The Trinity River Hatchery at Lewiston was built to mitigate for the loss of hundreds of miles of salmon and steelhead spawning and rearing habitat blocked by the construction of Trinity Dam. Iron Gate Hatchery on the Klamath River was also constructed to mitigate for blocked habitat above Iron Gate Dam. While the operation of these hatcheries may be necessary and worthwhile, it is possible that they can have negative impacts on wild runs of salmon and steelhead in the entire Klamath basin. This section examines potential side effects on native South Fork Trinity River salmon and steelhead caused by operation of large scale hatcheries in the Klamath basin. Potential problems discussed include 1) decreased fitness caused by interbreeding of hatchery fish with wild salmon and steelhead, 2) introduction of diseases, and 3) increased competition for wild fish due to over-planting. Harvest problems for natural stocks caused by mixed stock harvest are related to hatchery operation because fishing effort is often geared to the productivity of abundant hatchery fish (see Chapter VII).
The homing instinct of salmon and steelhead has led to the evolution of separate stocks of these fish (see Chapter II). Much of the information necessary for survival is passed from generation to generation through genetic material (Ryman and Utter, 1986). Behavioral traits, resistance to disease, physical features and other adaptations that favor survival in their native stream have been described for numerous salmon stocks (Ricker, 1972; Nicholas and Hankin, 1988). Hatchery fish may stray into the wild to spawn with native salmon and steelhead populations. Such interbreeding may have some negative impact on the genetic fitness of locally adapted native salmon and steelhead populations, particularly if hatchery stocks are not native to the basin, or if broodstock handling has caused changes in the hatchery population.
Salmon and steelhead populations in close geographic proximity are often very similar genetically (Parkinson, 1984). In areas farther apart, populations have evolved in isolation for a longer time and therefore, may have much more significant genetic differences. Problems may arise when hatchery broodstocks are founded on salmon or steelhead strains from far-distant basins. As these fish stray to spawn with wild native fish, offspring of non-native hatchery salmon or steelhead or hatchery/wild hybrids may lack critical survival traits (McIntyre et al., 1988).
For example, the widespread stock transfer of Trask River (Oregon) coho salmon into the Nehalem River resulted in reduced fitness of the total fish population. The Trask River coho lacked resistance to the disease Ceratomyxa shasta, which was present in the Nehalem basin. Progeny of hatchery coho showed no resistance to the disease, while hatchery/wild hybrid coho showed an intermediate susceptibility to C. shasta. Therefore, as hatchery coho spawned with wild fish they reduced survival considerably.
Studies by Solazzi and others (1983) showed that transplanting of non-native coho salmon throughout coastal Oregon led to a decrease in survival rate of smolts. No net increase in adult populations resulted from intensive stocking, due to increased competition in streams, but many of the spawners that later returned were of hatchery origin. The survival rate of smolts in the subsequent generation was lower, probably as a result of reduced fitness (Solazzi and others, 1983).
Behavioral differences can develop in salmon or steelhead that cannot be correlated with genetic differences (McIntyre et al., 1988). Consequently, even if salmon and steelhead show a high degree of genetic similarity, it may be desirable to prevent interbreeding to maintain critical behavior patterns. Riesenbichler and McIntyre (1977) found that interbreeding of hatchery and wild steelhead in Trout Creek (Deschutes River, Oregon) led to decreased smolt survival even though the hatchery broodstock was of local origin. McIntyre (1984) ascribed decreased survival rates to unintended selective pressure in the hatchery which led to changes in behavior or some other trait within just a few generations.
Introduction of hatchery fish of non-native origin may or may not bring about changes in the genetic structure of a locally adapted native salmon or steelhead population. If, for instance, hybrid offspring lack resistance to a disease that is prevalent, they may all die. There is an immediate cost in productivity, as wild fish would otherwise produce viable offspring. Complete mortality, however, prevents any lasting genetic impacts and there is a lack of what is termed "gene flow" between the non-native and native population.
Alternatively, other traits, such as survival mechanisms during drought, may or may not be tested in any given year. Hybrid offspring may survive well if there is a short term wet cycle, but future generations may be less fit to cope with droughts when they occur. In the latter case, gene flow did occur and detrimental effects are spread over time.
