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

Sequence of Habitat Needs for Anadromous Life Cycles (continued)

Juvenile Winter Rearing

Following emergence, survival and growth of fry depends on habitat conditions in areas that are accessible to them. During this life stage, low velocity areas are important, such as stream margins and backwater areas. In these areas, they can feed on food items that drift by without being swept downstream. Predation is significant during this life stage and seems to dominate selection of habitat by juveniles (Schlosser 1991). Because larger fish avoid shallow areas due to high risk of predation by birds or mammals, fry in shallow areas are less subject to predation by larger fish. Because fry can escape predators by taking refuge in spaces between rocks, large substrates contribute to juvenile survival.

The number of fry and juveniles that survive is influenced by the ease or difficulty of migrating upstream to additional rearing areas. While fry can easily move downstream, their ability to swim upstream is very limited. Relatively minor stream obstacles can block upstream migration of fry or juveniles and consequently limit areas available for smolt production. As they increase in size, the ability of juveniles to migrate upstream improves and thus additional habitats become available. Migration of fry and juveniles may also be blocked by areas of high predation risk.

Large woody debris in streams effectively increases the amount of habitat because it increases visual isolation among the fish. Because of visual isolation, more territories can exist in a stream reach and carrying capacity is increased. Woody debris also benefits juveniles by increasing food production and providing velocity shelter during high flows.

Some evidence suggests that spatial distribution of fry and juveniles is influenced by streamflow. In Hurdygurdy Creek, high flows in May and early June of 1988 apparently flushed most of the juvenile chinook downstream. During that year, the juveniles were only found in that stream reach from emergence until late August. However, in 1987, flows in May and early June were lower and the juvenile chinook cohort was found in that stream reach from emergence until late November (McCain et al. 1995). Extremely cold water temperatures are probably not a significant restriction on anadromous salmonid production in the Smith River (Tables 32, 33, and 34)

 

Table 32. Temperature requirements for life stages of salmon and steelhead in California (Flosi and Reynolds 1994).

Species/stock

Adult migration

Spawning

Incubation

Juvenile rearing

 

° F

° C

° F

° C

° F

° C

° F

° C

Fall chinook

51-67

10.6-19.4

42-57

5.6-13.9

41-58

5.0-14.4

45-58

7.2-14.4

Spring chinook

38-56

3.3-13.3

42-57

5.6-13.9

41-58

5.0-14.4

57-67

13.9-19.4

Coho

45-60

7.2-15.6

40-49

4.4-9.4

40-56

4.4-13.3

53-58

11.7-14.4

Steelhead

?

?

39-49

3.9-9.4

?

?

45-58

7.2-14.4

 

Table 33. Temperature tolerances of salmonid species (Bjornn and Reiser 1991).

 

Lower lethal temperature:

Upper lethal temperature:

Preferred temperatures:

Species

° Celsius

° Fahrenheit

° Celsius

° Fahrenheit

° Celsius

° Fahrenheit

Steelhead

0.0

32.0

23.9

75

10 - 13

50.0 - 55.4

Chinook

0.8

33.4

26.2

79.2

12 - 14

53.6 - 57.2

Coho

1.7

35.1

26

78.8

12 - 14

53.6 - 57.2

Cutthroat

0.6

33.0

22.8

73

?

?

Chum

0.5

32.9

25.4

77.7

12 - 14

53.6 - 57.2

Sockeye

3.1

37.6

25.8

78.4

12 - 14

53.6 - 57.2

 

Table 34. Water temperatures in the Smith River and its tributaries. This data was collected on a periodic basis rather than continuously (McCain et al. 1995).

 

Minimum temperature:

Maximum temperature:

Location:

° Celsius

° Fahrenheit

° Celsius

° Fahrenheit

Smith River:

3

37.4

24

75.2

South Fork:

7

44.6

22.5

72.5

North Fork:

13.9

57.0

21

69.8

Middle Fork:

12.2

54.0

23

73.4

Tributaries:

3

37.4

23

73.4

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