28 M.salmoldas
- 2 457*
- 6 1085 1 350 9 1892
- 3-M.americeana
- 3 411
- 1 13 5 442* 9 886 1 C.carplo
- 4 13000
- 1 2770 2 e973
- 7 22742
- 4 31 A. catus
- 2 474
- 1 2225
- 4 541
- 7 3239
- 4 4 L. mlcrolophus
- 1 207* 4 80e *
- 5 815* 3 M.saxamts 1 788 2 843
- 3 1630- 2 2-S.vxreum
- 1 757
- 1 757 1 1' P.niromaculatus 1 293
- 1 293' 1 0 L.rnmcrochinus 1 146
- 1 148' 1 0*
Total No.
- 52
- 51 22 34
- 182
- 100 Total W* 3295S 18098
- 7720
- 14328
- 73099
- 100
The numerically dominant species collected in the WIHTF in 2001 was channel catfish Ictalurus punctatus, followed by gizzard shad. The weight-dominant species in the WHTF in 2001 was common carp followed by gizzard shad, channel catfish.
Due to their relatively high numbers, gizzard shad have generally ranked high in biomass catch in both the lake and WHTF. The larger but less collected channel catfish, common carp and white catfish have consistently ranked high in biomass in both places with annual ranking depending on the variation in catch. Striped bass have consistently comprised a large portion of the biomass in the lake but not in the WHTF. A new species, quillback carp sucker Carpiodes cyprinus. was collected by gill netting in 2001. The new species was collected at the North Anna Ann Station in August. The origin of this fish is unknown but is probably the result of release from a bait bucket.
3.3 Fish Population Studies - Electrofishinz Methods Boat electrofishing was used in 2001 to evaluate the assemblage and abundance of fish populations which normally occupy the shoreline habitat. The techniques, stations, and frequency have remained virtually unchanged since 1972. Sampling was performed in February, June, August, and December at the stations identified in Figure 3.2-1. Each station is 100 meters in length and normally includes a brush pile except for the dike stations which are comprised of uniform rip-rap.
1
All fish collected were either returned to thc laboratory for processing or released in the field, e.g., larger game fish were measured, weighed, and released in the field. In the laboratory, at least twenty-five (25) individuals per species from each station were measured to the nearest millimeter total length and weighed to the nearest 0.1 gram. Those individuals over twenty-five (25) per species were enumerated and bulk weighed. Surface water temperature (°C), dissolved oxygen (mgA), pH and conductivity (Dmhos) were recorded at the time of each sample collection (Table 3.2-1).
Results Twenty-five (25) species of fish representing ten (10) families were collected by electrofishing operations in the lake and WHTF in 2001 (Table 3.3-1).
Table 3.3-1 Fishes colkted h Lake Anna and the WHTF by*lectrdfsiMng during 2001.
FAMILY SPfCiES LAKE WHTF Cuupeidae Alos aeesSair X Dorosoma cepedanum X Esocddae Esox nge X Cyptldae Cyprineb anabstana X X Cyprinus carpo X Nop hudsonlus X X Nobop' pocnse X X Ictalurkbe Ameiurus catus X X Ameiunus natals X X Ameiunus nebuosus X Idaluuss punctatus X X Aphredbdedae Aphredderus sayanus X Cypirodonidae Fund.Aus diaphanus X Poecieiae Gambusla inhins X Moronkae Mocme americana X Centrachkae Lepomisaurkis X X Lepomis cyanellus X X Lepomis gbbosus X Lepomis gulosus X X Lepoms maorod inus X X Lepomis microiophus X X Micnrterus sairnodes X X Pomoxis nigromaculatus X X Perckbe Etheostoma ohnsted X X Perca flavescens X PA
A record total of 7,213 fish weighing 88.2 kg was collected from the five stations in the lake and the four stations in the WVITF during the 2001 sampling period (Table 3.3-2).
The total number of 7,213 is greater than the 1998 total of 6,991 which was the previously recorded high. Electrofishing biomass in 2001 (88.2 kg) was lower than that of 2000 (105.4 kg) as well as 1999 (106.9 kg).
During 2001, Virginia continued under a prolonged period of reduced rainfall. For the first three quarters of 2001, Lake Anna remained at a stable level ranging from 250.4 feet (normal pool is 250 feet above mean sea level) to a low of 249.4 feet. This fluctuation of less than a foot is not unusual for the lake during a normal year. The lake level began a precipitous drop in September to 247.4 feet in December (Figure 3.3-2). The first three quarter samples were collected at or near normal full pool level; first quarter (February) level at 249.9 feet; second quarter (June), level at 249.7 feet and third quarter (August) level at 249.4 feet. The fourth quarter samples were collected in December with the lake level at 247.5 feet. This drop of over 2.5 feet below normal pool dewatered much of the shallow shoreline. This lake level reduction may have concentrated shoreline fishes around remaining structure such as the dike rip-raps and resulted in a record catch of 3,564 fish (86%, bluegill) in the December collection. This is above the historical average for the fall sample and resulted in the record catch for 2001. A similar increase in numbers was also reported in 1998 when the lake level dropped due to drought conditions.
'1
FIGURE 3.3-2 Lake level for Lake Anna measured in feet above sea level for 2001 251 -
_j250 .. .
