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Chapter 6 -- Changes and Trends in Stream Habitat and Fisheries (continued)

Overview of Fisheries Trends

All available reports indicate a decline in anadromous salmonid populations of the Smith River. However, due to the anecdotal nature of early information (Appendix B, McCain et al. 1995), there is little basis for determining the extent of the decline. Observations of the Smith River and its fisheries prior to 1935 were not recorded and subsequent observations were sporadic (Appendix F). There are few long-term studies of fish populations in the Smith River watershed. The most notable data set describes salmon spawning in Mill Creek from 1980 to the present (Waldvogel 1988, Table 36). Juvenile outmigration on Mill Creek was also sampled in 1994 (Table 29, Rellim Redwood Company 1994). Although ocean harvest records are available, they do not reveal the productivity of a particular fish population or watershed because stocks from many river systems are intermingled in the ocean.

 

Table 36. Results of spawning surveys on Mill Creek 1980-1995 (Waldvogel 1985, 1988, 1996).

 

Year

Adult

chinook

Hatchery

fish %

Coho

salmon

Chum

salmon

1980

128

--

11

0

1981

107

17

2

0

1982

155

18

4

0

1983

110

21

3

0

1984

111

37

6

4

1985

185

3

28

2

1986

180

4

11

8

1987

153

0

27

1

1988

249

4

5

5

1989

57

4

13

0

1990

31

0

2

0

1991

93

3

7

0

1992

144

0

7

0

1993

95

0

22

0

1994

148

2

9

0

1995

170

0

21

2

 

Spawning success and smolt production varies due to timing of rainfall and stream flow. As discussed previously, chinook spawning in the Smith River occurs in three pulses:

  • Mid-November to mid-December
  • Late December to mid-January
  • Late January to mid-February

The timing and success of these three pulses of chinook spawning is influenced by stream flow as documented in chinook spawning surveys in Mill Creek (Waldvogel 1988):

1983 season -- There was less than two inches of rain from 12/29 to 2/10. The first and second runs of chinook reached the study area of Mill Creek and spawned. Low flows greatly delayed the third run and reduced their numbers. When flows finally increased, only four or five salmon were observed. The majority of this run presumably spawned elsewhere.

1984 season -- There was less than one inch of rain from 12/15 to 2/10. The first run utilized the study area but the second run had to spawn in the lower one quarter mile of the study area and farther downstream. The third run was once again delayed by low flows. Only eight to ten fish from this run were observed and the rest of the run presumably spawned elsewhere.

1985 season -- Rainfall was abundant during the spawning season. Peak flows in February probably damaged the December redds.

1986 season -- Periods of low rainfall during January and February seemed to limit utilization of the study area by the second and third runs. These runs were observed to be low in number.

1987 season -- There was virtually no rain until 12/1. The first run was delayed but the number of spawners was high. Many spawners from the first run may have spawned in downstream areas before stream flow increased. During February and March, there was only two or three inches of rain. The third run was unable to utilize the study area.

In 1983-1984, water temperatures in the ocean increased due to El Niño effects, resulting in decreased salmon production. In 1983, a greater proportion of chinook salmon returned to freshwater at age 3, presumably due to unfavorable ocean conditions. El Niño conditions abated in 1985. Also in 1985, the Pacific Fisheries Management Council allowed no commercial salmon fishing and has greatly restricted the fishing season ever since. Chinook spawners in Mill Creek increased in 1985 and have remained at levels higher than pre-1985. Higher populations are presumably due to rapid recovery following the El Niño period and restrictions on commercial fishing (Waldvogel 1988).

Probably a combination of factors has caused the decline in anadromous salmonid populations. It is suspected that changes in the estuary are one such factor. Prior to modification of the estuary, the volume of the tidal prism was greater and there were more sloughs and tidal marshes (California Department of Water Resources 1974). It is virtually certain that the configuration of the estuary at that time provided more rearing habitat for anadromous fish. Beyond that, it is suspected that this loss of rearing habitat has a significant impact on overall anadromous salmonid productivity in the Smith River watershed.

Loss of habitat complexity is another factor that may be hindering anadromous salmonid production. One aspect of habitat complexity that has diminished is the abundance of large pools. Many decades ago, adult pre-spawners presumably benefited from larger holding areas provided by deeper pools in the estuary, the lower river, and the South Fork. The quantity of large woody debris in the streams, river, and estuary is another aspect of habitat complexity that may be limiting fish production.

High habitat complexity is important throughout the river system. Benefits of habitat complexity include protection from predation, larger cold water refuges, and high quality rearing habitat. It improves connectivity between habitats, which means that more fish survive when migrating between habitats. When migration becomes a less threatening option, there is more flexibility in life history patterns. This is especially relevant for juvenile and smolt stages of the life cycle (McCain et al. 1995). For juvenile salmonids, risk of predation is possibly the main factor restricting connectivity in the Smith River system. Greater connectivity allows these smaller fish to disperse throughout the stream and river network and more fully occupy suitable habitat. This also increases survival during outmigration. In general, habitat complexity increases the time period when successful migration is possible throughout the migration corridor. This results in larger numbers of smolts and/or larger size smolts entering the ocean, and ultimately greater success in the marine environment.

