Redwood Creek basin supports anadromous populations of fall run Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch), winter and summer runs of steelhead trout (O. mykiss), coast cutthroat trout (O. clarki clarki), and other valuable fisheries resources (Table 1). Although a recent estimate of the size of anadromous salmonid populations of the Redwood Creek basin has yet to be determined, a review of past fisheries studies, anecdotal information and data collected for this assessment indicates that the present populations are less abundant and less widely distributed compared to their historic presence (Hallock et al. 1952; Briggs 1953; USFWS 1960; Anderson 1988; Brown 1988; Busby et al. 1994; Van Kirk 1994; McEwan and Jackson 1996; NMFS 1998; McElhany et al. 2000; CDFG 2002). There are approximately 125 miles of stream habitat accessible to anadromous salmonid in the Redwood Creek basin. The mainstem Redwood Creek provides approximately 65 miles and tributaries provide approximately 60 miles of stream of accessible habitat.
Table 1. Fishery resources of the Redwood Creek Basin.
Streams in the Prairie Creek Subbasin provide anadromous salmonids the largest amount of tributary habitat of all the subbasins. The remainder of anadromous fish bearing tributary habitat is distributed between approximately 46 named tributary streams located in the Lower, Middle and Upper subbasins (Brown 1988). The steep channel gradient restricts access to only the lower reaches of most tributary streams in the Lower, Middle and Upper subbasins. The majority of suitable tributary habitat is found in only ten streams including Bridge, Emerald, and Tom McDonald creeks of the Lower Subbasin, Lacks, Minor, Coyote, Panther, and Wiregrass creeks of the Middle Subbasin, and Minon and Bradford creeks of the Upper Subbasin. Other tributary streams are still important as they cumulatively provide important habitat for anadromous populations and also contribute important water flows into Redwood Creek. In addition, resident populations of rainbow and coastal cutthroat trout exist in many tributaries above barriers to anadromous salmonids.
From the long-term perspective, anadromous salmonids of Redwood Creek, show declines from historic numbers and in distribution across the basin. In 1960, the U.S. Fish and Wildlife Service estimated spawner escapement of 5,000 Chinook, 2,000 coho, and 10,000 steelhead (USFWS 1960). These estimates were made based on data collected from other streams and applied to Redwood Creek. They were meant to provide a general magnitude of anadromous salmonid runs are not indicative of larger runs of prior years (USFWS 1960; CDFG 1965; and RNSP 2000) The data needed to determine if populations are continuing to decline, have stabilized, or are on the rise across the basin are not available.
The decline in anadromous salmonids populations is not unique to Redwood Creek. For example, in 1984-85 the statewide total of natural coho salmon spawners was estimated at 6 to 15% of the level of the 1940s (CDFG 2002). In addition, coho and Chinook populations drastically declined in the Eel River according to adult salmon counts at Benbow Dam, South Fork Eel River (CDFG 2002).
In response to California’s declining wild populations, Chinook, coho, and steelhead are listed as “threatened” under the Federal Endangered Species Act (FESA). In 2002, the California Fish and Game Commission found that North Coast coho salmon warranted listing as threatened, as defined under the California Endangered Species Act (CESA). In addition, several other plant and animal species living in the Redwood Creek basin receive special status protection under the FESA and CESA including coastal cutthroat trout, which is considered a California species of special concern by the Department of Fish and Game (Appendix D).
Freshwater and estuarine habitat degradation and has been identified as a leading factor in the decline of Redwood Creek’s anadromous salmonids (Ricks 1982; Larson 1982; Hofstra 1983; Anderson 1988; Brown 1988; Madej 1991; and CDF&G 2002). Widespread declines of summer steelhead, sea run coastal cutthroat, coho and Chinook salmon is likely linked to their sensitivity to degradation of specific habitat components necessary to complete the freshwater and/or estuarine phase of their life cycle. Because steelhead tolerate a wider range of habitat conditions than the other anadromous species, they are more widely distributed in the basin and have persisted in streams where other species have declined or are now rarely observed.
Similar to most north coast streams, there has been neither basin-wide quantitative assessment nor coordinated long term monitoring of all Redwood Creek’s anadromous salmonid stocks. There are recent population data such as downstream migrant studies and spawning surveys available for select streams. However these data are inconclusive because they lack of consistent effort across the study areas, or have not been ongoing for sufficient time to establish trends, and may require optimal environmental conditions to conduct observations. Coordinated studies such as downstream migrant trapping, spawner surveys, and other population assessment techniques may soon provide the level of information needed to make quantitative assessments of the current status and trends of Redwood Creek’s anadromous salmonid populations.