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HomeMy WebLinkAboutBradley River Salmon Escapement 1988I I I I I I --l David E. Erikson K. Michael McDowell Elizabeth A. Weisbrod Mary M. Pearsall DAMES & MOORE AECORLJ~ Rt.£· NO -rM"t" /-Hd 014/ ... "RECORD COPY" RETURN TO BRADLEY O&M FILES Dames&Moore BRADLEY RIVER SALMON ESCAPEMENI' MONITORING STUDY 1988 Prepared for: BECHTEL CIVIL, INC. AND ALASKA POWER AUTHORITY by David E. Erikson K. Michael McDowell Elizabeth A. Weisbrod Mary M. Pearsall DAMES & MOORE INTRODUCTION The Federal Energy Regulatory Commission {FERC) license granted to the Alaska Power Authority for the Bradley Lake Hydroelectric Project {Project No. 8221-000) stipulates that a plan be developed and implemented to monitor the abundance of salmon in the Bradley River. A salmon monitoring plan was submitted to FERC in June of 1986 {Alaska Power Authority, APA, 1986a). The intent of this monitoring plan is to pro- vide a yearly index of salmon abundance both during the pre-operational and post-operational periods to allow an appraisal of project impacts to the salmon resources of the Bradley River. This report summarizes the results of the third year (1988) of the pre-operational studies of adult escapement to the Bradley River per the proposed scope of work described in the Salmon Monitoring Plan. The salmon resources of the Bradley River have been documented in considerable detail through a series of studies {USFWS 1982; Woodward- Clyde Consultants 1983, 1984; Northern Technical Services 1985). The results of these early studies indicated that the pink salmon (Oncorhynchus gorbuscha) was the principal salmon species using the river for spawning although smaller numbers of chum (~ keta), coho (~ kisutch) and chinook salmon (~ tshawytscha) also spawned in the river. The 1985 study by Northern Technical Services represented the first year of study for the pre-operational salmon monitoring program. However, the sampling methodology was modified during the next season; therefore, comparable data have only been collected during the 1986 through 1988 field seasons. These later studies were conducted by Dames & Moore (APA 1986b, 1987). The 1986 and 1987 studies demonstrated that pink salmon were indeed the major spawners and that the river also sup- ported small runs of the other salmon species. considerable data on the abundance, distribution of spawning areas, and the timing of the runs have been collected over the last 3 years. The habitat available for spawning is restricted to a short segment of the river between an impassable waterfall upstream and the tide flats downstream. Portions of spawning habitat were altered during 1986 as a result of extensive flooding. The primary objectives of the 1988 field effort were similar to those of the 1986 and 1987 studies. Some minor modifications were made to the sampling techniques to address questions raised during the first 2 years of the multi-year study program. The objectives were to: 1 0 0 0 Duplicate sample methods used during 1986 and 1987 to compare abundance between years, Provide an index of abundance or estimate of the 1986 salmon escapement to the Bradley River with emphasis on pink salmon, and Provide an estimate of fish leaving the Bradley River from the primary study area with a hoop net at River Mile {RM) 3.2. STUDY AREA The primary study area was the same as during the last two seasons and consisted of a 2,011-m {6,600-ft) stream segment extending from the downstream end of Riffle Reach to the upstream end of Bear Island Slough {Figure 1). This portion of the study area encompasses almost all of the known spawning habitat in the Bradley River system. An additional hoop net site was established this year in the lower portions of the Bradley River (RM 3.2). A small clear-water tributary of the Bradley River, Fox Farm Creek, at RM 2. 5 was also monitored for salmon escapement as a part of this study program. METHODS Study Duration The study was conducted over a 9-week period from July 19 through September 15, 1967, similar to the period covered in 1966 and 1967. This sampling period was originally selected to coincide with the dura- tion of the pink salmon run based of the results of the earlier studies. The field crew traveled to the site on Monday of each calendar week and intensive sampling took place on every Tuesday, Wednesday, and Thursday. Since the sampling periods are based on the calendar week, the the starting date this year was 5 days later than 1987. Hoop Net Sampling Hoop nets were used as the primary sampling technique as in the 1966 and 1967 field efforts. This technique was originally selected to standardize sampling effort that would allow comparisons between years based on a catch-per-unit-effort {CPUE) index. Hoop nets proved to be 2 SCALE Job No. 12023-030 N Hoop Net Site 8 LOWER BRADLEY RIVER WITH SALMON ESCAPEMENT STUDY AREA Dames & Moore Figure 1 very successful at capturing adult salmon during the 1986 and 1987 field seasons. The hoop nets used for the 1988 study were the same as those used in last year 1 s study (Figure 2). These nets were made from 6. 