Volume 081 Article 07

Little River Spring Chinook tshawytscha Sport Harvest, 1986 to 1990

By Peter F. Hassemer Fishery Research Biologist

July 1991 TABLE OF CONTENTS

INTRODUCTION ...... 1

METHODS ...... 1 Sport Fishery Creel Survey ...... 1 1986 Creel Survey ...... 2 1987 Creel Survey ...... 4 1988 Creel Survey ...... 4 1990 Creel Survey ...... 5 Tribal Harvest ...... 5 Rapid River Hatchery Rack Returns ...... 6 Spring Chinook Run Prediction Models ...... 6

RESULTS ...... 6 Sport Fishery Effort and Harvest ...... 7 Nez Perce Tribal Harvest ...... 7 Hatchery Rack Returns ...... 12 Brood Year Return Analysis ...... 12 Spring Chinook Run Prediction Models ...... 12

DISCUSSION ...... 17

LITERATURE CITED ...... 19

i LIST OF TABLES

Table 1. Estimates of angler effort and harvest for the 1986 through 1990 Little chinook salmon sport fisheries. Estimates are stratified by weekend and weekdays periods. Number of days reported is the number of open fishing days, not angler days ...... 8

Table 2. Spring chinook sport fishery and Nez Perce Tribal harvest estimates and Rapid River hatchery rack returns for Rapid and Little Salmon rivers, 1984-1990. Nez Perce Tribal harvest estimates are from Mauney (1990) except as indicated ...... 10

Table 3. Little Salmon River/Rapid River area spring chinook salmon sport and Nez Perce Tribal harvests and hatchery rack returns classified by age, 1984-1990 ...... 13

Table 4. Little Salmon River/Rapid River area spring chinook salmon brood year returns by age class, and total brood year returns estimated from sport and tribal harvests and hatchery rack returns, 1984-1987. Brood year returns for 1986 and 1987 are incomplete ...... 15

Table 5. Models tested for predicting the returns of 4-year old and 5-year old spring chinook to the Rapid River/Little Salmon River area...... 16

ii LISTOFFIGURES

Figure 1. Effort (angler hours) and harvest in the 1990 spring chinook sport fishery on the Little Salmon River...... 9

Figure 2. Percent of spring chinook salmon returning to the Little Salmon River/Rapid River area accounted for at the hatchery rack and in the sport harvest and tribal harvest, 1986-90...... 11

Figure 3. Returns, by age class, of spring chinook salmon to the Rapid River hatchery rack, 1984 - 1990 ...... 14

Figure 4. Rapid River/Little Salmon River area spring chinook salmon brood year returns to the Rapid River hatchery rack and brood year harvests in the sport and Nez Perce Tribe subsistence fisheries, 1981 - 1985 brood years ...... 18

iii ABSTRACT

The Department of Fish and Game operates Rapid River hatchery as a spring chinook (Oncorhynchus tshawvtscha) production facility, with funding provided by Idaho Power Company. Estimated annual spring chinook returns to the Little Salmon River/Rapid River area have ranged from 3,344 to 10,008 for the period 1986 through 1990. Harvestable surpluses in 1986, 1987, 1988, and 1990 allowed limited sport fisheries in those years, and sport harvests ranged from 422 to 1,430 spring chinook. Chinook sport anglers harvested 6.3% to 14.3% of the total return to the Little Salmon River/Rapid River area when sport seasons were open.

iv INTRODUCTION

Rapid River hatchery is a spring chinook (Oncorhynchus tshawvtscha) production facility operated by the Idaho Department of Fish and Game (IDFG). Operational funds are provided by Idaho Power Company (IPC), as part mitigation for the Brownlee, Oxbow, Hells Canyon dam complex on the mid-Snake River. The spring chinook stock returning to the facility was developed from transplanted mid-Snake River chinook collected at Hells Canyon dam beginning in 1964 (Howell et al. 1985).

Rapid River is a tributary to the Little Salmon River, entering approximately four miles above the confluence of the Little Salmon and Salmon rivers. Spring chinook migrating through the Little Salmon River on their return to the hatchery have provided harvest opportunities for sport anglers. Members of the Nez Perce Tribe (NPT) also utilize spring chinook returning to Rapid River for ceremonial and subsistence harvest.

