Draft Imnaha Subbasin Summary November 30, 2001 Prepared for the Northwest Power Planning Council Subbasin Team Leader



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Spring Chinook

Historically, the Imnaha subbasin supported one of the largest runs of spring/summer chinook in Wallowa County (Wallowa County and Nez Perce Tribe 1993). Prior to the construction of the four lower Snake River dams, an estimated 6,7001 adult chinook escaped to the subbasin annually (USACE 1975). In 1957, peak escapement of chinook into the subbasin was 3,462 adults (Ashe et al. 2000; Mundy and Witty 1998).

Returns of natural origin chinook (not including jacks) have declined to levels below 150 individuals during some years (ODFW 1998b cited in Ashe et al. 2000), which is notable since it is estimated that up to 10% of the annual escapement of wild Snake River spring/summer chinook salmon are of Imnaha origin (NMFS 2001). Run reconstructions for Imnaha chinook have been derived from spawning ground surveys, age frequencies, mainstem and tributary harvest rates, and mainstem conversion rates for upstream passage of adults available from the 1940’s to present (Table 19).


Table 19. Mean  coefficient of variation (and range) for spawners, recruit and recruit per spawner numbers in aggregate and index populations of wild spring and summer chinook in the Imnaha subbasin (1939-1990). Values for recruits per spawner represent geometric means and standard deviations (coefficient of variation is standard deviation divided by the mean and expressed as a percentage) (reproduced from Beamesderfer et al. 1997).

Population

N1/

Spawners

Recruits to freshwater


Recruits per spawner

Mainstem

(1939-1990)



41

1,110  69%

(169 – 3,462)



2,845 90%

(125 – 10,720)2/



2.0  139%

(0.3 – 16.3)



Big Sheep/Lick

(1962-1990)



27

201 93%

(0 – 644)



349  140%

(0.0 – 1,895)3/



0.9  332%

(0.0 – 13.7)



1/ Number of brood years for which data was collected

2/ Represents the maximum and minimum number of freshwater recruits over 41 years

3/ Represents the maximum and minimum number of freshwater recruits over 27 years

Adult spring chinook begin entering the Imnaha in late-April, with peak entry in mid-to-late June (Ashe et al. 2000). Returning summer-run adult chinook enter the Imnaha later than the spring run, however the majority of chinook are probably in the Imnaha by the end of July. Peak spawning for both spring and summer chinook is in the late summer, occurring usually in late August to early September (Ashe et al. 2000; NMFS 2001). Spawning ground surveys conducted by the Oregon Fish Commission established peak spawning in the Imnaha slightly prior to August 24, although peaks may occur earlier or later depending upon the run year (Thompson and Haas 1960).

Spring chinook most commonly use the mainstem Imnaha between Summit Creek and the Blue Hole (RM 59.6) for spawning (Figure 18; Mundy and Witty 1998). In addition to this 17-mile reach, mainstem chinook spawning has been documented as far downstream as Freezeout Creek (RM 29.4). Fewer numbers of fish spawn in primary tributaries, including the South Fork Imnaha, Big Sheep Creek and Lick Creek. Although spawning has been observed in the South Fork Imnaha, it is not known if it occurs on an annual basis. The majority of spawning in Big Sheep Creek currently occurs from RM 29.4 to RM 33.4 (Ashe et al. 2000), while in Lick Creek, spawning locations are generally found in the lower 4.5 miles (B. Knox, ODFW, personal communication, April 12, 2001). Juvenile chinook use portions of the mainstem for rearing, but are also present in lower Cow, lower Lightning, lower Horse, Big Sheep, and Lick creeks (Gaumer 1968; Huntington 1994), and are suspected to use the lower reaches of Skookum (RM 53.7), Gumboot (RM 46.8), Mahogany (RM 45.0), Crazyman (RM 42.8), Summit (RM 37.5), Grouse (RM 34.7), and Freezeout creeks (RM 29.4) (Mundy and Witty 1998).