It seems likely that coho salmon are especially sensitive to loss of habitat complexity. in the estuary, lower river, and lower tributaries. Because coho salmon thrive in networks of sloughs and low gradient channels, it is likely that reduced quantity and complexity of habitat in the lower river and estuary are partly responsible for their reduced presence.

Reduced habitat complexity in the river system may have caused a reduction in the stability of anadromous salmonid populations due to fewer refuges from extreme events and less buffering of environmental change (Rieman et al. 1993). Furthermore, the apparent loss of high quality habitat in the the lower river and estuary possibly increases the dependence of anadromous salmonids on lower quality and more variable habitat (Rieman et al. 1993). It is likely that remaining patches of high quality habitat in the estuary and lower river play a disproportionately large role in maintaining the river community (Frissell et al. 1993).

Declines in anadromous salmonids may also be related to increased predation by marine mammals. Predation by pinnipeds (seals and sea lions) may have increased due to decreases in other prey species. Pinnipeds prefer to eat lamprey eels which have a high oil content. However in the last six or seven years, the population of lampreys has diminished. Other seal prey, including flatfish and eulachon, have also declined greatly. The reduction in these prey has probably lead to an increase in predation on salmonids by marine mammals (Waldvogel personal communication 1996).

Other factors may also contribute to reduction in anadromous salmonid populations. For example, Forest Service policies that spread timber harvest throughout the landscape may cause populations in all habitats to respond synchronously. During unfavorable periods over the region, such as drought, uniform response of all populations increases the likelihood of extinction (Rieman et al. 1993). Impacts on fish from habitat changes may be magnified by the combined effects from hatcheries, overfishing, and fluctuation in ocean conditions including "El Niño"; and the North Pacific Oscillation (Frissell et al. 1993). Due to the present status of the North Pacific oscillation, unfavorable conditions in the ocean are probably slowing recovery of the populations. Commercial and sport fishing also influence anadromous fisheries as indicated by studies in Mill Creek. Of the chinook salmon returning to Mill Creek between 1981 and 1987, 5.7% had hook scars indicating escape from hooking by commercial or sport fishermen (Waldvogel 1988).

When fish populations decline, there is a tendency for subpopulations to become isolated from each other (Rieman et al. 1993). For example, coho salmon in the Smith River are found in widely separated tributaries. Because smaller isolated populations are more sensitive to disturbances and upheaval, the overall viability of the meta-population is reduced.

Sediment loads are probably not a major cause of declines in the fisheries of the Smith River. Although sediment loads may be detrimental to fish in limited areas, in general the resistant geology and high stream power of the Smith River system create favorable substrates for fish. The assertion that sediment loads in the Smith River are not a major hindrance for anadromous salmonids is supported by the huge salmon harvests recorded in the 1890s (Appendix D). These harvests occurred when the river system was presumably transporting large volumes of sediment contributed by hydraulic mining operations. These harvests also occurred after the beginning of large scale logging in 1872.

The following hypotheses about fish/habitat relationships in the Smith River are suggested for further investigation using adaptive management strategies: 1) Decreased habitat complexity, especially low quantities of large woody debris, is (is not) restricting anadromous fish populations. 2) Reduction in the size of the estuary is (is not) restricting anadromous fish populations. 3) Isolation of the river from its flood plain is (is not) restricting anadromous fish populations.

Rowdy Creek, a tributary of the lower river, supported large runs of anadromous fish prior to extensive human influences especially logging (California Assembly 1961). Mill Creek joins the lower Smith River several miles upstream from Rowdy Creek. It is a highly productive tributary and is protected in part by state and national parks. The importance of Rowdy and Mill Creeks for anadromous fish production is increased by the relatively short distance from these tributaries to the estuary. Whenever these creeks provide favorable conditions for spawning and incubation, excess fry and juveniles are probably produced and then migrate or are swept downstream. The short distance from Rowdy Creek to the Smith River estuary contributes to the likelihood of succesful migration. The distance from from Rowdy Creek to the mouth of the Smith River was only 3.2 miles in 1856 (California Department of Water Resources 1974). If habitat complexity in lower Rowdy Creek and the lower Smith River was higher prior to extensive human intervention, this would further increase the rate of survival of fry and juveniles migrating from Rowdy Creek to the estuary. It is likely that large numbers of chinook and coho fry and juveniles from Rowdy Creek migrated to the estuary for rearing. Through the combination of production of excess fry from Rowdy Creek, the proximity of Rowdy Creek to the estuary, and higher habitat complexity in the migration corridor, large numbers of fish probably migrated to and reared in the estuary, greatly increasing overall productivity. Because of its proximity to the estuary, Rowdy Creek has the potential to produce huge numbers of chinook and coho salmon. Rowdy Creek is one of the most important subwatersheds in the basin for anadromous salmonid production and is a promising candidate for restoration.

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