> 249 - , - .
LU-j 248 -.-.
- -l20
< 247..-.
z'246 , .,
245 0 00 a (0 CD (0 CD t 0 CDfl0(
o oo M &o oo L o CO- Cj CJ - N-ZZ~ In r-. CO0 Of the 7,213 fish collected in 2001, 3,712 (51.8 kg) were collected from the lake and 3,501 (36.4 kg) were collected from the WHTF (Table 3.3-2). When the data are compared seasonally, the 2001 electrofishing results are similar to previous years with the greatest numbers of fish being collected in the winter (February - 1,895 individuals) and fall (December - 3,564 individuals) surveys. Typically, in the fall, recruitment of the young-of-year (YOY) plus the return of fish to shallow water as the weather moderates, combine to increase the number of fish available to collection by shoreline electrofishing.
22
TABLE 3.3-2 NUMBER AND WEIGHT (g) OF FISHES BY STATION COLLECTED BY ELECTROFISHING AT LAKE ANNA DURING 2001 STATION
- FEBRUARY' MAY
- AUGUST ' DECEMBER TOTAL
- CPUE LAGOON 1 *
- NUMBER 118
- 94
- 56 ^ 326
- 594 ' 149 WEIGHT 745
- 3065
- 543
- 1376
- 5729
- 1432 LAGOON 3 NUMBER
- 99. 67' 112* 125' 403* 101 WEIGHT
- 193' 430
- 496
- 2495
- 3613 ' 903
====== ======
DIKE 1-WHTF NUMBER 233' 176
- 102
- 763 ^ 1274
- 319 WEIGHT ^ 5603* 2910
- 697
- 5885 ' 15095
- 3774
==
= == ==== == ====
DIKE 3-WHTF NUMBER
- 587' 119' 71 ' 453 ' 1230' 308 WEIGHT
- 2665
- 1167 867 ' 7280
- 11979' 2995 DIKE 1-LAKE NUMBER
- 296' 108' 95
- 844 ' 1343' 336 WEIGHT
- 4117' 1582 1511
- 8223
- 15432' 3858 DIKE 3-LAKE NUMBER
- 275' 195' 62 544 ' 1076' 269 WEIGHT
- 3762' 1547
- 934 ' 3835 ' 10078' 2520 LOWER LAKE NUMBER
- 98' 86 ' 92
- 187 - 463 ' 116 WEIGHT 457' 892 ' 912
- 1599 ' 3860 ' 965 THURMAN ISLANI*
- S NUMBER 94
- 85
- 47
- 218' 444 ' 111 WEIGHT 1951
- 1814 ' 1208 ' 3156' 8129
- 2032
__===
NORTH ANNA AF NUMBER i 95' 132' 55- 104 386 ' 97 WEIGHT
- 4489' 7675 1105 1064' 14333 - 3583 TOTAL NUMBER
- 1895 ' 1062 692 3564' 7213 ' 200 TOTAL WEIGHT
- 23982 ' 21083 8271 34913' 88249 ' 2451 9.3
Table 3.2-2 also includes the average number and weight of fish collected per electrofishing sample for each station for comparison of catch per unit effort by number (CPUE-N) and weight (CPUE-W). CPUE-N for all stations combined in 2001 was 200 fish per sample while CPUE-W was 2.5 kg per sample.
These values are compared to CPUE in previous years (Figure 3.3-3). Over the last 10 years, CPUE-N has ranged from 112 to 200 with a mean of 143, while CPUE-W has ranged from 1.8 kg to 3.1 kg with a mean of 2.5 kg. The high 2001 CPUE-N was, as discussed previously, probably the result of a low lake level in the fourth quarter thereby concentrating large numbers of small fish at dike stations. CPUE-W was average in 2001 and within the range of previous biomass estimates. It is interesting to note that biomass decreased in 2001 while fish numbers increased reflecting the relatively high numbers of small fish concentrated at dike stations. This was also noted in the 1998 collections.
24
When the catch per unit effort among stations in 2001 is compared, CPUE-N ranged from a low of 97 fish per sample at the North Anna Ann Station to a high of 336 fish per sample at the Dike I - Lake Station (Table 3.3-3). CPUE-W ranged from a low of 0.9 kg per sample at the Lower Lake Station (consisting of mostly small bluegill) to a high of 3.7 kg at the North Anna Arnm Station (primarily due to the capture of common carp at this station).