Prior to their emigration in June, parr and presomolts will distribute throughout Big Sheep Creek and the upper, middle and lower Imnaha, and Snake River from September through winter and spring (Schwartzberg et al. in prep; Ashe et al. 2000). Gaumer (1968) documented some movement of fry and small parr into the lower Imnaha and lower Big Sheep Creek during spring months, however determined that the peak movement of parr into lower Big Sheep Creek occurred in November, while peak movement into the lower Imnaha occurred during October and November. The fact that little or no movement of juvenile fish occurred during summer months could be due to elevated water temperatures from July into September (Ashe et al. 2000). During summer months, water withdrawals by irrigation diversions in upper portions of Big and Little Sheep Creek may contribute to higher water temperatures in lower Big Sheep Creek and the lower Imnaha River due to a reduction in flow volume.

Naturally produced Imnaha chinook smolts exhibit different emigration patterns than hatchery-reared smolts. Naturally produced fish typically maintain a protracted emigration from the system, and have been documented passing the Cow Creek fish trap (RM 4) from the middle of September to the middle of July (Schwartzberg et al. in prep. and Ashe et al. 2000).



Figure 18. Spawning and rearing locations of Imnaha spring/summer chinook

Hatchery produced chinook salmon were documented to have short emigration periods in 1994 (Ashe et. al. 1995), 1995 (Blenden et. al. 1996), 1996 (Blenden et. al. 1997), 1997 (Blenden et. al. 1998), 1998 (Cleary et. al. 2000 in prep), and 1999 (Cleary et al. in prep). The emigration timing and pattern of arrival of hatchery chinook salmon at RM 4 may be influenced by the release strategy. The release strategies from 1994 to 1998 where either direct stream releases, acclimated forced stream releases, or a combination of direct and acclimated forced releases.

In 1999, the first volitional release of hatchery smolts occurred and resulted in fish passing the Cow Creek facility from early March to early June, and peaking between the middle of March and the middle of May. It appears that the acclimated volitional release strategy used in 1999 allowed for a more prolonged migration of hatchery chinook salmon at RM 4 in 1999. Arrival timing of natural and hatchery chinook salmon smolts at Snake River dams has been documented since 1992 (Table 20, Table 21). The observed median arrival dates for natural chinook salmon at Lower Granite Dam have ranged between April 22 and May 4 from 1993 to 1999, with 90% of arrivals occurring between May 6 and 22nd. Hatchery chinook have similar arrival timing at Lower Granite Dam with median arrival times of April 21 to May 12 and 90% arrival completed by May 6 and May 16th from 1992 to 1999. Overall, downstream movement of Imnaha chinook to the lower four Snake River dams, appears to be earlier than for other Snake River Basin populations (Mundy and Witty 1998; Ashe et al. 2000).

Season-wide estimates of juvenile chinook salmon survival from the mouth of Imnaha River to Lower Granite Dam have been made since 1993. Survival estimates of spring emigrating natural chinook salmon have ranged from 0.76 in 1994 to 0.909 in 1995 (Figure 19; Cleary et al. 2000, in prep.). Survival estimates of hatchery chinook salmon smolts have ranged from 0.671 in 1994 to 0.804 in 1997 (Figure 20; Cleary et al. 2000, in prep.).

Table 20. Arrival timing of spring PIT tagged Imnaha River natural chinook salmon smolts at Lower Granite, Little Goose, Lower Monumental, and McNary dams from 1993 to 1999 (Cleary et al. in prep).



