FISHERIES DATA SERIES NO. 45
COHO SALMON STUDIES IN SOUTHEAST ALASKA1
BY
Artwin E. Schmidt
Alaska Department of Fish and Game Division of Sport Fish
Juneau, Alaska 99802
June 1988
1 This investigation was partially financed by the Federal Aid in Sport Fish Restoration Act (16 U.S.C. 777-777K) under Project F-10-3, Job No. S-l-4.
Because the Alaska Department of Fish & Game receives federal funding, all of its public programs and activities are operated free from discrimination on the basis of race, color, national origin, ageI or handicap. Any person who believes he or she has been discriminated against should write to: O.E.O., U. S. Department of the Interior, Washington, D.C. 20240.
TABLE OF CONTENTS
LIST OF TABLES............................................... iii
LIST OF FIGURES ..............................................
LIST OF APPENDICES ...........................................
iv
V
ABSTREICT .....................................................
INTRODUCTION .................................................
1
2
MATERIALS AND METHODS........................................ 4
Adult Return............................................ 4
Study Design ....................................... 4 Data Analysis ...................................... 4
Adult Run Timing, Migration Routes, and Exploitation.... 5
Study Design ....................................... 5 Data Analysis ...................................... 5
Smolt Production and Population Estimation.............. 6
Study Design ....................................... 6 Data Analysis ...................................... 6
RESULTS AND DISCUSSION....................................... 7
Adult Return............................................ 7
Contribution to Fisheries............................... 10
Harvest Rate............................................ 10
Timing and Location of Harvest.......................... 10
Smolt Production and Population Estimates............... 10
Coho Salmon Pre-Smolt Marking in Salmon Lake ....... Coho Salmon Smolt Catch at Fyke Net Station ........ Valid Tagged Coho Salmon Emigrating from
Salmon Lake ................................... Estimate of Coho Salmon Juvenile Population
in the Fall ................................... Population Estimate of Coho Salmon Pre-Smolt ....... Salmon Lake Juvenile Tagging, 1987 .................
10 18
18
18 18 18
I
TABLE OF CONTENTS (Continued)
Page
LITERATURE CITED............................................. 24
APPENDIX..................................................... 25
ii
LIST OF TABLES
Table
1.
2.
3.
4.
5.
6.
7.
8.
Daily coho salmon escapement counts, water temperature, and stream depth at Salmon Lake weir, 1987........................................
Number of coho salmon sampled at Salmon Lake weir by sex, tag status, and age, 1987......................
Mean length at age (mid-eye to fork) of adult coho salmon from Salmon Lake, 1987..........................
Age composition of adult coho salmon from Salmon Lake, 1987......................................
Estimated commercial catch of Salmon Lake coho salmon by fishing district and time period, 1987.......
Daily smolt catches, rainfall, water temperature, and maximum stream depth at the Salmon Lake fyke net station, 1987......................................
Age composition of Salmon Lake coho salmon smolts, 1987...........................................
Length composition of Salmon Lake coho salmon smelts, by age, 1987...........................................
8
11
12
13
17
19
22
23
iii
LIST OF FIGURES
Figure Paze
1. Location of Salmon Lake research site and coho salmon index streams near Sitka, Alaska, 1987.......... 3
2. Relative length-frequency by lo-mm size class of 318 adult male coho salmon sampled at Salmon Lake weir, 1987........................................ 14
3. Relative length-frequency by lo-mm size class of 238 adult female coho salmon sampled at Salmon Lake weir, 1987........................................ 15
4. Relative length-frequency by lo-mm size class of 30 jack coho salmon sampled at Salmon Lake weir, 1987.. 16
5. Relative length-frequency by 5-mm size class of 733 coho salmon smolts sampled at Salmon Lake, 1987.... 21
iv
LIST OF APPENDIX TABLES
Appendix A Table Page
1. Number and species of fish caught in St. Johns Creek, lo-16 July 1987........................................ 27
2. Number and species of fish caught in Sinitsin Creek, 17-24 July 1987........................................ 28
V
ABSTRACT
A coho salmon Oncorhynchus kisutch research project was continued in 1987 to determine escapement goals, migration routes, run timing, harvest rates, and areas of harvest for the Salmon Lake system near Sitka. Coded-wire tagging of pre-smolt and smolt populations was conducted at Salmon Lake. Population sizes of these groups were estimated. The adult coho salmon escapement to Salmon Lake was estimated by weir count and foot surveys.
The estimated coho salmon escapement to Salmon Lake was 616 adults. The contribution of this stock of coho salmon to the commercial troll fishery was 702, or 51.9 percent of the overall annual production. Contribution to the sport fishery was 29 fish and the contribution to the seine fishery was 26 fish, or 2.1 percent and 1.9 percent of annual production, respectively. Survival of tagged smolt to adult return was 9.4 percent. Nearly all returns of coded-wire tagged fish were from the outer coastal area offshore of Baranof, West Chichagof, and Yakobi Islands. Peak catch occurred during the week of 26 July through 1 August 1987.
