Upper Columbia Spring Chinook Salmon, Steelhead, and Bull Trout Recovery
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- 3.9.1Spring Chinook
- 3.9.2Steelhead
- 3.10Interaction of Factors
3.9Factors outside the ESU and DPSThe most comprehensive and instructive index of spring Chinook and steelhead survival beyond the boundary of the ESU and the DPS (downstream from the mouth of the Yakima River) is smolt-to-adult return rate (SAR). It is a common survival index used to characterize the performance of salmonid populations throughout the Pacific Northwest. This survival index reflects all agents of mortality affecting the life cycle of salmon and steelhead from migrating smolts through returning adults. Various sources of mortality acting on populations during this portion of their life cycle include:63
Changes in ocean conditions can have large effects on SARs. For example, adult returns during the period 1980-1999, during periods of poor ocean conditions, were much lower than those during better ocean conditions (2000-2004). In the QAR assessment, results for Upper Columbia spring Chinook showed the survival improvement required to avoid the risk of extinction criteria was either 95, 47, or 2% depending on whether a historical time period back to 1980, 1970, or 1960 (a period of better ocean conditions) was used, respectively. If one were to add recent years (2000-2004, representing better ocean conditions) to the analysis, estimated required survival increases would decrease by about one third or more. Recovery will require sufficient abundance and productivity to withstand the periods of poor ocean conditions. SARs can be calculated in different ways. Juvenile salmonids implanted with either passive integrated transponder (PIT) tags or coded wire tags (CWT) can be used to estimate SAR, if returning adults can be sampled at strategic locations. Alternatively, the survival index can be calculated by estimating smolt abundance passing some site (e.g., a dam or the mouth of a tributary), then subsequently estimating adult returns to that location for a specific brood year. Often, SARs are expressed in terms of return rates to the mouth of the Columbia River. This calculation requires additional information such as estimates of in-river harvest and adult passage mortality. SARs expressed in terms of return rates to the mouth of the Columbia River are less useful when evaluating viability, because viability is based on how many fish reach the spawning grounds, not the Columbia River mouth. 3.9.1Spring ChinookHistorical estimates of SARs for naturally produced spring Chinook in the Upper Columbia Basin have been reported by Mullan et al. (1992) and Raymond (1988). Mullan et al. (1992) estimated smolt-to-adult return rates for the collective populations produced in the Wenatchee, Entiat, and Methow rivers for the years 1967 -1987. Over that period, SARs ranged from 2.0 to 10.1%. These estimates reflected corrections for adult passage mortality as well as marine and in-river harvest. Therefore, these rates overestimate the survival of adults back to the spawning grounds. Raymond (1988) estimated percent returning hatchery and naturally produced adults to Priest Rapids Dam for the years 1962 through 1984. Values for naturally produced and hatchery spring Chinook ranged from 0.3 to 4.9% and 0.1 to 4.5%, respectively, over those years. One reason Raymond’s values were generally lower than those reported by Mullan et al. (1992) may be that his estimates were not adjusted for adult passage mortality and marine harvest, whereas Mullan’s were. Also, the reference locations for calculating SARs differed, with Raymond focusing on dam counts and the other investigators referencing the spawning grounds. Therefore, Raymond’s estimates of SAR would also overestimate the survival of adults back to the spawning grounds. WDFW (unpublished data) recently calculated an eight-year (1993-2000) geometric mean SAR for naturally produced spring Chinook from the Chiwawa River, a watershed in the Wenatchee Subbasin. They calculated SARs using broodstock, tributary spawning escapement, and harvest estimates. They derived spawning escapement estimates from total ground redd counts, expanded by the male to female ratio of broodstock collected from the Chiwawa Weir. They estimated harvest rates by using a surrogate stock (spring Chinook from the Leavenworth National Fish Hatchery), which have a probability of harvest similar to naturally produced Chiwawa stock. WDFW estimated an eight-year geometric mean SAR of 0.63 (standard deviation of ±0.63). Unlike other SARs, this estimate reflects survival of adults back to the spawning grounds, which provides the most relevant assessment of viability.
Presently, harvest has been greatly reduced from historic levels, dams are addressing ways to increase passage and reservoir survival, hatcheries are addressing spatial structure and diversity issues, and habitat degradation is being reduced by implementation of recovery projects, voluntary projects, voluntary efforts of private landowners, improved land management practices on public and private lands, and changing regulations. Nevertheless, additional actions must be taken within all the Hs in order for listed stocks in the Upper Columbia Basin to recover. Actions taken within one or two Hs will not recover listed populations. For example, hatcheries can only be effective to sustain a fishery if habitat also remains in good condition. In the same way, changes only within the hydropower system will not in itself lead to recovery. Because all the Hs, and their interactions, affect the viability of listed populations in the Upper Columbia Basin, actions implemented within all Hs are needed to recover the populations. Populations within the Upper Columbia River Basin were first affected by the intensive commercial fisheries in the lower Columbia River. These fisheries began in the latter half of the 1800s and continued into the 1900s and nearly extirpated many salmon and steelhead stocks. These fisheries largely affected the abundance, productivity, and diversity of stocks in the Upper Columbia Basin. With time, the construction of dams and diversions, some without passage, blocked salmon and steelhead migrations, fragmented bull trout populations, and killed upstream and downstream migrating fish. Dams and diversions reduced the abundance and productivity of stocks, but also affected their spatial structure by blocking historic spawning and rearing areas. Early hatcheries constructed to mitigate for fish loss at dams and loss of spawning and rearing habitat were operated without a clear understanding of population genetics, where fish were transferred without consideration of their actual origin. Although hatcheries were increasing the number of natural spawners, they also decreased the diversity and productivity of populations they intended to supplement. Concurrent with these activities, human population growth within the basin was increasing and numerous land uses (agriculture, mining, timber harvest, transportation systems, and urban and rural development), in many cases encouraged and supported by governmental policy, were degrading and polluting salmon and trout spawning and rearing habitat. In addition, exotic (non-native) species were introduced by both public and private interests throughout the region that directly or indirectly affected salmon and trout. All these activities (harvest, hydropower, hatcheries, and habitat) acting in concert with natural disturbances (e.g., drought, floods, landslides, fires, debris flows, and ocean cycles) have decreased the abundance, productivity, spatial structure, and diversity of Chinook salmon, steelhead, and bull trout in the Upper Columbia Basin. One way to assess the effects of different Hs and their interactions is to integrate smolts/redd estimates (measure of tributary productivity) and SARs (measure of factors outside the subbasin) and examine the interaction of the two factors on population viability. WDFW (unpublished data) calculated smolts/redd and SARs for naturally produced spring Chinook in the Wenatchee subbasin. These data suggest that at current smolts/redd estimates for the Wenatchee subbasin, SARs need to be higher than 1% to reach a population growth rate of 1.0 (returns/spawner) (Figure 3 .29). Lower SARs (1.0%) result in population growth rates of 1.0 if tributary habitat is capable of producing more than 300 smolts/redd. However, at the high spawner abundances needed for recovery, juvenile productivity (smolts/redd) is expected to decrease because of density-dependent effects (Figure 3 .30). The available data suggest that the pristine habitat of the Chiwawa River can only produce 200-300 smolts/redds at the abundances that will be required to meet adult spawner targets for recovery (Figure 3 .30).64 During periods of poor ocean conditions, tributary productivity will need to be sufficiently high to maintain a population growth rate of 1.0. Currently, these estimates are only available for spring Chinook in the Wenatchee subbasin. Similar data are needed from other populations within the Upper Columbia Basin. Further development of this analysis and application to other populations is needed to assess the contribution of tributary actions to recovery.
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