Evaluation of Angler Effort and Harvest of Rainbow Trout 

(Onchorhynchus mykiss), Lake Scanewa, Washington, 2010

Open-File Report 2011–1178

Prepared in cooperation with the Public Utility District #1 of Lewis County, Washington

U.S. Department of the Interior

U.S. Geological Survey

Evaluation of Angler Effort and Harvest of 

Rainbow Trout (Oncorhynchus mykiss), 

Lake Scanewa, Washington, 2010 

By Theresa L. Liedtke, Tobias J. Kock, Brian K. Ekstrom, Ryan G. Tomka, and Dennis W. Rondorf 

Prepared in cooperation with the Public Utility District #1 of Lewis County, Washington 

Open-File Report 2011–1178 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

KEN SALAZAR, Secretary 

U.S. Geological Survey 

Marcia K. McNutt, Director 

U.S. Geological Survey, Reston, Virginia: 2011 

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copyright owners to reproduce any copyrighted material contained within this report. 

Suggested citation: 

Liedtke, T.L., Kock, T.J., Ekstrom, B.K., Tomka, R.G., and Rondorf, D.W., 2011, Evaluation of angler effort and 

harvest of rainbow trout (Onhorhynchus mykiss), Lake Scanewa, Washington, 2010: U.S. Geological Survey OpenFile Report 2011-1178, 24 p. 
Contents 

Abstract ......................................................................................................................................................................... 1

Introduction.................................................................................................................................................................... 2

Methods......................................................................................................................................................................... 3

Creel Survey .............................................................................................................................................................. 3

Estimating Angler Effort and Rainbow Trout Harvest ................................................................................................. 4

Fish Marking .............................................................................................................................................................. 5

Rainbow Trout Stomach Contents ............................................................................................................................. 6

Results........................................................................................................................................................................... 7

Observed Angler Effort, Catch, and Catch Rates....................................................................................................... 7

Proportion of Daylight Hours Surveyed ...................................................................................................................... 7

Boat Surveys.............................................................................................................................................................. 8

Estimated Angler Effort .............................................................................................................................................. 8

Targeted Species....................................................................................................................................................... 8

Estimated Angler Effort and Harvest of Rainbow Trout.............................................................................................. 8

Angler County of Residence ...................................................................................................................................... 9

Tagged Rainbow Trout Recoveries............................................................................................................................ 9

Rainbow Trout Stomach Contents ............................................................................................................................. 9

Discussion ................................................................................................................................................................... 10

References Cited......................................................................................................................................................... 12

Figures 

Figure 1. Map showing the Upper Cowlitz River Basin and Lake Scanewa study area ...................................... 13

Figure 2. Flow chart showing the process that was used to estimate angler effort and harvest numbers of 

rainbow trout in Lake Scanewa during June-November 2010.................................................................................. 14

Figure 3. Graph showing the proportion of anglers targeting rainbow trout, salmon, or northern pikeminnow in 

Lake Scanewa during June-November 2010........................................................................................................... 15

Figure 4. Graph showing the proportion of PIT-tagged rainbow trout that were recovered at three locations in 

Lake Scanewa during June-November 2010 following release at one of four release locations.............................. 16

Figure 5. Graph showing the distribution of elapsed times from release to recapture for PIT-tagged rainbow trout 

in Lake Scanewa during 2010.................................................................................................................................. 17

Figure 6. Graph showing the percent of rainbow trout stomachs that contained fish from February 2010 to 

February 2011 ......................................................................................................................................................... 18

Tables 

Table 1. Numbers of rainbow trout released into Lake Scanewa annually from 1994 to 2010 ................................ 19

Table 2. Numbers of rainbow trout released at four release sites in Lake Scanewa during 2010 ........................... 19

Table 3. Numbers of fish that were reported in the catch by boat and shore anglers in Lake Scanewa during a creel 

survey in June-November 2010............................................................................................................................... 20

Table 4. Catch per hour estimates for rainbow trout anglers in Lake Scanewa during June-November 2010......... 20

Table 5. Summary of the total hours of daylight in each month during June-November 2010, the total number of 

hours that a creel survey was conducted during this period, and the proportion of daylight hours that were sampled 

during each mont..................................................................................................................................................... 21

iii 
iv 

Table 6. Summary of the number of anglers that were observed from a boat during a creel survey in Lake Scanewa 

during 2010.............................................................................................................................................................. 21

Table 7. Summary of the estimated number of hours that anglers spent in Lake Scanewa during 2010 ................ 22

Table 8. Summary of observed angler effort, proportion of daylight hours that were surveyed, estimated angler 

effort, observed catch rates, and estimated catch in Lake Scanewa during 2010 ................................................... 23

Table 9. Summary of the number of anglers that were interviewed from various counties in Washington state during 

June-November 2010 .............................................................................................................................................. 24

Conversion Factors 

Inch/Pound to SI 

Multiply By To obtain 

Length 

inch (in.) 2.54 centimeter (cm) 

inch (in.) 25.4 millimeter (mm) 

foot (ft) 0.3048 meter (m) 

mile (mi) 1.609 kilometer (km) 

mile, nautical (nmi) 1.852 kilometer (km) 

Area 

acre 0.4047 hectare (ha) 

Mass 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

SI to Inch/Pound 

Multiply By To obtain 

Length 

centimeter (cm) 0.3937 inch (in.) 

millimeter (mm) 0.03937 inch (in.) 

Area 

hectare (ha) 2.471 acre 

Mass 

gram (g) 0.03527 ounce, avoirdupois (oz) 
Evaluation of Angler Effort and Harvest of 

Rainbow Trout (Oncorhynchus mykiss), 

Lake Scanewa, Washington, 2010 

By Theresa L. Liedtke, Tobias J. Kock, Brian K. Ekstrom, Ryan G. Tomka, and Dennis W. Rondorf 

Abstract 

A creel evaluation was conducted in Lake Scanewa, a reservoir on the Cowlitz River, to monitor 

catch rates of rainbow trout (Oncorhynchus mykiss) and determine if the trout fishery was having 

negative impacts on juvenile anadromous salmon (Oncorhynchus spp.) in the system. The trout fishery, 

which is supported by releases of 20,000 fish (2 fish per pound) per year from June to August, was 

developed to mitigate for the construction of Cowlitz Falls Dam in 1994. The trout fishery has a target 

catch rate of at least 0.50 fish per hour. Interviews with 1,214 anglers during the creel evaluation found 

that most anglers targeted rainbow trout (52 percent) or Chinook and coho salmon (48 percent). The 

interviewed anglers caught a total of 1,866 fish, most of which were rainbow trout (1,213 fish; 78 

percent) or coho salmon (311 fish; 20 percent). We estimated that anglers spent 17,365 hours fishing in 