Impoundment

Year

Sample Size

n

Date Range

Arrival Timing

From

To

Median

90%

Lower Granite

1999

1,288

Mar 28

Jul 15

Apr 27

May 22




1998

1,630

Apr 1

Jun 27

Apr 25

May 6





1997

74

Apr 6

May 18

Apr 22

May 11




1996

421

Apr 6

Jun 12

Apr 30

May 18




1995

184

Apr 11

Jul 11

May 1

May 11




1994

348

Apr 14


Jun 23

Apr 24

May 11




1993

109

Apr 21

Jun 12

May 4

May 14




Little Goose

1999

2,099

Apr 9

Aug 1

Apr 29

May 22




1998

837

Apr 14

Jun 25

May 3

May 12


1997


70

Apr 15

May 22

Apr 26

May 11




1996

358

Apr 12

Jun 16

Apr 27

May 20




1995

144

Apr 15

Jul 15

May 7

May 20




1994

194

Apr 23

Jun 17

Apr 28

May 7




1993

46


Apr 27

Jun 2

May 3

May 16




Lower Monumental

1999

688

Apr 9

Aug 4

May 1

May 23




1998

289

Apr 19

Jun 8

Apr 30

May 11




1997

74

Apr 20

Jun 1

Apr 30

May 14




1996

359


Apr 13

Jun 15

May 10

May 22




1995

142

Apr 19

Aug 4

May 8

Jun 4




1994

215

Apr 25

Jul 26

May 1

May 24




1993

37

May 3

Jun 2

May 8

May 13




McNary

1999

152


Apr 18

Jun 27

May 6

May 21




1998

187

Apr 19

Jun 2

May 1

May 15




1997

24

Apr 22

May 19

May 1

May 12




1996

148

Apr 19

Jun 8

May 14

May 24




1995

89

Apr 28


Jul 9

May 12

May 21




1994

229

Apr 29

Jul 16

May 12

May 28




1993

20

May 3

Jun 15

May 9

May 21

Table 21. Arrival timing of PIT tagged Imnaha River hatchery chinook salmon smolts at Lower Granite, Little Goose, Lower Monumental, and McNary dams from 1992 to 1999 (Cleary et al in prep).



Impoundment

Year

Sample Size

n

Date Range

Arrival Timing


From

To

Median

90%

Lower Granite

1999

267

Apr 18

May 25

May 5

May 14




1998

696

Apr 15

May 22

May 2

May 9




1997

227

Apr 16

May 22

May 5

May 14




1996

169

Apr 13


May 26

May 7

May 16




19951

128

Apr 13

Jun 7

May 2

May 13




19952

83

Apr 16

May 22

May 8

May 15




1994

129

Apr 24

May 18

May 12

May 12




19923

273

Apr 12


Jun 6

Apr 21

May 6

Little Goose

1999

387

Apr 16

Jun 6

May 10

May 19




1998

391

Apr 25

May 26

May 7

May 14




1997

267

Apr 20

May 27

May 9

May 18




1996

131

Apr 23


Jun 6

May 13

May 20




19951

114

Apr 26

Jun 11

May 10

May 20




19952

67

Apr 27

Jun 7

May 12

May 23




1994

65

Apr 28

Jun 2

May 14

May 21




19923

116

Apr 17

May 22


Apr 27

May 5

Lower Monumental

1999

124

Apr 23

May 25

May 11

May 20




1998

143

Apr 23

May 26

May 8

May 15




1997

199

Apr 25

Jun 3

May 10

May 19




1996

136

Apr 23

May 29

May 15


May 23




19951

106

Apr 27

Jun 10

May 12

May 21




19952

71

Apr 29

Jun 9

May 17

May 26




1994

73

Apr 30

Jun 7

May 14

May 20

McNary

1999

56

May 2

May 26

May 19

May 24




1998

53

May 2

May 30

May 11

May 19




1997

61

May 1

Jun 1

May 10

May 19




1996

55

May 1

May 27

May 16

May 23




19951

67

Apr 29

Jun 9

May 16

May 23



19952


36

May 3

May 30

May 16

May 22




1994

119

May 6

Jun 17

May 21

May 26




19923

61

Apr 27

Jun 1

May 8

May 17

Figure 19. Season-wide survival estimates for natural chinook salmon released from the Imnaha River trap to Lower Granite Dam, from 1993 to 1999. Error bars indicate 95% confidence limits. Asterisks indicate upper confidence levels greater than 100% (Modified from Cleary et al. 2000 and Cleary et al in prep).