25
TABLE 3.3-3 ELECITIOFISH
SUMMARY
2001 ELECTROFISH -LAKE STATION:ALL STATIONS FEBRUARY MAY AUGUST DECEMBER TOTALS % OF TOTAL SPECIES *NUMBER WEIGHT(g) NUMBER WEtGHT(q) *NUMBER WEIOHT(g) NUMBER WEIGHT(g) NUMBER WEIGHT(g) *NUMBER WEIGHT Lmaerochitus
- 677 7036 405 3175S 238 2423
- 1565 10481
- 2885 23115 *78 45 Lauditus
- 25 559 52 571 *22 *330 60 1369 159 2829 4 5 Lcynnellus
- 22 240
- 40 493 *17 189 *73 534 *152 1458 4 3 1-gulosus *8 153 26 487 18 359 58 868 110. 1846 3 4 Msasimoldes
- 25 4799
- 23 3247 *22. 598 20 3002 *90 11644 *2 22 Akaestfvmlls
- 76 1501 *7 228
- 3 1728 2 3 Lmicrolophus Is1 424 9 287 3 71 43 400 70 1183 2 2 C.analostanna 1 3* 9 21 so5 47 e0 71 2 0 P.flavescent
- 40 1 13 12 70 1 34 15 157 0 0 N.hudsonlIus I 10 *14 13 is250 N.procne 4 5 9 is 13 21 0 0 P. nlgromaculatus *3 220 a 502 11 722 *0 1 AXnatalis
- 2 6I 10 1. 26701 E.nicer I 210 6 1050 7 1260 0 2 E.olmsledl 2 3 *2 3 3 4 7 11 0 0 M.amnercana *6 .224 *6 22A 0 a O~copedlanum *2 328 3 573
- 902 *0 2 A.nebulosus *2 458 1 28 3 484 *0 1 I.Puntatus *1 27 I. 21D I 51 3 288 0 1 A.catus *1 63 1 S 2 68 0 0 A.sayanus *I 10 I .10 2 20 .0 0 COcarplo *1 3500 1 3500 0 7 I-Vibbosus . 12 1 12 0 0 F.diaphenus 1 2 1 2 0 0 Total No. 858 dos8 351 11897 3712 *100 Total Wt.(g) 14776
- 13511 * .569
- 7877 51833 *100 ELECT1ROFISH TOTASI S................t...........
W T.......................................... ........
STATION:ALL STATIONS FEBRUARY MAY AUGUST OCTOBER TOTALS % OF TOTAL SPECIES *NUMBER WEIGHT(g) NUMBER WEIGHT(g) NUMBER WEIGHT(g) NUMBER WEIGHT(g) NUMBER WEIGHT(g) *NUMBER WEIGHT Lmacrochirus
- 935 7290
- 355 3474
- 287 1410
- 1501 12697
- 3078 24871
- 868 Leyenellus
- 56 358
- 40 794 *37 731 *80 1042 *213 2934 *6 a M.salmoldes 10 907
- 26 1792 *10 338 *18 1877 *64 4914 2 13 Lrmlerolophus
- 21 214 -10 SS3* 2 14 20 285 53 106S 2 3 Laurtlus *I S *3 93 28 583 32 681 1 2 Lgulosus *9 358 S 169* 1 59 11. 108 28 693 1 2 Lpunctatus 3 61 11 682 1 13* 1 348 16 1103 0 3 A~catus *4 59* 4 59* 0 0 NJhudsonrtus *2 3 *2 1 4 4 0 0 G~affinls . 3 2 3 2 0 0 P.nlgromeculatus 1 38 I 3S 2 73 0 0 Aknatalis *2 11 *2 11 0 0 Caenalostana *2 4 *2 4 0 0 N.procne *1 2 I2 0 0 E.olmstedl .*1 1
- 1 I 0 0 Total No.
- 1037
- 456 341
- 1667
- 3501 *100 Total WI.(g) 9206
- 7573
- 2602
- 17035 36417 *100
The numerically dominant species collected in both the lake and WHTF by boat electrofishing in 2001 was the bluegill (Table 3.3-3). Bluegill ranked also first in terms of weight in both the lake and WHTF. Largemouth bass ranked second in weight in both the lake and WHTF. These results are similar to those of 2000 and 1999 as well as those in the historical records.
When lake gill netting and electrofishing data for selected species are combined and examined for size class distribution, the data indicate certain population trends. Similar to 1999 and 2000, young-of-year (YOY) was the predominant size class of largemouth bass in 2001 although all the three size classes were fairly well represented each year (Figure 3.3-4).
Fewer intermediate (INT) and harvestable (HAR) size bass were collected in 2001 than in 1999 and 2000, while more YOY bass were caught.
FIGURE 3.3-4 Composition of largemouth bass catch in Lake Anna and WHTF (1999-2001) 80 60 [IC199
- 40) ic20001 20 - 3200 0
YOY INT HAR yoy<199 Int<300 har>300 Performing a similar analysis for bluegill (Figure 3.3-5) demonstrates an increase in the relative abundance of the YOY class and a decrease in the relative abundance of bluegill intermediate and harvestable size classes from 1999 to 2001. The increase in YOY bluegill was influenced by the result of the record December catch and the number of smaller bluegill.
27
Lake Anna ranked second in 2001 among lakes in the State of Virginia for largemouth bass citations with 50 being reported. A citation for largemouth bass is awarded for fish greater than 55.9 cm in length or 3.6 kg in weight. The lake was also third in black crappie citations as well with 18 being reported in 2001 (greater than 38.1 cm in length of 0.91 kg in weight).
Overall, the data for gill netting and electrofishing in 2001 reveal no major changes in the lake ecosystem when compared to past data. Lake Anna continues to support a healthy, well-balanced fish community.