In addition to funding hatchery operations, IPC also has provided funds to monitor and evaluate the sport fishery in years when it was open. The purpose of this report is to provide estimates of sport harvest from 1986 through 1990. Also included are tribal harvest estimates and hatchery rack return information. Returns by brood year are provided and estimates of brood year return are made. Finally, models were developed to predict returns of 4-year and 5-year old spring chinook salmon using previous brood year return information.

METHODS

Sport Fishery Creel Survey

Chinook salmon sport fisheries on the Little Salmon River were allowed most recently in 1986, 1987, 1988, and 1990. Season structures varied among years to satisfy specific management objectives for each year. Changes in season structure required modifying the format of the creel survey used to estimate sport harvest each year. Each year's survey format is described separately below. While conducting creel survey angler interviews all fish harvested by interviewees were sexed and measured (fork length, nearest cm). Length measurements were used to determine the age composition of the catch. Spring chinook returning to Rapid River are classified as either jacks, 4-year olds, or 5-year olds (see Rapid River Hatchery Rack Returns for age descriptions).

The 1986 through 1988 sport fisheries were limited to the 4 mile section of the Little Salmon River from its mouth upstream to the mouth of Rapid River.

1 The fishing area was extended in 1990 to include approximately 15 miles of the Little Salmon River above Rapid River.

1986 Creel Survey

Length of a fishing day was 17.5 hours (4:00 AM to 9:30 PM). Each fishing day was divided into three 3-hour periods (strata) within which angler counts and interviews were conducted. The 3-hour periods were: 6:00 to 9:00 AM, 12:00 noon to 3:00 PM, and 6:00 to 9:00 PM.

A roving creel survey (Neuhold and Lu 1957) using a stratified, sampling with replacement sample design was used to estimate angler effort and harvest. Count/interview sessions were conducted during two of the three 3-hour strata each day. Angler counts were made at the beginning and end of each stratum, with angler interviews conducted between the counts in each stratum. All angler counts were completed within one hour and are considered instantaneous counts. The two strata to be sampled on the first survey day of the fishing season were randomly chosen. On the second and subsequent survey days the one strata not sampled on the previous survey day was automatically selected to be sampled on that survey day. The second strata to be sampled on a survey day was randomly selected from the other two strata.

Fishing effort (angler hours) was estimated using the angler counts. Angler interviews were used to estimate catch and harvest rates. Because of increased angler effort on weekends, estimates of effort, catch rates, and harvest were stratified by weekend and weekday periods (holidays were considered weekend days). Total effort and harvest for the season were obtained by summing the weekend and weekday effort and harvest estimates. Interviews with anglers who had not completed their fishing trips were used to estimate catch and harvest rate. The use of incomplete trips to make the estimates may bias the results. It is nearly impossible to conduct interviews at the end of a fishing trip because road access along the entire length of the fishing area allows anglers to quickly leave the area upon completion of fishing.

Angler interviews were conducted to contact 25% of the anglers in each survey strata. Survey personnel interviewed every fourth angler encountered during the survey. Using this interview scheme the number of interviews conducted was proportional to the amount of effort expended in each survey strata (Neuhold and Lu 1957).

2 Effort (angler hours) for weekend and weekday periods were calculated separately as: __ Ei=Di*H*A i, (1) where:

Di = number of days (weekend or weekday) in the fishing season, i

= subscript for weekend days or weekdays,

H = number of hours in a fishing day = 17.5 , and

Ai = mean daily angler count for the fishing season for weekend days or week

and where:

Ajkl = angler count on survey day j, strata k, count 1 ,

d = number of weekend or weekday survey days completed, and I =

total number of instantaneous counts conducted = d * 2 * 2.

Mean catch rate (fish/angler hour) for weekend and weekday periods were calculated separately as:

where:

Cijkl = number of fish caught on weekend or weekday survey day j by angler 1 interviewed in strata k,

i = subscript denoting weekend day or weekday,

d = number of weekend or weekday survey days completed,

n = total number of weekend or weekday angler interviews, and

3 Tijki= number of hours fished on weekend or weekday survey day j by angler 1 interviewed in strata k.

Season harvest for weekend and weekday periods were calculated separately as: Hi =

__ Ei *Ci , (4) where:

i = subscript denoting weekend days or weekdays, and __ Ei and Ci are as described as above.