Lake Scanewa from June to November 2010. Catch rates for boat anglers (1.39 fish per hour) exceeded 

the 0.50 fish per hour target, whereas catch rates for shore anglers (0.35 fish per hour) fell short of the 

goal. The combined catch rates for all trout anglers in the reservoir were 0.96 fish per hour. We 

estimated that anglers harvested 7,584 (95 percent confidence interval = 2,795–12,372 fish) rainbow 

trout during the study period and boat anglers caught more fish than shore anglers (5,975 and 1,609 fish, 

respectively). This estimate suggests that more than 12,000 of the 20,000 rainbow trout released into 

Lake Scanewa during 2010 were not harvested, and could negatively impact juvenile salmon in the 

reservoir through predation or competition. We examined 1,236 stomach samples from rainbow trout 

and found that 2.1 percent (26 fish) of these samples contained juvenile fish. Large trout (greater than 

300 millimeters) had a higher incidence of predation than small trout (less than 300 millimeters; 8.50 

and 0.06 percent, respectively). A total of 39 fish were found in rainbow trout stomachs and 13 (33 

percent) of these were juvenile salmon. These data and uncertainties associated with movement patterns 

and survival rates of rainbow trout in Lake Scanewa suggest that future evaluations would be helpful to 

better understand the potential effects of the mitigation trout fishery on juvenile salmon in the reservoir. 

1 
Introduction 

Thousands of rainbow trout are released annually into Lake Scanewa, a reservoir on the upper 

Cowlitz River (fig. 1), to support a popular sport fishery that was created to mitigate for the construction 

of Cowlitz Falls Dam in 1994. The fish releases are funded by Lewis County Public Utility District 

(LCPUD) to meet a license requirement for the operation of Cowlitz Falls Dam. This requirement was 

established by the Federal Energy Regulatory Commission (FERC) to create a sport fishery in Lake 

Scanewa with catch rates that meet or exceed 0.50 fish per hour. Creel surveys were conducted during 

1994, 1995, and 2000 to quantify angler effort, determine by-catch, and document catch rates in Lake 

Scanewa. These surveys showed that catch rates exceeded the 0.50 fish per hour goal in 1994, but not in 

1995 or 2000 (Neeley, 1995; Tipping and Serl, 2000). Annual releases initially comprised 12,500 fish 

per year (1994–95), and 25,000 fish have been released annually since 1996 (table 1). Based on their 

findings, Tipping and Serl (2000) recommended that releases be increased to 30,000 fish per year to 

achieve the desired catch rates for the fishery. However, increasing the number of rainbow trout that are 

released into the reservoir each year could have negative impacts on other species in the system. 

The upper Cowlitz River basin supports anadromous populations of winter steelhead 

(Oncorhynchus mykiss), coho salmon (O. kisutch), and Chinook salmon (O. tshawytscha) and concerns 

have been raised about the possibility of planted rainbow trout becoming predatory and feeding upon 

juvenile anadromous salmon either rearing in, or migrating through Lake Scanewa (National Marine 

Fisheries Service, 2009). Life history data and observations from the field suggest that juvenile coho 

salmon and Chinook salmon would be most susceptible to predation by rainbow trout (John Serl, 

Washington Department of Fish and Wildlife, oral commun., 2010). Juvenile steelhead smolts are 

relatively large (about 160–200 mm fork length) compared to coho salmon and Chinook salmon (about 

100–130 mm fork length). Furthermore, steelhead parr tend to rear in areas upstream of Lake Scanewa, 

whereas coho salmon and Chinook salmon parr are frequently encountered in the reservoir (John Serl, 

Washington Department of Fish and Wildlife, oral commun., 2010). Tipping and Serl (2000) examined 

stomachs of rainbow trout collected during their creel survey and found that salmonids were present in 

only 1.1 percent of the small trout (less than 300 mm fork length) they examined. However, 13.6 

percent of the stomachs from large trout (greater than 300 mm fork length) contained salmonids 

(Tipping and Serl, 2000). The researchers were able to identify two of the salmonids in the trout 

stomachs as coho salmon and a third fish was identified as a Chinook salmon. Given the observed levels 

of predation identified in the Tipping and Serl (2000) study, it seems likely that increasing stocking 

levels of rainbow trout would pose a risk to juvenile salmon in the reservoir. 

We conducted a creel survey in Lake Scanewa during 2010 to collect information that could be 

used to inform future management actions aimed at finding an acceptable balance between maintaining 

recreational trout fishing opportunities in Lake Scanewa and minimizing risks to juvenile anadromous 

species in the system. These evaluations included a creel survey designed to monitor angler effort and 

harvest in Lake Scanewa from June to November 2010. The creel survey provided the opportunity to: 

• determine angler effort in Lake Scanewa; 

• estimate catch rates to determine compliance with the FERC license requirement; 

• estimate total harvest of rainbow trout during the fishing season; and 

• collect stomachs from rainbow trout caught in the fishery to examine for the presence of juvenile 

salmonids. 

We also used passive integrated transponder (PIT) tags to mark a subsample of the rainbow trout 

that were released into Lake Scanewa to better understand growth rates, elapsed time to capture, and 

movements in the reservoir. 

2 
Methods 

Creel Survey 

A creel survey was conducted from June to November 2010 to document angler effort and 

harvest in Lake Scanewa following the guidance outlined in the biological opinion (BiOP) for the 

operation of Cowlitz Falls Dam (National Marine Fisheries Service, 2009). The BiOP provides specific 

details about the sampling design that is to be used during creel surveys. These details are summarized 

below. 

1. Creel surveys are to be conducted every 5 years to estimate monthly angler effort and harvest by 

species from June 1 through November 30. 

2. Boat and shore anglers are to be counted every 2 hours, from 1 hour after first light to 1 hour 

before dark, for four randomly assigned weekdays and four weekend and holiday days per 

month. The four, 16 h days from each stratum will be broken into 2 days of 8 h each, thus a total 

of 8 week days and 8 weekend days will be sampled monthly (totaling 128 h each month). 

During June and July, anglers and boat trailers are to be counted every 2 h at the Day Use Area 

from 0630 to 1230 h, or from 1430 to 2030 h. These hours will be shortened monthly for the 

remainder of the creel survey as daylight diminishes. 

3. On one weekday and weekend day per month, anglers will be counted from a boat to develop a 

correction factor for anglers not observed from shore. 

4. In between counts, anglers will be interviewed for hours fished, catch by species, number of fish 

released, length of fish caught, and county of residence. 

5. A minimum of 100 stomachs will be taken from trout caught by anglers each month during 

June-September to check for the presence of juvenile fish. 

6. The data collected during the creel survey will be extrapolated to provide monthly estimates of 

angler effort and catch rates. These data will then be used to estimate harvest of rainbow trout. 

These specifications provided the basis of the sampling design that was used during the creel 

survey in 2010. Additional data also were collected to provide new insights into fishery issues in the 

reservoir and are described in section, “Fish Marking.” 

