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Chapter 5 -- Anadromous salmonids and Their Habitats (continued)

Life History Patterns of Anadromous Salmonids (continued)

Coho

Coho salmon (Oncorhynchus kisutch) native to the Smith River usually spend two years in the ocean and return to spawn as three-year-olds (Waldvogel personal communication 1996), although some males return after only a few months. In the Smith River, adult upstream migration and spawning begins in November and December. Compared to chinook, coho typically utilize smaller streams and prefer smaller spawning gravel. However, there is overlap between coho and chinook spawning habitat. After emerging from the redd, coho generally remain in the river for their first year. As yearlings, they may migrate downstream in the spring, and enter the ocean when five to six inches long. In many river systems, coho enter the ocean in fall as subyearlings while only one to three inches long (Sandercock 1991). Likewise, in some river systems of the Pacific Northwest, coho salmon fry rear in estuaries (Hassler 1987). It is not known if either of these life history patterns exist, or once existed, on the Smith. A relatively consistent proportion of the coho males from any given age class return from the ocean after only a few months as "jacks". Therefore, the number of "jacks" provides an estimate of the size of a particular cohort that is still in the ocean (Waldvogel personal communication 1996).

Coho are present in high numbers in Mill Creek (Rellim Redwood Company 1994, Table 29) and have been observed in at least ten tributaries and subtributaries of the lower river including Rowdy Creek, Morrison Creek, Little Mill Creek, Sultan Creek, Peacock Creek, and Clarks Creek. Coho also have been observed in certain upper tributaries including Patrick Creek, Shelley Creek, Rock Creek, and Jones Creek (Figure 4 will be added, Scriven in progress). However, with the exception of Mill Creek and Rowdy Creek, coho are not present every year (Scriven personal communication 1997, Moyer personal communication 1996).

 

Table 29. Juvenile outmigration estimates based on downstream migrant trapping, East Branch Mill Creek, 1994 (Rellim Redwood Company 1994). Outmigration occurs in waves by species and age class. YOY = young-of-the-year juveniles.

Week

Steelhead

Cutthroat trout

Chinook

Coho

(1994)

Smolt

Parr

YOY

Non-smolt

Smolt

YOY

YOY/Parr

1+ Smolt

4/3

363

424

0

176

45

337

171

34

4/10

179

445

0

95

8

2813

87

61

4/17

405

616

0

376

59

887

18

126

4/24

144

832

0

216

39

405

47

118

5/1

126

1387

0

229

8

6687

416

445

5/8

47

1337

13

210

24

8837

332

361

5/15

0

800

253

39

11

2458

242

37

5/22

0

368

168

74

47

1334

108

29

5/29

0

266

1608

39

24

1821

126

5

6/5

0

561

1432

74

20

1766

289

8

6/12

0

366

1689

53

17

1637

142

0

6/19

0

216

1792

92

3

1568

47

0

6/26

0

84

2963

71

3

2487

258

0

7/3

0

76

4092

42

3

1581

758

0

7/10

0

47

3650

16

0

963

832

0

7/17

0

0

1739

8

3

387

187

0

 

Because coho are abundant in Mill Creek but are found in low numbers in other scattered tributaries, careful management of Mill Creek is crucial. Maintaining Mill Creek as a highly productive "source" habitat is critical because other areas may lack sufficient populations or habitat quality to survive independently. "Stray" coho from the Mill Creek source population are very important in survival of the overall coho "meta-population" throughout the watershed. Coho from Mill Creek can contribute greatly to reinhabitation of the entire river system. If the habitat in Mill Creek is degraded, the larger meta-population of the species may be threatened.

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