3.4 Aciuatic Veaetation Methods Hydrilla is an exotic, submerged, aquatic macrophyte which, in most bodies of water, has the ability to grow and spread rapidly. The primary method of reproduction is by fragmentation. Hydrilla also produces overwintering structures in two (2) separate areas of 28
the plant: tubers, produced by the roots in the hydrosoil; anid turions, formed at the leaf axils of the plant. Each has the ability to produce new plants at the beginning of each new growing season.
An annual aerial survey is normally conducted to map hydrilla growth in Lake Anna.
Due to the tragedy that occurred on September 11, 2001, the security forNorth Anna Power Station was increased for the protection of the power station and also the citizens of Virginia.
Consequently, a national no-fly restriction was issued for all nuclear power stations including Surry and North Anna Power Station. This no-fly restriction was in effect during October and November when the aerial survey is normally conducted.
In addition to the air space restriction, a drop of 2.7 feet in lake level occurred from September to December 2001. This drop resulted in the dewatering of a major portion of the lake that typically supports hydrilla growth. The combination of the no-fly restrictions during the peak growth period and the drop in lake levels reducing the area that would be inhabited by hydrilla would not provide accurate information as to hydrilla growth in 2001 and resulted in the cancellation of the survey. The survey will continue in 2002.
3.5 Conclusions
° North Anna Power Station in 2001 operated at generation levels comparable to 1990, 1991 and 1996.
° The 2001 water temperature data from the continuous recorders indicated water temperatures within the historical ranges.
29
o Thermal stratification patterns measured in 2001 indicated similar stratification patterns to those in 1998 and 1999 and followed closely previously reported data.
o Gill netting and clectrofishing data showed increases in composition of the fish population for 2001.
o Based on numbers of citation largemouth bass and black crappie reported by anglers, Lake Anna ranked as the second best trophy lake for both largemouth bass and black crappie in the state for 2001.
3.6 Recommendations o Continue the biological monitoring of Lake Anna and the WHTF at its present level.
o Reduce the lake temperature surveys to twice a year. The data collected continues to show consistent thermal patterns which have been historically reported. Reducing the surveys to twice a year will have no adverse effect on the environmental monitoring of Lake Anna and will fully meet the permit requirements.
30
4.0 North Anna River 4.1 Temperature Methods
- Water temperatures (C) were recorded hourly at station NAR-1 in the lower North Anna River during 2001 (Figure 4.1-1) using an Onset temperature recorder. This instrument has an accuracy range of +/-0.50C. Station NAR-1 is located approximately 1 km below the Lake Anna dam.
S4tystvanis County LouibsCounty Caorline County K.
t"To Fredericksburg Hanover County MIC99 . ? . 4 Klometcs ! 2 4
'I. 33 UAmr cs la I.icom" Figure 4.1-1 Location of Worth Anna River temperature I
recording, electrofishing, and snorkel survey stations.
31
Results and Discussions Water temperatures in the lower North Anna River for 2001 were highest from June through September (Table 4.1-1). The maximum water temperature measured was 32.2'C in August 2001. Historically, maximum water temperatures have been recorded during July and/or August. The lowest water temperature measured was 5.00 C in January 2001.
Table 4.1-1 Mean, Maximum, and minimum hourly water temperatures (C) recorded in the North Anna River, at station NAR-1 by month, during 2001. Sample size (n)equals the number of hourly observations recorded each month.
NAR-1 Month Mean Max Min n January 8.7 10.9 5.0 744 February 9.4 11.3 5.8 672 March 10.5 12.0 8.4 744 April 15.5 21.0 10.2 719 May 21.8 24.7 18.4 744 June 26.6 31.5 22.8 720 July 28.3 30.5 26.2 744 August 29.3 32.2 26.3 744 September 26.1 29.9 21.3 720 October 20.2 23.4 16.8 744 November 16.0 19.6 13.4 720 December 13.5 16.8 9.3 744 32
4.2 River Flow Methods River discharge (cfs) data were obtained from the United States Geological Survey (USGS) to document the timing and magnitude of hydrologic events. These events, along with water temperature, are among the most important abiotic factors affecting the abundance
-and distribution of stream organisms. Data were obtained from USGS gaging station 01671020 (Hart's Corner) nearDoswell, Virginia. The station is located approximately 37 km downstream of the Lake Anna dam at NAR-6 (Figure 4.1-1).
Results and Discussion The historical pattern of seasonal flows in the North Anna River has generally been characterized by high flows in the winter and spring, reduced flows during summer, and even lower flows during late summer and early autumn. This is a pattern commonly exhibited by many rivers draining the eastern United States, and is generally reflective of annual rainfall patterns.
In 2001, North Anna River flows for the period January - March were below the 1980-2001 average with mean monthly flows between 150 and 600 cfs (Figure 4.2-1). River flows generally decreased from March to July with the exception of a "spike" in June following a two day rain event early in the month (flows exceeding 1250 cfs). The maximum daily mean recorded in 2001 was 3670 cfs on March 31 and was associated with a short-term rain event. Three additional days where flows ranged from 1800-2750 cfs occurred in March 33
and were also associated with rain events. Eighty-five percent, or 155 of the 182 days during the six month period, were below 50 cfs.