During each month of the creel survey, we randomly selected 8 weekdays and 8 weekend or 

holiday days to sample. Each sampling day consisted of a continuous 8 h shift during either the first 8 

daylight hours (a.m. shift) or the last 8 daylight hours (p.m. shift) of each day. During each month, four 

a.m. shifts and four p.m. shifts were conducted (randomly) to achieve the 8-day goal for each weekday 

and weekend/holiday group. To account for changing daylight hours throughout the sampling period 

(and time changes due to daylight savings time), a.m. shifts were conducted from 0630 to 1430 h from 

June to August, from 0730 to 1530 h from September to October, and from 0630 to 1430 h during 

November. Similarly, p.m. shifts were conducted from 1230 to 2030 h from June to August, from 1130 

to 1930 h during September, from 1030 to 1830 h during October, and from 0930 to 1730 h during 

November. 

3 
Creel surveys were conducted primarily at the Day Use Area (fig. 1) and several types of data were 

collected during each shift. Trout anglers can either fish for trout in Lake Scanewa, or in the Derby Site, 

which is a small inlet to Lake Scanewa located near the boat launch at the Day Use Park. The entrance 

into the Derby Site is netted off each summer and stocked with 5,000 rainbow trout for anglers to target. 

However, because the site is netted off and all fish are presumably harvested by anglers, there are likely 

no effects to salmonids in the system. For this reason, we did not interview anglers at the Derby Site. 

Staff conducting the creel surveys recorded the number of shore anglers observed from the Day Use 

Area along with the number of boat trailers present at the boat launch every 2 h throughout each shift. 

Additionally, anglers were interviewed to determine: (1) number of hours fished, (2) target species, 

(3) catch by species, (4) number of fish released, (5) whether they were fishing from a boat or from the 

shore; and (6) the location (by zone) where each fish was caught. We used the following zones for 

classifying catch locations: 

1. Cowlitz Arm zone.—The Cowlitz Arm zone included the area on the Cowlitz River side of Lake 

Scanewa located upstream of the confluence of the Cowlitz and Cispus Rivers. 

2. Cispus Arm zone.—The Cispus Arm zone included the area on the Cispus River side of Lake 

Scanewa located upstream of the confluence of the Cowlitz and Cispus Rivers. 

3. Reservoir zone.—The Reservoir zone included the area of Lake Scanewa located downstream of the 

confluence of the Cowlitz and Cispus Rivers. 

4. Cowlitz Falls zone.—The Cowlitz Falls zone was not an option for anglers and included only those 

fish that were collected at the Cowlitz Falls Dam Fish Collection Facility. 

 Successful trout anglers were asked to voluntarily provide additional data from fish that were 

captured and retained. When possible, survey staff measured (fork length, in centimeters) and weighed 

(total weight, in grams) each trout, removed the stomach, and examined each fish for the presence of a 

PIT tag. 

During 1 weekday and weekend/holiday day each month, survey staff conducted a boat census 

on Lake Scanewa to document the number of shore and boat anglers that could not be observed from the 

Day Use Area. This information was used to develop a correction factor for estimating angler effort in 

Lake Scanewa. 

Estimating Angler Effort and Rainbow Trout Harvest 

Data from angler interviews and boat surveys were used to estimate total angler effort in Lake 

Scanewa from June to November 2010 (fig. 2). Observations from the creel surveys were adjusted to 

account for angler effort that occurred during daylight hours when creel surveys were not performed. 

We assumed that angling in the reservoir during nighttime hours was negligible and therefore nighttime 

angling was not used to estimate total angling effort in our analysis. A correction factor for hours not 

surveyed was developed by dividing the total number of hours surveyed each month by the total number 

of daylight hours in that month to determine the monthly proportion of hours that were surveyed (fig. 2). 

For example, if a total of 50 h of creel surveys were conducted in a month that contained 200 total 

daylight hours, then 50/200 = 0.25, which represents the proportion of daylight hours that were 

surveyed in the month. The total number of observed angler hours from the monthly creel survey were 

then divided by the daylight correction factor to estimate the total number of angler hours that occurred 

in that month. If a total of 100 angler hours were observed in the above example, then 100/0.25 = 400 

estimated angler hours for that month. Total angler effort estimates were calculated for boat and shore 

anglers. Boat surveys found that some shore anglers were not visible from the Day Use Area during 

4 
creel surveys, so the estimates of total angler hours by shore anglers were corrected to account for this 

factor. This correction was accomplished by dividing the total number of visible and non-visible (as 

determined by the boat surveys) anglers by the total number of visible anglers. For example, if 10 

anglers were visible from the Day Use Area and 5 additional anglers were observed from the boat, then 

the correction factor was calculated as 15/10 = 1.5. This correction was then multiplied by the total 

number of shore angler hours to determine the final estimate for shore angler hours. In the above 

example, 400 angler hours × 1.5 = 600 total estimated angler hours for shore anglers. Estimates of 

angler effort for boat and shore anglers were then summed to determine the total number of angler effort 

hours that occurred during the sampling period. 

Estimates of total angler hours were used to estimate angler effort and harvest numbers of 

rainbow trout in Lake Scanewa from June to November 2010. The goal of the creel survey was to 

determine catch rates of rainbow trout in the reservoir while also providing information on the potential 

impacts that rainbow trout could be having on anadromous salmonids in the system. As a result, we 

estimated total harvest of rainbow trout during the sampling period as a means of understanding the 

number of rainbow trout that possibly remained in the reservoir after the fishing season. During the 

creel survey, anglers were interviewed to determine target species in each month. Target species were 

then grouped into three categories (rainbow trout, salmon, other) and the proportion of each targeted 

group was determined for boat and shore anglers each month (fig. 2). For example, if 10 shore anglers 

were interviewed in a month and 5 were targeting rainbow trout, 3 were targeting salmon, and 2 were 

targeting northern pikeminnow (Ptychocheilus oregonensis), then the proportion of targeted species for 

that month would be 0.5 for rainbow trout, 0.3 for salmon, and 0.2 for other species. The proportion of 

anglers targeting rainbow trout each month were multiplied by the total angler effort estimates to 

determine total angler effort for rainbow trout by boat and shore anglers each month (fig. 2). Using the 

previous example, 600 estimated angler hours × 0.5 = 300, which would be the estimate for the total 

number of angler hours expended by shore anglers for rainbow trout in that month. Monthly catch rates 

for rainbow trout were determined by dividing the total number of trout caught by each angler during 

the period of time in which they fished. This number was then multiplied by the rainbow trout angler 

effort estimates to estimate the number of trout harvested by boat and shore anglers each month. For 

example, if the monthly catch rate by shore anglers was calculated as 1.5 fish per hour, then 300 angler 

hours targeting trout × 1.5 = 450, which is the estimated number of trout harvested by shore anglers in 

the above example. Boat and shore estimates were summed to determine the total harvest estimate for 

all anglers during the sampling period. 