1987 Creel Survey

The 1987 season was divided into three separate openings (5/29 to 6/1, 6/5 to 6/8, and 6/12 to 6/28). Separate effort and harvest estimates were made for each opening, and the three harvest estimates were summed to provide a season total harvest estimate.

Angler counts and interviews were conducted each day during the first two openings. During the third opening, survey days (one weekend day and three week days each week) were selected randomly.

Each survey day was divided into five 3-hour strata (0400 to 0700, 0700 to 1000, 1000 to 1300, 1300 to 1600, and 1600 to 1900 hours) and one 2.5-hour stratum (1900 to 2130 hours). Strata to be surveyed each survey day were selected randomly. During the first opening, two strata were selected for the first day and three strata were selected for each of the remaining three days. Four strata were selected for each of the first three days of the second opening, and three strata were selected for the fourth (last) day. Four strata were selected for each survey day of the third opening.

Formulas used in all calculations were the same as those used in 1986, with appropriate modifications for the number of strata sampled each survey day.

1988 Creel Survey

During 1988 open fishing periods were initially set from 12:00 noon Friday through 9:00 PM the following Monday (four days). This structure was used for the periods May 6-9, 13-16, 20-23, 27-30, June 3-6, and 10-13. By June 17 a sufficient number of fish had returned to Rapid River hatchery to satisfy egg- take requirements. On June 17 the sport season was reopened (12:00 noon) and remained open until 9:00 PM July 9.

4 A creel survey was conducted every day during open fishing periods. Count intervals and angler interview procedures were the same as those used in 1986. Separate estimates of harvest and effort were made for each open fishing period from May 6 through June 6. Estimates of harvest and effort for each opening were stratified by weekday (Friday and Monday) and weekend (Saturday and Sunday) periods. Weekday and weekend harvest and effort estimates were summed to provide totals for each separate opening. For openings from June 10 through July 9 a separate estimate of effort and harvest was made for each day of the fishery. Season total harvest and effort estimates were obtained by summing all separate estimates.

Formulas used in all calculations were the same as those used in 1986, with appropriate modifications for the four-day and one-day estimates.

No fish lengths from the sport harvest were available in 1988. To determine age-class composition the proportions of three-, four-, and five-year old fish collected at the hatchery weir in 1988 were used.

1990 Creel Survey

The format for the 1990 creel survey was the same as that used in 1986. A sport quota of 550 spring chinook was set prior to the opening of the sport fishery. The quota was based on the harvestable surplus of the predicted return to the Little Salmon River/Rapid River area and harvest sharing with the Nez Perce Tribe. Total catch estimates for the season were made each Monday of the season. When the quota was reached the sport fishery was closed. The season opened on May 12 and was closed on June 7.

Nez Perce Tribal Harvest

Nez Perce Tribe ceremonial and subsistence harvest is monitored by NPT fishery biologists. Fishing seasons and methods used to estimate seasonal harvest are described in Mauney (1990).

Length-frequency information and sex composition of the catch is not collected from the NPT catch. Age class (and brood year) composition on the NPT harvest each year was determined by using age class proportions from the Rapid River hatchery rack returns. The predominant gear types used by NPT fishers are the dip-net and gaff pole (Mauney 1990), and it was assumed that this gear was not selective for various sizes of fish. Therefore we expect the hatchery return to be representative of the NPT harvest.

Mauney (1990) notes that some tribal fishers voluntarily release jacks. If voluntary release does occur our estimates of age class composition may be

5 biased. In most years the proportion of jacks in the rack return is small. We feel any biases incurred by estimating tribal harvest composition using rack return information is small and does not significantly influence estimates of total brood year return.

Rapid River Hatchery Rack Returns

Spring chinook are trapped at a site on Rapid River approximately 1.5 miles below the hatchery facility. Fish normally begin returning about mid-May. The last date of adult spring chinook migration varies among years. Criteria used to identify the end of the spring chinook run are low daily trap catch and the arrival of larger, more silvery summer-run chinook. All spring chinook trapped are held at the hatchery and spawned at a later date. At the time of trapping, size of each fish is measured (fork length, nearest cm) and sex is determined. Spring chinook 54 cm (21 in) and less are classified as jacks or 3- year olds (12 or one year of ocean rearing), 55 cm to 79 cm (22 in to 31 in) fish are classified as 4-year olds (22 or two years of ocean rearing), and those 80 cm (32 in) and larger are 5-year olds (32 or three years of ocean rearing).

