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

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Escapement Goals -

LSRCP compensation goals for Imnaha program is 2,000 hatchery steelhead adults to the Snake River, above Ice Harbor Dam. The current US v. OR wild adult escapement goals is 2,000 to the Imnaha basin (All Species Review, 1996).





    1. Date program started or is expected to start:

The Imnaha subbasin summer steelhead program (stock 029) began in 1982.


    1. Expected duration of program:

The program will continue indefinitely with the objective of mitigating for loss and degradation of habitat and fish passage caused by the construction and operation of four lower Snake River dams.


    1. Watersheds targeted by program:

Summer steelhead stock 029 are released into the Imnaha River subbasin.


SECTION 2.0. RELATIONSHIP OF PROGRAM TO OTHER MANAGEMENT OBJECTIVES



    1. List all existing cooperative agreements, memorandum of agreement, or other management plans or court orders under which program operates. Confirm HGMP consistency.




    1. Status of natural populations in target area.




      1. Geographic and temporal spawning distribution

Migrating adults enter the Imnaha basin in the spring (between February and May), and typically spawn in May.

      1. Annual spawning abundance for as many years as available





      1. Progeny to parent ratios, survival data by life stage, or other measures of productivity for as many brood years as available.


2.2.4 Annual proportions of hatchery and natural fish on natural spawning grounds for as many years as possible.

The number of adults returned to Little Sheep Creek is reported in Table 1. Since 1996, the number of wild adults returned to Little Sheep Creek has varied from eight returns in 1991 to 60 returns in 1993. The proportion of wild adults returned to the river, in relation to the proportion of hatchery adult returns, declined significantly from those wild fish returned to Little Sheep Creek in 1992, 1993 and 1994.


In 1993, spawning surveys conducted by ODFW personnel in the Imnaha River subbasin showed that 82% (14 of 17) of the observed spawners were of wild origin (NE Region Stock Status Review, 1993).


      1. Status of natural population relative to critical and viable population thresholds.




    1. Relationship to harvest objectives.

Direct mortality to wild/natural fish shall remain below 15% for group A steelhead runs of 75,000 or less (All Species Review, 1997). All steelhead released into Imnaha subbasin are adipose clipped, such that they are distinguishable from naturally produced fish. Only adipose fin clipped steelhead may be retained in the sport fishery.

2.4) Relationship to habitat protection and recovery strategies.

This program does not include habitat protection and recovery strategies, although habitat projects are underway in the Imnaha..



    1. Ecological interactions

No information specific to this program is available.


SECTION 5. ORIGIN AND IDENTITY OF BROODSTOCK

5.1) Source

Broodstock is indigenous to Little Sheep Creek and has been collected at Little Sheep Creek annually since the start of the program (1982) (ODFW Steelhead Plan, 1995). Imnaha stock is the only acceptable stock for release into the Imnaha River drainage (IHOT, 1995).




      1. History

Adult collection and subsequent egg-take and fry ponded since 1990 are reported in Table 2. There have been no out-of-basin transfers used to supplement egg-take and program needs. All adults needed for broodstock were collected, held and spawned at Little Sheep Creek acclimation facility. Following egg-take and fertilization, viable eggs were transferred to Wallowa Hatchery and incubated through eye-up. Eyed eggs are then transferred to Irrigon Hatchery to rear until pre-smolt, at which time many were returned to Little Sheep Creek Acclimation Pond to rear for another three-to-four weeks before release. An anomaly to the standard program occurred in 1998: 1,122,000 eyed eggs were transferred to a satellite incubation and early rearing facility. This allotment was incubated and reared for 4-6 weeks and was released as fry (39,074 into the Imnaha River and 287,511 into Big Sheep Creek).

Table 2.Adult summer steelhead collected, number spawned, number of egg transferred and fry ponded at Little Sheep Creek, 1990 - 1999. Data taken from ODFW HMIS database, and ODFW staff.















Adults Collected








Egg






Brood Year

Collection Facility

Adults Counted

#

Males Spawned

# Females Spawned

Spawning Ratio (M:F)

Egg

Take

(in 1,000’s) Little Sheep Cr Facility

Transfers

(in 1,000's)

[In/Out]

Wallowa Hatchery


Fry

Ponded

(in 1,000's) /1

Irrigon Hatchery

Other

Stock Transfers

Ponded

1990

Little Sheep Creek Trap

981

157

179

0.88

849

849 / 536

425

0

1991

Little Sheep Creek Trap

395

133

130

1.02

455

0 / 339

326

0


1992

Little Sheep Creek Trap

789

205

177

1.16

749

0 / 506

456

0

1993

Little Sheep Creek Trap

1,872

158

134

1.18

647

0 / 483

437

0

1994

Little Sheep Creek Trap

194


22

102

0.13

454

454 / 352

347

0

1995

Little Sheep Creek Trap

295

102

99

1.02

342

342 / 310

306

0

1996

Little Sheep Creek Trap

489

114

159

0.68

728

728 / 559

471

0

1997

Little Sheep Creek Trap

968


184

184

1.0

877

877 / 438

123

0

1998

Little Sheep Creek Trap

719

192

346

0.55

1,691

1,066 / 890

1,122 / 0/2

384

0


0

0


1999

Little Sheep Creek Trap

344

127

127

1.0

607

607 / 516

506


0

/1 Fry are ponded and reared to pre-smolt age at Irrigon Hatchery.