KEY WORDS: coho salmon, Oncorynchus kisutch, escapements, smolt, production, coded-wire tagging, weir, fyke net, harvest rates.
INTRODUCTION
Coho salmon Oncorhpchus kisutch are important to commercial, recreational, and subsistence fisheries in southeast Alaska. Coho salmon harvests have re- covered from the lows during the 1960s and 1970s. The recreational angler harvest in southeast Alaska increased from 36,000 coho salmon in 1977 to 60,000 coho salmon in 1985 (Mills 1986).
Relatively little is known about the migration routes, run timing, exploitation rates, or escapements of discrete coho salmon populations in southeast Alaska. This information is just now beginning to be collected and understood. Without such information, proper stock management cannot be accomplished.
The Alaska Department of Fish and Game's (ADF&G) Divisions of Sport Fish and Commercial Fisheries have developed a cooperative coho salmon research program. Under this plan, Sport Fish personnel concentrate their efforts on stocks of coho salmon in and near the major urban areas (Figure 1), while Commercial Fisheries' activities focus on coho salmon in remote areas.
The goal of this project is to acquire information needed for more precise management of southeast Alaska's coho salmon stocks. The adult coho salmon stream surveys conducted by the Division of Sport Fish in select index streams provides one of the necessary pieces of information to obtain this goal. Similar data obtained by the Division of Commercial Fisheries and companion Division of Sport Fish projects provide further information.
The Salmon Lake project provides estimates of coho salmon adults in the escapement, and the emigrant smolt population size. Smolt from the Salmon Lake system are injected with coded-wire tags (CWT). The coded-wire tagging and subsequent recapture information provides estimates of harvest rates and the areas of harvest for this specific population. This project will document the population dynamics of coho salmon in the Salmon Lake system and will allow production estimates for other systems in the Sitka management area.
The objectives of this study were to:
1. Estimate the migration route, run timing, numbers caught, exploitation rate, and areas of harvest of Salmon Lake coho salmon in the various southeast Alaska fisheries.
2. Estimate the freshwater age composition, sex composition, and mean length at age of l-ocean (.l) adult coho salmon returning to Salmon Lake in 1987.
3. Estimate the number of coho salmon smolts emigrating from Salmon Lake between 15 April and 1 June 1987.
4. Estimate the age composition and mean length at age of coho salmon smolts emigrating from Salmon Lake in 1987.
2
Salisbury Sound
vl \ Baranof Island KEY MAP
Sinitsin Creek St. John Creek
Kruzof Island
+ l-l-l
Figure 1. Location of Salmon Lake research site and coho salmon index systems near Sitka, Alaska, 1987.
Sitka Sound
n N
3
I
5. Estimate the number of coho salmon juveniles greater than or equal to 85 mm fork length in Salmon Lake between 15 August and 15 September 1987.
MATERIALS AND METHODS
The Salmon Lake watershed was chosen as the first long-range study site by the Division of Sport Fish. This system is near Sitka, contributes to the local sport fishery, and is representative of several lake systems in the Sitka Management Area. This report summarizes the results from the fourth year of marked coho salmon returning to Salmon Lake.
Adult Return
The study design and data analysis procedures for the adult return of coho salmon to Salmon Lake were as follows:
Study Design:
A metal picket weir was operated at the outlet of Salmon Lake from 15 August to 5 October 1987. Daily counts were made of all species entering the weir's fish trap. All coho salmon were electrically anesthetized with a 12-volt shocking basket (Gunstrom and Bethers 1985). Coho salmon were examined for missing adipose fins and classified by sex, length (mid-eye to fork), and ocean age (jack or adult). Scale samples were taken from every third coho salmon less than 350 mm or greater than 450 mm in length. Scale samples were taken from all coho salmon between 350 and 450 mm to confirm their ocean age. All coho salmon captured in the weir's fish trap were marked with an opercular punch, which was changed weekly to allow a stratified population estimate to be made if necessary.
Data Analysis:
The weir remained operational until 5 October, so no population expansion calculations were necessary. Data collected were recorded on the Division of Sport Fish's standard age-weight-length (AWL) mark-sense forms. These forms were electronically scanned, and the data were compiled by the Division of Sport Fish's Research and Technical Services (RTS) unit in Anchorage.
Total escapement was obtained by adding the weir count, the number of fish seen jumping over the weir on 30 September during high water, and the number of fish counted below the weir prior to it becoming inoperable on 5 October.