Figure 4.2-1 North Anna River Mean Monthly Streamflows 1980-2001
.- 2001 Monthly Means -m-- Monthly Means 19802001 1000 l
~800 IL 400 -
Cu 200 -
Jan Feb Mar Apr May Jun Jul Mg Sep Oct Nov Dec Month For the period 1999-2001, central Virginia experienced ongoing extreme drought conditions resulting in decreases in the water level of Lake Anna. In an effort to slow lake level reductions, in October 2001, flow releases from the Lake Anna dam were reduced from 40 cfs (minimum flow) to a new minimum flow of 20 cfs. A low-flow plan that included monitoring for various parameters was established as a part of the recent NPDES permit for North Anna Power Station (Attachment 1). Results of the monitoring will be reported separately from this report.
34
4.3 Fish Population Studies-Electrofisbing Methods Abundance and species composition data for the North Anna River fish assemblage in 2001 were collected during electrofishing surveys. Consistent sampling techniques have been used in all North Anna River electrofishing surveys since 1981.
An approximately 70-m reach of riffle/run type habitat is sampled at each station with an electric seine (Virginia Power 1986). Prior to sampling, each reach is blocked at the downstream ends with a 6.5-mm mesh net. Sampling is conducted by working the electric seine from bank to bank in a zigzag pattern from the upstream to the downstream end of the section. Nearby pool type habitats are then sampled for 10 minutes of effort with a backpack electrofisher. Fish sampled by electric seine and backpack electrofisher are collected using 6.5-mm, mesh dip nets.
Most fish collected are preserved in 10% formalin and transported to the laboratory for appropriate processing. Some larger fish are weighed and measured in the field and released. In the laboratory, a maximum of 15 individual specimens of each species is weighed to the nearest 0.1 g and measured to the nearest one (1) mm total length (DL). If more than 15 specimens of a species are collected, those in excess of 15 are counted and weighed in bulk. Electric seine and backpack electrofisher collections are then pooled by station and survey month for analyses.
Sample frequency for electrofishing is typically once per month each year in May, July and September. In 2001, electrofishing surveys on the North Anna River were conducted in May, August, and October.
35
Results and Discussion A total of 1,675 fish was collected from the North Anna River during electrofishing surveys conducted in 2001 (Table 4.3-1). The 2001 collection includes 27 species representing eight (8) families. Over the past 20 years of collections, 49 species of fish have been collected from the North Anna River (Table 4.3-2) with annual totals ranging from 18 to 32 species.
7.bM 4.-. dUt 0s bloX d (50 8t tc0d. ^r,~n Mq gust an Sepf,~*2001 sItWfi~ng '?
DM1Wgkrt~AnM Fdwr.
kAR-1 tlAR-7 liAPANlt oa Fra" 1 5.2 1 2.3 2 7.5 dAb mrb 1" 2996C 37 31S1 51 1010- 1C 153A 254 4553.9 7 17.2 55 1115 47 U4 56 54 165 225.7 17C 5Mss 7 14.5 44 5s 37 39 331 25 d st p 1 4.5 C 100.6 7 . 15.1 scods n*, o 554.1 6 101.5 4 655 Ab-1aie0035 1 11.2 1 11.2 t>&OPtls enus 3 .2 1 02 2 a.'
- 13
,bwpfSkmnkA 1 14Z2 1 14.2 AbeW.pivcm 1 1.2 11 17 7 10.1 a63 s5 Z2 7n2 hbbvps ibe&i 2 IL1 23 41.2 4 3.6 29 5a5s 5m6Anto c rs 2 77.7 21 21U 42 257.5 21 255.3 SItCS C"ostodda Ed1zon dobwus 1 4I 4 40-1 5 457 Ie nna t 4 4713 3 621 5 257.6 1 54o 13 413 Idalduddad Amekqms af 1 1.5 1 '.S ktWUnw t 1 2.3 1 2.3 Mkass Vyrhgs 3 13. 3 16 t&,a kslyds 52 307.3 3 1422 5 1417 26 I.X 152 73Z0 LepOfi* Swfaa H 1613 . as 44 U 71 59 5ao0 3 41712 LapoftMWVVCM0 7 .167.5 3 24.2 1 64 5 21.5 1C 2116.
Ltonmsft xkohus I 1447 1 1457
.JAxpON AAnb 3 *37.7 1 Z't 4 440-8 xavpeon Sawomm a 1072.5 3 200.0 1 12.5 12 121.0 Pwdda*
Eo#KeOo4mombdi 7 14.3 Is Z2.2 24 31.7 10 L3 59 765 VOeabn hyu 22 24.0 22 24.0 1t2 4S5 14 324 3 11.7 4. 8t2 37 5tt Esoddao Esoroa. 2 107.5 2 10MS s
522 3n2 397 1I51. 407 3&44.5 343 1774.1 1675 15765.3 NaWTbrofsped&& 15 17 20 19 27 36
Table 4.3-2 Fishes collected from the North Anna River during annual electrofishing surveys.
1981-2001.
