Yale Reservoir Kokanee (Oncorhynchus nerka) Escapement Report 2016

Transcription

1 Yale Reservoir Kokanee (Oncorhynchus nerka) Escapement Report 2016 North Fork Lewis River Hydroelectric Project Yale FERC No Prepared by: Jeremiah Doyle, PacifiCorp April 4, 2017

2 1.0 INTRODUCTION Since 1979, PacifiCorp biologists, along with various state and federal agencies, have conducted annual surveys to estimate spawning escapement of kokanee (Oncorhynchus nerka) in Cougar Creek, a tributary to Yale Reservoir. This report presents results of kokanee spawner surveys conducted on Cougar Creek and the Constructed Channel within the Swift Bypass Reach in Surveys are performed per Article 402(b) of the Yale and Swift Federal Energy Regulatory Commission (FERC) operating licenses and Article 402(c) of the Merwin FERC operating license. 2.0 STUDY AREA Surveys for kokanee spawners were performed on Cougar Creek and the Constructed Channel in Cougar Creek is a third order stream and tributary to Yale Reservoir in Southwest Washington. The creek pours directly from an underground lava tube for approximately 1,700 meters before flowing into Yale Reservoir. The Constructed Channel flows from a valve off of the Swift Power Canal for approximately 200 meters before entering the Lewis River channel within the Swift Bypass Reach. The valve that controls flow into the Constructed Channel is set to a level to contribute a constant flow of 14 cubic feet per second (cfs) (Figure 1). Figure 1. Survey area map. 2

3 3.0 METHODS To enumerate kokanee spawners two biologists, one on each side of the stream, walked together from the stream mouth upstream to its anadromous fish barrier. Each biologist counts spawning and holding kokanee on his/her side of the stream, including side-channels. This process is repeated on three to four occasions over the course of the kokanee spawn time-frame, mid-september through early-november, in order to garner a count at the peak of the spawning run. The highest count during the survey period is considered the peak, and is preceded and followed by surveys with a lower kokanee count. 4.0 RESULTS Cougar Creek Peak kokanee escapement estimates substantially decreased from 2015 (20,942) to 2016 (3,634). The 2016 spawning estimate of 3,634 fish (Figure 2) is the lowest count on record ( ). As in previous years, Cougar Creek was surveyed on foot with two surveyors. Kokanee were enumerated from the stream mouth upstream to its origin, a distance of approximately 1,700 meters. For survey purposes, the accessible anadromous fish habitat in Cougar Creek is broken into five survey reaches. There are a series of three major log jams in Reach 2 and 3 of Cougar Creek. In 2016, the upper extent of kokanee spawning was observed to be just below the first downstream log jam in Reach 2. Cougar Creek was surveyed for kokanee four times in 2016 (Table 1). Survey conditions during the sampling time period (Sep Nov) were ideal prior to the second week of October, at which time record rainfall visited the area and made surveys difficult due to high water. However, even with the higher stream flows, water clarity during each survey was ideal. 4.1 Distribution and Timing The peak kokanee count was recorded on October 24, 2016 (Table 1). This peak timing of kokanee abundance in 2016 is later than typically observed, but within historical timeframes on record ( ). Most kokanee were observed in Reach 2, which is consistent with prior years. This largest concentration of kokanee occurs just below the first log jam encountered on their travel upstream. 3

4 Table 1. Distribution and peak counts of kokanee in Cougar Creek in 2016 * Estimate uses a 2.3 multiplier of the peak count (Graves unpublished data, 1982) Kokanee Escapement Recruiting to Cougar Creek 2016 Reach 9/20 10/11 10/24 11/ Spawning Estimate 0 1,541 3,634 2, Escapement The kokanee spawning escapement in 2016 is estimated at 3,634 fish (Figure 2). This is the lowest spawner count on record and a substantial decrease from the peak observed in 2015 (20,942). Kokanee escapement into Cougar Creek has been less than the historical running average of 72,614 since 2006 (Table 3). This year s estimate is also well below the ten-year average of 26,224 fish. Kokanee Spawning Population Trend - Cougar Creek No. of Kokanee 200, , , , , ,000 80,000 60,000 40,000 20, Year Figure 2. Kokanee spawning estimates for Cougar Creek,