Estimates of mean length by age group were calculated; a 95% confidence interval (CI) for the mean of each age-sex group was calculated according to the standard t-statistic equation:
(1) 95% CI - x f (ta + 2,df)(sdx n1j2)
where:
- x = the age-sex category mean length
n Xxi+n
i-l
n= sample size for the number of fish in the age-sex category
x. = 1
=
an individual fish length
Student's t-statistic with a + 2 = 0.05 i 2, and degrees of freedom (df) = n - 1
sdx = standard deviation of the lengths
= [ ; (Xi - ;)2 + (n - 1) Ill2
i-l
Adult Run TiminP. Migration Routes, and EXDlOitatiOn
Study Design:
Recovery of coded-wire tagged adult coho salmon from the harvest provides the information necessary to estimate their run-timing, migration routes, areas of harvest, and exploitation rates. Tag return information was obtained from the Division of Commercial Fisheries' port sampling program. The commercial harvest was estimated by quadrant and week as described in Clark and Bernard (1987). The Sitka marine creel census provided harvest estimates by sport anglers. Recovery of tagged adults at the Salmon Lake adult weir completed the recovery effort.
Data associated with tag deployment during the fall and spring tagging activities were recorded on the "Salmon Lake Smolt Tag and Recovery" data forms. The Division of Fisheries Rehabilitation, Enhancement, and Develop- ment's (FRED) standard CWT deployment forms were completed for all tags deployed.
Data Analysis:
Data recorded on AWL forms were reviewed for errors and sent to RTS for scanning, compilation, and return. Data recorded on the FRED Division tag deployment forms were forwarded to the FRED Division tag lab. Heads recovered and tag recovery forms were also forwarded to the FRED tag lab for decoding and processing. All data recorded on the "Salmon Lake Smolt Tag and Recovery" data forms were reviewed for errors and summarized.
Tags returned in the commercial fishery and collected by the Division of Commercial Fisheries' port sampling program were forwarded to the FRED tag lab. The lab provided the following information: (1) number and location of tags returned in the fishery and (2) harvest by time, area, and fishery.
Harvest estimates were calculated according to Clark and Bernard (1987, equation 14 and 15).
Smolt Production and Ponulation Estimation
Study Design:
Juvenile coho salmon were captured in the lake during the fall of 1986, and those fish greater than 85 mm fork length were marked with an adipose clip and CWT. Length frequency data from previous years demonstrated 85 mm to be the minimum size for smolting coho salmon at Salmon Lake. Juvenile coho salmon were also captured in the lake during March and April 1987 prior to smolt emi- gration. Those fish captured which had been tagged the fall before (August 1986) received a dorsal caudal clip. Those fish captured which were greater than 85 mm fork length and had not been tagged the fall before received a ventral caudal clip. The caudal clips allowed the fish to be iden- tified for inclusion in both the smolt and pre-smolt population estimation procedures.
Recovery of tagged and untagged out-migrating smolt occurred in the outlet stream's fyke net station (Schmidt 1986). The fyke net station was operated from 13 April through 22 May 1987. Each captured coho salmon smolt was clas- sified as either tagged (fall 1986) or untagged. Previously marked fish were examined for finclips and appropriately recorded. All coho salmon not previ- ously tagged received an adipose finclip and CWT.
The age and length at age composition of emigrant coho salmon smolt was determined using systematic random sampling. Fork length data of scale sam- ples were collected from every 15th fish captured in the fyke nets.
Data Analysis:
Estimates of mean length by age group of the emigrant coho salmon were obtained with the same procedures as noted for the adult return (see section, above). A simultaneous 95% CI for each age composition (proportion) estimate was calculated using (Goodman 1965):
(2) 95% CI - pi f [BiPi)(l -pi) + nl1i2
where:
1
pi = the estimated proportion of the age-sex category
=n.in 1
n. 1 = number of fish in a particular age-sex category
n = total number of fish in the sample
6
B = a tabled chi-squared statistic for a + 1 - (0.05 + k) and degrees of freedom = 1 [Note: a computer-generated value of B was obtained from the Statistical Analysis System's (SAS 1985) CINV function]
k = number of different age-sex categories possible
Population estimates for both the spring and fall populations were derived by use of the Chapman modified Petersen population estimator (Seber 1982). Specifically, the estimator used was:
(3) N = [(nl + l)(n2 + 1) + (m2 + 1)] - 1
where:
N = the population estimate;
nl = the number of marked fish released during the first capture occasion;
n2 = the number of fish captured (both marked and unmarked) during the second capture occasion; and
m2 = the number of marked fish in the second capture occasion sample.
Confidence intervals for the estimate were derived utilizing the procedures as outlined in Seber (1982; see section 3.1.4, equation 3.4).