Suring Chinook Run Prediction Models

Simple linear and multiple regression analyses were used to evaluate models for predicting returns of 4-year old and 5-year old spring chinook to the Little Salmon River/Rapid River area. Independent variables used in the analyses included smolt releases (1983 through 1989), jack returns (1984 through 1990), 4- year old returns (1985 through 1990), and 5-year old returns (1986 through 1990).

Analyses were done using the SYSTAT statistical package (Wilkinson 1988). Criteria used to evaluate the fit of each model were the coefficient of determination (R2), F-statistic (ANOVA, ps0.05), and the significance of regression coefficients in the linear equation (t-statistic, 1) 0.05). All models were evaluated both with and without y-intercepts (constants) included in the regression equation.

RESULTS

Results presented in this report are for the 1986 through 1990 run years. Tables used to present this information include information for the 1984 and 1985 run years. It was necessary to include this information for the brood year return analysis, as the 1986 and 1987 adult returns included fish from the 1984 and 1985 brood years.

6 Sport Fishery Effort and Harvest

As expected, more angler hours sport fishing for salmon were exerted on weekend days than weekdays, even though there were more weekdays open to fishing each year (Table 1, Fig. 1). In all years except 1986, more than 50% of the total season harvest was taken on weekends. Total sport harvest ranged from 422 to 1,430 spring chinook during the four years covered in this report (Tables 1 and 2). The sport harvest typically is dominated by 4-year old (2-ocean) fish. Harvests by age class are listed in Table 3.

Sport harvests ranged from 6.3% to 14.3% of the total adult spring chinook salmon return to the Little Salmon River/Rapid River area for the 1986- 1990 sport fisheries (0% in 1989, Table 2, Fig. 2). Also, from 1986 through 1990 sport harvests ranged from 14.8% to 53.3% of the total harvest (sport and tribal combined) of spring chinook in years when the sport fishery was open.

During the 1990 sport fishery very little angler activity was observed on the open section of the Little Salmon River above the mouth of Rapid River. Effort was estimated at 197 and 34 angler hours for weekend and week day periods, respectively. Effort estimates for the Little Salmon River above the mouth of Rapid River are not included in Table 1. Estimated harvest for weekend periods was zero fish. Harvest could not be estimated for week day periods. No anglers could be contacted on week day surveys; anglers had left the fishing area prior to completion of the instantaneous counts and before the interview period began. It is assumed that harvest for weekday periods also was zero for this section of the river.

Nez Perce Tribal Harvest

Tribal spring chinook harvest estimates from 1986 through 1990 ranged from 544 to 3,520 fish (Table 2). The 1990 estimate of 970 chinook harvested was provided by Nez Perce Tribe fisheries personnel. Harvests by age class, where age class distribution was determined from hatchery rack returns, are listed in Table 3.

Tribal harvests ranged from 14.1% to 44.0% of the total adult spring chinook salmon return to the Rapid River/Little Salmon River area from 1986 through 1990 (Table 2, Fig. 2). Also, tribal harvests ranged from 56.5% to 85.2% of the total harvest (sport and tribal combined) of spring chinook in years when the sport fishery was open. In 1989 sport angling was not allowed, therefore 100% of the harvest was taken by NPT fishers.

7 Table 1. Estimates of angler effort and harvest for the 1986 through 1990 Little Salmon River chinook salmon sport fisheries. Estimates are stratified by weekend and weekdays periods. Number of days reported is the number of open fishing days, not angler days.

Weekdays Weekend Days Hours Harvest Days Hours Harvest Days Season Total Yea No. % No. % No. % No. % No. % No. % Hours Harvest Days ----r ------1986 8,544 45.6% 846 59.2% 34 66.7% 10,212 54.4% 584 40.8% 17 33.3% 18,756 1,430 51

1987 5,275 31.0% 111 26.3% 15 60.0% 11,722 69.0% 311 73.7% 10 40.0% 16,997 422 25

1988 7,009 36.8% 303 43.8% 27 56.3% 12,035 63.2% 389 56.2% 21 43.8% 19,044 692 48 0.0% 0 0 0 8 1989 0 0.0% 0.0% 0 0.0% 0 0.0% 0 0.0% 0

1990 6,667 48.7% 265 46.9% 18 66.7% 7,009 51.3% 300 53.1% 9 33.3% 13,676 565 27 9

Table 2. Spring Chinook sport fishery and Nez Perce Tribal harvest estimates and Rapid River

hatchery rack returns for Rapid and Little Salmon rivers, 1984 - 1990. Nez Perce Tribal

harvest estimates are from Mauney (1990) except as indicated.