Se ies f~ ~~a per &t -
appendix Petromyzontidae Lampetra appendix X X X Petromyzon marinus X x x x Anguillidae Anguila rostrata X x X X Clupeida e AMosa aestivalis X Dorosoma cepedianum X Esocidae Esox americanus X Esox niger X x X X
Cyprinidae Cyprinella analoslana X x X X
Hyboganthus reglus X Luxilus cornutus X X Lythrurus ardens X x X Nocomis leptocephalus X x X X
Nocomks micropogon X x X X
x Notemigonuxc crysoleucas x x X X
X Notropls smoenus x x X X
Notropis hudsonlus X Notropis procne x K X Notropis rubellus x x X X
Phozinus oreas X X Rhinichthys atratulus Semotilus corporalis X x X X
Catostormidae Catostomus commersoni x X Erlmyzon oblongus X x X Hypentelium nigricans K K X X AMoxostoma macrolepidotum Kx X X Ictaluridae Ameriurus natalis X X K Ameriurus nebulosus K X x Ictalurus punctatus K x
Noturus gyrinus x Noturus insignis X X K Aphredoderldae Aphredoderus sayanus X X Percichthyidae Morone americana X Centrarchidae Acantharchurpomotis K Centrarchus macropterus X Enneacanthus glorlosus X Lepomis auritus x X K X Lepomis gibbosus K X K X Lepomis gulosus X Lepomks macrochirus K X K X Lepomis microlophus K X X Micropterus dolomleu x K X Micropterus salmoldes K X K X Pomoxis nlgromaculatus K X K X Percidae Etheostoma olmstedl x X x X Etheostoma vitreum K X K X Perca flavescens x X Percina notograma X K X Percina peltata K X K X Soleidae Trinectes maculatus X na/xU042298 37
A common characteristic of stream systems is the tendency for a few species to numerically dominate the stream fish assemblage (Matthews 1982). Six (6) to 10 species have accounted for greater than 80 percent of the North Anna River electrofishing catch from all stations in any year since sampling began in a consistent manner in 1981 (Table 4.3-3).
This trend continued in 2001 with seven (7) species accounting for greater than 80 percent of all fish collected. These seven (7) species are presented in decreasing order: redbreast sunfish Lepomis auritus; redfin shiner Lythrurus ardens; american eel Anguilla rostrata; satinfin shiner Cyprinella analostana: margined madtom Noturus insignis; fallfish Semotilis oralis: and swallowtail shiner Notropis procne. These species have routinely been collected in relatively high numbers during electrofishing surveys of the North Anna River since 1981.
38
Table 4.3-3. Ranked abundancot species comprising grester than 60 percent of the pooled annual North Anna Rivelr *ectrmtahfng catch from all stations 1931.2001.
A species rank of I Indicates It was the most abundant 11th collected.
Speclet 1911 19t2 1)63 184 l1ts 16s I1t? 1988 1)69 1,90 1)81 1192 19)3 1994 19)3 196 lg7 1eat 1)99 2000 2001 Nolropbe proeno 2 1 I I I 4 7 3 2 2 4 - 7 2 I Cyprfn"lS anelostene 1 2 2 3 2 2 a 2 3 2 I 3 2 _ 4 2 I 4 Lepomls surtfus 3 3 3 2 3 4 2 3 2 1 4 2 I 3 1 Notropi, ruboltus - 8 8 10 3 4 4 3 3 6 4 3 a a Notunju Insignts a a
- 7 t 4 7 e 5 a S PerCMnt pe0t1ti 7 4 a a 4 10 _
6 - S I 6 Angulil roti rae 4 4 4 6 1 - 7 7 6
- 7 4 4 7 3 I_ 6 a 3 Lythrurus ardente 7 7 7 4 7 7 2 3 2 5 3 2 Nocomis m/cropogon _ - 8 8 _ 1 _
a _
Nocomls leptocephalus &
(0 Semollus corporans * - 4 9 _ _ _ _ _ _ _
S 1 Notropie Smoenus 7 6 - 7 _ _ - - 6 - _ _ _ _ _ _
Hypentellum nlgrtcans t _ - - - _ _ _ _
Notamfgonus crysolteucs _ S _ _ _ _ _ _ _ _ _
Pomoxls nlgromeculetus 5 _ _ _ _ _ _ _ _ _
Lepomls mocroehirurs Total number of species collected 26 27 29 31 31 29 32 30 1t 25 25 2) 25 23 22 20 24 26 28 23 27 Number of apedes, accounting for >80% 8 I 7 10 t 7 7 8 I 7 7 10 8 7 a 7 Percent of etectroflshlng catch 83 82 81 63 83 83 so 82 tO sO t4 83 83 es 82 82 84 sO 82 83 84
'-Indlcatee specles was not among those compreting greeter than 80% of the tlectrofishing catch
Table 4.34 indicates that in 2001 station NAR-1 )ielded the greatest numerical catch followed by in decreasing order, NAR4, NAR-2 and NAR-6. Biomass (total weight) in 2001 ranked in the same order as the catch numbers.
