One might logically expect to find a reciprocal relationship between gradient and distance the rearing chinook move upstream, but the data show this relationship to be very weak (r2=0.14; Figure 3). An obvious complicating factor would be presence of barriers such as beaver dams, debris dams, and high velocity culverts. It would have been too time-consuming to walk each stream looking for barriers, but in general, they should be more common in smaller streams. However, the observed relationship between stream size and distance moved upstream is also weak (r2=0.21; Figure 4). An unexpected variable, the river mile at which the tributary enters, shows the strongest correlation with the distance juveniles move upstream in the tributary (r2=0.31; Figure 5). One might logically think that there would be more juveniles entering downstream tributaries, perhaps as a result of excess fry dumping by Coleman Hatchery, which usually releases excess fry in the vicinity of Red Bluff (RM 244), and that crowding forces the juveniles further up the tributaries. However correlation between river mile and juvenile density in the mouth of tributaries is very weak (r2=0.10; Figure 6) and there is no correlation between juvenile density in the mouth of tributaries and distance they move upstream (Figure 7). There is a correlation between river mile and the gradient of tributaries studied (r2=0.27; Figure 8), however, and this plus random chance may explain the correlation between river mile and the distance juveniles move upstream. It will be interesting to see if this relationship persists in other years.
One surprise was the short distance the juveniles moved upstream in Stillwater and Churn Creeks. Both are low-gradient streams with what appears to be suitable habitat and both had good populations near the mouth, yet the apparent upstream movement was only about 10% of what was expected from observations in similar creeks.
| Area | Juvenile Salmon Captured | |||||||
| Trips | Sites Sampled | Total | per site | Fall | Spring | Winter | Late Fall | |
| Down River from Red Bluff | 24 | 68 | 2243 | 33 | 1366 | 783 | 96 | 0 |
| Up River from Red Bluff | 14 | 49 | 667 | 14 | 584 | 47 | 16 | 20 |
Catch per unit effort was about twice as great below Red Bluff. This seems to relate more to the fact that juvenile chinook are going further upstream than to the density at the mouths of the tributaries (See Figure 5 and Figure 6). If releases by Coleman Hatchery were the cause, one would expect greater density at downstream tributary mouths, as well as capture of some coded wire tagged fish (none were captured this year). The phenomenon of more juveniles, particularly in the Spring chinook size category, in tributaries downstream of Red Bluff was also observed by (Maslin, et al. 1996a, 1996b), who suggested a relationship with the Spring chinook spawning streams (Mill, Deer, and Big Chico). Genetic analysis to reveal the origin of tributary rearing juveniles may shed more light on this phenomenon.
| Estimated Juvenile Chinook Present in March, 1997 | |
|---|---|
| Creek | Number |
| Mud | 32,000 |
| Elder | 4,000 |
| Toomes | 10,000 |
On Mud, Elder, and Toomes Creeks, we have been able to explore the length of the habitat used and consequently have a good idea of how representative the sample sites are. Calculations from density and distance are reduced by 30% for Mud Creek to account for about 30% of the creek being lower quality habitat than the average sample site. For Elder and Toomes Creeks, we believe the sample sites are representative of available habitat.
These population estimates only include the main cohort of juveniles in the stream. A different (much smaller) cohort may have used the tributary during the early part of the season and have already emigrated by mid season. The probable growth of this cohort is shown by line W on Figure 12, whereas the growth of the major cohort is shown by line F. Potentially, a third cohort may enter the tributary past the mid season peak. That was not observed during the (relatively dry) 1997 season but may be clearly seen in Mud and Blue Tent Creeks in 1996 (Figures 13B and Figure 16). Indication of the extended time period of juveniles entering the tributaries are also seen in the small sizes present throughout much of the season in some tributaries during the 1995 and 1996 seasons (Figures 13 through 16). The single point at the bottom right of Figure 12 (arrow) does represent the appearance of a new cohort in Olney Creek, but this cohort was apparently spawned in the creek and thus does not represent non-natal rearing.
One difference between the 1997 sample year and former years is suggested from careful observation of juvenile size ranges at different times (Figures 13-16). In 1997, essentially all the juveniles entered the creeks at one time in conjunction with the only mild winter storm. The cohort of fish entering then can be followed through time as they grew in size all the way into late April. In fact, because of lack of spates to move them out, the juveniles remained longer and grew larger than usual. Except for winter chinook which appear at large sizes in February or March in several years (Kusal, stream km 4 in 1994 [Figure 14]; Mud Creek in 1994, 1995, and 1996 [Figure 13]), only 1994 and 1997, both low rainfall years, show any quantity of juveniles exceeding 100 mm fork length. Observation in wetter years suggested that most juveniles left the tributaries at fork lengths between 80 and 90 mm (Maslin, et al. 1996a).
A single entry time is characteristic of dry years, and shows up in the data for most streams in 1994 and 1997. Multiple invasions are characteristic of wetter years such as 1995 and 1996 and can be seen in the graphs for Toomes, 1995; Figure 15) and Mud Creek at stream km 4 in 1995 and especially 1996 (Figure 13-B).