Sport Fishery NPT Harvest Hatchery Rack Total Harvest Only

Year No. % No. % No. % Return Total Sport % NPT %

1984 0 a 0.0% 100 4.1% 2,35 95.9% 2,456 100 0.0% 100.0%

6

1985 2,313 20.9% 2,023 18.3% 6,727 60.8% 11,063 4,33 53.3% 46.7%

6

1986 1,430 14.3% 1,855 18.5% 6,723 67.2% 10,008 3,285 43.5% 56.5%

1987 422 6.3% 2,430 36.5% 3,80 57.2% 6,660 2,852 14.8% 85.2%

8 1

0 1988 692 8.7% 3,520 44.0% 3,780 47.3% 7,992 4,212 16.4% 83.6%

1989 0 0.0% 544 16.3% 2,800 83.7% 3,344 544 0.0% 100.0%

1990 565 13.6% 970b 23.4% 2,60 62.9% 4,141 1,53 36.8% 63.2% 6 5

a From IDFG files. b Estimate from James Mauney, NPT fishery biologist. 11 Hatchery Rack Returns

Rack returns ranged from a high of 6,723 jack and adult spring chinook in 1986 to 2,606 in 1990 (Table 2). The proportion of fish returning to the rack ranged from 47.3% to 83.7% (1986 - 1990) of the total return to the Rapid River/Little Salmon River area each year (Table 2). Rack returns in all years are predominantly 4-year old fish (Table 3, Fig. 3). The proportion of 5-year olds (3- ocean) returning to the rack varies considerably among years, although it has been as high as 41.2%.

Brood Year Return Analysis

Sport and NPT harvests and hatchery rack returns by age class for brood years 1981-1986 are listed in Table 4. Total brood year hatchery rack returns and brood year sport and NPT harvests also are listed in Table 4, and are shown in Figure 4. Only returns for the 1981-1985 brood years are complete at this time. Returns for the 1986 and 1987 brood years are incomplete, as fish from these brood years will continue to return through 1991 for the 1986 brood year and 1992 for the 1987 brood year.

Brood year returns to the hatchery rack ranged from 50.7% to 77.4% of the total brood year returns for 1981 through 1985 brood years. Sport harvest, for brood years, ranged from 4.9% (1985 brood year) to 19.6% (1981 brood year). The low value for the 1985 brood year harvest rate (4.9%) is partly a function of closed sport fishery in 1989, which would have harvested the 1985 brood year fish as four-year olds. Nez Perce Tribal brood year harvest rates ranged from 18.1% to 40.4%.

Total return rates to the Rapid River/Little Salmon River area were similar for the brood years 1981 through 1984 (0.3112% to 0.4387%, Table 4). Percent total return for the 1985 brood year was only 0.1074%.

Spring Chinook Run Prediction Models

Four models for predicting the returns of 4-year old spring chinook were tested, and 14 models for predicting the returns of 5-year old spring chinook were tested (Table 5). The model

R4 = 12.142 * R3 , (5) where: R4 = predicted number of 4-year olds returning for a brood year and R3 = return of 3-year olds (jacks) for the same brood year, was selected as the best model for predicting returns of 4-year old spring chinook (R2=0.936, F=73.451, p<0.001). To predict the return of 5-year old fish the model

12 Table 3. Little Salmon River/Rapid River area spring chinook salmon sport and Nez Perce Tribal harvests and hatchery rack returns classified by age, 1984 - 1990.