Table 4.3-4 Station total numbers and weights for 1999-2001 in the North Anna River 1999 2000 2001 Station # weight # weight # weight NAR-1 624 7741.0 252 4167.0 528 8364.0 NAR-2 693 2476.0 104 1418.0 397 1982.0 NAR-4 609 3146.0 204 1130.0 407 3645.0 NAR-6 332 2212.0 128 1295.5 343 1775.0 Past surveys have indicated that high winter and spring flows often result in decreased North Anna River catches. In 1993, the relationships between flow and annual fish abundance were examined. Based on the results of Spearman's correlation analysis (Hollander and Wolf 1973), low late winter/early spring flows tend to be conducive to relatively high electrofishing catches later in the year, and conversely, the high flows early in the year tend to result in low electrofishing catches (Virginia Power, 1994). This may have contributed somewhat to the lower numbers of fishes collected in 2000 when early spring flows were near the nonnal high flow conditions for the twenty year period 1980-2000. However, in 2001, moderately low flows occurred in March which is somewhat atypical of early spring flows, based on historical data (Virginia Power, 1994). These low flows continued throughout the summer and into the fall and winter months (Figure 4.2-1) and may have resulted in higher catches in 2001 compared to 2000.
40
4.4 Fish Population Studies- Direct Observation Methods To further amplify and understand fish population studies in the North Anna River, abundance and distribution data for smallmouth bass Micropterus dolomieu and largemouth bass are gathered via direct observation using snorkel surveys. Consistent observation techniques have been used in snorkel surveys since 1987 with some variation in sampling frequency at some stations among years due to instances of high river flow conditions, electrical storms, etc.
Snorkel surveys are conducted during July, August, and September. Four (4) stations (NAR-1, NAR-2, NAR4 and NAR-5) are monitored twice per month in July and August (Figure 4.1-1). Only one survey was conducted in September, 2001, as opposed to the normal two (2) surveys due to a number of issues including scheduling conflicts.
Abundance estimate procedures are identical to those employed since 1987 (Virginia Power 1988). Counts of smallmouth bass (SMB) and largemouth bass (LMB) are made while swimming 100 m transects along the north and south banks of each station. Transects folow an approximately one meter depth contour.
All bass sighted are categorized by species as to young-of-year (YOY) (<120 mm),
stock-size (120<SMB<280 mm or 120<LMB<305 mm), or quality-size (SMB>280 mm or LMB>305 mm). In addition to size group, all bass sighted are categorized as to type of cover being used; bedrock ledge (Ledge), boulders (Boulder), instream woody debris (Wood),
aquatic vegetation (Vegetation), or no apparent cover use (Open). Fish have to be within 41
0.5 m of a cover object at the moment of sighting to be included in a cover use category other than the Open category. Aquatic vegetation was included as a cover type beginning in 1993 due to annual increases in the amount of vegetation observed from 1990 through 1992, and apparent associated increased use by fish.
During each survey, three successive counts at each station are made at each bankside transect. Each observer makes an independent estimate of the distance that YOY smallmouth bass (T1h<120 mm) could be distinguished from YOY largemouth bass (CTL120mm) at each station. Lateral visibility at each station is estimated by averaging the independent estimates of both observers. Counts of smallmouth bass and largemouth bass are converted to density estimates (number/hectare of bankside channel) to account for differences in average visibility among survey days and sampling stations. Density estimates for all smallmouth bass and largemouth bass larger than YOY size are then pooled by species, station, and sample year to facilitate identification of species-specific and station-specific changes over time.
Calculations of median density estimates by sample year and associated 95% confidence intervals are based on Walsh averages (Hollander and Wolfe 1973). YOY densities are not calculated as it was doubtful that YOY are as susceptible to the observation technique as are larger fish, due primarily to their small size and cryptic nature.
Cover utilization data from the first of three sets of observations obtained during each snorkel survey are used to examine differences in cover use by smalimouth bass and largemouth bass. Data from only the first count are used because it is assumed fish observed during the first count would be relatively undisturbed by divers, whereas fish observed on the second and third counts may change their positions in response to divers passing by during the first count.
42
Results and Discussion Snorkel surveys for 2001 were conducted between 0812 and 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />. River temperatures at time of surveys ranged from 20.0 to 30.1 C and average visibility ranged from 1.5 to 4.0 meters. In 2001, observations were typical of surveys prior to 2000 where largemouth bass generally dominated the upper stations (NAR-I and NAR-2) and smallmouth bass the lower (NAR-4 and NAR-5) (Table 4.4-1). However, both species are occupying the entire study area. Variability between the north and south bank at any station appeared to be related to habitat complexity, i.e., fewer fish were observed along banks characterized by monotypic habitat than along banks with a variety of habitat types.
43
Table 4.4-1. Number of smafimouth bass and largemouth bass observed during Norlh Anna River snorkel surveys conducted In 2001. Sample sIze (n) equals the number of times each count was performed hI2001.
Smallmouth bass' Largemouth bass 2 Station Bank Count n SMBYOY SMB<1 1 SMB1>11 LMBYOY LMB<12 LMB>12 5_____.