35-cm (2.5-inch) stretch mesh nylon with 1.8-m (6-ft) diameter hoops. Net wings were attached to the main frame of the net in various configura- tions depending on the location of net in the river. The hoop net sites established in 1986 and modified to some extent in 1987 were reoccupied again this year. No significant stream course alterations occurred since the end of sampling last fall. Thus it was not necessary to relocate any of net sites from those used in 1987. However, some minor reorientations were necessary for hoop net 3 because of changes in current patterns during the study period. During each weekly sampling period, the hoop nets in the primary study area were set Tuesday morning and fished until Thursday morning for a total of 48 hours, after which they were removed from the water until the following week. The additional hoop net at RM 3.2 was ini- tially set the third week of the study period and fished for 24 hours each week through the last week of the study period. This net was usually set on Wednesday morning and pulled on Thursday morning. During typical operations, each net was checked every 4 hours during the daytime and then left to fish overnight. The fish were removed at each check, identified to species, sequentially numbered Flay spaghetti tags. tagged using a different colored Flay tag. measured, and tagged using Each salmon species was Since sockeye salmon (2..:_ nerka) only occasionally wander into the Bradley River, they were only marked by splitting the left pectoral fin. Sex and spawning condition were also recorded for all salmon captured. Spawning condition codes were the same as those used during the 1987 season C.~PA 1987). Scale samples were taken from selected chinook salmon for aging by Alaska Department of Fish and Game (ADF&G) personnel. Beach Seine Sampling Beach seining was used primarily as a technique to capture and tag adult salmon in addition to those caught in the hoop nets and secondarily as a index of abundance. The beach seine utilized was same as was used in 1987 CAPA 1987). The seine was deployed in the same manner as in previous years by tying one end to shore and feeding the remainder off the bow of the boat as it traveled in reverse making a broad sweep down 4 c.. 0 0' z 0 1\) 0 1\) (,) I 0 (,) 0 -n IS. c ""' (!) 1\) 5' ~ "' go i: 0 0 ;; 2 112• STRETCH MESH NETTING THROUGHOUT FLOATS 12• THROAT 1a• THROAT ~ 8.\..M. HOO/. / 6' SQUARE FRAME OPENING LEAD WEIGHTS I...: 16' ..,.1 BRADLEY RIVER HOOP NET DESIGN the river and back to the beach. If fish were captured, the effort was repeated up to three times. captured fish were processed in the same manner as for the hoop net catch. A majority of the effort this year was focused on the best seine sites, Site A and D (Figure 3), and these sites were sampled each week except the last week (September 13-14) when no seining was conducted. At Site B, problems were encountered in attempting to make consistant sets that limited the use of this area. Seine Site E could not be sampled this year because of consistantly high water at this location. Electroshocker Electroshocking was primarily used as a means of delineating areas used by spawning fish and secondarily for capturing fish for mark and recapture. A Coffelt backpack shocker was used for the first 2 weeks until problems developed with this unit. A Smith-Root Type XI backpack electroshocker was used both from the boat and on foot in shallow riffle areas during the remainder of the season. Electroshocking was conducted at regular intervals throughout the the study period and the areas covered were essentially the same each week. Fish captured with this method were processed in the same way as those captured in hoop nets and beach seines. Numbers of fish stunned but not captured were also recorded. carcass counts A shallow, 6-m (20-ft) long net wing was stretched between several stakes in the shallow water at the downstream end of Riffle Reach (Figure 1) for the purpose of catching carcasses as they wash down- stream. This net was set during the third week and left set for the remainder of the study period. The net was checked at least two times per week for dead fish and any encountered were checked for tags. High water during weeks six and seven covered the top of the net so it could not monitored. Low water during week eight left the net out of water. Miscellaneous Observations At the end of the 1986 season several pink salmon tags from fish tagged in our study area were were found in a small clear water tributary to the Bradley River, Fox Farm Creek. Periodic visits were made each week during the 1987 season to census Fox Farm Creek for tagged fish. This weekly stream census was continued this year throughout the study period. The presence of harbor seals and other biological events were noted when appropriate. 6 -z--,.-- KEY: >= Hoop Nets @ Seine Site 0 300 Scale in Feet Job No. 12023-030 I Hoop Net Site 8 + (see Figure 1) 1988 HOOP NET SITES AND BEACH SEINE LOCATIONS Dames & Moore Figure 3 Population and Escapement Estimation The methods used for estimating populations were the same as those from previous years (APA 1986b, 1987). Population estimates were calcu- lated for abundant salmon in the river during each week based on the Peterson model, as modified by Chapman (Ricker 1975). The formula (see Table 3) reduces the potential bias in mark-recapture population estima- tes, particularly when the number of recaptures is relatively small. The 1986 data were also recalculated using this formula. These estima- tes are based on the following assumptions: 1. Salmon numbers remained stable during the 3-day sample period. 