The Flow/Travel Time/Survival Hypothesis

Until very recently, the cornerstone of flow theory was that lower flows slow down the salmon, and that conversely, if flow in the river is speeded up, the salmon migrate faster. Most people appear to assume that juvenile salmon are like tiny pieces of flotsam, drifting downstream with the current, but this is plainly untrue. As the Northwest Power Planning Council’s Independent Science Group recently concluded, “once migration is initiated, downstream migration is more aptly characterized as a discontinuous, spiraling movement rather than as the continual linear progress characteristic of a water particle”.58 The salmon swim actively, and often remain stationary at particular locations to feed or wait until dark when it is safer to move downstream.

Fall chinook salmon in particular do not seem to migrate downstream faster with higher flows.59 A detailed review of fall chinook migration behavior led the Northwest Power Planning Council’s Independent Science Group to conclude that “[r]iver flow and velocity seem to be little involved”.60 There are many examples where fall chinook have experienced longer travel times and higher survival.61

Results on juvenile spring/summer chinook salmon seem to show little relationship between travel time and flow. The most recent completed study was conducted by five biologists using tens of thousands of PIT-tag interrogations of individual juvenile salmon between 1992 and 1995. Their work, published in the North American Journal of Fisheries Management in 1997, covered spring/summer chinook, fall chinook, and other salmonids. Their conclusions? First, "there is no evidence that subyearling [fall] chinook respond to changes in river discharge, as observed over a broad range of flow levels".62 "Evidence for flow effects was not apparent [for spring/summer chinook]" either.63

Since the best scientific evidence suggests no measurable benefits will accrue from flow augmentation, conservation biologists are beginning to speculate that there are many stocks of salmon with different migration strategies, some of which might be advantaged by efforts to increase flows and some of which might be disadvantaged.64 No one really knows.

The latest speculation from the flow theorists is that there is some sort of “event horizon”, a magic window of time during which flow may assist fish. Unfortunately, it would be almost impossible to measure because the effects would be different for each fish—only when the fish are developmentally ready to move would there be any effect, and no one knows when the fish are ready. Measurements of large groups of fish cannot disprove the theory.65

The Northwest Power Planning Council’s Independent Science Group has gone even farther, finding it “tempting to suggest” that yearling chinook salmon catch waves from flow surges “much like a surfer catching a wave on a beach”.66 They admit, however, that “[n]o fisheries research could be found on this subject”.67

Ironically, even if one assumes that the salmon migrate precisely at the same speed as water particles, the effect of flow augmentation on the travel time of water particles is not very large. A multi-year study conducted by the Corps, BPA and the Bureau Reclamation, the System Operation Review, concluded that (again assuming that flow augmentation speeded fish) that no matter how one operated the dams and reservoirs, travel time of Snake River fish could be speeded up by only four days, and mid-Columbia fish by three days—a small portion of the overall migration time.68

The National Research Council agreed, concluding in 1995 that flow augmentation “is unable to reduce the water-particle travel times through the pools in average flow years by more than a few days—probably biologically insignificant—beyond the levels already achieved by [the Northwest Power Planning Council’s] 85-kcfs [thousand feet per second] Lower Granite Dam target”.69 Regrettably, the National Research Council did not examine the question whether additional flows beyond earlier, lower targets than the 85 kcfs made much difference. In all likelihood, flow augmentation has no measurable effect except in the very driest of years, when salmon populations have always suffered.

58 ISG, Return to the River 198.

59 A. Giorgi et al “Migratory Behavior and adult contribution of summer outmigrating subyearling chinook salmon in John Day Reservoir”, NMFS Final Report to BPA under Contract No. DE-A179-83BP39645 (1990); D. Chapman et al., “Status of Snake River chinool salmon, Report to PNUCC (1991); but cf. D. Rondorf & W. Miller, Identification of the spawning, rearing and migratory requirements of fall chinook salmon in the Columbia River Basin, BPA Annual Report, Contract No. DE-A179-91BP21708-2 (1994).

60 ISG, Return to the River 208.

61 See, e.g., D. Chapman et al., “Status of summer/fall chinook salmon in the mid-Columbia region”, Feb. 28, 1994, at 114 (D. Chapman Consultants) (“Travel times for median arrival at McNary Dam for wild and hatchery fish, respectively, were about 39 days in 1991 and 24 days in 1992. Thus survival should have been considerably greater in 1992 than in 1991. Recovery percentages show that it was not.”).

62 A. Giorgi et al., "Factors that Influence the Downstream Migration Rates of Juvenile Salmon and Steelhead through the Hydroelectric System in the Mid-Columbia River Basin", North American Journal of Fisheries Management, 17:268-82 (1997), at 278.

63 Id. at 280.

64 ISG, Return to the River 235.

65 Id. at 220.

66 Id. at 222.

67 Id. at 223.

68 SOR, Final EIS, at 4-99.

69 NRC, Upstream 210 (Prepub. ed.).

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