Data gathered in such an atypical water year cannot easily be extended to generalizations applicable to most years. Probably the number of juvenile chinook rearing in tributaries was substantially lower than usual. Eggs and fry may have been swept out of the system by the early-season high flows. The number of winter-run juveniles observed is probably depressed even more than the total because of our inability to sample effectively during much of the early part of the season when winter-run would be expected to be most abundant. The lack of subsequent storm events has several probable impacts on the number and distribution of juveniles in tributaries: First, it eliminated a major stimulus which causes juveniles to move around looking for suitable habitat, thereby reducing the number entering the tributaries. Second, it probably resulted in juveniles not moving as far up the tributaries for the same reason. Finally it reduced size diversity since most juveniles entered the tributaries on the same high water event.
| "Race" | Fall | Late Fall | Spring | Winter |
|---|---|---|---|---|
| Number Captured | 2951 | 20 | 984 | 111 |
Because of the faster growth in the tributaries and because of the difficulty in determining how long a fish has been in the tributary growing at that faster rate, tributary juveniles cannot be classified by size into races with any confidence. Figures 18-23 show the size distribution of juvenile chinook captured at each site against a background of date-specific size ranges for each race from the Sacramento River Daily Length Table. Very small juveniles (40 - 50 mm fork length), having recently emerged from redds and found their way into the tributaries, will be close in size to juveniles rearing in the mainstem. Although the cut-off between races may be at a slightly larger size, the distribution of very small fish should cluster on the proper side of the dividing line. Toomes Creek on 3/8/97 (Figure 21 A and B) provides clear examples. The smaller-size cohort in Kusal Slough on 2/5/97 (Figure 19B) provides a much more ambiguous case, since the distribution clusters exactly on the dividing line. However, one can apply the rule of a slightly larger cut-off size for tributaries and assign them to the fall race. The group of much larger fish on that date are probably not fall-run, but there is no certainty that they are winter-run. On 3/22/97, the smaller-size cohort falls clearly into the spring-run size, but these are probably the same fish assigned to the fall-run on 2/5/97. The 4/26/97 distribution adds more confusion. If the fish continued growing faster than the river rate, the mode should have moved closer to the right edge of the spring distribution, but instead, it has become very diffuse and, if anything, closer to the left edge of the spring distribution. The probable explanation is that most of the larger members of the cohort smolted and left. An experienced researcher can generally make a guess about the race based on relative size and adjustments for faster tributary growth, but it will be, at best, an educated guess.
Because of the lack of spates to move fish around this year, it is probable that most samples at the same site on different dates represent subsamples from the same population. In several instances summarized below it is apparent that the population at a site would be classified as different races on different dates.
| Figure | Creek | Site | Date 1-race 1 | Date 2-race 2 |
|---|---|---|---|---|
| 18-B | Mud | km 3.9 | 3/5 - Fall | 4/16 - Spring |
| 18-D | Mud | km 8.4 | 3/5 - Fall | 4/16 - Spring |
| 19-A | Kusal | km 4.0 | 2/19 - Fall | 3/22 - Spring |
| 20-A | Pine | km 6.4 | 2/26 - Fall/Spring | 4/26 - Spring/Winter |
| 21-B | Toomes | km 1.5 | 3/8 - Fall | 4/30- Fall/Spring |
In all these instances the apparent change in race from date to date could have resulted from the same cohort growing at a rate similar to those reported for tributaries by Maslin, et al., 1996b.
Despite the difficulty of classifying juveniles to race, it is likely that several races utilize tributaries for rearing. Figure 12 shows the pattern of growth of two distinct cohorts of fish, most probably winter and fall races. In Figures 13-16, distinct groups of juveniles can be followed, as they enter the tributaries at different times, grow, and eventually emigrate. Distinct size groups can also be seen in Figures 18A&B, 19A&B, 22 and 23. Such diverse size groups were more conspicuous in wetter years (Maslin, et al., 1996b). Also, in previous years, we captured coded-wire-tagged chinook which were verified to be of winter, fall, and late-fall hatchery-released fish (Maslin, et al., 1996a). (No hatchery spring chinook were being tagged in the system.) The variety of hatchery races found, coupled with the variety of dates juveniles enter the tributaries and the variety of sizes of juveniles present at any one date, suggests that some members of all races enter tributaries for rearing. Probably the only way to verify this is with genetic testing.
Species other than fish also use seasonal streams extensively. Baetid mayflies and Capniid stoneflies, specialized for life in a temporary habitat, are common. Both are important food sources for rearing chinook (Moore, 1997). Pacific treefrogs, western toads and spadefoot toads use drying pools of seasonal streams as spawning areas. Cliff swallows and bats nest or roost under bridges and feed on emerging aquatic insects. Mallards and wood ducks nest along the intermittent pools.