2. All fish marked during the previous 2 sample weeks were still present in the study area. 3. Fish marked 3 or more weeks prior to the sample week were no longer present in the study area. 4. Marked and unmarked fish were equally susceptible to capture. As evident from these assumptions, the resultant population esti- mates should be treated with caution. It is likely that assumptions regarding immigration and mortality/emigration that form the basis for mark-recapture population estimates are violated by andromous salmonids during a spawning run. However, the approach and sampling methods used in these studies were specifically designed to minimize these potential sources of bias. The nature of the spawning run is likely to cause an underestimate of the population during the early part of the run when immigration rates are greatest. Conversely, later in the run when mer- tali ty rates increase, these methods are likely to overestimate the actual population. An approach consistent with that used by the Alaska Department of Fish and Game (Pirtle and McCUrdy 1980) was used to derive a rough estimate of the total salmon escapement to the Bradley River. In this method, weekly population estimates are combined and then divided by 2.5. 8 RESULTS Overall catch All species of North American Pacific salmon were captured in the Bradley River during the 1988 field season which is similar to the results of the 1986 and 1987 studies. The pink salmon was again the most abundant species but total catch was significantly lower than the previous two seasons (Table 1). Chinook salmon were second in overall catch closely followed by Coho Salmon. The catch of sockeye was several times higher this season with a total catch of 61 (11 were recaptured). The total catch for churns was low again this year with most of the indi- vidual fish being caught in the first week. The percentage of recap- tures of tagged fish was quite variable among species. Coho and pink salmon had the lowest recapture rates, 10 and 13 percent, respectively. While churn and chinook salmon had much higher rates of recapture (34 and 29 percent, respectively). The only other species caught in the river this year were slimy sculpins ( Cottus cognatus) and Dolly Varden (Sal velinus rnalrna). Most Dolly Varden are small enough to escape through the mesh of the hoop nets and the seine so accurate counts were not possible. catch rates of the larger Dolly Varden was very low in comparison with previous years. Hoop Net Sampling Hoop nets again proved to be a good, standardized method of sampling salmon in the highly turbid waters of the Bradley River. Their effectiveness is especially great during years of very low escapement, such as 1988, when fish densities are too low to effectively sample using other methods. Water levels in the Bradley River remained con- sistantly high throughout most of the field season which afforded uni- form sampling effort for most all of the nets. Some minor adjustments were necessary for nets 3 and 5 to assure that they fished properly. Pink Salmon The hoop net catch data for pink salmon for each site, by week (Table 2 and Figure 4) indicate that the pink run could be considered a near failure. The run was in progress during the first week of the study with 8 captured and tagged and built only slightly to a peak of 24 new fish tagged during week six (August 22-24). The total catch fell off considerably in week seven and by week eight and nine, only a few 9 TABLE 1 TOTAL ADULT SALMON CATCH FOR ALL SAMPLE METHODS COMBINED (recapture percentage in parentheses) Pink Chum Chinook Coho Sockeye Total Sample Week Salmon Salmon Salmon Salmon Salmon Salmon 1 July 19-21 8(0) 21< 30) 24(8) 0(0) 4(0) 57 ( 16) 2 July 26-28 10 (0) 6(17) 20(25) 0(0) 0(0) 36(17) 3 Aug 2-4 13(8) 10(33) 15 ( 27) 0(0) 6(17) 44(20) 4 Aug 9-11 16(6) 6(50) 13 (54) 1( 0) 3(0) 39 ( 31) 5 Aug 16-18 15(7) 3(67) 6(50) 5(0) 5(0) 34(21) 6 Aug 23-25 32 (19) 1(0) 5(0) 16(6) 22(18) 76 (14) 7 Aug 30-Sept 1 22(23) 0(0) 1( 0) 43(12) 11 ( 27) 77(17) 8 Sept 6-9 2 (100) 0(0) 1(0) 9(22) 5(60) 17(35) 9 Sept 13-15 5 ( 20) 0(0) 0(0) 9(0) 5(0) 19(5) Study Total 123 (13) 47 (34) 85(29) 83 (10) 61< 18) 399 (19) SAMPLE SAMPLE YEAR WEEK TC 1988 1 8 2 9 3 13 4 12 5 13 6 29 7 22 8 1 9 5 1987 1 3 2 14 3 36 4 54 5 205 6 247 7 154 8 74 9 31 1986 1 5 2 18 3 95 4 152 5 143 6 190 7 236 8 145 9 63 PINK CPUE 0.026 0.027 0.040 0.036 0.039 0.087 0.066 0.003 0.015 0.010 0.040 0.110 TABLE 2 BRADLEY LAKE MONITORING STUDY TOTAL CATCH AND CATCH-PER-UNIT EFFORT SUMMARY DATA -All SPECIES BASED ON HOOP NET DATA 1986 THROUGH 1988 CHUM COHO TC CPUE TC CPUE 21 0.069 0 o.ooo 6 0.018 0 o.ooo 8 0.025 0 0.000 6 0.018 1 0.003 2 0.006 5 0.015 1 0.003 16 0.048 0 0.000 43 0.129 0 0.000 9 0.027 0 0.000 9 0.026 2 0.006 0 0.000 6 0.020 0 0.000 18 0.050 0 0.000 0.160 11 0.030 0 0.000 0.620 2 0.006 3 0.007 0.750 1 0.003 11 0.030 0.460 0 0.000 12 0.040 0.260 5 0.020 2 0.010 0.390 1 0.003 17 0.050 0.030 21 0.140 0 0.000 0.070 57 0.220 0 0.000 0.310 131 0.420 0 0.000 0.460 95 0.290 0 0.000 0.410 67 0.190 14 0.040 0.810 19 0.080 16 0.070 1.510 0 0.000 1 0.010 0.440 1 0.005 56 0.170 0.180 1 0.005 38 0.110 SOCKEYE CHINOOK TC CPUE TC CPUE 4 0.013 24 0.079 0 o.ooo 19 0.057 6 0.019 15 0.046 3 0.009 lJ 0.039 5 0.015 6 0.018 21 0.063 5 0.015 11 0.033 1 0.003 5 0.015 1 0.003 5 0.015 0 o.ooo 0 0.000 2 0.006 0 0.000 1 0.003 0 0.000 8 0.024 2 0.006 7 0.021 0 0.000 6 0.018 1 0.003 6 0.018 2 0.006 5 0.015 1 0.003 0 0 0 0.000 0 0 2 0.012 3 0.020 1 0.004 7 0.030 2 0.007 10 