5 4.3 Length Distribution Due to low escapement numbers and high flows, kokanee carcasses were difficult to find in 2016, therefore lengths were only measured from 7 male and 15 female kokanee (Figure 3). Lengths came from both Cougar Creek and Constructed Channel kokanee. Lengths of kokanee in both reaches were similar to each other in 2016, and due to the low numbers of recovered carcasses were pooled. The average lengths of male and female kokanee in 2016 were 341 and 315 millimeters, respectively. Combined mean fork length of all kokanee observed in 2016 (323 millimeters) was larger than what was observed during 2015 (289 millimeters). Historically, mean fork length is a general indicator of number of spawners. The larger the fish, the less spawners observed; conversely, the smaller the mean fork length of spawners, the higher the spawner escapement. Fork Length Distribution No. of Kokanee Male Female Fork Length Figure 3. Length frequency histogram of male (n=7) and female (n=15) kokanee lengths (FL) sampled in Cougar Creek and the Constructed Channel, Washington 2016 The average length of this year s female kokanee (315 mm) was larger than the average female length observed in 2015 (289 mm). The average female fork length in 2016 is greater than the historical running average of 288 millimeters ( ). With the regression line established in Figure 4, the average fork length size for females in 2016 is under-estimated from the equation by two percent. The fitted line suggests that given the spawning population estimate the female average length should be 309 millimeters, instead of the observed average of 315 millimeters, an underestimate of 6 millimeters. This observed difference in estimation of two percent is neglible and may indicate that during the 5

6 reservoir life-cycle of this brood year that productivity was ideal for proper fish growth and development for this brood escapement estimation. The size at spawning estimate may be a good indication of reservoir production in terms of food availability and fish growth. When kokanee are smaller than anticipated (based on size at spawning and spawning escapement) it may be an indication that reservoir productivity was limited at some point during their residency in Yale Reservoir. Female Kokanee Mean Fork Length Vs. Escapment Abundance Mean Female Fork Length (mm) y = x R² = , , , ,000 Kokanee Escapment Estimate Figure 4. Relationship between mean kokanee fork length (female) and spawning escapement in Cougar Creek ( ). Red dot represents Constructed Channel One Constructed Channel kokanee spawner survey was completed on November 7, 2016 from its confluence with the Swift Bypass Reach upstream to its anadromous fish barrier, a distance of approximately 200 meters. A peak count of 890 kokanee spawners was recorded (Table 2), along with fork length measurements from one male and five female which were recorded and combined with the Cougar Creek data for an overall kokanee spawner length analysis. No kokanee spawner surveys were performed of this reach in 2015, so for comparison purposes numbers observed in 2014 were utilized. The escapement estimate in 2016 (2,047) is almost double to what was estimated in 2014 (1,035) (Table 2). It is important to note that the flows within the Constructed Channel come straight off the Swift Power Canal via a mechanically controlled stem valve that is set to release a constant 14 cfs. Habitat improvements to the Constructed Channel were completed by PacifiCorp in 2010, and the constant flow rate of 14 cfs has been in effect since that time. 6

