Hatchery Disease Problems and Possible Effects on Wild Fish

Because of the crowded conditions within hatchery rearing trays and raceways, epidemics of disease are more likely to occur than in the wild. Importing eggs or fish to a hatchery from other river basins increases the risk of introducing diseases to which native fish have little resistance (PNFHPC, 1989). Foott (1992) found that Trinity River Hatchery salmon and steelhead have significant problems with several disease organisms, including IHN (infectious hematopoietic necrosis) and BKD (bacterial kidney disease). He noted that "disease may be influencing smolt survival in several Trinity River stocks." There is also a possibility that disease organisms have been spread to wild fish, although lack of baseline information makes it impossible to prove this conclusively.

Infectious hematopoietic necrosis (IHN): The virus known as IHN attacks the liver of salmon or steelhead and is much more pathogenic when water temperatures are cold. The disease is "vertically transmitted" which means that it can be passed from fluids within the gut of female fish to eggs of the next generation. Chen (1984) suggested that various strains of IHN exist, and if salmonids evolve with a specific strain they will develop resistance to it. He suggested that if IHN was transferred from one basin to another, its virulence could be substantially increased. Stock introductions of steelhead and coho salmon at Trinity River Hatchery in the early years of operation may have imported a more virulent strain of IHN. Stray fall chinook salmon from hatcheries on the Rogue River and Sacramento River that return to the Trinity River Hatchery (Bedell, 1990) could also introduce non-endemic strains of IHN. The cold water coming from deep below the surface of Lewiston Dam that supplies Trinity River Hatchery has likely exacerbated the problem with this disease.

One to two million juvenile chinook salmon were lost annually due to IHN in the late 1980's (Bill Wingfield, personal communication). Foott (1992) noted that mortality of spring chinook salmon juveniles was still occurring due to IHN in 1991. He also found that juveniles infected with IHN were not found in samples of downstream migrants captured at Willow Creek. Two hypotheses were offered for this finding: either IHN infected fish migrated more slowly than uninfected fish or they did not survive (Foott, 1992).

Several steps have been taken in recent years to fight IHN problems at Trinity River Hatchery. An anti-viral agent, iotophore, has had some success in reducing mortality of chinook salmon juveniles. The U.S. Fish and Wildlife Service Fish Disease Center in Anderson, California, has initiated studies to determine additional steps that need to be taken (Foott, 1992).

Bacterial kidney disease (BKD): BKD results from infection by a bacteria called Renibacterium salmonarium which attacks the kidney of salmonids, just as its name implies. This disease can be transmitted "horizontally" which means that it can be passed from fish to fish in the wild through fecal material. Recent low returns of steelhead to Trinity River Hatchery are at least partly the result of increased incidence of BKD (John Hayes, personal communication). As of 1991, Foott stated that hatchery coho "were judged to be in poor health primarily due to severe bacterial kidney disease." This disease is subtle, because juvenile salmon or steelhead may survive well in their journey downstream, but be unable to make appropriate changes in kidney function for a successful transition to sea-water (Foott, 1992). Stress during migration may also cause this disease to come out of remission (Schreck, 1987).

Potential Effect on Wild Fish: Straying of hatchery fish into the South Fork Trinity basin may have increased incidence of disease in wild fish, but there is currently no direct evidence of this. Transmission of IHN would be through spawning of infected hatchery females whereas BKD could be spread without interbreeding. For example, the coho that strayed into the basin in 1985 (Jong and Mills, in press) could have spread BKD even without successfully reproducing. Samples taken by Foott (1992) of wild chinook salmon juveniles at the Willow Creek downstream migrant trap showed no problems with disease, but wild steelhead showed a 21% incidence of BKD which he considered "unusual as there are few reports of BKD in wild steelhead."

In 1987, female late run fall chinook salmon were trapped in the lower Trinity River to test them for the presence of IHN (Bill Wingfield, personal communication). These fish were thought to be of wild origin and tested positive for IHN. The conclusion drawn by the California Department of Fish and Game was that this disease was probably present in the system before its discovery at the Trinity River Hatchery. There were no disease studies on wild salmon and steelhead in the Trinity River Basin before hatchery operations and subsequent straying began. Consequently, tests to determine whether or not disease transmission has occurred are inconclusive.