0.030 0 0.000 lJ 0.040 3 0,009 2 0.010 0 0.000 11 0.050 0 o.ooo 0 o.ooo 2 0.006 0 0.000 1 0.003 2 0.010 Job No. 12023-030 co LJ} ~ oo ~ w ~ ~ n N o 0 0 0 0 0 0 0 0 0 CPUE by Week -Pink Salmon Dames & Moore Figure 4 pinks were still in the river. Spawned out pinks were captured in the hoop nets from week five through week nine, which indicated some spawning did occur. Chum Salmon The chum salmon run was underway by the time the first hoop nets were set in week one (July 19-20; Figure 5) and the largest catch during the season occurred during this week (14 fish tagged). The catch fell off steadily after the first week and only a few individuals were pre- sent in the river after the third week of the study (August 2-3). The recapture rate was high which suggests a large portion of the spawning population was being captured in the hoop nets. A total of 30 individual fish was tagged over the course of the study. Of these, 13 were in the process of spawning when captured and only 1 was spawned out. This would tend to suggest that very little spawning activity occurred in the river again this year. Chinook Salmon The CPUE data indicate that chinook salmon were present in the river at the start of the hoop net sampling (July 19-20) with 24 indivi- dual fish tagged the first week (Figure 6). The catch decreased steadily after the first week to only one individual caught during weeks seven and eight. From the progression of the reproductive condition of the fish it was assumed that peak of spawning occurred around weeks three and four (August 9-17). Thirty-four percent of the total chinook catch were recaptures, which indicates the hoop nets are catching a significant number of spawners. Only three individuals were recaptured more than once. Of the 60 individuals tagged, 17 were females, 33 mature males, and 10 were small, precocious males (jacks). The pattern of chinook distribution within the river appeared to center around Tree Bar Reach (nets 5 and 6) in the upper portion of study area. Both of these nets are located in backwater areas off the main stream. In Bear Island Slough <net 6), a number of fish was cap- tured during the first week but numbers fell off after that. Only two chinook were recaptured in the slough. Net 5 had fairly consistant catches of chinook throughout the season and many of the recaptures were from this net. 13 L[) ~ 0 Job No. 12023-030 L[) !"') 0 !"') 0 L[) N 0 N 0 L[) 0 0 L[) 0 0 0 en IX) IX) en lO IX) en CPUE by Week -Chum Salmon Dames & Moore Figure 5 OJ 0 0 Job No. 12023-030 r--- 0 0 1..0 0 0 L.() 0 0 "<t 0 0 I"') 0 0 C\J 0 0 0 0 0 0 0 OJ OJ OJ (j) CPUE by Week -Chinook Salmon Dames & Moore Figure 6 Scale samples taken and read from 23 of the adult chinook salmon showed a wide range, and a nearly equal distribution of age classes, in the Bradley River population (seven 2-ocean, eight 3-ocean, and eight 4-ocean fish). Only 17 of these scales had a complete record of both freshwater and saltwater growth rings. These were compared with scales from two returns of hatchery-reared chinook in Kachemak Bay (Halibut Cove and Homer Spit). Bradley River fish The freshwater rings on the scales of six of the strongly resembled the hatchery-reared chinook returning to these locations (S. Hammerstrom, Alaska Department of Fish and Game, personal communication). These hatchery-reared fish included four different age classes and therefore were derived from different releases. The remaining chinook were believed to be wild fish. Coho Salmon The catch statistics for coho salmon indicate that coho moved into the river during week four with the first coho being caught on 10 (Figure 7). The CPUE steadly increased throughout August to during week seven <August 30-31) and then decreased during the weeks of the study period. Fish were still entering the river August a peak last 2 by the time the sampling was discontinued. Recapture rate for coho was very low with only 8 of the 70 fish tagged captured a second time. The progression of reproductive condition suggested the majority of spawning activity occurred sometime after the middle of September. No spawned out coho were observed by the end of the study and only two males were in the process of spawning when captured. Sockeye Salmon Sockeye salmon were captured in the hoop nets throughout most of the 9-week sampling period (Figure 8). The catch statistics indicate numbers peaked during week six and steadily declined in following weeks. A total of 48 sockeye was captured and fin-clipped and of these, 31 were small, precocious males. The recapture rate for sockeye was relativly high (18 percent) but since these fish were not individually marked it was not possible to determine if the recaptures were the same fish, or when the these fish were initially marked. All of the sockeye recaptures were precocious males. 16 o ~ ro ~ ill ~ ~ ~ N o ~ ro ~ ill ~ ~ ~ N o N 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ill ~ N ro ro ~ CPUE by Week -Coho Salmon Dames & Moore Job No. 12023-030 Figure 7 ['-. 