Fish Marking 

We used PIT tags to mark approximately 10 percent of the rainbow trout that were released into 

Lake Scanewa during 2010 to better understand fish movements and residence time in the reservoir. The 

PIT tags allowed unique identification of marked individual fish. Rainbow trout were released into Lake 

Scanewa six times from June to August 2010 to provide angling opportunities throughout the summer 

fishing season (table 2). Fish typically are released at four sites on each release day (fig. 1): (1) the Bud 

Allen Campground; (2) the Cispus Arm of Lake Scanewa; (3) the Day Use Area; and (4) the PUD Boat 

Launch. Fish were PIT tagged and released at each release site on each scheduled release date and then 

monitored for PIT-tag presence during creel survey events and at the Cowltiz Falls Fish Collection 

Facility. Re-collection of PIT-tagged fish provided several pieces of information. For example, we could 

examine movements from release locations by comparing the location where each fish was recovered to 

the location where it was released. We also could examine residence times in the reservoir by 

subtracting the recovery date of a given fish from its release date. 

5 
On each stocking date, fish were transported from the rearing facility near Orting, Washington 

(about 1 h transport time) to the Cowlitz Falls Fish Facility where we transferred approximately 12 

percent of the fish to be released into a concrete raceway for PIT tagging. Once we obtained fish for 

tagging, the transport trucks proceeded with normal release procedures in the reservoir. For tagging, fish 

were hand-netted from the raceway in groups of 4–10 fish, and placed into an electro-anesthesia unit for 

sedation. Once fish were immobilized, 12.5 mm PIT tags (Biomark; Boise, Idaho) were injected into 

each fish near the pelvic girdle. Tagged fish were then transferred to a second electro-anesthesia unit 

where fork length measurements (to the nearest millimeter) were taken. Tagged fish were then weighed 

(to the nearest gram) and transferred into an oxygenated holding container that received a continuous 

supply of river water. We tagged a higher proportion of rainbow trout for the Bud Allen Campground 

and PUD Boat Launch release sites because we anticipated that these fish would have a lower 

probability of being harvested than fish from the other release sites. During the study, fish selected for 

marking (75-107 fish; table 2) from a given release group were tagged, then transported and released. 

The tagged fish typically were released within 6 h of untagged fish from the same release group. 

Rainbow Trout Stomach Contents 

Rainbow trout stomachs were collected using several techniques from February 2010 to 

February 2011. Stomachs were collected and preserved for later inspection to understand food habits of 

rainbow trout in Lake Scanewa and to document predation on juvenile salmonids. To collect stomach 

samples outside of the creel survey periods, we angled for trout in the reservoir. We angled from 

February to May 2010, before creel surveys began, and during February 2011. From June to November 

2010, stomachs were collected voluntarily from anglers through the creel survey process. Additionally, 

stomach samples were obtained from all rainbow trout that were collected at the Cowlitz Falls Fish 

Facility from April to August 2010. Stomach samples were preserved in 85 percent ethanol and were 

examined in the laboratory using a dissecting microscope. Diet items were divided into one of the 

following categories: (1) insects, (2) fish, (3) organic items (for example, sticks, rocks, etc.), and (4) 

unidentifiable items. Fish were identified to species using direct observation when possible. Partially or 

fully digested fish were identified based on bones that were recovered in the stomach. Once diet items 

from individual fish were categorized, the total weight of each category was measured to the nearest 

0.001 g. 

6 
Results 

Observed Angler Effort, Catch, and Catch Rates 

We interviewed 1,214 anglers who spent 4,594 h fishing in Lake Scanewa from June to 

November 2010. These anglers targeted rainbow trout (52 percent; 629 anglers), salmon (48 percent; 

580 anglers), and northern pikeminnow (less than 1 percent; 5 anglers). Trout angling was most popular 

from June to September and most anglers pursued salmon in October and November (fig. 3). Boat 

angling (67 percent; 816 anglers) was more popular than shore angling (32 percent; 398 anglers) and 

comprised 77 percent (3,518 h) of the angling effort. Anglers expended the most effort during 

November (1,470 h), followed by October (1,239 h), August (605 h), July (528 h), September (449 h), 

and June (303 h). More anglers fished during weekends (737 anglers) than during weekdays (477 

anglers). This relationship was reflected in the number of hours fished during these periods (weekends, 

2,868 h; weekdays, 1,726 h). 

A total of 1,866 fish were caught by anglers who were interviewed during the sampling period. 

Most of the catch was comprised of rainbow trout and coho salmon, although small numbers of Chinook 

salmon and northern pikeminnow also were caught (table 3). Anglers also caught suckers (Catostomus 

spp.), mountain whitefish (Prosopium williamsoni), and cutthroat trout (O. clarki) but these species 

comprised less than 1 percent of the total observed catch. Boat anglers accounted for most of the fish 

that were caught (table 3). Most rainbow trout were caught in August (51 percent; 713 fish) and July (25 

percent; 356 fish). Lesser numbers of rainbow trout were caught during September (14 percent; 199 

fish), October (5 percent; 66 fish), November (3 percent; 47 fish), and June (2 percent; 30 fish). Salmon 

anglers caught most of their fish in November (63 percent; 277 fish) and October (31 percent; 137 fish) 

while few fish were caught from June to September (6 percent; 26 fish). 

Catch rates of rainbow trout were substantially different between boat and shore anglers but 

overall catch rates exceeded the 0.50 fish per hour goal. Boat anglers averaged catch rates of 1.39 fish 

per hour throughout the study period, ranging from a low of 0.17 fish per hour in June to a high of 2.05 

fish per hour in August (table 4). Shore angler catch rates generally were low, averaging 0.35 fish per 

hour during the study. The November shore angler catch rates (4.09 fish per hour) were the highest 

observed for all months regardless of whether anglers were fishing from a boat or from the shore (table 

4). Boat anglers exceeded the 0.50 fish per hour goal in all months except June (no boat anglers 

targeting rainbow trout were interviewed in November). Shore anglers exceeded the goal in November 

only. Overall, combined catch rates (0.96 fish per hour) exceeded the 0.50 fish per hour goal during the 

study period. 

Proportion of Daylight Hours Surveyed 

Creel surveys were conducted 16 or 17 d each month from June to November 2010 and sampling 

occupied approximately one-third to one-half of the daylight hours in each month. A total of 778 h of 

creel surveys were conducted during the study which represented 32 percent of the daylight hours 

during that period (table 5). Creel surveys were conducted during 27 percent of the daylight hours that 

occurred from June to August, and then increased to a maximum of 48 percent in November as day 

length decreased. Creel surveys exceeded the 128 monthly hours required in the BiOp (16 shifts × 8 

hours per shift) every month except September, when a scheduling error resulted in failure to meet the 

monthly requirement. However, our overall creel effort was 778 h, exceeding the requirement by 10 h 

(table 5). 

