Inverse Relationship of Fish Densities and High StreamTemperatures
Salmon, steelhead and trout require cool water temperatures and adequate levels of dissolved oxygen to thrive (Reiser and Bjornn, 1979). Optimal temperatures for salmon and steelhead range between 46-58°F. Many streams in the South Fork Trinity River basin experience summer temperatures that are far higher than the optimal range for fish, and some measured temperatures even exceed what are considered lethal levels (Reiser and Bjornn, 1979). Dissolved oxygen levels are directly correlated with stream temperatures, so low D.O. levels may be contributing to increased fish stress, mortality, and low fish densities in some stream reaches. For most streams there is a general inverse relationship between increased stream temperatures and density of juvenile salmonids (Table 3-2).
The highest densities of juvenile steelhead were found in South Fork Trinity River tributaries with cool water temperatures such as Plummer Creek, Eltapom Creek, Butter Creek, Rusch Creek, and upper Salt Creek (Table 3-2). Warmer streams, such as Hayfork Creek and various reaches of the South Fork Trinity River, had very low fish densities. Streams that do not exhibit this relationship are the East Fork of the South Fork, Rattlesnake Creek, Dubakella Creek, and lower Salt Creek. The low density of juvenile salmonids in the East Fork may be related to elevated fine sediment concentrations and resultant low biological productivity. Relatively high fish densities in lower Salt Creek may have been caused by 0+ steelhead migrating out of the warmer main stem channel system. The reason for low densities of fish in Dubakella and Rattlesnake Creek is not apparent.
High stream temperatures may result from removal of riparian trees during logging, stream widening due to aggradation, over-grazing of riparian zones, flow depletion and agricultural runoff. When debris flows inundate channels, riparian zones can also be devastated. The stream bed may remain unstable for a long duration, making recolonization of stream side trees difficult even by invasive species such as willows or alders (Lisle, 1985). Lower reaches of Pelletreau Creek and the South Fork Trinity River at Hyampom are classic examples of this problem. The linkage between sediment build up and changes in riparian canopy are described more completely in Chapter IV.
South Fork Mountain has numerous tributaries that are not accessible to anadromous fish but that have traditionally supplied cool water to the main stem of the South Fork throughout the summer months. Many of these tributaries such as Charlton Creek, Sulphur Glade Creek, and Marie Creek have experienced inner gorge failure in the past and may lack sufficient riparian canopy to keep temperatures low in summer. Field work by CDFG has found stream temperatures in Sulphur Glade Creek have now dropped back into the high 50's during summer (CDFG, 1993), indicating that riparian in this tributary is now in recovery.
Nawa et al. (1990) documented stream temperature increases in rivers of south coastal Oregon due to riparian canopy removal. As upper tributary temperatures cooled after 10 to 20 years of revegetation, lower main river areas showed a lag time in recovery. This delay was ascribed to continuing channel widening and aggradation from more recent disturbances in the basin or from reworking of channel-stored sediment. While some sub-basins such as Madden, Plummer and Potato Creeks are probably showing cooling trends, the temperature in the main stem of the South Fork seems to be remaining extremely high (Figure 3-5).
Livestock will often graze near streams preferentially, stand in the shade of riparian trees during the heat of summer, or cross through riparian zones to get water. Over long periods of time, over-use of stream side areas by livestock can cause loss of riparian vegetation. Streams in Oregon lacking riparian cover were shown to experience temperature rises of one degree per mile (Ziller, 1985). Flow depletion due to agricultural diversion makes streams shallower and subject to warming, and return flows from irrigated pastures can further elevate stream temperatures. Streams heavily impacted by grazing in the South Fork Trinity River basin include Carr Creek, lower Salt Creek and its tributaries, lower Big Creek, Lower Tule Creek, lower East Fork of Hayfork Creek and the main stem of Hayfork Creek in Hayfork Valley.