While fall chinook and spring chinook salmon stocks at Trinity River Hatchery were founded on locally adapted populations, coho salmon and steelhead stocks have included numerous contributions of fish imported from other river basins (USFWS, 1991). California Department of Fish and Game South Fork Trinity River studies (Jong and Mills, in press; Mills and Wilson, 1991) have found that hatchery salmon stray into the basin frequently. Historical and recent potential problems related to straying on native South Fork Trinity River steelhead, chinook salmon, and coho salmon stocks are discussed below.
Fall Chinook Salmon
Returns of fall chinook salmon to the South Fork Trinity River between 1984 and 1991 were comprised of 4% to 28.8% hatchery strays (Jong and Mills, in press). Coded wire tagged individuals represent only a fraction of hatchery releases. The number of tagged hatchery fish captured at weirs or during spawning surveys is expanded according to the ratio of marked to unmarked fish released at the hatchery. The rate of straying and hatchery origin of strays for those years are shown in Table 8-1. While Trinity River Hatchery release groups often constituted the bulk of stray fall chinook salmon in the South Fork Trinity basin, fish from other hatcheries were also common (Jong and Mills, in press).
According to Jong and Mills (in press), coded wire tag analysis of Trinity River Hatchery release groups showed that young chinook salmon released as fingerlings in the spring were least likely to stray. Off-site release groups typically exhibit a higher stray rate, yet they accounted for only 1% of strays in the South Fork Trinity River. Hatchery chinook salmon juveniles held for release until October (yearlings), and experimental groups held for over one year and released in spring (yearling+), showed the highest stray rates.
The genetic effects of straying of Trinity River Hatchery fall chinook into the South Fork Trinity River are unknown. Given the proximity of the two watersheds, some low rate of straying between these populations may have occurred naturally. If negative effects are occurring, they would likely be expressed as some form or measure of reduced fitness caused by unintended selection at the hatchery. Introduction of diseases by Trinity River Hatchery fall chinook strays may be a more significant problem than genetic or behavioral changes, and will be discussed in the following section.
Off-site releases of Iron Gate Hatchery fall chinook juveniles at Klamath Glen caused increased straying into the South Fork Trinity River in 1985 (Jong and Mills, in press). CDFG no longer allows any off-site releases of salmon or steelhead from either of the basins' large hatcheries (CDFG, 1993). Approximately 11% of returning fall chinook salmon returning to the South Fork in 1985 were of Iron Gate Hatchery origin (Table 8-1). It is likely that there are significant differences between native South Fork Trinity River fall chinook stocks and those from Iron Gate Hatchery.
Although Iron Gate fall chinook salmon are derived from local native broodstock, their run timing is significantly earlier than South Fork Trinity River fish and other differences may have evolved between the two stocks because of the substantial difference in the nature of the basin areas to which they return. The negative impacts of strays from Iron Gate Hatchery fall chinook may, therefore, be greater than those from Trinity River Hatchery.
Table 8-1.
Stray Rates of Hatchery Fall Chinook into the South Fork Trinity River Basin
(1984-1990).
Origin of Strays
Number of Number of Total
Year of fish strays strays by %
Unknown TR Hatchey Iron Gate Small Scale*
1984 73 21 28.8% 24.7% 4.1% 0 0
1985 176 42 23.8% 0 11.3% 11.4% 1.1%
1986 264 10 3.8% 0 3.4% 0.4% 0
1987 455 95 21% 0 18.3% 0.3% 2.4%
1988 368 55 15% 0 4.9% 0 10.1%
1989 52 5 9.6% 0 0 0 9.6%
1990 223 9 4.0% 0 0 0 4.0%
*
Small scale hatcheries include Hoopa Fisheries,Horse Linto Creek, and Cappell Creek
Hatchery.
Information from Jong and Mills(in press).