RESULTS AND DISCUSSION
Adult Return
The total coho salmon escapement to the system was estimated at 616 adults. Between 15 August and 3 October, 556 adult coho salmon passed through the weir (Table 1). On 30 September, a minimum of 15 adult coho were observed jumping over the weir during a period of high water. On 3 October, an estimated 45 coho were observed below the weir for a short period, although only three coho passed through the weir that day. During the night of 4 October and through 5 October, water ran over the top and around the sides of the weir. A minimum of 22 adult coho salmon were observed swimming over the weir, and it's likely all the fish observed the previous day passed by the weir. The weir was no longer operational after 5 October. High water levels pre- vented a foot survey of the stream for salmon until 9 October, at which time no coho salmon were observed in the stream. After 5 October, no coho salmon were observed passing the weir site or at the stream mouth/estuary area. The total escapement estimate was derived by summing the number of adults passed through the weir (556), the minimum number observed jumping over the weir on 30 September (15), and the minimum number observed below the weir on 3 October (45).
The peak count of coho salmon occurred on 29 September when 113 adults and 1 jack passed the weir. Of the 556 adults examined at the weir, 329 (59.2%)
Table 1. Daily coho salmon escapement counts, water temperature, and stream depth at Salmon Lake weir, 1987.
Date
Average Water
Temperature coo
Maximum Number Stream Adult
Depth (m) Coho
Number Jack Coho
15 Aug 11.5 16 Aug 11.5 17 Aug 12.0 18 Aug 12.0 19 Aug 12.0 20 Aug 13.0 21 Aug 13.0 22 Aug 12.5 23 Aug 13.5 24 Aug 13.5 25 Aug 13.5 26 Aug 13.5 27 Aug 14.0 28 Aug 14.0 29 Aug 15.0 30 Aug 13.0 31 Aug 11.5 01 Sept 12.5 02 Sept 12.0 03 Sept 11.5 04 Sept 11.0 05 Sept 11.0 06 Sept 11.0 07 Sept 11.0 08 Sept 11.0 09 Sept 11.0 10 Sept 10.5 11 Sept 10.0 12 Sept 9.5 13 Sept 9.5 14 Sept 9.0 15 Sept 9.5 16 Sept 9.0 17 Sept 9.0 18 Sept 9.0 19 Sept 9.0 20 Sept 8.5
0.42 1 0 0.50 4 0 0.46 6 0 0.39 0 0 0.32 0 0 0.29 0 0 0.26 0 0 0.25 0 0 0.23 0 0 0.22 0 0 0.20 0 0 0.20 0 0 0.21 0 0 0.21 0 0 0.20 0 0 0.33 0 0 0.45 0 0 0.49 0 0 0.42 0 0 0.46 2 0 0.53 0 0 0.60 14 3 0.41 2 0 0.47 0 0 0.53 8 1 0.73 3 1 1.00 7 0 0.71 42 1 0.57 2 0 0.54 3 0 0.47 0 0 0.44 0 0 0.61 0 0 0.80 6 1 0.97 22 3 0.65 11 6 0.62 4 0
-Continued-
Table 1. Daily coho salmon escapement counts, water temperature, and stream depth at Salmon Lake weir, 1987 (continued).
Date
Average Water
Temperature (OC>
Maximum Number Stream Adult
Depth (m) Coho
Number Jack Coho
21 Sept 8.5 0.55 3 0 22 Sept 8.5 0.46 0 0 23 Sept 9.5 0.40 0 0 24 Sept 9.0 0.36 0 0 25 Sept 8.5 0.44 0 0 26 Sept 8.0 1.26 23 1 27 Sept 8.5 0.72 54 8 28 Sept 8.0 0.64 86 2 29 Sept 8.5 1.05 113 1 30 Sept 8.5 1.36+ 52l 0 01 Ott 9.0 0.93 55 1 02 Ott 9.0 1.04 45 1
03 Ott 8.5 0.71 0
04 Ott 05 Oct3
8.5 1.25 &,3 0 8.5 l.36+4 0 0
Totals 616 30
Includes 15 adult coho observed jumping the weir.
These fish counted below weir on 3 October swam over the weir during flood of 4 October.
Weir no longer operational after night of 4 October, morning of 5 October.
Exceeded measuring device maximum of 1.36 m.
9
were missing adipose fins. In addition, 30 jacks were enumerated, of which 10 (33.3%) were missing adipose fins. Table 2 summarizes the sex, tag status, and age of the coho salmon past the Salmon Lake weir. Table 3 lists mean length at age of coho salmon sampled at the Salmon Lake weir. Table 4 pre- sents the age composition of Salmon Lake coho salmon adults, 1987.
Relative length frequencies of adult male, female, and jack male coho salmon are presented in Figures 2 through 4.
Contribution to Fisheries
The estimated catch of coho salmon bound for Salmon Lake was 757 fish, with a standard error of 63 fish. The commercial troll fishery harvested an esti- mated 702 adult coho salmon, while the purse seine fishery harvested an estimated 26 adult coho salmon from Salmon Lake. The Sitka marine sport fishery harvested 29 Salmon Lake coho salmon.