USFS Monitoring Program Temperature and Fine Sediment Findings
The USFS (1990a, 1991a) initiated an extensive monitoring program after the 1987 Fires to try to detect impacts from the fire and subsequent salvage logging. Further discussions of the monitoring program can be found in Chapter XIII, but relevant findings on temperature and fine sediment are discussed below.
As part of their ambitious monitoring program, the USFS installed many continuous temperature data recorders at various locations within the South Fork Trinity River basin. A listing of most stations monitored during 1989 and 1990 can be found in Table 3-3. An unusually cold period during early June in 1990 caused significantly lower minimum temperatures in that year (Figure 3-5). Maximum temperature readings were generally slightly higher for 1990 versus 1989 at most stations.
Table 3-3. Maximum and Minimum Stream Temperatures from USFS Monitoring Program
(USFS 1990a, 1991a), collected May 1 to October 1,1989 and 1990.
Location (Year Data Collected) Minimum Temp. Maximum Temp.
Hayfork Creek below Miner Creek (1989) 59° 74°
Lower Hayfork Creek at Hyampom (1990) 49° 85°
Bear Creek (1989) 45° 64.5°
Upper Olsen Creek (1990) 46° 55.5°
Lower Olsen Creek (1990) 45.5° 64.5°
Flume Creek (1989) 48° 70°
Upper Rattlesnake Creek (1990) 46.5° 75°
Lower Rattlesnake Creek (1990) 46° 71°
Cave Creek (1990) 46° 63°
Butter Creek (1990) 46° 70.5°
E.F. of South Fork Trinity River (1990) 42.5° 68°
S.F. Trinity R. above Powell Cr (1990) 47° 67°
S.F. Trinity River at East Fork (1990) 48° 71°
S.F. Trinity River below Cave Cr (1990) 45.5° 75.5°
S.F. Trinity R. below Butter Cr (1990) 47.5° 78.5°
S.F. Trinity R. below Jesse Cr (1989) 58° 78°
S.F. Trinity River at Slide Cr (1990) 49.5° 78°
There are several interesting trends yielded by this extensive monitoring effort. Upper Rattlesnake Creek seems to be a major source area of temperature increase in that stream, rising to 750 F while lower Rattlesnake Creek attained a maximum temperature of 710 F. Headwater streams tend to be cooler than lower reaches of most streams because increasing stream width allows greater opportunity for warming. The USFS data suggests that lack of riparian canopy may be a problem on upper Rattlesnake Creek and deserves further analysis.
Temperature on the main stem South Fork Trinity showed a warming trend from above Powell Creek to just below Butter Creek. This is not surprising given the open nature of the stream and the known past problems with channel widening and decreased pool depth. An unexpected result was that the South Fork Trinity below Slide Creek at the base of Hyampom Valley did not increase in temperature even with the addition of warm water from Hayfork Creek. The USFS (1991a) advanced the hypothesis that cool water flowing sub-surfacethrough the gravel deposits in Hyampom Valley might be responsible for this phenomenon.
The substantially warmer temperature of Hayfork Creek as it converges with the South Fork is very telling (Figure 3-5). While it is quite likely that Hayfork Creek historically had a moderating influence on South Fork Trinity River main stem temperatures, it now seems to be exacerbating thermal problems.
Figure 3-5. Maximum water temperatures in lower Hayfork Creek at Hyampom compared to the South Fork Trinity River below Butter Creek between May 1 and October 1, 1990. Taken from USFS 1991a. NOT AVAILABLE IN ELECTRONIC FORMAT
Long Term Temperature Trends and the Success of Exotic Fish Species
Exposure to the summer sun has always warmed the lower river somewhat and the South Fork Trinity River at Salyer in 1954 was measured at 74°F in late summer (Coots, 1954). More recently, however, Dale (1990) found that the South Fork reached 81°F below Hyampom, the highest temperature ever recorded. Nawa et al. (1990), in studies in southwestern Oregon, found that coho salmon disappeared from streams that exceeded temperatures of 72°F and that steelhead densities dropped substantially when temperatures exceeded 74°F, particularly 1+ and 2+ fish. The loss of coho salmon from lower Hayfork Creek and severely low numbers in the South Fork Trinity River, as well as avoidance of main river habitats by chinook salmon juveniles, may be a direct result of high stream temperatures. Extremely low densities of 1+ and 2+ steelhead in reaches with high stream temperatures are also consistent with these findings.