Very few of the stream reaches visited could be assessed as being in proper functioning condition as defined by the Bureau of Land Management, 1995. Some are functioning at risk because of the destabilizing influence of human structures or activities in adjacent reaches. Unfortunately, a high proportion must be classified as non-functioning. While we did not have a multidisciplinary team to assess the reaches by the standard protocol, we made educated guesses based on our observations as compared with PFC protocol. Our approximation of PFC classification is included on Table 3. It should be emphasized that non-functioning refers to the physical stability of the stream reach and not to its ability to serve as fish habitat. Many non-functioning reaches still serve as rearing habitat for chinook. However, that habitat is probably substantially poorer than it could be and may be vulnerable to further degradation.
The poor showing of these tributaries relative to proper functioning condition results primarily from the long-standing attitude of managing agencies and riparian landowners that these small tributaries serve primarily as drainage ditches that should be straightened and cleared to transport storm water efficiently. Unfortunately this approach is exactly opposite to the concept of proper functioning condition, a primary goal of which is to keep water on the land as long as possible. Such an ingrained lack of understanding of stream function can only be countered by extensive education.
Anthropogenic barriers
A few streams have clearly observable anthropogenic barriers that impede upstream movement of juvenile chinook. These fall into two categories:
It should be noted that such obstructions serve as fish filters rather than absolute barriers. A few juvenile chinook have been observed upstream of most of them.
Riparian Vegetation
As suggested in Figure 2, riparian shade can be critical in preventing diurnal thermal maxima from reaching dangerous levels, thereby extending the usable season for these small streams. Riparian vegetation serves another function. Aphids, tree hoppers, etc., falling from overhanging vegetation, are an important source of food for rearing chinook early in the season before the invertebrate fauna has had time to develop in intermittent streams, and a supplemental food throughout the season.
Table 7 lists stream reaches shown on the GIS Riparian Plot (Geographical Information Center, 1997) to be deficient in riparian vegetation. In most of these reaches the devegetation resulted from deliberate management decisions by landowners or controlling agencies. Restoration would therefore involve an educational component probably far more difficult than the replanting component. In fact, in most sites the riparian vegetation would regenerate on its own if not continually suppressed.
Destabilization from Upland Activities
In other creeks the stream degradation results primarily from upland destabilizing activities such as mining, construction, logging, or improper grazing, perhaps in a geologically fragile soil or substrate. The result is mass movement of rock debris. This tends to deposit in lower gradient reaches of the stream, producing high gravel bars which are difficult for plants to colonize and which force lateral scouring widening the channel and disrupting lateral riparian vegetation. The resultant channel has an extremely high width to depth ratio (See Table 3) and very poor habitat quality. In many cases this problem has been compounded by attempts to mechanically shape the agraded channel. Examples are found at:
Elder Creek is a special case. While it has the mass movement of small rock debris typical of west side streams, it has been artificially confined between levees which prevent lateral scour. Consequently it has a very unstable bed, and an almost uniform flow rather than the stair-step of riffles and pools characteristic of most streams. Riparian vegetation is slowly recolonizing the artificial banks, but it is still small, providing little fish cover and no recruitment of large woody debris to force the scouring of pools. The combined effect is to reduce available cover for fish to a minimum. A possible long-term solution might be to plant its banks with large-growing trees such as cottonwoods and western sycamores. Of course, stabilizing the headwaters would facilitate restoration.
Sulphur Creek probably never recovered from extensive historical gold dredging, but it appears to have also been recently destabilized, probably as a result of residential development. This year many salmon and steelhead adults (probably several hundred of each) migrated into Sulphur Creek to spawn. Rapid dewatering of the cobble-filled bed led to interrupted flow which stranded adult steelhead and caused eggs of both species to be lost. (We also observed evidence of spawning in Middle, Olney, and Churn Creeks.) Whether the extensive spawning activity is a regular phenomenon in tributaries just downstream of Keswick Dam or just a function of the unusual water year should be investigated.
Diversion
Most of the streams probably experience either opportunistic or regular diversion for irrigation or stock watering. Unfortunately, our sampling protocol did not readily identify upstream diversions. Residents of Bear Creek complained that both base flow of the creek and runs of adult chinook and steelhead were much reduced from former years and attributed this to upstream diversion. (Bear was one of the creeks in which we identified spawning success.)
Some anthropogenic changes may even enhance the suitability of small streams for salmonid rearing. Leakage of water from the ACID Canal into Olney Creek keeps the volume up and temperature down late in the season. Anderson Creek may benefit from the same phenomenon. Judicious diversion of small amounts of Sacramento River water from existing canals into tributaries could potentially enhance the survival of non-natal rearing chinook. One stream-side resident even suggested that it would require relatively simple engineering to divert water from Shasta Reservoir down Churn Creek to make it more suitable for both spawning and rearing. (Several adult carcasses were observed in Churn Creek, but flow became reduced or interrupted before successful hatching and no fry were observed.)
To: Discussion