Harvest Rate
The harvest rate for a particular fishery was obtained by dividing the number of coho salmon taken in a particular fishery by the total annual production of coho salmon from Salmon Lake. Total production was the sum of escapement (616)) troll harvest (702), seine harvest (26), and sport harvest (29), or 1,373 fish. Harvest rates for each fishery are as follows: troll fishery, 51.1%; seine fishery, 1.9%; and sport fishery, 2.1%. The combined commercial harvest rate, 53.0%, is very similar to last year's combined commercial harvest rate of 56.5%.
Timing and Location of Harvest
The commercial catch of coho salmon from Salmon Lake was estimated for each fishing district which had randomly recovered tags by statistical week obtained during the port sampling program (Table 5). The majority of fish came from District 113, the area immediately offshore of Baranof and Chichagof Islands, and the peak catch occurred during statistical week 31 (26 July- 1 August). The troll fishery was closed from 3-12 August, which resulted in lowered catches and landings for statistical weeks 32 and 33.
Smolt Production and Pooulation Estimates
The coho salmon smolt population in Salmon Lake was studied from 24 March through 25 May 1987.
Coho Salmon Pre-Smolt Marking in Salmon Lake:
In August 1986, 3,690 juvenile coho salmon greater than 85 mm fork length received coded-wire tags and adipose finclips. On 24 March and 3 April 1987, 2,217 coho salmon pre-smolts greater than 85 mm fork length were captured. Of these, 371 had been tagged in August 1986 and were given dorsal caudal clips. The remaining 1,846 (untagged) juvenile coho salmon were given ventral caudal clips. This provided marked juvenile coho salmon in the population to estimate the spring smolt emigration at the fyke net station.
10
Table 2. Number of adult coho salmon sampled at Salmon Lake weir by sex, tag status, and age, 1987.
Number of Fish Male Female
Age Tagged Untagged Tagged Untagged Total
1.1 0
2.1 10
3.0 1
3.1 24
4.0 2
4.1 7
5.0 0
x.ol 7
X.ll 144
0
22
1
14
7
3
2
10
94
0 1 1
8 16 56
0 0 2
17 10 65
0 0 9
8 4 22
0 0 2
0 0 17
114 60 412
Totals 195 153 147 91 586
1 X = Undetermined.
11
Table 3. Mean length at age (mid-eye to fork) of adult coho salmon from Salmon Lake, 1987.
Sex Age Number Mean Length (mm) 95% Confidence Interval
Lower Limit Upper Limit
Female 1.1 1 650 Female 2.1 24 682 Female 3.1 27 641 Female 4.1 12 655
iii iii 633 676 618 676
Male 3.0 3 369 153 585 Male 4.0 5 369 343 394 Male 5.0 2 366 42 690 Male 2.1 28 633 608 659 Male 3.1 37 612 584 640 Male 4.1 9 650 597 704
Table 4. Age composition of adult coho salmon from Salmon Lake, 1987.
Brood Year 1984 1983 1982 1981
Age 1.1 2.1 3.1 4.1 Total
Sex
Male Sample Number Percent Composition 95% Confidence Interval Standard Error
Female Sample Number Percent Composition 95% Confidence Interval Standard Error
Both Sexes Sample Number Percent Composition 95% Confidence Interval Standard Error
0 0.0 . . . . . .
1 24 27 12 64 0.7 17.4 19.6 8.7 46.4
0.0-2.7 8.7-26.1 10.5-28.6 2.2-15.1 36.9-55.9 0.7 3.2 3.4 2.4 4.2
1 52 64 21 138 0.7 37.7 46.4 15.2 100.0
0.0-2.5 27.4-48.0 35.8-57.0 7.6-22.9 . . . 0.7 4.1 4.2 3.1 . . .
28 37 9 74 20.3 26.8 6.5 53.6
11.1-29.5 16.7-37.0 0.9-12.2 46.1-63.1 3.4 3.8 2.1 4.2
8
7
6
5
4
3
2
1
0 305 335 365 395 425 455 485 515 545 575 605 635 665 695 725 755
Midpoint Length (mm>
Figure 2. Relative length-frequency by lo-mm size class of 318 adult male coho salmon sampled at Salmon Lake weir, 1987.
11
10
9
3
2
1
0 425 465 485 515 545 575 605 635 665 695 725
Midpoint Length bun)
Figure 3. Relative length-frequency by lo-mm size class of 238 adult female coho salmon sampled at Salmon Lake weir, 1987.
77 76 75 74 73 72
‘w z5 3k5 355 365 J/~ --
295 305 375 Midpoint Length (-1 ampled at
ize class of 30 jack c oho salmon s
length-frequency bY lOem ' Figure 4.
Relative Salmon Lake weir,
1987.