Hatchery Rack Returns Sport Harvest NPT Harvesta ---- Age ---- Age 32 ------Age ---- Age 2------eYear No. 2 % 2 % Age 32 -% - -- Age 12 -% No. % ---- Age 12 ------Age 22 --- - No. - No. 2 - - No. % ------1984 651 27.6% 1,349 57.3% 356 15.1% 0 0.0% 0 0.0% 0 0.0% 28 27.6% 57 15 15.1% 57.3 1985 351 5.2% 6,177 91.8% 199 3.0% 121 - b 2,124 - 68 - 106 5.2% 1,858 60 3.0% 91.8 1986 177 2.6% 5,090 75.7% 1,456 21.7% 37 2.6% 935 65.4% 458 32.1% 49 2.6% 1,404 402 21.7% 75.7 1987 210 5.5% 2,443 64.2% 1,155 30.3% 17 4.0% 203 48.0% 203 48.0% 134 5.5% 1,559 737 30.3% 64.2 1988 172 4.6% 2,051 54.3% 1,557 41.2% 31 375 - 285 - 160 4.6% 1,910 1,450 41.2% 54.3 1989 428 15.3% 1,993 71.2% 379 13.5% 0 0.0% 0 0.0% 0 0.0% 83 15.3% 387 74 13.5% 71.2 1990 41 1.5% 2,430 93.3% 135 5.2% 0 0.0% 449 79.4% 116 20.6% 15 1.5% 905 50 5.2% 93.3 % a Estimated for each year from age class composition of Rapid River Hatchery rack return. b Dash indicates no fish lengths from the sport harvest were available for age class composition estimation; proportions per age class from the hatchery rack return in the same year were used to estimate age class composition of the sport catch. 14 Table 4. Little Salmon River/Rapid River area spring chinook salmon brood year returns by age class, and total brood year returns estimated from sport and tribal harvests and hatchery rack returns, 1984 - 1987. Brood year returns for 1986 and 1987 are incomplete.

Brood Releas 12 ------Age ------Age 22 ------Age 32 ------Year Yeare Rtn Yr Rack Sport Tribal Rtn Yr Rack Sport Tribal Rtn Yr Rack Sport Tribal ------1981 1983 1984 651 0 28 1985 6,177 2,124 1,858 1986 1,456 458 402

1982 1984 1985 351 121 106 1986 5,090 935 1,404 1987 1,155 203 737

1983 1985 1986 177 37 49 1987 2,443 203 1,559 1988 1,557 285 1,450

1984 1986 1987 210 17 134 1988 2,051 375 1,910 1989 379 0 74

1985 1987 1988 172 31 160 1989 1,993 0 387 1990 135 116 50

1986 1988 1989 428 0 83 1990 2,430 449 905 1

5 1987 1989 1990 41 0 15

------

Total Brood Year Returns Brood Release Number Hatchery Rack Sport Fishery NPT Fishery______% of Year Year Released No. % No. % No. % TOTAL Release 1983 ------1981 2,998,103 8,284 63.0% 2,582 19.6% 2,28 17.4% 13,153 0.4387% 7 1982 1984 3,246,197 6,596 65.3% 1,258 12.5% 2,24 22.2% 10,101 0.3112% 7 1983 1985 2,491,238 4,177 53.8% 524 6.8% 3,05 39.4% 7,759 0.3114% 8 1984 1986 1,594,688 2,640 51.3% 392 7.6% 2,118 41.1% 5,150 0.3229%

1985 1987 2,836,400 2,300 75.5% 148 4.9% 598 19.6% 3,046 0.1074%

1986 1988 2,630,200

1987 1989 2,319,500 Table 5. Models tested for predicting the returns of 4-year old and 5-year old spring chinook to the Rapid River/Little Salmon River area.

Analysis of Variance Regression Coefficientsb ------a 2 Model R - F P a B1 B2 B3 ------

------

R4 = a + BR3 0.654 7.575 0.051 -1117.924 14.449 - -

R4 = BR3 0.936 73.451 0.000 - 12.142 - -

R4 = a + 81S8Y + B2R3 0.655 2.852 0.202 -1399.322 0.000 14.139 -

R4 = 81SBY + 82R3 0.937 29.981 0.004 - -0.000 13.776 -

R5 = a + BR4 0.237 0.931 0.406 478.036 0.215 - -

R5 = BR4 0.751 12.070 0.025 - 0.286* - -

R = a + B1R3 + 8 R 0.700 2.329 0.300 2257.593 -12.547 0.867 -

5 2 4

R5 = B1R3 + 82R4

0.794 5.764 0.094 - -4.887 0.643 - 1 6 0.155 0.184 0.845 -313.246 0.001 -0.473 - R5 = a + 81SBY + a2R3