Sharp Rise in Pre-Spawning Mortality a Cause for Concern

There has been a documented increase in pre-spawning mortality of female adult salmon in the South Fork Trinity River and in the main stem Trinity River in recent years (Jong and Mills, in press; Zuspan, 1991). LaFaunce (1967) found only a 1% pre-spawn mortality rate of fall chinook salmon females in his 1964 survey on the South Fork Trinity River. Recent carcass surveys in the basin have found female pre-spawn mortality rates averaging 24% and ranging from 0 to 71% (Jong and Mills, in press). The highest rates were 71% in 1985 and 50% in 1990 (Table 8-2), although the 1990 sample was based on only eight fish. Pre-spawning mortality has also shown an increasing trend in the main stem Trinity River below Lewiston Dam. Average pre-spawning mortality before 1970 was approximately 4% while 1987 and 1988 were 31% and 45%, respectively (Zuspan, 1991). The possibility that elevated pre-spawning mortality is linked to disease introduction cannot be ruled out. Pathology studies by CDFG did not find evidence of disease in main stem Trinity River female chinook that died before spawning (CDFG, 1993), but those findings have not been published so details were not available for this report.


Table  8-2.                                                                                 
Pre-spawn Mortality Rate For Female Fall Chinook Salmon in the South Fork Trinity
and Upper Trinity River 1955-1990 (Jong and Mills, in press).
                                                                              
                                                                            
 Year    South Fork                            Main Stem                             
          Trinity                               Trinity                              
           River                                 River                               
           Total      Unspawned   Pre-Spawn      Total      Unspawned    Pre-spawn   
         Carcasses    Carcasses   Mortality    Carcasses    Carcasses    Mortality   
 1955        --          --           --          2108          32          1.5%     
 1956        --          --           --          3657         219          6.0%     
 1963        --          --           --          5191         238          4.6%     
 1964        ND          ND          1.0%         ----         --           --       
 1968        --          --           --          1618         124          7.7%     
 1969        --          --           --          1912          23          1.2%     
 1970        --          --           --           666          34          5.1%     
 1985        35          25         71.4%         ----        ----          --       
 1986        65           5          7.7%         ----        ----          --       
 1987        22           3         13.6%         ----        ----          --       
 1988         9           0           0           3299        1015         30.8%     
 1989        33           4         12.1%          899         399         44.9%     
 1990         8           4         50.0%         ----        ----          --       




Competition of Hatchery Fish with Wild South Fork Trinity River Fish

Stempel (1988) pointed out the potential for competition between hatchery fish and wild salmon and steelhead in the Trinity River basin. He noted that hatchery and wild juvenile chinook salmon were intermixed in the main Klamath and Trinity River, as well as in the estuary. Mills (personal communication) noted that as main river temperatures increased during late summer to above 700 F, that high concentrations of wild and hatchery chinook salmon juveniles inter-mixed at the mouth of cold water tributaries. He also found hatchery-marked juveniles as much as a mile up some of the larger tributary streams. Intense competition may occur at the mouth of cold water tributaries, or in their lower reaches, between native and hatchery fish. Because sizeable quantities of sediment have filled main river pools and the estuary, it may have substantially reduced carrying capacity of both these environments (USFWS, 1991). This may also have the effect of increasing the potential for competition between hatchery and wild fish.

Dale (1990) and Gilroy et al. (1992a) found very few juvenile chinook salmon rearing in the main stem of the South Fork Trinity River or in tributaries of the lower river. It is therefore likely that South Fork chinook salmon juveniles must share rearing space in the mainstem Trinity and Klamath Rivers, and in the estuary, with more numerous hatchery fish and other wild fish throughout much of the summer. A PFMC sub-committee exploring the reason for poor escapements of fall chinook salmon from 1990-1992 (PFMC 1993a) found that hatchery operation may have been partly responsible (See Chapter VII).

The combined output of chinook salmon from Iron Gate and Trinity River hatcheries rose from an average of about 5.3 million fingerlings and yearlings during 1979 to 1984, to an average of over 12.3 million juveniles between 1986 and 1989 with the bulk of the releases being fingerlings (Figure 8-1). Brood years that are of concern with regard to the 1990-1992 low abundance of fall chinook salmon were 1986-1988. Staff of U.S. Fish and Wildlife Service found that hatchery yearlings migrate downstream rapidly while fingerlings migrate through the system at a much slower rate (PFMC, 1993a).