/2 In 1998, 110,000 eyed eggs were transferred from Wallowa Hatchery and 1,011,000 viable eggs were transferred from Little Sheep Creek Acclimation Pond to a satellite incubation and early rearing facility operated by the NPT.
5.2.2) Annual Size

Past hatchery escapement goals were based upon annual smolt production needs. In the recent past, a return of 383 adults was needed to meet the annual green egg-take goal (538,000) which supplied 330,000 smolts to the Imnaha River subbasin (AOP, 1999). Annual number of adults collected, spawned and used for broodstock purposes are reported in Table 3.


5.2.3) Past and proposed level of natural fish in brood stock

In 1993, egg-takes were to include a 10% wild component (NE Region Stock Status Review, 1993). Current annual operation plans call for incorporating three of every five wild adult returns and three of nine hatchery adult returns into the brood. All remaining wild fish and four of nine hatchery fish were to be released above the weir at Little Sheep Creek acclimation pond. Refer to Table 2 regarding the past number of adult wild steelhead incorporated into the hatchery broodstock. Since 1995, percent wild component has been less than 4.5%; hence, 1993 wild recruitment goals have not been met. New proposed level of natural fish in the hatchery broodstock has not been determined.



5.2.4) Genetic and ecological differences

Information specific to this program is not currently available. However, the broodstock was originally founded from the Imnaha which is expected to minimize differences between the broodstock and wild fish.

5.2.5) Reasons for choosing

Little Sheep Cr. summer steelhead were chosen as the brood source for the Imnaha River subbasin program because they are indigenous to the basin.




    1. Unknowns:



SECTION 6.0. BROODSTOCK COLLECTION



    1. Supporting Information:

      1. Proposed number of each sex

Past hatchery goals were to have a spawning population of 383 fish (145 males and 138 females) with a 5:4 male-to-female spawning ratio (AOP, 1999). Spawning ratios for 1994 and beyond are reported in Table 3.


      1. Life-history stage to be collected (e.g., eggs, adults, etc.)

Returning adults are collected for broodstock. Age composition of returning adults are three, four and five.


      1. Collection or sampling design

Little Sheep Creek fish trap opens in early March and runs until fish no longer enter the trap; typically in late-May. Fish are processed and spawned every Monday and Thursday.


      1. Identity -

  1. Methods for identifying target populations (if more than one population may be present).

A portion (50,000 steelhead (15% broodstock production)) of the Imnaha stock are tagged with a coded wire tag, and marked with an adipose fin clip (Ad+CWT). CWT tag data allow differing hatchery stocks to be differentiated based upon their tag code; hence, the number of out-of-basin stray adults returning to the Imnaha River drainage and alternate subbasins can be monitored.



  1. Methods for identifying hatchery origin fish from naturally spawned fish.

From 1990 to present, all hatchery steelhead reared at Irrigon Hatchery have been adipose-clipped. For 1990 and 1991 broods, approximately 27% all steelhead produced at Little Sheep Creek were adipose fin clipped prior to release. Beginning with broodyear 1992, all hatchery reared summer steelhead have been marked with an adipose fin clip.


      1. Holding -

Adults are collected and held throughout the run at Little Sheep Creek acclimation facility. Adults retained for broodstock purposes are spawned on-site.


      1. Disposition of carcasses - Priorities set as of 1999

All deceased adults are taken to a local landfill.

SECTION 7.0. MATING



    1. Selection method

      1. Adult Selection -

Fish are mixed and randomly selected (from early, mid and late returns) for spawning. Hatchery origin fish (adipose fin clipped) along with some wild fish are used for broodstock. Prior to brood year 1992, not all steelhead were mass marked and identifiable from wild brood. Naturally produced adults are intentionally incorporated into the broodstock.


      1. Selection of Egg Take -

If the hatchery reduces the number of eggs retained, a representative sample of each male/female cross is culled. Exceptions may occur if there is a high degree of disease or epidemics associated with certain parents; if this occurs, offspring of diseased parents may be culled, in order to maximize long-term survival of the brood.



    1. Males

Target sex ratio for this program has been a 5:4 male-to-female spawning ratio. See Table 2 for actual spawning ratios from 1994 to present. Males are held early in the run to compensate for the lack of males at the end of the run.


    1. Fertilization

      1. Fertilization Scheme -




      1. Fish Health Procedures -

In addition to the Department-wide fish disease control and disease prevention programs, Wallowa and Irrigon Hatchery monitors fish health, fish and egg movement, therapeutic and prophylactic treatments, and sanitation activities (IHOT, 1995). In addition, prespawning mortality and virus monitoring plans are conducted regularly (AOP, 1999).


    1. Cryopreserved gametes

The NPT is investigating the possibility of cryopreserving wild sperm (AOP, 1999).

SECTION 9. RELEASE

9.1) Life history stage, size, and age at release

Juvenile Releases
Table 3 shows the history of summer steelhead releases into the Imnaha River subbasin, since 1990. Summer steelhead are primarily released as age one smolts; they rear in the hatchery environment for 12-14 months. For broodyears 1990 to 1998, the size of the steelhead at the time of release has averaged:

Snake River (R-1) (1990 only)


= 57.08 fish/lb. -- Fall Release Group (grade-outs)

Little Sheep Creek (1990-1999)

= 5.31 fish/lb. (4.68 - 6.40 fish/lb.) -- Spring Release Group

= 125.00 fish/lb. -- Fall Release Group (1999 only)



Imnaha (1990-1994)

= 6.51 fish/lb. (5.30 - 8.30 fish/lb.) -- Spring Release Group

Big Sheep Creek (1998-1999)

= 59.00 fish/lb. -- Fall Release Group (1998)

= 125.00 fish/lb. -- Fall Release Group (1999)




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