0 0 Job No. 12023-030 \.0 0 0 L[) 0 0 "¢ 0 0 n 0 0 0J 0 0 0 0 0 ro (f) y co co en L[) w n w ~['-. ro en \.0 co en CPUE by Week -Sockeye Salmon Dames & Moore Figure 8 River Mile 3.2 The hoop net set at RM 3.2 yielded very few fish over the 6 weeks it was set. The first fish captured was an unmarked pink salmon during week five. The only other pink was a spawned out male caught in the on the last set during week nine (September 14). TWo bright coho were captured in this net during week six. One of these was marked with a fin clip to see if it would be recaptured in the study area farther upstream. The next day this fish was found in net 4 in Riffle Reach. The location of this net made it susceptible to complete reversals in the current due to the tides. This prevented the net from fishing properly during some stages of the tidal cycle. To ensure efficient sampling of this site in the future, the net should be set on a falling tide and pulled before the current reverses direction. Beach Seining The standardized beach seining proved to be very unproductive this year primarily because of the low density of pink salmon in the river. In total, only three pink salmon (one recapture), three chum, one chi- nook and one coho salmon were caught using this method. The results of the beach seining hauls reconfirmed the results of the hoop net sampling, which indicated very low numbers of pinks using the river this year. Electroshocking Electroshocking also proved to be an unproductive method of cap- turing and tagging fish, but was useful in reconfirming the low catch results of the hoop net and beach seine sampling. This year it was par- ticularly helpful in delineating the spawning areas used by the fish in a year when escapement was very low (Figure 9). As has been the case in previous years, low conductivity in the Bradley River made it difficult to stun the fish enough to catch them. Many of the fish encountered were startled and swam off rapidly; others came to the surface where it was often possible to see if they were tagged. A total of 9 pinks (1 recapture) and 1 chum were captured and tagged with this method and an additional 40 pink, 3 chum, 4 chinook, and 4 coho salmon were stunned but not caught. Only one of the pink salmon had a color coded tag from an earlier capture. Overall results of the electroshocking indicated the density of spawning pink salmon was very low throughout the river. From the number of total sightings, the majority of the pink salmon spawning probably 19 ... z----- KEY: Spawning Areas for- ¢ Pink Salmon (f!!!Jl Pink and Chum Salmon Yf.. King Salmon 0 300 Scale in Feet Job No. 12023-030 DISTRIBUTION OF SPAWNING SALMON Dames & Moore Figure 9 occurred in the Tree Bar Reach area with a small number using the Riffle Reach area. All of the chinook salmon were located in the Tree Bar Reach. carcasses Only two pink salmon carcass (without tags) were recovered in the carcass fence both during week five (August 17). Three additional car- casses were found incidential to the carcass fence and these included one untagged chinook in Bear Island Slough (week two), a tagged chinook near net 2 (week six) and a tagged pink adjacent to Seine Site D in Tree Bar Reach. The lack of shallow areas or obstacles such as fallen trees to catch the dead or dying fish is the likely reason so few carcasses are found. Daily flushing of the lower reaches of the Bradley River by tidal currents may also flush the dead fish from the river. The highly turbid waters of the·river also make detection of carcasses difficult. Stream Life Pink Salmon Of the 15 recaptures over the course of the study period, 14 were had been tagged that week or in the previous week. One was recaptured 4 weeks (28 days> after being tagged in bright condition on July 26. Churn Salmon A total of 16 churn salmon was recaptured after initially being tagged and 13 of these were recaptured in the same week they were tagged. The remaining churn salmon were all caught within 1 week of their initial tagging. This would suggest most of the chum salmon had been in the river some time prior to their initial tagging. Chinook Salmon Of the 23 chinook which were captured more than once, 19 were recaptured within 2 weeks of being tagged and 3 were tagged 3 weeks earlier. One large male was recaptured 28 days after being tagged on July 19. 21 Coho Salmon Recaptures were insufficient to provide any insight into stream residency of adult coho in the Bradley River. A total of eight· coho was caught more than once and, of these, three had been in the river at least 2 weeks and one was tagged 3 weeks prior to its recapture. This would suggest that some coho remain in the river for a period of time but whether they stay to spawn is not known. Sockeye Salmon There was a total of 61 captures of sockeye salmon in the hoop nets in 1988. However, the total number of fish was impossible to estimate because this species was not tagged with individual numbered tags since significant numbers of this species were not expected in the Bradley River. Mark and Recapture Population Estimate Pink Salmon weekly mark-recapture population estimates for pink salmon from 1986, 1987, and 1988 are presented in Table 3. The low numbers of fish in the river during the 1988 season resulted in no recaptures until the sixth week of the study. Thus, this is the first week a population estimate can be calculated. Population estimates for the remaining weeks of the study showed a declining trend (Figure 10). These estima- tes suggest the 1988 peak of the pink salmon run (435) occurred before or during the sixth week of the study or l week earlier than in the pre- vious 2 years. This corresponded with the highest total catch in the hoop nets. The statistical reliability of the mark-recapture estimates increases with the number of recaptures and the proportion of marked fish in the population. Thus, the very low recapture rates and lower proportions of marked fish increases the potential for bias in these estimates in comparison to those from the previous years. The catches from beach seining and electroshocking included insuf- ficient recaptures to provide reliable, independent verification of the weekly population estimates. 