Figure 8-1. Total chinook salmon yearling and fingerling output from Trinity River and Iron Gate hatcheries in millions, 1978-1988. Taken from PFMC (1993a). NOT AVAILABLE IN ELECTRONIC FORMAT


Another finding was that fingerlings released at a small size migrate more slowly than if planted at a larger size. It was common during years of high production at Iron Gate Hatchery to release fall chinook fingerlings at a very small size, known as pre-smolts, because of lack of rearing space. The USFWS study covered the 1988 and 1989 brood years and a pre-smolt release from the 1988 brood showed the slowest migration rate of any group. Drought conditions prevailed from 1986-1988 and river temperatures exceeded 70°F (PFMC, 1993a). Slow migrating hatchery fingerlings and wild fish were confronted with very adverse conditions. Survival rates of fingerling release groups from both hatcheries in these years were extremely low (Figure 8-2).

Extremely low abundance of natural fall chinook spawners in 1990-1992, following dramatic increases in hatchery output, are consistent with exceeding the carrying capacity of the Klamath and Trinity River ecosystems. An alternative hypothesis is that high mortality could have been the result of poor ocean survival. If over-production of hatchery fish relative to the carrying capacity of the river and estuary did occur, it could also decrease survival of wild salmon and steelhead (USFWS, 1991).


Figure 8-2. Percent survival of fingerling release groups to Age 2 from Trinity River and Iron Gate hatcheries from 1979-88. NOT AVAILABLE IN ELECTRONIC FORMAT


When steelhead trout fail to emigrate to the ocean, and remain in the river as residents, they are known as "residuals." This pattern of behavior has been documented for steelhead from the Trinity River Hatchery during the early 1970's (Kerstetter and Keeler, 1976). More recently, Foott (1992) found that Trinity River Hatchery steelhead took an inordinate amount of time reaching the Willow Creek downstream migrant trapping station. One explanation offered was a possible "lack of migratory behavior." If steelhead remain in the stream as residuals, they may prey upon young salmon and steelhead, and increase competition. This potential problem is also discussed in Chapter IX.

California Department of Fish and Game to Limit Hatchery Output

During the summer of 1992, the chairpersons of the Klamath River Task Force, the Klamath Fisheries Management Council and the Trinity River Task Force requested a review of production at Iron Gate and Trinity River hatcheries (CDFG, 1992a). Participants were concerned that "potential competition between hatchery and naturally produced juvenile fish for limited rearing habitat in the river system may depress the survival of naturally produced salmon and steelhead," and that genetic variability of wild stocks might be decreased because of increasing reliance on hatchery fish (CDFG, 1992a).

While review team members thought that a shift should be made to only yearling releases and no fingerlings. CDFG cited lack of rearing space, lack of ability to meet mitigation, and the need for fingerling releases for harvest management as reasons to maintain the status quo. Another factor is the increased stray rates and shorter ocean residence of Trinity River Hatchery yearling releases of chinook salmon which make complete reliance on yearlings at that facility undesirable. CDFG's Natural Stocks Assessment Program will be given the charge to examine competition between fingerling releases and wild fish to determine if harmful levels of competition are taking place (CDFG, 1992a). The possibility of increased emphasis on the yearling program at Iron Gate Hatchery will also be studied.

CDFG operates Iron Gate and Trinity River hatcheries primarily to meet mitigation requirements, but in recent years has also released additional fish over mitigation requirements as an "enhancement" measure (USFWS, 1991). The review team members expressed concern that any production over mitigation requirements might have undesirable side effects (CDFG, 1992a). CDFG agreed to return to its policy of releasing only those fish required for mitigation. Egg take at Iron Gate Hatchery will be decreased from 18 million to 12 million and no fingerlings will be planted before they reach a weight of 90 to the pound. Juvenile fish from excess eggs, taken as insurance against lack of late run fish or accidental losses, will be destroyed or used in non-anadromous programs, such as at Folsom Lake.

Conclusion

While there is no large scale hatchery facility in the South Fork Trinity River basin at this time, operation of other large fish culture facilities certainly have the potential to affect native fish populations of the basin. The restoration of wild runs of salmon and steelhead in the South Fork Trinity River basin will require cooperation in all phases of management. Over-production of hatchery fish, high straying rates, disease introductions, and mixed stock fisheries problems can all confound the success of restoration even if habitat in the South Fork Trinity River basin is restored. The recent recognition by management entities of possible side effects of over production at hatcheries (CDFG, 1992a; PFMC, 1993a) is cause for optimism that such problems will be avoided in the future. Recent studies identifying disease problems (Foott, 1992) should lead to improvement of fish health at Trinity River Hatchery as well Chapter 8 continued.

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