7 
 Boat Surveys 

Boat surveys were conducted twice each month to develop a correction factor for anglers that 

were not visible from the Day Use Area during standard creel surveys. Creel survey staff counted shore 

and boat anglers during these surveys but found that all boat anglers were accounted for at the Day Use 

Area, therefore corrections were only applicable to shore anglers. Low numbers of anglers were 

observed during all boat surveys and correction factors ranged from 1.0 (no correction) to 5.3 (table 6). 

Most shore anglers that were not visible from the Day Use Area were located on the Cispus Arm of 

Lake Scanewa where boat angling also was very popular. 

Estimated Angler Effort 

We estimated that anglers spent in excess of 17,000 h fishing in Lake Scanewa from June to 

November 2010. Angler effort was greatest during October (4,253 h) when most anglers were targeting 

coho salmon (fig. 3; table 7). Angler effort also was high during August (3,732 h), July (3,394 h), and 

November (3,053 h; table 7). Angler effort in the reservoir was relatively low during June (1,103 h) 

when trout stocking at the Derby Site occurred. Boat anglers spent more time fishing (9,764 h) in the 

reservoir than shore anglers (7,689 h). 

Targeted Species 

Anglers were interviewed to determine which species they targeted while fishing in Lake 

Scanewa. Most anglers targeted rainbow trout from June to September but few anglers pursued trout in 

October and November when coho salmon were the primary species of interest (table 7; fig. 2). The 

proportion of anglers that targeted rainbow trout was similar between boat and shore anglers during 

each month of the study period (table 7). Few anglers (less than 3 percent per month) targeted species 

other than rainbow trout or salmon during the study period. 

Estimated Angler Effort and Harvest of Rainbow Trout 

We estimated that anglers spent nearly 10,000 h fishing for rainbow trout in Lake Scanewa from 

June to November 2010. Boat anglers expended the most effort during July (1,209 h) and August (1,845 

h) and did not fish for rainbow trout in November (table 8). Shore anglers pursued rainbow trout 

primarily from July to September (table 8). We estimated that total angler effort for rainbow trout was 

9,863 h (table 7). These estimates indicated that shore anglers expended 1,139 h more than boat anglers 

during the sampling period (5,501 h for shore anglers; 4,362 h for boat anglers; table 8). 

Estimates of rainbow trout harvest suggest that boat anglers were more successful than shore 

anglers and total harvest of rainbow trout was estimated to be 7,584 fish during the study period. 

Monthly harvest by boat and shore anglers was highest in July and August (table 8). Boat anglers caught 

3.7 times as many rainbow trout as shore anglers (5,976 fish compared to 1,608 fish; table 8). Boat 

anglers harvested 3,783 rainbow trout in August, which represented 50 percent of the total harvest for 

boat and shore anglers during the entire study period. We estimated that total harvest of rainbow trout 

by boat and shore anglers combined was 7,584 fish (95-percent confidence interval = 2,795–12,372 

fish) from June to November 2010. 

8 
Angler County of Residence 

Most anglers interviewed during the creel survey were from Lewis County, or other neighboring 

counties, which suggests that the Lake Scanewa fishery consists mostly of anglers located a short 

distance from the reservoir. Lewis County residents comprised 42 percent of the anglers who were 

interviewed followed by Pierce County residents (27 percent), Yakima County residents (13 percent), 

and Thurston County residents (13 percent; table 9). Collectively, these counties produced 89 percent of 

the anglers who were interviewed during the creel survey in 2010. Small numbers of anglers were either 

from other counties throughout the State or other States (table 9). 

Tagged Rainbow Trout Recoveries 

We recovered 88 of the rainbow trout that were PIT tagged during our study. Most recovered 

PIT-tagged fish were caught by anglers (50 fish in the Cispus Arm of Lake Scanewa; 12 fish in the 

Cowlitz Arm of Lake Scanewa), although some fish were recovered following collection at the Cowlitz 

Falls Fish Collection Facility (26 fish). The 88 fish that were recovered during the study accounted for 4 

percent of the fish that were PIT-tagged and released (2,082 fish). Tag recoveries showed that fish 

dispersed from the various release sites and contributed to catches in the Cowlitz and Cispus Arms of 

Lake Scanewa, as well as captures at the Cowlitz Falls Fish Collection Facility (fig. 4). The unique 

identification of the PIT tags allowed us to calculate the elapsed time from release to recapture for 

recovered PIT-tagged fish. The mean elapsed time from release to recapture was 27.5 d (SD = 23.4) and 

ranged from a minimum of 1 d to a maximum of 100 d (fig. 5). 

Rainbow Trout Stomach Contents 

We collected a total of 1,236 rainbow trout stomachs during the study period and examination of 

these samples showed that some trout were predatory in Lake Scanewa. Most stomach samples were 

obtained from fish that were caught in the Cispus Arm of Lake Scanewa (859 fish), followed by fish 

from the Cowlitz Falls Fish Collection Facility (271 fish), and fish from the Cowlitz Arm of Lake 

Scanewa (106 fish). Predation rates were highest for fish from the Cispus Arm of Lake Scanewa (2.7%; 

23 of 859 fish), followed by fish from the Cowlitz Falls Fish Collection Facility (1.5%; 4 of 271 fish), 

and fish from the Cowlitz Arm of Lake Scanewa (0.009%; 1 of 106 fish). A total of 28 trout stomachs 

(2.3 percent) contained fish, showing a low overall level of predation. Of the trout that consumed fish, 

we found 13 salmonid prey and 26 non-salmonid prey. Of the salmon that were consumed, 9 were found 

in stomachs of fish from the Cispus Arm of Lake Scanewa, 4 were from stomachs of fish from the 

Cowlitz Falls Fish Collection Facility, and none was found in stomachs of fish from the Cowlitz Arm of 

Lake Scanewa. A higher percentage of large trout (greater than 300 mm fork length; 8.5 percent) had 

fish in their stomachs compared to small trout (less than 300 mm fork length; 0.06 percent). Of the trout 

stomachs containing fish, 77 percent (20 of 26 fish) were from large trout. Most of the fish in trout 

stomachs were non-salmonid species (67 percent; 26 fish). Only 13 of the 39 fish in trout stomachs were 

from salmon species. We observed that predation by large trout varied seasonally based on the month in 

which trout stomachs were obtained (fig. 6). Predation was highest during February, March, and May 

and was relatively low (less than 10 percent) during July–September. 