22 TABLE 3 BRADLEY LAKE SALMON MONITORING STUDY MARK-RECAPTURE POPULATION ESTIMATE CALCULATIONS 1988 DATA POPULATION SAMPLE ESTIMATE WEEK MARK CATCH RECAP. -95% R +95% R N -95% N +95% N 1 0 8 0 2 8 9 0 3 18 13 0 4 21 12 0 5 26 13 0 6 28 29 1 5.6 0.1 435 132 791 7 37 22 3 8.8 0.6 219 89 546 8 41 1 3 8.8 0.6 21 9 53 9 18 5 1 5.6 0.1 57 17 104 1987 DATA SAMPLE WEEK MARK CATCH RECAP. -95% R +95% R N -95% N +95% N 1 0 3 0 2 3 14 0 3 17 36 2 7.2 0.2 222 81 555 4 46 54 2 7.2 0.2 862 315 2154 5 103 205 14 23.5 7.7 1428 874 2463 6 243 247 27 39.2 17.8 2161 1505 3219 7 357 154 17 27.2 9.9 3083 1968 5091 8 300 74 16 26 9.2 1328 836 2213 9 194 31 5 11.7 1.6 1040 491 2400 1986 DATA SAMPLE WEEK MARK CATCH RECAP. -95% R +95% R N -95% N +95% N 1 0 4 0 2 4 36 1 5.6 0.1 93 28 168 3 31 158 8 15.8 3.4 565 303 1156 4 156 259 29 41.6 19.4 1361 958 2001 5 308 270 51 65.9 37 1610 1252 2204 6 381 262 43 57.9 31.1 2283 1706 3130 7 426 236 36 49.8 25.1 2735 1992 3877 8 397 156 33 46.3 22.7 1838 1321 2637 9 277 68 14 23.5 7.7 1279 783 2205 Modified Peterson Formula: Estimated Population = (Total Marked +1) X (Total Catch +1) (Recaptures + 1) Recapture -Tagged fish caught from previous 2 weeks Marked -Total salmon marked within previous 2 weeks N 0 ro W ~ N 0 ro W ~ N 0 ro W ~ N 0 ~ ~ N N N N N 0 0 0 0 0 (spuosno1..1.1) NOI.lVlndOd 03.lVV\II.lS3 ro ro 01 0 + w ro 01 0 Population by Week -Pink Salmon Dames & Moore Job No. 12023-030 Figure 10 Total Escapement Pink Salmon Applying the ADF&G escapement formula to the weekly population estimates derived from the Chapman modification of the Peterson formula, a total escapement of 293 pink salmon was estimated for 1988. Using this same method on the 1986 and 1987 data, provided escapement esti- mates of 4706 and 4049, respectively. Based on these estimates, the 1988 pink salmon escapement was only about 7 percent as large as the 1987 run. 01um Salmon The number of recaptured chum salmon was considered too low to pro- vide a meaningful estimate of the spawning population. catch data indi- cate that there were fewer than 50 chum salmon in the river during 1988. Chinook Salmon Catch data for chinook salmon were not sufficient to calculate a meaningful population estimate. The total catch for chinook was low (albeit greater than in previous years) and the recapture rate was high indicating a relatively small population. Numbers of chinook in the river year was probably around 100. Coho Salmon Little can be said about the coho population since the recapture rate was very low and they were still coming in to the river at the end of the study period. Sockeye Salmon Little can be said about the sockeye population because individual tags were not placed on these fish. There appeared to be greater num- bers in the river this year as compared with the previous two seasons. Miscellaneous Observations Fox Farm Creek Weekly censusing of this clear water tributary of the lower Bradley River showed a small number of chum salmon (7) in the stream during the first week of the study period. Twelve were sighted during the second 25 week. Chum salmon were not seen again in the stream until week six when a lone male with a color-coded tag was spotted. The fish could not be retrieved to check the tag number or to see if it had already spawned due to its position under some fallen trees. The first pink salmon (one individual) was seen during the second week but not until week six did any more pinks move into the stream. A total of 13 pinks (none with tags) was present in week six and numbers fell steadily in weeks seven and eight. By week nine, no pinks were left in the stream. Peak numbers of both pinks and chum salmon in Fox Farm creek corresponded to the peaks on the main spawning grounds farther upstream. Total numbers for both chum and pink salmon in Fox Farm creek were very low in comparison to previous years. Miscellaneous Tag Recoveries The only tag recovered from outside the Bradley River system was a coho salmon tag recovered from a fish caught in a subsistence net at McNeil canyon on the north side of Kachemak Bay. This fish was origi- nally tagged on August 31 and recovered 2 days later on September 2, which indicates it left the river just after it was tagged. Mammals Observations Harbor Seals Harbor seals regularly swim up Bradley River to feed on the spawning salmon. Seals were seen as far up as lower portions of the Tree Bar Reach but usually fed in the Riffle Reach. The frequency of seals in the study area appeared to be lower this year than in the past two seasons possibly because of the low numbers of spawning pinks. Only one seal was caught in a hoop. net this season and it was released unharmed at the next check of the nets. Beavers Beavers were not the problem this year as they were last season. One beaver was captured live in a net in Riffle Reach but it was released before it could do any damage to the net. 26 Mountain Goats The body of a two-year old, female mountain goat washed ashore along shallows of lower Riffle Reach on August 24. The actual cause of