7 Table 2. Historical Constructed Channel peak counts and estimated spawning escapement. Constructed Channel Year Peak Count Estimated Spawning Escapement , ,400 7, , , , DISCUSSION Kokanee spawning numbers within Cougar Creek in 2016 were the lowest observed on record. Smolt to adult returns observed in 2016 (0.06 percent) have also been observed in the past after significant stochastic events such as the eruption of Mt. St. Helen s in 1980 and the massive high water event in 1996, both of which experienced smolt to adult returns in the years after as low as 0.02 percent. Unlike these prior two occurrences in 1980 and 1996, where low returning spawning adult numbers could be attributed to an obvious event that preceded the low return, low escapement in 2016 has no such link to a preceding stochastic event during No unusual storm causing extremely high flows which could scour or compact redds occurred during this time period. It should be noted that anecdotal reports of large numbers of dead and floating adult kokanee were reported by fisherman while fishing Yale Reservoir during the spring of Biologists from PacifiCorp and the Washington Department of Fish and Wildlife (WDFW) investigated the reports with reservoir surveys, but no dead fish were observed. Supposed dead specimens from the anecdotal fish kill were brought by a fisherman to the Speelyai Fish Hatchery at which time hatchery staff sent in the carcasses to the WDFW s toxicology lab for analysis of cause of death by a certified fish health specialist. Cause of death was identified as hypoxia, but the results were inconclusive as to what could have caused the anoxic conditions within Yale Reservoir that lead to the death of an unknown number of kokanee. There was a high flow event on the Lewis in December This resulted in turbid conditions in the reservoir for several months through the winter and spring of 2016 which most likely reduced the plankton populations and created conditions that made it difficult for kokanee to effectively feed. It s possible this situation led to weakened immune systems in the kokanee which would have made them susceptible to disease organisms, though without further pathological investigation it is impossible to know the real cause. In the past, decreases in the trend-line (especially due to stochastic events), were quickly followed (within 2 to 3 years) by years of higher production as female size and fecundity 7

8 increased, presumably due to lack of competition. Spawning surveys in the next few years will provide insight on this suspected response. Table 3. Summary of data collected from Cougar Creek kokanee surveys from 1978 to Spawn Peak Estimated Moving Number of Length (mm) Mean Total % Year Count Date Escapement* Average Females** Females Fecundity+ Eggs Survival^ ,064 73,747 35,930 36, ,468, ,136 60,113 66,930 30, ,485, , ,999 86,620 62, ,237, ,614 58,912 79,693 29, ,176, ,750 13,225 66,399 6, ,736, ,875 6,613 56,435 3, ,226, ,915 22,805 51,630 11, ,760, , Sep-85 58,933 52,543 29, ,707, , Oct ,664 58,890 54, ,960, , Sep ,834 67,584 72, ,234, ,865 3-Oct ,790 75,421 76, ,138, , Oct ,658 77,608 50, ,008, ,859 9-Oct ,076 80,105 55, ,931, ,993 7-Oct ,584 87,854 94, ,462, ,801 2-Oct ,042 90,400 63, ,713, ,260 6-Oct ,998 95,999 89, ,480, , Sep ,609 97,094 57, ,763, , Oct-95 28,957 93,309 14, ,955, ,508 9-Oct-96 33,368 90,154 16, ,880, , Oct-97 18,789 86,586 9, ,041, ,435 6-Oct-98 5,601 82,729 2, ,502, , Oct-00 18,998 79,832 9, ,410, , Oct-00 49,439 78,511 24, ,265, , Sep-01 47,405 77,215 23, ,783, , Oct-02 56,925 76,403 28, ,901, ,004 9-Oct-03 87,409 76,827 43, ,598, ,964 8-Oct-04 16,017 74,574 8, ,104, ,226 7-Oct-05 32,720 73,080 16, ,245, , Oct-06 26,181 71,462 13, ,130, , Oct-07 14,203 69,554 7, ,810, ,780 3-Oct-08 15,594 67,813 7, ,602, , Sep-09 25,473 66,490 12, ,084, ,030 4-Oct-10 18,469 65,035 9, ,832, ,610 10/11/ ,103 64,449 22, ,893, ,150 10/8/ ,845 64,260 28, ,243, ,910 10/14/ ,393 63,236 13, ,735, ,620 10/3/ ,626 62,435 16, ,265, ,105 10/29/ ,942 61,008 10, ,086, ,580 10/24/2016 3,634 59,864 1, ,009, MEAN 26,028 59,864 72,614 29, ,804,823 *Peak Count x 2.3 (Graves unpublished data, 1983) **Assuming a 1:1 ratio + From the model: Fecundity = x Length of Females (Graves unpublished data, 1983) ^ Estimated Escapement of Adults (3 year-olds) / estimated number of eggs 8