408 E VARIABILITY IN PINK SALMON ESCAPEMENTS ESTIMATED FROM SURVEYS ON FOOT SPEaAL SOENTFK REPORT-FISHERIES Na 408 This work was financed by the Bureau of Comnnercial Fisheries under Contract Nos. 14-19-008-2453 and 14-19-008-9327, with funds made available under the Act of July 1, 1954 (68 Stat. 376), commonly known as the Saltonstall-Kennedy Act. UNITED STATES DEPARTMENT OF THE INTERIOR, STEWART L. UDALL, SECRETARY Fish and Wildlife Service, Clarence F. Pautzke, Comnnissioner Bureau of Connn-iercial Fisheries, Donald L. McKernan, Director VARIABILITY IN PINK SALMON ESCAPEMENTS ESTIMATED FROM SURVEYS ON FOOT by Williann L. Sheridan Contribution No. 115, College of Fisheries, University of Washington United States Fish and Wildlife Service Special Scientific Report--Fisheries No. 408 Washington, D. C. March 1962 CONTENTS Page Introduction 1 General description of streams 1 Variability in estimates 2 Testing procedures 2 Results of first set of tests 2 Results of second set of tests: Test IIA 4 Test IIB 4 Test lie 4 Evaluation and recommendations 5 Summary and conclusions 7 Acknowledgments "7 Literature cited 7 SCALE Figure l.--Area of biological investigations of effects of logging on salmon by Fisheries Research Institute, 1956-58. VARIABILITY IN PINK SALMON ESCAPEMENTS ESTIMATED FROM SURVEYS ON FOOT by William L. Sheridan Senior Fisheries Biologist Fisheries Research Institute University of Washington Seattle, Washington ABSTRACT Spawning pink salmon were enunnerated in five study streanns in the Hollis area of Southeastern Alaska. One stream was logged, two were being logged, and two were unlogged. Because enumeration required the ground survey as well as other methods, tests were made to assess variability in estimates of pink salmon abundance from surveys on foot between different observers and between successive counts by the same observer. Variability was lower when observers counted spawning salmon in well-defined riffle areas than when they counted in both pools and riffles. A method is proposed for obtaining more reliable indices of abundance from routine foot surveys. INTRODUCTION Because of increased logging in South- eastern Alaska, a need arose to evaluate the effects of logging on salmon. To satisfy this need the Alaska Forest Research Center began a study of physical changes in logged and unlogged streams in 1949, and the Fish- eries Research Institute started biological in- vestigations in 1956 under a contract awarded by the U.S. Fish and Wildlife Service utilizing Saltonstall-Kennedy funds. The Hollis area of Kasaan Bay in South- eastern Alaska was the principal location for the Institute's research (fig. 1). Study streams were Harris River and Twelvemile Creek, which are being logged; Maybeso Creek, which had been logged; and Indian and Old Tom Creeks, which are unlogged and were used as control streams. One of the factors studied was the size of yearly escapements of spawning salmon. This information was needed to define levels and patterns of escapements before and after logging so that postlogging changes might be detected. The abundance of spawners was assessed by various methods, such as sur- veys from the air and on foot, counting from towers, and nnark and recovery techniques. Surveys on foot have been used extensively to determine abundance of salmon in streams in Alaska and other West Coast States for many years. Although it has been recognized that variability existed in estimates made on such surveys, seldom has this variability been evaluated quantitatively. Since we were using foot surveys as one of our methods, we tested variability in esti- mates of pink salmon (Oncorhynchus gorbuscha) made on foot surveys by different observers under different conditions. GENERAL DESCRIPTION OF STREAMS Streamflow in all five of the streams studied is subject to wide and rapid variation because of precipitation, which is usually heavy in October and November. In all but Old Tom Creek most pink salmon spawn in intertidal zones, and chum (0. keta) and coho (0. kisutch) salmon usually spawn above tidal influence. Harris River, the largest of the five streams is 40 to 150 feet wide and has a watershed of 32 square miles. About 8 miles of the stream is used by salmon. Average gradient for the first 3.3 miles is 0.30 percent (James, 1956). Indian Creek, 15 to 50 feet wide, is con- fluent with the Harris River at approximately the 12-foot tide level. It has a watershed of 9 square miles and an average gradient of 1.0 percent for 1.8 miles (James, 1956). Only Note. --The author is presently with the Alaska Department of Fish and Game, Kodiak. about one-half of this stream is used by pink