Warm water fish species, such as green sunfish and brown bullhead, have been stocked in farm and mill ponds in the Hayfork Valley since the 1950's (Irl Everest, personal communication). Occasionally these fish would escape into Hayfork Creek but they rarely survived the high flows and cold temperatures of winter. Downstream migrant traps have been set in Hayfork Creek since 1988 to capture young steelhead (Wilson and Mills, 1992). These traps have been catching high numbers of both green sunfish and brown bullhead. Mike Dean (personal communication) found over 200 green sunfish in one backwater pool on the main South Fork Trinity River in 1992. Of 28 fish sampled by electroshocking, over half were old enough to reproduce (2+) and many had small fish in their stomachs. This suggests that, during the recent drought, green sunfish have become well established both in Hayfork Creek and in the lower South Fork Trinity River. High stream temperatures have given a competitive edge to these fish over salmonids during summer and it is likely that young of the year steelhead are falling prey to green sunfish.
There are substantial limiting factors affecting the productivity of the South Fork Trinity River basin for salmon and steelhead. The major limiting factors include: 1) chronic problems with sediment, 2) low stream flows, and 3) warm water temperatures (Plate 2). Many streams exhibiting higher channel gradients have flushed substantial amounts of introduced coarse sediment, similar to a pattern of recovery described by Lisle (1985) and Hagans et al. (1986). Headwater streams have also, in some cases, experienced re-growth of riparian zones during the recent drought, helping to lower stream temperatures. However, reaches of the main stem South Fork, and lower Hayfork Creek, seem to be lagging in recovery both in terms of flushing recently introduced sediment and lowering water temperatures. In fact, recent drought years have produced record high temperatures in the South Fork Trinity River (Dale, 1990).
Accounts of anglers from the 1950's describe how it was possible to catch 50 to 100 "trout" in one day while fishing Hayfork Creek and the main South Fork Trinity River below Hyampom. Today fish densities in these areas are extremely low and juvenile salmonids inhabit fast moving and falling water habitats almost exclusively. If cooler water temperatures could be achieved and fine sediment problems remedied, salmon and steelhead juveniles could distribute throughout most habitat types and productivity could be greatly increased. The congregation of all age classes of juvenile salmonids into very limited habitat areas such as bubble curtains or the mouths of cold water tributaries is probably leading to competition and predation resulting in "density dependent mortality."
Studies by Wilson and Mills (1992) and Wilson and Collins (1992) indicate that almost all returning adult winter steelhead have spent two to three years in freshwater before entering the ocean. Lack of suitable habitat due to high stream temperatures, shallowness of pools, and lack of food production in the mainstem appears to be a habitat bottleneck for production of winter steelhead. During recent years, few spring chinook juveniles have been found in the main stem South Fork Trinity River. Plummer Creek is the only major tributary stream in the basin supporting young spring chinook during summer, which suggests that a shortageof suitable rearing habitat is also severely limiting recovery of this species.
High temperatures in the South Fork and Hayfork Creek may also be affecting the survival of adult spring chinook during summer. Dean (in press) estimated 50% mortality for spring chinook adults during recent years. Fine sediment from stream side landslides is also suspected of capping spring chinook redds in the main stem of the South Fork, and lowering the survival of eggs and alevin (Mike Dean, personal communication). Shifting bedload during low to moderate storm events is another potential limiting factor on spring chinook spawning success.
The increase in abundance and survival of warm water species may be indicative of an ecological shift. If action is not taken to decrease stream temperatures and improve overall water quality in the South Fork Trinity River watershed, the severely depleted salmonid populations could be impacted still further.