R5 = B1SBY + 81R3 0.734 4.144 0.137 - 0.001 -0.547 -

B R R5 = a + B1SBY + 2 4 0.273 0.376 0.727 -398.917 0.000 0.172 -

R5 = B1SBY + B2R4 0.771 5.037 0.110 - 0.000 0.172 -

R5 = a + 81S8Y + 132R3 + B3R4 0.859 2.029 0.467 658.732 0.001 -14.706 0.886

R5 = 81S8Y + B2R3 + B3R4 0.951 13.020 0.072 - 0.001 -14.128 0.860

R5 = a + 8R(3+4) 0.222 0.855 0.423 488.842 0.198 - -

8R * R5 = (3++4) 0.746 11.769 0.027 - 0.266 - -

8 R R5 = a + 81R3 + B2R4 + 3 (3+4) 0.844 1.806 0.489 8234.893 -28.627 -0.001 0.002

0.870 4.456 0.189 - -6.158 1.086 -0.001 R5 = 81R3 + B2 R4 + a3R(3+4) ------a R = adult return, subscript denotes age, all returns within each model are for the same brood year. SBY = brood year smolt release to produce adult returns a = constant (y-intercept) in regression equation B = regression coefficients b Asterisk denotes significance (psO.05), all others are not significant. R5=0.286 * R4, (6)

where: R5 = predicted number of 5-year olds returning for a brood year and R4 = return of 4-year olds for the same brood year, was selected as the best model (R2=0.751, F=12.070, p=0.025).

A statistically valid prediction of the 1991 4-year old return, based on the 1990 jack return, cannot be made using equation 5. The low estimated jack return in 1990 (56 jacks) was the lowest observed since 1984, and is outside the range of observations used in developing the model. The prediction models should be re-evaluated each year after new return information becomes available.

The predicted return of 5-year old spring chinook in 1991, using equation 6 and the 1990 4-year old return (3,784 fish) is 1,082. This predicted return is greater than the estimated returns of 5-year olds in 1989 and 1990, but is substantially less than the estimated 5-year old returns of 1986-1988.

DISCUSSION

Until 19901 the Little Salmon River/Rapid River area had provided the only opportunity in the state for chinook sport fisheries since the end of general chinook seasons in 1978. Angler participation in the Little Salmon River chinook sport fishery is considerably high, demonstrating the public desire for salmon fisheries. Several different season structures were employed for sport seasons open since 1986, to distribute effort and harvest over a longer period. Since the majority of angler effort and harvest for each of the seasons occurred on weekends, it appears that mid-week closures offer little to extending the fishing season. In 1990, with a sport quota of 550 fish, the season lasted a total of 27 days. For comparison, the 1987 season was open Thursdays through Sundays only and lasted 25 days, with nearly 74% of the harvest taken on weekends. The 1988 season, open Fridays through Mondays, lasted 48 days, although total angler hours spent fishing was not substantially greater than for seasons lasting nearly half as many days. Because of the limited benefit of mid-week closures, future fisheries should be open throughout the week to minimize potential enforcement problems.

A final area of concern is the decreasing brood year return rates observed beginning with the return of the 1981 brood year release (Figure 4). Reasons for the declining return rates are unknown at this time. Information from future returns is necessary to determine if this trend continues.

1 In 1990 a portion of the Clearwater River was open to sport harvest of hatchery spring chinook returning in excess of hatchery broodstock needs.

17 18 LITERATURE CITED

Howell, P., K. Jones, D. Scarnecchia, L. LaVoy, W. Kendra, and D. Ortmann. 1985. Stock Assessment of Anadromous Salmonids. Volume 1: chinook, Coho, Chum, and Sockeye Salmon Stock Summaries. U.S. Department of Energy, Bonneville Power Administration. Contract No. DE-AI79-84BP12737, Project No. 83-335. Portland, OR.

Mauney, J. 1990. A survey of the Nez Perce subsistence fishery for spring chinook salmon at Rapid River, Idaho, 1988. Technical Report 89-10. Nez Perce Tribe of Idaho, Department of Fisheries Management. Lapwai, ID.

Neuhold, J.M. and K.H. Lu. 1957. Creel census method. Utah State Department of Fish and Game Publication 8. Salt Lake City, UT.

Wilkinson, L. 1988. SYSTAT: The System for Statistics. SYSTAT Inc. Evanston IL.

19 9