and chum salnnon. Maybeso Creek is 20 to 60 feet wide, and has a watershed of 15 square miles. More than 5 miles of stream are accessible to salmon. Average gradient is probably higher than for the other study streams (James, 1956, gives the gradient for 500 feet as 4.66 per- cent, but this high gradient does not prevail upstream from the area measured). This stream has an obstruction which may block salmon. A stepped falls at the mouth has, on periods of low stream discharge and small high tides, caused pink and chum salmon to die unspawned because they could not enter the stream. Twelvemile Creek is 30 to 70 feet wide and has a watershed of 14 square miles. About 5 miles are accessible to salmon, but spawn- ing occurs mostly in the lower reaches. Average gradient for 8,750 feet from lower intertidal zone upstream is 0.12 percent (per- sonal communication from G. A. James, Alaska Forest Research Center). Old Tom Creek has a watershed of 7.5 square miles. It is the only stream of the five that is connected to lakes, of which there are two: one is 85 acres, the other 62 acres. The streann forks about a mile above tidewater. Average gradient is about 0.79 percent (James, 1956). VARIABILITY IN ESTIMATES Counts nnade on foot surveys give rough indices of numbers of salmon using the streams. Foot surveys have usually been conducted in Alaska by making two to five visits to a stream during a spawning season. Stream surveyors walk up a stream and esti- mate total numbers of live salmon in pools and on riffles. Spawners are not a static pop- ulation because they continually move in and die throughout the season. Therefore, although periodic counts give a point estimate in time, a peak count is a reliable index only insofar as escapement curves are the same shape year after year. However, if we know the average duration of life of spawning salnnon and if we confine counts to riffles, by conducting several surveys we can correct for this type of error (Gangmark and Fulton, 1952). Counts must be restricted to riffles because (1) nunnbers of fish in deep pools cannot be estimated reliably and (2) variabil- ity in length of life of salmon in pools is probably greater than variability in length of life of salmon after they commence spawning and are on the riffles (we have observed tagged pink salmon in pools for weeks, while average length of time on riffles is 5 to 12 days). In this paper differences between estimates and the true population are not considered. Discussion is limited to variability between estimates of different observers and between successive estimates by the same observer. Although this type of variability has been discussed by Bevan (1961) for aerial surveys, it has not been evaluated for foot surveys. Testing Procedures Tests of variability were conducted under two sets of conditions in Mollis area streams in 1956 and 1957. The first set ofconditions is termed "ideal" and the second, "nornnal." In the first set counts were made only on shallow spawning riffles where salmon were clearly visible, boundaries were clearly de- fined, and there was little in and out movennent. Counting was done from the bank so that fish would not be disturbed. Each observer made a series of counts, one immediately following the other; each used the same path and had the same angle of vision. Light or other conditions changed little in the short time needed to complete an experiment (usually less than one-half hour). In most cases Polaroid glare shields were worn. In the second set counts were made on either a large part or the entire length of a stream that included both pools and riffles. This method is similar to that used on routine foot surveys in the past. Observers were coded by number in all tests. Veeder-Root hand counters with the tabulation covered with tape were used, and results were recorded without informing ob- servers of the nunnber on the counter. All observers were briefed on proper procedure. Resiilts of First Set of Tests Basic data, mean, standard deviation (s), and coefficient of variation (C.V.) for four tests conducted under ideal conditions show the variation to be expected between observers and between successive counts by the same observer when 30 to 250 salmon are on a riffle (table 1). When the number of salmon to be estimated is low, variation is high. It decreases with increasing numbers of salmon up to a point and then again increases with increasing numbers of salmon. Analysis of variance (table 2) shows a signifi- cant F value (95 percent) only once out of eight times, and this in relation to difference between observers in test IB. In all four experiments variance ratio was higher between observers than between successive counts by the same observer. 