Table 5. Estimated commercial c tch of Salmon Lake coho salmon by fishing district and time period, 1987. B
Statistical Week Dates
Fishing District
104 109 113 114 116 154 156 189
27 27 June-04 July 28 05-11 July 29 12-18 July 30 19-25 July 31 322
26 July-01 Aug
332 02-08 Aug 09-15 Aug
34 16-22 Aug 35 23-29 Aug 36 30 Aug-05 Sept
15
46 4 88 4
10 56 14 4 79 15 3
188 20 8 48 5 12 21
4 80 10 15 19 7
4
Totals 15 14 640 22 49 23 12 4
' Commercial troll fishing season was from 20 June to 20 September 1987.
2 The troll fishery was closed from 3-12 August 1987.
Coho Salmon Smolt Catch at Fyke Net Station:
Coho salmon smolt were captured in fyke nets and coded-wire tagged from 15 April through 22 May 1987. During this period, 10,952 coho salmon smolt were captured (Table 6). A representative length-frequency histogram of these smolts is shown in Figure 5. The age composition of the coho salmon smolt population is presented in Table 7. The length of these coho salmon smolts by age group is presented in Table 8. There were 1,234 adipose clipped recap- tures (fall CWT), 233 adipose and dorsal caudal clipped recaptures (fall CUT and spring marked) and 996 ventral caudal clipped (spring mark) recaptures.
There were 9,464 CWT inserted in previously untagged smolt and 39 CUT inserted in smolt which had lost tags. These spring tagged fish suffered a posttagging mortality of 12 individuals, so the net release was 9,491 tags. The over- winter tag retention of fall-tagged fish was 1,428 of 1,467, or 97.34%.
Valid Tagged Coho Salmon Emigrating from Salmon Lake:
There were 3,690 juvenile coho salmon tagged in the fall of 1986. This lot experienced no handling mortality and had a 97.34% tag retention for a release of 3,592 tags with code 04/03/18. This does not account for overwinter mortality.
The release of 9,491 spring tagged smolts was assumed to have the same tag retention as the fall tagged fish (97.34%). This results in a net valid release of 9,238 smolts with tag code 04/27/01.
Estimate of Coho Salmon Juvenile Population in the Fall:
The fall juvenile population was estimated from the recapture of fall tagged fish during fyke net operations (15 April to 22 May). A total of 10,952 coho salmon were sampled, which included 1,467 of the original 3,690 fall-marked fish. The point estimate was 27,538.
Population Estimate of Coho Salmon Pre-Smolt:
The total smolt emigration was estimated from the recapture of 1,229 spring marked fish (233 dorsal caudal and 996 ventral caudal) of the 2,217 originally marked in the lake prior to emigration. The point population estimate was 19,750. The 95% confidence interval ranged from 19,056 to 20,444. This pre-smolt population is used as an estimator of the smolt emigration as nearly all marked pre-smolt emigrate during the smolting period.
Salmon Lake Juvenile Tagging, 1987:
A total of 2,268 juvenile coho salmon greater than 85 mm fork length were tagged in Salmon Lake from 13 August through 19 September. Fifty-nine large funnel traps were set throughout the lake during this period. The traps were fished about 24 hours at depths between 0.5 m and 3 m. The average catch was 38.4 pre-smolts per trap set. Sampling efforts recaptured 625 of these
18
Table 6. Daily smelt catches, rainfall, water temperature, and maximum stream depth at the Salmon Lake fyke net station, 1986.
Date Rainfall
(cm> Average H20
Temp ('C) Highest Stream Number of Smolts
Depth (cm) Coho Sockeye Steelhead
15 Apr 0.0 3.0 0.53 16 Apr 2.2 3.0 0.59 17 Apr 3.1 snow 4.0 0.45 18 Apr 1.0 snow 4.0 0.36 19 Apr 0.5 4.0 0.35 20 Apr 3.1 3.5 0.49 21 Apr 2.5 3.5 0.56 22 Apr 2.7 4.0 0.51 23 Apr 0.0 5.0 0.39 24 Apr Trace 4.0 0.34 25 Apr 0.8 4.5 0.32 26 Apr 0.3 4.0 0.30 27 Apr 2.5 4.0 0.46 28 Apr 0.5 4.0 0.49 29 Apr 1.0 4.0 0.49 30 Apr Trace 5.0 0.44 01 May Trace 5.0 0.43 02 May Trace 5.0 0.40 03 May Trace 5.0 0.37 04 May 4.1 4.0 0.83 05 May 2.3 5.0 0.50 06 May 0.5 5.0 0.67 07 May 2.0 5.0 0.56 08 May 0.8 5.0 0.44 09 May 0.8 5.0 0.40 10 May 0.8 5.0 0.39
198 180 107
75 1
105 41 19 50
1
69 25
1
51 71
120 1
241 66
7 1
401 470 371 676
1
0 0 0 0 0 0 0 0 0 0 0 0 1 2 0 1 0 2 0 0 0 1 0 1 0 0 0 2 1 6 0 5 0 0 6 4 0 0 0 0 0 0 6 2 6 10
11 2 13 4
0 0
-Continued-
Table 6. Daily smolt catches, rainfall, water temperature, and maximum stream depth at the Salmon Lake fyke net station, 1986 (continued).