9 
Discussion 

Results from the 2010 creel evaluation show that catch rates for trout anglers exceeded the 0.50 

fish per hour goal. Catch rates and angler effort varied between boat and shore anglers and few anglers’ 

targeted rainbow trout during October and November. The combined catch rates for boat and shore 

anglers (0.96 fish per hour) were nearly double the 0.50 fish per hour catch rate goal, which suggests 

that the mitigation trout fishery is successful in Lake Scanewa. Boat anglers were particularly successful 

as evidenced by the 1.39 fish per hour catch rates observed over the course of the study period. Shore 

anglers were less successful with overall catch rates (0.35 fish per hour) that did not meet the 0.50 fish 

per hour goal. However, these catch rate estimates did not include angling that occurred in the Derby 

Site fishery. The Derby Site is a highly popular shore fishery near the Day Use Area, which is netted off 

from the reservoir during the fishing season. As a result, fish are contained in a relatively small area 

(approximately 0.3 ha) where most or all of the 5,000 fish that are planted are presumably harvested. 

Catch rate data at this site were not collected as part of our study, but preliminary estimates suggest that 

catch rates in the Derby Site fishery probably exceeded those which were observed for boat anglers in 

Lake Scanewa during 2010 (Mike Kohn, Lewis County PUD, oral commun., 2010). Given these data, 

the mitigation trout fishery in Lake Scanewa appears to provide good angling opportunity, with some 

risk of negative impacts to anadromous species in the system. 

We estimated that trout anglers harvested about 38 percent (7,584 fish) of the rainbow trout that 

were planted into Lake Scanewa during 2010. This harvest estimate leaves nearly 12,500 planted fish 

unaccounted for that could prey upon, or compete with juvenile anadromous salmon in the system. 

Catch data from Cowlitz Falls Dam showed that 352 rainbow trout were collected at the fish facility 

during 2010, which suggests that some fish move downstream and pass the dam. The movements of 

rainbow trout in Lake Scanewa have not been studied so it is not possible to quantify how many fish 

could be passing the dam through turbines or the spillway. Catch data at the fish collection facility show 

significant annual variability in the number of rainbow trout that are collected, ranging from a low of 97 

fish in 2008 to a high of 1,009 fish in 1998. Survival rates of rainbow trout in the reservoir are currently 

not known so we can not estimate the size of the population in the reservoir after the angling season is 

closed. These limitations prevent us from determining if competition or predation are major factors 

affecting juvenile salmon in the system, but examination of stomach samples collected during 2010 

show that predation is occurring. 

Examination of the stomach samples revealed that rainbow trout are preying upon fish in Lake 

Scanewa and the incidence of predation is higher for larger trout. The creel survey conducted by 

Tipping and Serl (2000) identified differences between large trout (greater than 300 mm) and small trout 

(less than 300 mm; 13.6 percent predation compared to 1.1 percent predation). We used this size criteria 

for estimating predation rates of large and small trout during 2010 and observed a similar relationship, 

although predation rates were lower for both groups in our study. We found that 8.5 percent of large 

trout and 0.6 percent of small trout had fish in their stomachs but only 2.6 and 0.2 percent had 

salmonids in their stomachs. Tipping and Serl (2000) reported only the proportion of trout with 

salmonids in their stomachs, yet their observed predation rates on juvenile salmon were approximately 

five times higher than this study. We sampled 2,098 rainbow trout prior to release for PIT tagging and 

found that 6 percent of these fish were larger than 300 mm. Given this relationship, about 1,200 (6 

percent of the 20,000 fish) of the rainbow trout likely were larger than 300 mm when released during 

10 
2010. This is a significant size for a predator population considering that these fish could consume 

36,000 juvenile salmon in a 30-d period if they remained in the reservoir and each preyed upon one 

juvenile salmon per day. These data clearly show that subsequent evaluations will be needed to 

adequately address questions concerning rainbow trout predation on juvenile salmon in Lake Scanewa. 

The possible effects of predation by rainbow trout on juvenile salmonids in Lake Scanewa are 

cause for concern and the current requirements for monitoring stomach contents during the creel survey 

may not be adequate for addressing this issue. The current guidance for collecting stomach samples as 

part of creel surveys includes collecting at least 100 stomach samples per month from June to 

September for a total of 400 samples that are to be examined for the presence of juvenile fish (National 

Marine Fisheries Service, 2009). This approach may not be adequate for several reasons. First, rainbow 

trout are released from June to August when most juvenile salmon in the system are smolt-sized (that is, 

greater than 100 mm), which may make many of these fish too large to be prey items for trout. Second, 

the trout that are released have been reared in a hatchery facility and their feeding habits in a natural 

system will likely develop over time. Thus, fish that may become predaceous may not do so until late 

summer or early fall. This effect would not be observed if efforts to collect stomachs are ended in 

September. Additionally, food habits will change over time as food availability changes so it could be 

insightful to examine stomachs throughout the year to better understand these patterns. Finally, fry and 

parr presence in the reservoir likely peaks during the fall, winter, and early months of the year. Because 

these fish are appropriately sized to be prey items for rainbow trout, stomach content analysis would be 

particularly insightful during this time. We made additional efforts to collect stomach samples to 

address these issues: our final sample size was approximately three times as large as the minimum 

requirement, and some samples were collected during February, March, and May (fig. 6). Although 

sample sizes during these periods were small, the results from these samples support our hypothesis that 

predation could peak from October to May each year. Future evaluations should focus efforts on data 

collection associated with predation by rainbow trout in Lake Scanewa, as this appears to be the most 

significant threat associated with the current mitigation trout fishery. 

Tipping and Serl (2000) proposed that angler bycatch and hooking mortality from the mitigation 

trout fishery could have negative consequences for juvenile anadromous salmon but we found little 

evidence to support these concerns during 2010. Anglers that we interviewed reported catching a total of 

1,866 fish, and only one of these was a juvenile anadromous salmonid (cutthroat trout), that was 

released. Given the low bycatch that we observed, hooking mortality may not currently be an issue for 

juvenile anadromous salmonids in Lake Scanewa. Since Mongillo (1984) reported that hooking and 

release mortality rates can approach 50 percent, we recommend monitoring bycatch rates during future 

creel evaluations. 

Using PIT tags to monitor rainbow trout during our evaluation provided additional information 

that was not previously available from creel evaluations in Lake Scanewa. For example, we found that 

fish from the various release sites all contributed to collections in the Cowlitz and Cispus Arms of Lake 

Scanewa and at the Cowlitz Falls Fish Collection Facility (fig. 4). Additionally, we found that the mean 

time from release to recapture for PIT-tagged fish was 27.5 d and that many fish were harvested within 

30 d of being released (fig. 5). This was an important finding because we had planned to obtain growth 

data from PIT-tagged fish but the limited amount of time that fish spent in the reservoir prior to 

recapture provided little information about growth rates over time. Additional evaluations using radio or 

acoustic telemetry would provide more information regarding movement patterns and survival rates of 

rainbow trout in the reservoir. 