Strays from small scale local hatcheries in the Klamath Basin, such as Horse Linto Creek, Hoopa Valley, and Cappell Creek in the lower Klamath region, constituted the bulk of fall chinook strays into the South Fork Trinity River in 1988-1990 (Table 8-1). The largest influx came from a release group from Hoopa Valley Fisheries rearing programs in Tish Tang Creek. While the number of strays into the South Fork Trinity River Basin from small scale hatcheries is low, the straying of fish from these facilities needs closer monitoring. Again, the effect of straying of fall chinook on local native stocks is unknown.
Spring Chinook Salmon
No stray hatchery spring chinook have been found during recent studies in the South Fork Trinity River basin (Dean, in press). In 1973, over 900,000 spring chinook salmon juveniles were transplanted into the South Fork Trinity River at Forest Glen. This attempt to restore the run that was devastated by the 1964 flood seems to have led to increased returns to the river in 1976 (See Chapter II). The effect of this transplant of Trinity River Hatchery spring chinook juveniles on gene resources or survival of locally adapted South Fork Trinity stocks is unknown. The hatchery stock is of native origin and some low straying rate between the two basins probably occurred naturally. However, it is still possible that South Fork stocks may have evolved unique survival traits that could be compromised by such stock transfers.
Coho Salmon
A few hundred native coho salmon were trapped for initial fish cultural operations during construction of Trinity Dam (Murray, 1965). Unfortunately, water quality problems and disease led to the loss of these fish. Eggs were imported from Cascade Hatchery in the Columbia River basin, the Eel River and the Noyo River in California to found the Trinity River Hatchery coho salmon broodstock. (USFWS, 1991).
Of 109 coho salmon entering the South Fork Trinity River in 1985, 39 bore hatchery fin clips (Jong and Mills, in press) and it is quite possible that all were of hatchery origin. Since pre-spawn mortality of females was nearly 100%, no genetic impact on any locally adapted coho population could have occurred. In 1990, another coho run that had no hatchery marks returned to spawn in mid-January. This may be a portion of the remnant wild population. If this latter pulse is indicative of native run timing, then differences in spawn timing may prevent interbreeding when hatchery coho strays enter the system.
Steelhead
While steelhead from Trinity River Hatchery have not been seen in the South Fork Trinity basin in recent years, past hatchery practices may have led to some straying during the 1970's. In early years of operation of Trinity River Hatchery, there was a substantial problem with very low return rates of adult steelhead (Bedell, 1970). While the original broodstock was of local origin, chronic low returns necessitated importation of eggs from other basins to allow continued production of steelhead for dam-mitigation purposes. Steelhead were imported from the Eel River, three Oregon hatcheries, and the Skamania Hatchery in Washington (USFWS, 1991).
It was discovered that most steelhead juveniles released from the hatchery never migrated to the ocean (Kerstetter and Keeler, 1976). In an attempt to induce ocean migration, steelhead smolts were planted in downstream areas (Bedell, 1972). Planting fish away from the hatchery (out-planting) has been shown to lead to very high rates of straying (Royal, 1972) and there is substantial evidence that these steelhead release groups strayed widely throughout the Klamath basin. During the early 1970s, substantial numbers of steelhead from the Trinity River Hatchery were documented to have returned to Klamath River Iron Gate Hatchery (Marshall, 1974), located over 140 miles upstream of the Trinity River and Klamath River confluence. Stray hatchery steelhead were also noted in Manzanita Creek, a Trinity River tributary near Big Bar (Hubbell et al., 1982). Therefore, it is likely that stray Trinity River Hatchery steelhead also entered the South Fork Trinity River.
Since there were no studies or creel census conducted in the South Fork Trinity River during this period, there is no direct evidence that such straying occurred. If straying did occur then interbreeding of these non-native steelhead with wild steelhead may have caused chronic or short-term problems with fitness. Recent genetic analysis by Baker (1988) and Hodges et al. (1989) showed that native South Fork Trinity River steelhead are still distinctly different from Trinity River Hatchery steelhead. Given the harsh environmental conditions in the South Fork Trinity River, intensive selection pressure may have prevented significant gene flow. Different spawn timing of strays and native fish could have negated any potential influence as well. Chapter 8 continued