Date Rainfall
(cd Average H20
Temp ('C) Highest Stream Number of Smolts
Depth (cm) Coho Sockeye Steelhead
11 May 12 May 13 May 14 May 15 May 16 May 17 May 18 May 19 May 20 May 21 May 22 May
Trace 5.0 0.39 897 26 5 0.3 5.0 0.34 388 33 7 0.8 5.0 0.35 574 62 7 0.3 6.0 0.36 952 60 6 0.0 5.0 0.35 831 178 7 1.8 5.5 0.42 736 160 3 0.5 6.0 0.36 1,260 271 14 Trace 6.0 0.32 705 429 26 0.0 6.0 0.33 384 586 4 Trace 6.0 0.32 403 500 10 0.0 7.0 0.32 304 696 8 0.0 7.0 0.31 175 551 15
Totals 10,952 3,596 154
1 Catch this date included in next daily catch figure.
16
15
14
13
12
11
4
3
2
1
0 4
82.5 92.5 102.5 112.5 122.5 132.5 142.5 152.5 162.5 172.5 182.5
Midpoint Length (mm)
Figure 5. Relative length-frequency by 5-mm size class of 733 coho salmon smolts sampled at Salmon Lake, 1987.
Table 7. Age composition of Salmon Lake coho salmon smolts, 1987.
Brood Year 1985 1984 1983 1982 1981
Freshwater Age 1 2 3 4 5 Total
Sampling Dates: 15 April to 22 May
Sample Number 4 422 230 39 2 697 Percent 0.6 60.5 33.0 5.6 0.3 100.0 95% Confidence Interval 0.0-1.3 55.8-65.3 28.4-37.6 3.4-7.8 0.0-0.8 Standard Error 0.3 1.9 1.8 0.9 0.2
Table 8. Length composition of Salmon Lake coho salmon smolts by age, 1987.
Brood Year 1985 1984 1983 1982 1981
Freshwater Age 1 2 3 4 5
Sampling Dates: 15 April to 22 May
Average Fork Length (mm) 95.0 103.5 119.0 136.6 172.0 95% Confidence Interval 83.7-106.3 102.5-104.5 117.3-120.6 132.8-140.5 70.4-273.6 Standard Error 3.5 0.5 0.8 1.9 8.0 Sample Size 4 422 230 39 2
h) W
pre-smelts during the period. These recaptured marked fish had an average short-term tag retention rate of 96% (600/625).
LITERATURE CITED
Clark, J. E. and D. R. Bernard. 1987. A compound multivariate binomial-hypergeometric distribution describing coded microwire tag recovery from commercial salmon catches in southeastern Alaska. Alaska Department of Fish and Game Informational Leaflet No. 261. 113 pp.
Goodman, L. A. 1965. On simultaneous confidence intervals for multinomial proportions. Technometrics 7:247-254.
Gunstrom, G. K., and M. Bethers. 1985. Electrical anesthesia for handling large salmonids. Progressive Fish-Culturist 47:67-69.
Mills, M. J. 1986. Alaska statewide sport fish harvest studies. Alaska Department of Fish and Game. Federal Aid in Sport Fish Restoration, Annual Report of Performance, 1985-1986, Project F-10-1, 27 (RT2). 137 pp.
SAS. 1985. SAS user's guide: basics, version 5 edition. Statistical Analysis System Institute, Incorporated, Cary, North Carolina, USA.
Schmidt, A. E. 1986. Salmon studies in Southeast Alaska. Alaska Department of Fish and Game. Federal Aid in Sport Fish Restoration, Annual Report of Performance, 1985-1986, Project F-10-1, 27(S-1-4).
Seber, G. A. F. 1982. The estimation of animal abundance. MacMillan Publishing Company, New York, New York, USA.
24
APPENDIX
Investigation of Juvenile Coho Salmon Populations
in St. John and Sinitsin Creeks, 1987
25
INTRODUCTION
The research being conducted on wild stock coho salmon in southeast Alaska has been done primarily on lake rearing systems or large complex river systems. A large portion of the annual coho salmon production comes from smaller streams scattered throughout Southeast. Escapement of adult coho salmon to many of these small stream systems has been depressed in recent years and has probably been below the minimum escapement needed for optimum smolt production.