NAR-1 North 1 5 1 0 0 24 7 10 2 5 o 0 0 22 7 3 3 5 2 1 0 26 5 1 South 1 5 1 0 0 10 4 17 2 5 2 0 0 10 7 13 3 5 3 1 0 5 8 16 NAR-2 North 1 5 4 0 0 3 7 1 2 5 4 1 1 2 5 3 3 S 4 4 0 1 5 3 South I 5 4 0 0 4 6 5
. 2 5 2 2 0 3 8 3 3 5 3 2 0 1 8 4 NAR-4 Norh 1 1 4 1 4 9 3
. 2 5 1 2 2 3 3 3 3 5 1 1 2 5 5 0 South 1 5 5 7 4 2 4 1 2 5 5 3 3 1 2 0 3 5 2 10 2 1 5 0 NAR-5 North 1 4 12 11 2 7 4 2 5 3 13 6 0 8 3 3 5 2 7 12 2 3 2 South I 5 0 4 4 3 10 2 2 5 2 5 2 6 5 2 3 .5 1 5 5 2 3 1
'SMYOY were less than or equal to 120 mm, SMB<11 were 121-279 mm, SMB>1 1were larger than or equal to 280 mm TL 2
LMBYOY were less than or equal to 120 mm, LMBc11 were 121-304 mm, LMB>11 were lalger than or equal to 305 mm TL Density estimates for largemouth bass and smallmouth bass observed in 2001 for stations NAR-1, NAR-2, NAR4 and NAR-5 are compared to historical density estimates in Figures 4.4-1 through 4.4-4. These estimates do not include young of year (YOY) size fish (TL# 120 mm) as it is doubtful that the smaller individuals are as susceptible to the observation techniques as are larger fish. Largemouth bass densities in 2001 at NAR-1 and NAR-2 averaged approximately 55 and 33 fish/hectare respectively while densities for 44
largemouth averaged approximately 21 and 17 fish/hectare at NARA and NAR-5. A comparison of largemouth bass densities in 2001 with those of 2000 indicates an overall increase in the number of fish/hectare at all four stations.
Figure 4.4-1. NAR-1 smailmouth and largemouth bass median densities, and mean visibilities, 1987-2001.
100- 3.5_
8~00 -
';i 2 Ic:5 CEl
= 20 0-C ~0.
1987 1989 1991 1993 1995 1997 1999 2001 Year 1JA-MB - l --LMB -*Visibilityl Figure 4. 4-2. NAR-2 smallmouth and largemouth bass median densities, and mean visibilities, 1987-2001.
50 - 3.5
~40-2.5~
30-2 C1 IC 10 s 0.5 00 Year
--*.-SMB-.-- LMB -- Visibilityl.
45
Figure 4.4-3. NAR-4 smallmouth and largemouth bass median densities, and mean visibilities, 1987-2001.
60- - 3.5 _
e50- 3 E
-2.5 Z a p40 -
-2 c I.. 30 -
- 1.5 ,e C £ E 20- -1 c 3 10- -0.5 E 0* I I - V. 1 . . - . -. 1 . >0
-A 9-b 1-91Sp . 99q9N99 9 9 9t99d
- Year I--SMB -.--LMB -dI-Visibilityl Figure 4.4-4. NAR-5 smalimouth and largemouth bass median densities, and mean visibilities, 1987-2001.
50 - 3.5 3.0 £ E 40-2.5 .?:
- a 30- 2.0 8 0,20 1.5 U E 1.0 c M 10 I 0.5 E 0- - 0.0 Year 1--a-SMB --#-LMB -*-Visibilityl 46
Smallmouth bass densities for 2001 at stations NAR-i and NAR-2 were calculated to be zero which also held true in 2000. Since 1998, smallmouth densities have decreased at NAR-1 and NAR-2 (Figure 4.4-1 and Figure 4.4-2). This is in contrast to the results from NAR-5 where smalimouth densities have remained relatively high (Figure 4.4-4). At NAR-(Figure 4.4-3), smallmouth bass and largemouth bass densities were about equal.
Observations of cover use by smallmouth bass and largernouth bass are difficult'to interpret without accounting for the availability of various cover types. For this reason, cover use data obtained in 2001 are primarily presented for documentation purposes (Table 4.4-2).
When cover use data are pooled for all stations in 2001 (Table 4.4-3) smallmouth bass were usually associated with boulder, open water, vegetation and wood when it was available.
Largemouth bass were mostly associated with vegetation (63%) and to a lesser degree with boulder (16%) and wood (13%). With the recent increases in the abundance of aquatic vegetation in the lower North Anna River, largemouth bass and smallmouth bass appear to be shifting from making nearly exclusive use of wood and boulder habitat to aquatic vegetation.
47
Table4.A-Z Covwueby ma~Rmouthbass and lrgemouith bass nh~e NorthAma Rkveobs a~d&xlnthe tstof tgee coiflmade dufrg snrkela surveys conducted In2001.
cover Type Cover Type MAR-I Ledge roldr Wood vegtton open NAR.4 iLedge Bdet Wood Vegetaton Open ShUSYOY 0 0 0 1 1 SMBYOY a 2 1 3 0 SM8<11 0 0 0 0 0O SM8<11 0 6 1 2 2 6 M0>' I o 0 0 0 0 SM81>11 0 2 1 0 1 UABYoY O 0 2 31 3 o o 0 5 1 UABei2 0 5 0 Ll18<12 O 6 4 3 1 LM8>12 0 0. 2 8 0 LM3>12 0 1 0 2 WM-2 Ledge Boulder Wood Vegetation Open NAR-S Ldge Boulder Wood Vegetton Open SMBYOY 0 0 0 6 2 SMBYOY 0 2 0 1 . I SMB<11 0 0 0 0 0 SM13