Figure 20. Season-wide survival estimates for hatchery chinook salmon released from the Imnaha River trap to Lower Granite Dam, from 1993 to 1999. Error bars indicate 95% confidence limits (Modified from Cleary et al. 2000 and Cleary et al in prep).

In comparison with spring chinook pre-smolts from other Snake River subbasin streams, the mean length and weight of juvenile chinook sampled from the Imnaha in late September each year between 1988-1990 were among the smallest recorded (Mundy and Witty 1998). The mean length and weight of the same pit-tagged Imnaha smolts interrogated at Lower Granite dam was considerably greater however, than other Snake River chinook. The difference suggests that the Imnaha population probably increases in length and weight during the winter faster than other Snake River chinook populations, and that this difference may account for their earlier arrival at the lower four hydroelectric facilities on the Snake River (Mundy and Witty 1998).

Spring chinook harvest in the Imnaha has fluctuated over the years. Sport harvest restrictions were first imposed by the State of Oregon on spring chinook anglers in 1916, where the daily bag limit was set at 50 pounds of chinook per day (Mundy and Witty 1998). This limit was reduced to 20 pounds per day in 1925, and eventually reduced to two fish per day, or 10 jacks per day, at the close of the fishing season in 1978 (Ashe et al. 2000).



Accompanying bag limits were restrictions on season of harvest and location of harvest. Fishing was prohibited above Grouse Creek circa 1944-1954 in an effort to protect spawning chinook. The upper boundary gradually moved downstream to Freezeout Creek restricting anglers to waters below Freezeout Creek Bridge. Between 1974 and 1979, the sport-fishing season was closed three times due to declines in adult returns (Table 22). Adult returns have not been sufficient to support a sport fishery since 1978 despite hatchery supplementation efforts (Ashe et al. 2000).

Table 22. Sport harvest of Imnaha river chinook salmon between 1953 and 1997 (Beamesderfer et al. 1997). Table 22 reflects results from the PATH analysis. Data are from punch card records that were adjusted for non-response bias and for entries that showed harvest during times of the year when there was not an open season on the Imnaha


Year

Sport

Tribal

Total

Year

Sport

Tribal

Total

1953

149

149

298

1971

19

19

37

1954

15

15

30

1972

17

17

34

1955

20

20

39

1973

107

107

214


1956

21

21

41

1974

0

0

0

1957

187

187

374

1975

0

0

0

1958

117

117

234

1976

0

0

0

1959

168

168

336

1977

44

44

88

1960

201

201


402

1978

0

0

0

1961

42

42

84

1979

0

0

0

1962

9

9

18

1980

0

0

0

1963

14

14

28

1981

0

0

0

1964

0

0

0

1982

0

0

0

1965

3

3

6

1983


0

0

0

1966

24

24

49

1984

0

0

0

1967

10

10

21

1985

0

0

0

1968

61

61

121

1986

0

0

0

1969

9

9

19

1987

0

0

0

1970

4

4

7

1988-2000

0


0

0



Fall Chinook


Fall chinook salmon are present in the Imnaha subbasin, however their abundance is significantly reduced from historic levels. Anecdotal accounts suggest that fall chinook may have historically used the lower 19.5 miles of the Imnaha mainstem for spawning, and generally did not occur above the town of Imnaha (Chapman 1940). Others contend that fall chinook spawning occurred as far upstream as the confluence of Freezeout Creek (Fernan Warnock personal communication cited in Mundy and Witty 1998).