death was not determined, but it may have died in a fall farther upstream in Bradley Canyon. This was the first observation of this kind recorded on the Bradley River. DISCUSSION Comparison with 1986 and 1987 Seasons Abundance Indices Pink salmon escapement suffered a significant drop in 1988 compared with that of the last two seasons (1986, 1987). This drop was evident from the CPUE statistics derived from the hoop net data, and from popu- lation and escapement estimates (Figure 10). The reason for this drastic decline in the pink salmon can be traced back to 1986 and a series of floods which occurred during the late summer (mid-August) and fall <October and December). The flood conditions in mid-August hap- pened just as the pink run was at its peak. Disruption of spawning activity was evident from the hoop net catches and significant scouring of spawning beds probably occurred at this time (APA 1986b). Later that fall, two 50-year floods occurred within a span of 2 months CR. Rickman, u.s. Geological Survey, personal communication). The October flood had high flows of approximately 11,000 cfs when normal mean monthly flows are between 200 and 1,000 cfs during this time of year. The following summer, damage to the spawning areas used the previous year was evident (APA 1987). Portions of the river had been rechanneled and extensive erosion of the streambed and stream banks had occurred. This high degree of interannual variability in escapement due to natural phenomena validates the requirement for a multiyear pre-project monitoring period if the effects of the project are to be distiguished from these natural fluctuations. The CPUE statistics for chum salmon indicated escapement was down only slightly from 1987 but overall numbers were very low. This slight decline comes after a 90 percent decline in numbers between the 1986 and 1987 seasons. The peak of the chum run appeared to occur approximately two weeks earlier this year but with such low numbers it is difficult draw conclusions. 27 This year <1988) saw the highest return of chinook salmon recorded over the 3 years in which data have been collected using hoop nets in the Bradley River. Examination of scale samples by ADF&G indicated that a significant number of these fish < 30 percent) may originate from hatchery releases in support of terminal fisheries in other parts of the bay. There are no spawning streams to which these fish can return at these locations and apparently some stray into nearby systems. There are no data on chinook salmon in the Bradley River prior to these enhancement projects so it is possible these hatchery-reared fish have routinely spawned in the Bradley River over the years. It is possible these strays established the chinook run in the Bradley or may have augmented a small, natural run. If the later is the case, there has probably been genetic interchange between the natural run and the hatchery-reared chinook salmon. Mark and Recapture Estimates The validity of mark and recapture techniques for spawning salmon populations is discussed in detail in the 1986 Salmon Monitoring Report CAPA 1986b). The weekly population estimates for this year indicated as great a decline in the pink run as the CPUE data. The calculated esti- mates for this season are probably higher than the actual number of pinks using the river. This was attributed to lower percentage of recaptures during 1988 through the peak of the run, in comparison to previous years. Since the model is very sensitive to the number of recaptures, a lower percentage of recaptures results in wider confidence limits for population estimates. Examination of Figure 10 indicates that populations in both 1986 and 1987 were quite similar, while the 1988 population was significantly lower. It is believed that population estimates will be useful in comparing pre-operational and post-operational population levels in the Bradley River. Given the shortcomings of the population estimates under the prevailing conditions in the Bradley River, the methods applied to reduce sources of bias and error appear to provide consistent results from year to year. Thus population estimates, in conjunction with CPUE statistics, provide good measure of pre-operational pink salmon abun- dance for use as a bench mark for comparison with population levels after project operation begins. 28 Comparisons With Other Streams Most of the salmon producing streams which empty into Kachemak Bay are moni tared by the Alaska Department of Fish and Game on a yearly basis. Aerial and ground surveys are used to estimate total salmon escapement on each of six streams. These streams include Humpy Creek, the largest producer of pink salmon, Olina Poot Creek, Barabara Creek, Seldovia River, Tutka River, and Port Graham River. In comparison to these systems, the Bradley River has the smallest run of pink salmon with exception of Barabara Creek. Pink salmon returning to the streams in Kachemak Bay exhibit an odd/even year abundance cycle with the highest escapements occurring during the odd-number years. However, the 1987 run was considered a failure CR. Morrison, Alaska Department of Fish and Game, personal communications). Escapements for pink salmon in 1988 were expected to be less than 1987 escapements but the outcome of the this year • s pink salmon runs was significantly lower than predicted. The escapement goal for Humpy Creek this year was 50,000 but the