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Results indicate that under ideal conditions, variability in riffle counts was low between different observers and between successive counts by the same observer. Resxilts of Second Set of Tests Test IIA.--Five observers counted live pink salmon in the Harris River intertidal zone (containing both pools and riffles), first in an upstreann direction and then in the same area in a downstream direction. Results are given in table 3. Analysis of variance of these data shows no significant difference (95 percent) either between observers or between counts. Test IIB.-- Three observers counted live pink salnnon in Harris River from the 13-foot tide level to the Fisheries Research Institute terminus (about 8,000 feet; such a ternninus nnarks the end of a survey area and is usually located upstream from greatest abundance of spawners). The counting area was divided into three sections and subdivided into pools and riffles (some variability may have occurred be- cause of an observer's idea of what constituted a pool and what a riffle, but these were fairly well defined). Results are given in table 4. In this test variability be twee nob servers was generally high and was higher in estimates of numbers of salmon in pools than on riffles. Very high variation in counts of salmon in pools in section 2 (C.V, almost 100 percent) is an indica- tion of what we can expect from pool estinnates. Test lie. --The observers who conducted test IIB counted live pink salnnon in the same portion of the Harris River again on Septem- ber 11, 1957. Results are shown in table 5. Table 3. — Test IIA conducted in Harris River intertidal zone, September 10, 1957 Count UDStream Count downstream Observer (no . of fish) (no . of fish) Mean C.1 C.V. 2 2 258 220 239 26.9 11.2 6 192 205 199 9.2 ii.6 7 163 177 170 9.9 5.8 8 181 2li2 212 I43.I 20.3 10 170 188 179 12.7 7.1 Mean 192.8 206.h 8 38.08 2-5.79 C.V. 19.8 12.5 ^ standard deviation. 2 Coefficient of variation (in percent). Table h. — Test IIB conducted in Harris River for a distance of 8,000 feet, September 2, 1957 Observer Section 2 Pools Riffles Section 3 Pools Riffles Section h Pools I Riffles Total for stream 8 515 10i( 110 U6 hS 8 9 93 128 li6 21 121 9 10 1?7 67 79 37 128 17 Mean 21^5 100 78 35 98 11 567 s^ 233 31 32 13 I46 5 227 C.V.2 95.3 30.8 I1O.9 36.6 li7.0 13.8 39.9 ^ standard deviation. ^ Coefficient of variation (in percent), Table 5. -Test lie conducted in Harris River for a distance of 8,000 feet, September 11, 1957 Section 2 Pools I Riffles Section 3 Pools Riffles Section h Pools Riffles Total for stream 8 10 lJi8 100 13 60 35 9 66 129 0 0 79 hi 10 22 I61i 32 23 9^ 55 Mean 33 11^7 ai* 12 78 1^6 359 si 29 18 52 12 17 10 35 C.V.2 90.1 11.9 117.2 96.5 21.9 22.1 9.8 Standard deviation Coefficient of variation (in percent) Variability of estimates was again high in pools in section 2 and was also high in riffles in section 3. It is difficult to explain why ob- server 9 saw no fish in section 3, particularly since section division points were well marked. Apparently this was an error on the part of the observer. Differences in variation between pool and riffle estimates by three observers in par- ticular sections on September 2 and 11 appear random. Tests IIA, IIB, and IIC all involved more than two observers. Four additional tests, IID, HE, IIF, and IIG, were made to compare one observer's estimate with another's. Variability between observers in these tests is apparent (table 6). Data were analyzed on the bases of significance of differences of means and by analysis of variance. In some instances difference between means of ob- servers was significant, in others not. Anal- ysis of variance showed a significant dif- ference between observers in only one test, IID, The degree of variation is more apparent from the data in table 6 than it would be from analyses of variance of the data, and there- fore no analyses are presented. Evaluation and Recommendation Variability between different observers estimating numbers of live pink salmon was higher under normal than under ideal condi- tions. Under normal conditions variability Table 6. --Results of tests IID through IIG where one observer's estimate of number of fish is compared with another's, HoUis area streams, 1956 Test IID - Twelvemile Creek, September 1, 1956 Test UE - Twelvemile Creek, September 11, 1956 Observer 2 Observer 3 Section Ob server 3 Observer 4 Pool 1 Riffle Pool 1 Riffle 1 512 403 1 301 379 142 331 2 0 0 2 0 23 0 27 3 14 6 3 0 44 0 31 4 17 22 4 24 63 20 43 5 200 141 5 0 79 0 66 6 200 