Fall chinook redd surveys, which have occurred since 1964, document the occurrence of spawners along the lower four miles of the Imnaha (Figure 21), although spawning fish have been observed as high as Fence Creek (RM 14.3). Due to the low escapement, the contribution of spawning to brood-year recruitment has not been demonstrated (Chapman and Witty 1993), and it is likely that some of the spawners represent hatchery strays (Wallowa-Whitman National Forest 1999; Neeley et al 1993). A total of nine fall chinook redds were observed in the lower Imnaha [RM 0.0 (mouth) – RM 4.0 (Cow Creek Bridge)] during nine searches in 1999. Two additional flights from Cow Creek up to Freezeout Creek (RM 35) did not identify any redds.

The suitability and availability of fall chinook spawning substrate does not appear to be a factor limiting production of the species. Surveys conducted by Thompson and Hass in 1959 identified 2,566 square yards of good, and 12,967 square yards of marginal fall chinook spawning gravel in the Imnaha River between Imnaha and the mouth (Mundy and Witty 1998). Thompson and Haas (1960) reported enough gravel was available for the construction of 600-fall chinook redds in the mainstem between Horse Creek and the mouth.

Some have suggested that excessively low temperatures may limit embryonic development of Imnaha fall chinook and consequently reduce production (Mundy and Witty 1998), although supporting data is limited. Others suggest that juvenile fish may be swept out of the system during spring runoff, however this theory is also speculative and currently unfounded.

Information relating to juvenile fall chinook rearing in the Imnaha subbasin is limited. Development of parr is considered to be rapid, with fish initiating their seaward migration in July and August as zero-aged smolts (Mundy and Witty 1998). Differentiation between fall and spring chinook (Table 23) may be inferred by studies conducted on growth and movement patterns of other Snake River fall chinook populations (Connor et al. 1993).



No surveys from ’68-‘87

Figure 21. Number of fall chinook salmon redds counted in the Imnaha River between the years 1964 – 1999 (from Garcia 2000; Mundy and Witty 1998).


Table 23. Maximum and minimum fork lengths for in-season race identification of fall chinook salmon seined on the Snake River (Connor 1993).

Limit

Estimated fall chinook salmon size (mm) by date

5/21

5/28

6/4

6/11

6/18

6/25

7/2

7/9

7/16

Maximum

70

73


76

78

81

84

87

89

92

Minimum

55

55

55

55

55

58

61

64

66



Bull trout

Historical accounts of bull trout populations in the Imnaha are limited. Short segments of historic resident bull trout spawning and rearing habitat have been identified in upper Little Sheep Creek and Cabin Creek (USDA Forest Service 2000a). Unlike other salmonids, it is doubtful that bull trout occupied all accessible streams at any one time (USDA Forest Service 2000a), due to their current patchy distribution in even pristine, “stronghold” habitat types (Rieman and McIntyre 1993; Rieman and McIntyre 1995). In the Imnaha, historic distribution likely was similar to current distribution ((M. Hanson, ODFW, personal communication, April 23, 2001). Anecdotal accounts from anglers who fished the Imnaha River in the 1940’s describe the river as “a good Dolly Varden stream” with large bull trout being caught frequently (Buchanan et al. 1997).

Bull trout currently occur in the mainstem Imnaha River and its tributaries. Imnaha bull trout are also suspected to use habitat outside of the subbasin, including Granite Creek, Sheep Creek and some portions of the Snake River from Hells Canyon Dam downstream to a point as yet undefined (M. Hanson, ODFW, personal communication, April 23, 2001). The Imnaha bull trout recovery unit team, a group lead by ODFW biologists, suspects that the Imnaha/Snake Recovery Unit contains up to two core areas, but for the purposes of recovery should be considered as one core area. These areas include the Imnaha Core Area, which is comprised of all tributaries containing local populations (both current and potential as identified by the recovery unit team), and the mainstem Imnaha River from the headwaters downstream to the confluence with the Snake River (M. Hanson, ODFW, personal communication, April 23, 2001). Sheep and Granite Creek populations could constitute a separate core area. The lack of understanding of Snake River utilization by Imnaha bull trout currently represents a research need (M. Hanson, ODFW, personal communication, April 23, 2001).