actual escapement was less than half this number, with only 21,500 returning (N. Dudiak, Alaska Department of Fish and Game, personal communications). The decline in the pink salmon in the Bradley River Cover 90 percent from 1987) is comparable to the low numbers of pinks in these other systems. Although chum salmon are not considered a major species in the Kachemak Bay area, surveys this year showed good returns of chums with the highest count in Port Graham River (3,477). The trend in the Bradley River this season did not correspond to the other systems in the other parts of the bay. The 1988 CPUE for chum salmon was down only slightly from 1987. However, it is difficult to draw any conclusions regarding these patterns since chums are not widely distributed and overall numbers are relatively low. RECOMMENDATIONS FOR FUTURE YEARS 1. Continue use of the hoop nets during the pre-operational moni- toring phase as the most reliable means of indexing population abundance. Hoop nets may not be useful for post-operational monitoring due to the predicted reduction of flow. 2. Continue to use beach seining as a supplemental method for mark and recapture estimates. A.n increase in length of the beach 29 seine by 18 m ( 60 ft) would increase the efficiency of this method especially at Sites A and D. 3. Continue marking all salmon species~ extend tagging to include sockeye salmon. 4. Continue to census Fox Farm Creek on a weekly basis to monitor the presence of tagged fish. 5. Continue the use of the mark and recapture population estimates. 6. Maintain a three-person field crew. 7. Continue the general study timing and duration established in 1986 and 1987 for species other than coho salmon and continue the 3-day intensive sampling period each calendar week. Lengthening the study duration into October would aid in understanding the timing and magnitude of the coho salmon run in the Bradley River. Starting the sampling period two weeks earlier would give a better picture of the abundance and timing of the chinook and chum runs in the Bradley River. 8. Continue electroshocking efforts as an alternate method of mark and recapture and as a method of determining distribution of fish in the river. 9. Continue to use the hoop net site at RM 3.2 to intercept tagged fish leaving the upper spawning area after being tagged. This net should be set on an out-going tide and checked prior to the reversal of the current (approximately 10 hours). An increase in the length of the net wings by 12 m (40 ft) would increase the efficiency of the net. 10. Equipment items and study logistics as employed in the 1988 field season were adequate to accomplish the stated tasks. Since the hoop nets have been heavily used for 3 years it may be necessary to replace some nets or sections of webbing and purchase some new net wings. 11. A 2-day trip to the study area during late spring when flows are at a minimum is needed to remove snags and boulders at the seine sites and to set some permanent anchors for the hoop nets. 30 REFERENCES Alaska Department of Fish and Game. 1986. Lower Cook Inlet fin fish report. COmmercial Fisheries Division. 440 pp. Alaska Power Authority. 1986a. Salmon monitoring plan for Federal Energy Regulatory Commission Project No. P-8221-000. Prepared by Stone and Webster Engineering Corp., Anchorage, Alaska. 1986b. Bradley River salmon escapement monitoring report 1986. Prepared by Dames & Moore under contract to Bechtel Civil & Minerals, Inc. for the Alaska Power Authority, Bradley Lake Hydroelectric Project. Anchorage, Alaska. • 1987. Bradley River salmon escapement monitoring report 1987. Prepared by Dames & Moore under contract to Bechtel Civil & Minerals, Inc. for the Alaska Power Authority, Bradley Lake Hydroelectric Project. Anchorage, Alaska. Dudiak, N. (Alaska Department of Fish and Game). 1988. Personal communication with Mary Pearsall, Dames & Moore. Hammerstrom, s. (Alaska Department of Fish and Game). 1988. Personal communication with Dave Erikson, Dames & Moore. Morrison, R. (Alaska Department of Fish and Game). 1988 Personal communication with Mary Pearsall, Dames & Moore. Northern Technical Services, Inc. 1985. 1985 Salmon escapement survey report. Prepared for Alaska Power Authority, Anchorage, Alaska. 29pp. Pirtle, R.B., and M.L. McCUrdy. 1980. Prince William Sound general districts 1976 pink and chum salmon aerial and ground escapement surveys and consequent brood year egg deposition and pre-emergent fry index programs. Alaska Department of Fish and Game Technical Data Report No. 51. Ricker, W.E. 1975. Computation and interpretation of biological statistics of fish populations. Bull. Fish. Res. Board can. 191. 383 pp. Rickman, R. (U.S. Geological survey). 1988. Personal communication with Dave Erikson, Dames & Moore. u.s. Fish and Wildlife Service. 1982. Appendix B: Bradley Lake Hydroelectric Project. Homer, Alaska. Final Coordination Report. USFWS Western Alaska Ecological Services. Anchorage, Alaska. 13lpp. In: u.s. Army Corps of Engineers. 1982. Bradley Lake Hydroelectric Project, Alaska. Final Environmental Impact Statement. Alaska District, u.s. Army Corps of Engineers. Woodward-Clyde Consultants. 1983. Bradley River instream flow studies. Prepared for Alaska Power Authority, Anchorage Alaska. 77 pp. 31 Woodward-Clyde Consultants. 1984. Report on salmon fry sampling in the Bradley River. Prepared for Alaska Power Authority, Anchorage Alaska. 6 pp. 32