53 6 0 112 100 98 7 34 35 7 0 165 0 117 8 120 90 8 760 149 372 125 9 178 139 9 0 266 0 248 10 112 86 10 516 283 200 250 11 596 420 11 0 659 50 513 12 103 64 12 550 108 400 104 Total 2,086 1,459 Total 2 , 151 2,330 1.284 1,953 Test IIF - Indian Creek, Septennber 2, 1956 Section Observer 2 Pool I Riffle Observer 3 Pool I Riffle 1 124 74 73 69 2 0 5 0 4 3 573 1,164 428 918 Test IIG - Indian Creek, September 10, 1956 Observer 3 Pool Riffle Observer 4 Pool f Riffle 1 144 2 0 3 121 163 89 26 76 0 72 977 0 1,198 Total 697 1,243 501 991 Total 265 l,2l6 89 1,296 was higher when observers estimated num- bers of salmon in pools than when they esti- mated them on riffles. In addition, variation generally increased with increase of mean estinnate. Such results indicate that to obtain the best indices of abundance of salmon from foot surveys, pools should be ignored, and num- bers of salmon should be estimated only on riffles. Therefore, I suggest that in small streanns a sufficient number of estimates should be made of salmon on riffles to form anabundance curve. If average length of time salmon re- main on riffles is known (this can be deter- mined from small-scale tagging experiments), then total number of salmon can be calculated for the season. In larger streams where, for sonne reason, fish cannot be counted on all the riffles, well- defined spawning riffles should be chosen at random (in some streams stratification with regard to upstream and intertidal zone or other classifications may be desirable). Sum- mation of estimates for each index riffle fur- nishes an index of abundance for the stream that is comparable from stream to streann and from year to year. This type of enumeration decreases variabil- ity because numbers of salmon in pools are not estimated. Second, it allows surveyors (in large streams) to concentrate on a few index riffles rather than attempt to estimate the nunnber of salmon in the entire stream. Finally, it does away with the need to use the peak count as an index. Environmental conditions such as light dif- ferences, turbidity, rain dimpling water sur- face, and stream stage can increase variability in estimates. Hence, time of counting should be standardized as much as possible around these variables. SUMMARY AND CONCLUSIONS 1. A cooperative researchprogram between the Fish and Wildlife Service, the Forest Service, and the Fisheries Research Insti- tute to study effects of logging on salmon streams in Alaska started in 1956. Part of the program involved estimating abundance and distribution of adult salmoninfive streams in the HoUis area of Kasaan Bay, Southeastern Alaska. 2. Tests of variability of estimates of dif- ferent observers and of the same observer counting the sanne area more than once were made in 1956 and 1957. Results showed that: a. In tests made under ideal field condi- tions (riffles only), variability of estimates of pink salmon (between different observers and between successive counts made by the same observer) was low. b. In tests conducted under normal conditions (pools and riffles), variability between observers counting salnnon in pools was much higher. Therefore, it is suggested that periodic counting be restricted to shallow riffle areas so that an index of abundance can be obtained by using a method such as Gangnnark and Fulton's (1952). Further, counting should be standardized around such variables as amount of available light, stream levels, and others. ACKNOWLEDGMENTS I would like to acknowledge the assistance of the following people: Donald E. Bevan, who developed basic techniques to assess variabil- ity of different observers in estinnates of abundance of salmon on spawning grounds; William F. Royce and Robert L. Burgner, who made many helpful suggestions in preparation of this manuscript; and Charles Junge, Jr., who examined statistical treatment of data and made suggestions. William J. McNeil, Donald Hansler, Thomas Calkins, Donald Day, Donald Campbell, Walter Vaux, Richard Tyler, Roger Meyers, and Patrick McGunnigle were the observers. LITERATURE CITED BEVAN, DONALD E. 1961. Variability in aerial counts of spawn- ing salnnon. Journal of the Fisheries Research Board of Canada, vol. 18, no. 3, p. 337-348. GANGMARK, HAROLD A., and LEONARD A. FULTON. 1952. Status of Colunnbia River blueback salmon runs, 1951. U.S. Fish and Wild- life Service, Special Scientific Report- - Fisheries No. 74, 29 p. JAMES, GEORGE A. 1956. The physical effect of logging on salnnon streams of southeast Alaska. U.S. Department of Agriculture, Forest Service, Alaska Forest Research Center, Station Paper No. 5, 49 p. MS #1139 GPO 9 26 7 2B MBL WHOI Library ■ Serial 5 WHSE 01535