11 
Our study provided numerous insights into the status of the mitigation trout fishery in Lake 

Scanewa and identified several research needs that could inform management processes aimed at 

maintaining a balance between the mitigation trout fishery and anadromous salmonid populations in 

Lake Scanewa and the upper Cowlitz River Basin. We found that catch rates were well above the 

management goals and observed that some degree of predation is occurring in the reservoir, although 

current information deficiencies prevented us from quantifying predation throughout the year. Data 

obtained during this study should prove useful in developing future studies that inform management 

decisions in the upper Cowlitz River Basin. 

References Cited 

Mongillo, P.E., 1984, A summary of salmonid hooking mortality: Washington Department of Game, 

Olympia, Washington. 

National Marine Fisheries Service, 2009, Endangered Species Act Section 7(a)(2) Consultation: 

Biological Opinion and Magnuson-Stevens Fishery Conservation and Management Act Essential Fish 

Habitat Consultation: NOAA, Log number 2002/00945. 

Neeley, D., 1995, Creel surveys at the Cowlitz Falls Reservoir: 1995 Report, InSTATS, Oregon City, 

Oregon. 

Tipping, J.M., and Serl, J.D., 2000, Lake Scanewa creel census for 2000: 2000 Report, Washington 

Department of Fish and Wildlife, Olympia, Washington. 

12 
Cowlitz 

River

Cispus 

River

Lake Scanewa

Cowlitz

Falls Dam

Bud Allen

Campground 

release site

Day Use Area

release site

Cispus Arm

of Lake Scanewa

release site

PUD Boat

Launch release

site

WASHINGTON

Figure 1. Map showing Upper Cowlitz River Basin and Lake Scanewa study area, Washington. 

13 
Creel survey data

(Observed angler effort)

Divide by proportion

of daylight hours that 

were surveyed

(Estimated total angler 

effort)

Multiply by proportion

of targeted species

each month 

(Estimated angler effort 

per species)

Total estimated 

angling effort

for salmon

Total estimated 

angling effort

for other species

Total estimated 

angling effort

for rainbow trout

Multiply by monthly

catch rates for boat

and shore anglers

(Estimated monthly

rainbow trout harvest)

Total estimated

rainbow trout 

harvest

Figure 2. Flow chart showing process that was used to estimate angler effort and harvest numbers of rainbow trout 

in Lake Scanewa, Washington, June–November 2010. 

14 
Month

June July Aug. Sept. Oct. Nov.

Percent of anglers

0

20

40

60

80

100

1

18

99

1

193 199

106

23

9 2 1

18

245

299

Figure 3. Graph showing proportion of anglers targeting rainbow trout (filled circles), salmon (open circles), or 

northern pikeminnow (filled triangles) in Lake Scanewa, Washington, June–November 2010. Salmon anglers were 

targeting Chinook salmon (June–August) and coho salmon (September–November). Numbers above symbols 

represent the number of anglers targeting each species. 

15 
Recovery location

Cowlitz Arm Cispus Arm CFFF

Percent of fish

0

10

20

30

40

50

60

70

80

Bud Allen Campground

Day Use Area

Cispus Arm 

PUD Boat Launch 

2

9

1

6

10

19

15

4 4

6

12

Figure 4. Graph showing proportion of PIT-tagged rainbow trout that were recovered at three locations in Lake 

Scanewa, Washington, June–November 2010, following release at one of four release locations (Bud Allen 

Campground, Day Use Area, Cispus Arm of Lake Scanewa and PUD Boat Launch). Recovery locations included 

the Cowlitz Arm of Lake Scanewa, the Cispus Arm of Lake Scanewa, and the Cowlitz Falls Fish Collection Facility 

(CFFF). All fish were recovered by anglers except those from the CFFF which were recovered through the 

collection process. 

16 
Number of days from release to recapture

0 10 20 30 40 50 60 70 80 90 100

Number of fish

0

1

2

3

4

5

6

7

8

Figure 5. Graph showing distribution of elapsed times from release to recapture for PIT-tagged rainbow trout in 

Lake Scanewa, Washington, 2010. 

17 
Month

Jan. Feb. Mar. Apr. MayJuneJulyAug.Sep. Oct. Nov.Dec.

Percent of trout with 

fish in their stomachs

0

10

20

30

40

50 Large trout (> 300 mm)

Small trout (< 300 mm)

Figure 6. Graph showing percentage of rainbow trout stomachs that contained fish from February 2010 to February 

2011. 

 

18 
Table 1. Numbers of rainbow trout released annually into Lake Scanewa , Washington, 1994– 2010. 

[Fish sizes vary substantially for fish released at the Derby Site] 

Reservoir releases 

Year 1 fish per pound 2 fish per pound 3 fish per pound 

Derby Site 

Releases 

Total number of 

fish released 

1994 12,500 – – – 12,500 

1995 12,500 – – – 12,500 

1996 12,500 – 12,500 – 25,000 

1997 12,500 – 12,500 – 25,000 

1998 12,500 – 12,500 – 25,000 

1999 12,500 – 12,500 – 25,000 

2000 12,500 – 12,500 – 25,000 

2001 – 25,000 – – 25,000 

2002 – 25,000 – – 25,000 

2003 – 25,000 – – 25,000 

2004 – 25,000 – – 25,000 

2005 – 20,000 – 5,000 25,000 

2006 – 20,000 – 5,000 25,000 

2007 – 20,000 – 5,000 25,000 

2008 – 20,000 – 5,000 25,000 

2009 – 20,000 – 5,000 25,000 

2010 – 20,000 – 5,000 25,000 

Table 2. Numbers of rainbow trout released at four release sites in Lake Scanewa, Washington, 2010. 

[Numbers in parentheses are the number of fish that were PIT tagged from each release group. A total of 20,000 rainbow 

trout were released during 2010 and 2,082 of these were PIT tagged] 

Date Bud Allen 

Campground 

Cispus Arm of Lake 

Scanewa Day Use Area PUD Boat Launch 

June 24 750 (101) 2,000 (76) 1,500 (75) 750 (100) 

July 01 1,000 (101) 2,000 (75) 1,500 (77) 500 (101) 

July 15 450 (107) 1,650 (100) 900 (77) 0

July 29 450 (102) 1,200 (78) 900 (79) 450 (100) 

August 12 300 (106) 800 (81) 600 (82) 300 (100) 

August 26 300 (103) 800 (77) 600 (79) 300 (105) 

Total 3,250 (620) 8,450 (487) 6,000 (469) 2,300 (506) 

19 
Table 3. Numbers of fish that were reported in the catch by boat and shore anglers during a creel survey, Lake 

Scanewa, Washington, June–November 2010. 