A pilot study on Sinitsin and St. John Creeks near Sitka (Figure 1) was begun in July of 1987. A good escapement history for coho salmon is available for both of these streams. The goal of this pilot study was to determine if it is possible to obtain reliable population estimates of juvenile coho salmon in streams of this size so comparison of adult escapement and subsequent potential smolt production can be correlated. In particular, the objective was to estimate the number of rearing juvenile coho salmon in St. John and Sinitsin Creeks which will be of smolt size (285 mm) by spring 1988.
METHODS
Juvenile coho salmon were captured with fish traps during July in St. John Creek (Baranof Island) and Sinitsin Creek (Kruzof Island). Fry traps baited with salmon roe were fished for time periods ranging from 2 to 24 hours. Captured fish were anesthetized with MS-222, counted, and rearing coho equal to or greater than 65-mm fork length were given dorsal caudal clips for future identification. All rearing areas of the creeks were randomly sampled with small or large fry traps depending upon depth of water at the sampling sites. Scale samples were collected from four selected coho salmon from each trap for size-age comparisons.
After initial marking, each creek was given at least a l-week rest period for fish to redistribute throughout the creek. Each creek was then retrapped, and coho salmon greater than or equal to 65 mm were examined for finclips. Popu- lation estimates of the juvenile coho salmon were calculated from these data.
St. John Creek was trapped again in October to verify the population estimate made in July. Baited minnow traps were used, and all captured juvenile coho salmon greater than 65 mm were examined for caudal clips. Those coho salmon which showed evidence of clipping (i.e., wavy dorsal caudal rays) were mea- sured to determine the minimum size of the size/age group of the 508 fish that were marked in July.
RESULTS AND DISCUSSION
The initial marking of juvenile coho salmon occurred from 10 to 16 July in St. Johns Creek and 17 to 24 July in Sinitsin Creek. A total of 508 juvenile coho salmon greater than or equal to 65 mm fork length were marked in St. John (Appendix Table 1) and 689 juvenile coho salmon greater than or equal to 65 mm fork length were marked in Sinitsin Creek (Appendix Table 2).
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Appendix Table 1. Number and species of fish caught in St. Johns Creek, lo-16 July 1987.
Sample Date Total No. Marked No. Marked Total Juvenile Recaptures 65 mm Total Dolly No.of
Coho Fork Length Rainbow Varden Traps Set
10 July 237 0 170 141 147 14
14 July 166 19 91 68 74 16
15 July 185 23 74 56 62 12
16 July 287 47 173 150 120 17
Appendix Table 2. Number and species of fish caught in Sinitsin Creek, 17-24 July 1987.
Sample Date
No. Marked Total No. Marked 2 65-mm No. of
ss Recaptures Fork Length No. Rb No. D.V. Traps Set
17 July 83 0 73 123 166 13
21 July 222 48 162 403 459 15
22 July 192 56 122 245 380 15
23 July 363 35 296 320 368 8
24 July 126 80 36 82 165 5
Total 689
Population Estimation of Juvenile Coho Salmon Greater Than or Eaual to 65 mm Fork Length, St. John Creek. 1987
Recapture effort occurred on St. Johns Creek on 27 and 28 July. During this 2-day effort 446 juvenile coho salmon greater than or equal to 65 mm fork length were captured, of which 207 had been previously dorsal caudal marked. The point estimate of this juvenile coho salmon population was 1,093. The 95% confidence interval ranged from 1,050 to 1,135.
Trapping for juvenile coho salmon in St. John Creek was conducted on 16 October and 18 October 1987 in an effort to verify the juvenile coho salmon estimate made in July. Rearing fish were examined for previous finclips, and all fish with finclips were greater than or equal to 65 mm fork length. A total of 66 juvenile coho salmon greater than or equal to 65 mm fork length were captured, of which 29 had been previously marked. The estimate of juve- nile rearing coho salmon greater than or equal to 65 mm at the time of marking was 1,135 with a 95% confidence interval of 989 to 1,283. Ninety-four percent (124/132) of the juvenile coho salmon greater than or equal to 65 mm fork length were age 1.0 and from brood year 1985. Only 5.4% were age 2.0 (brood year 1984).
Population Estimate of Juvenile Coho Salmon Greater Than or Eaual to 65 mm Fork Length. Sinitsin Creek. 1987
Trapping was conducted in Sinitsin Creek on 29-30 July to recapture juvenile coho. During this 2-day effort 437 juvenile coho salmon greater than or equal to 65 mm fork length were caught, of which 320 had finclips. The population estimate of juvenile coho salmon greater than or equal to 65 mm fork length was 940. The 95% confidence interval ranges from 920 to 960. Ninety-eight percent (101/103) of sampled juvenile coho salmon greater than or equal to 65 mm fork length were age 1.0 and from brood year 1985. The remaining 2% were age 2.0 and were from brood year 1984.
29
Recommended