Potential subpopulations of bull trout have been identified in the Imnaha subbasin. These include the Imnaha River above and below Imnaha Falls, Big Sheep Creek and Little Sheep Creek (USDA Forest Service 2000a). Based on sampling of bull trout densities (Table 24) ODFW believes there are greater than 2,000 bull trout in the upper Imnaha River and Big Sheep Creek and fewer than 500 in Little Sheep Creek.

Table 24. Estimated density of bull trout in selected streams in the Imnaha subbasin sampled in 1992 (ODFW data presented in Buchanan et al. 1997)

Stream


Site

Number


Estimated density (fish/100 sq. m)

By size class1



1 to 75 mm

76 to 300 mm

Big Sheep Creek

1

2

3



0.00

18.32


0.00

0.00

5.61


7.40

Salt Creek

1

5.87

18.77

Lick Creek

1

2


0.66

55.49


0.00

15.76


Little Sheep Creek

1

2


0.00

0.00


0.00

0.00


McCully Creek

1

2

3



1.74

0.57


0.00

7.84

7.35


5.79

1/ Size class 1 to 75 mm considered to be 0+ age, while fish 76 to 300 mm are considered to be older than 0+ age.

Both resident and fluvial forms of bull trout occur in the Imnaha subbasin. Generally, most bull trout occurring above Imnaha Falls are considered to be resident forms, while those occurring below the falls are considered fluvial. Fluvial populations occur throughout the mainstem up to Imnaha falls (Figure 22) (USDA Forest Service 2000a). Fluvial forms are also found in Big Sheep Creek and Little Sheep Creek. Although unconfirmed, it is likely that fluvial forms of Imnaha bull trout use the Mid-Snake River for overwintering and as a migration corridor, as bull trout occurrence has been reported from the mouth of the Imnaha up to Hells Canyon Dam (Buchanan et al. 1997). Idaho Fish and Game personnel have observed bull trout in Idaho streams entering this reach of the Snake River at the mouth of Sheep, Granite, Deep, and Wolf creeks (T. Cochanaur, Idaho Fish and Game, personal communication, November 1995 cited in Buchanan 1997).

Resident forms are most common in the North Fork and Middle Fork of the North Fork Imnaha (USDA Forest Service 2000a). The recent decommissioning of the “Power” canal has not improved connectivity between bull trout populations occurring in McCully, Ferguson, Canal, and Redmont Creeks (USDA Forest Service et al. 2001), since the presence of the Wallowa Valley Improvement Canal continues to isolate populations from downstream groups of fish (Buchanan et al. 1997; M. Hanson, ODFW, personal communication, April 23, 2001). The resident population in Big Sheep Creek, estimated at less than 2,000 individuals, exists above the Wallowa Valley Improvement Canal in both the North and South forks of Big Sheep Creek (USDA Forest Service et al. 2001).

Imnaha River bull trout rearing and migratory habitat primarily occurs below (Freezeout Creek Service 2000a). Spawning occurs in Big Sheep Creek above its confluence with Carrol Creek (RM 25) and in Little Sheep Creek above the USFS boundary (RM 28) (USDA Forest Service 2000). Presence of 0+ age fish in big Sheep Creek and its tributaries (Lick and Salt Creek), McCully Creek, Cliff Creek, and the South Fork Imnaha indicate that these streams are also used for spawning (Buchanan et al. 1997).

Samples for genetic analysis were taken in 1995 from the North Fork Imnaha River, McCully Creek, and Lick Creek, and compared to bull trout throughout Oregon, Washington, and elsewhere in the Columbia Basin (Buchanan 1997). Analysis from these data show that populations from the John Day Basin and Northeastern Oregon (including the Imnaha River basin) comprise major genetic lineages (Spruell and Allendorf 1997).

Figure 22. Bull trout rearing, spawning and migration corridors in the Imnaha subbasin




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