Species Catch by boat anglers Catch by shore anglers Total catch 

Rainbow trout 1,213 fish (78%) 198 fish (63%) 1,411 fish (76%) 

Coho salmon 311 fish (20%) 100 fish (32%) 411 fish (22%) 

Chinook salmon 18 fish (1%) 11 fish (4%) 29 fish (2%)

Cutthroat trout 0 fish 1 fish (<1%) 1 fish (<1%) 

Northern pikeminnow 5 fish (<1%) 5 fish (<1%) 10 fish (<1%) 

Suckers 2 fish (<1%) 1 fish (<1%) 3 fish (<1%) 

Mountain whitefish 1 fish (<1%) 0 fish 1 fish (<1%) 

Total 1,550 fish 316 fish 1,866 fish 

Table 4. Catch per hour estimates for rainbow trout anglers in Lake Scanewa, Washington, June–November 2010. 

Month Angler type 

(number of anglers) 

Catch per hour 

(standard deviation) 

Boat (50) 0.17 (0.43) 

June Shore (49) 0.01 (0.07) 

Combined (99) 0.09 (0.32)

Boat (102) 0.97 (0.87) 

Shore (91) 0.41 (0.83) July Combined (193) 0.71 (0.89) 

Boat (158) 2.05 (1.79) 

August Shore (41) 0.18 (0.48) 

Combined (199) 1.67 (1.78) 

Boat (39) 1.59 (1.56) 

Shore (67) 0.14 (0.43) September Combined (106) 0.67 (1.22) 

Boat (19) 0.90 (0.80) 

October Shore (4) 0.00 (0.00) 

Combined (23) 0.75 (0.80) 

Boat (0) n/a 

November Shore (9) 4.09 (3.97) 

Combined (9) 4.09 (3.96) 

Boat (368) 1.39 (1.53) 

Total Shore (261) 0.35 (1.15) 

Combined (629) 0.96 (1.48) 

20 
Table 5. Summary of the total hours of daylight in each month during June–November 2010, the total number of 

hours that a creel survey was conducted during this period, and the proportion of daylight hours that were sampled 

during each month, Lake Scanewa, Washington. 

[Hours were rounded to the nearest whole number] 

Month Daylight hours 

per month 

Creel survey hours 

per month 

Proportion of daylight 

hours sampled 

June 473 h 130 h 0.27 

July 477 h 130 h 0.27 

August 465 h 128 h 0.27

September 376 h 124 h 0.33 

October 337 h 130 h 0.39 

November 283 h 136 h 0.48 

Total 2,412 h 778 h 0.32 

Table 6. Summary of the number of anglers that were observed from a boat during a creel survey in Lake 

Scanewa, Washington, 2010. 

[Visible anglers were those that could be seen from the Day Use Area. Non-visible anglers were those that could not be seen 

from the Day Use Area. The correction factor was calculated by dividing the total number of anglers by the number of 

visible anglers] 

Month Number of 

visible anglers 

Number of non-visible 

anglers 

Total number 

of anglers 

Correction 

factor 

June 3 0 3 1.0 

July 3 6 9 3.0 

August 3 13 16 5.3

September 4 2 6 1.5 

October 1 2 3 3.0 

November 7 0 7 1.0 

21 
Table 7. Summary of the estimated number of hours that anglers spent in Lake Scanewa, Washington, 2010. 

Month Angling group 

Estimated 

angling effort 

Proportion of anglers 

targeting rainbow trout 

Estimated rainbow trout 

angling effort 

Boat 837 h 0.75 624 h 

June Shore 266 h 0.96 255 h 

Total 1,103 h 879 h 

Boat 1,209 h 1.00 1,209 h 

July Shore 2,185 h 0.99 2,161 h 

Total 3,394 h 3,370 h 

Boat 1,856 h 0.99 1,845 h 

August Shore 1,876 h 0.98 1,831 h 

Total 3,732 h 3,676 h 

Boat 456 h 0.95 433 h 

September Shore 1,374 h 0.80 1,096 h 

Total 1,830 h 1,529 h 

Boat 2,690 h 0.09 249 h 

October Shore 1,563 h 0.06 100 h 

Total 4,253 h 349 h 

Boat 2,627 h 0.00 0 h 

November Shore 426 h 0.14 58 h 

Total 3,053 h 58 h 

Boat 9,675 h 4,360 h 

Total Shore 7,690 h 5,501 h 

Total 17,365 h 9,861 h 

22 
Table 8. Summary of observed angler effort, proportion of daylight hours that were surveyed, estimated angler 

effort, observed catch rates, and estimated catch in Lake Scanewa, Washington, 2010. 

Month 

Observed 

angling effort 

Proportion of daylight 

hours surveyed 

Estimated angler 

effort 

Observed catch 

rates 

Estimated 

catch 

Boat Anglers 

June 171 h 0.27 624 h 0.17 fish/hr 106 fish 

July 329 h 0.27 1,209 h 0.97 fish/hr 1,173 fish 

August 505 h 0.27 1,845 h 2.05 fish/hr 3,783 fish

September 139 h 0.32 433 h 1.59 fish/hr 689 fish 

October 96 h 0.39 249 h 0.90 fish/hr 224 fish 

November 0 h 0.48 0 h 0.00 fish/hr 0 fish 

Total = 1,243 h 4,361 h 5,975 fish 

Shore Anglers 

June 70 h 0.27 255 h 0.01 fish/hr 3 fish 

July 196 h 0.27 2,161 h 0.41 fish/hr 886 fish 

August 94 h 0.27 1,831 h 0.18 fish/hr 330 fish 

September 241 h 0.32 1,096 h 0.14 fish/hr 153 fish 

October 13 h 0.39 100 h 0.00 fish/hr 0 fish 

November 28 h 0.48 58 h 4.09 fish/hr 237 fish 

Total = 642 h 5,501 h 1,609 fish 

23 
24 

Table 9. Summary of the number of anglers that were interviewed from various counties in the State of 

Washington, June–November 2010. 

County of residence Number of 

anglers

Percentage of 

anglers 

Benton 1 0.08 

Chelan 9 0.74 

Clark 10 0.82

Cowlitz 16 1.32 

Grant 3 0.25 

Grays Harbor 4 0.33 

King 40 3.29 

Kitsap 2 0.16 

Lewis 513 42.26 

Mason 1 0.08 

Pacific 10 0.82 

Pierce 330 27.18 

Skamania 2 0.16 

Snohomish 15 1.24 

Stevens 1 0.08 

Thurston 69 5.68 

Yakima 163 13.43 

Out of State 25 2.06 

Total 1,214 100.00 
Publishing support provided by the U.S. Geological Survey

Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the 

Director, Western Fisheries Research Center

U.S. Geological Survey, 6505 NE 65th Street

Seattle, Washington 98115

http://wfrc.usgs.gov/
Liedtke and others— Evaluation of Angler Effort and Harvest of Rainbow Trout (Onchorhynchus mykiss), Lake Scanewa, Washington, 2010—OFR 2011-1178