II.10.2 - Transport Survival Calibration

• spring chinook transport survival = 89%
• fall chinook transport survival = 83%
• steelhead transport survival = 91%

That model calibration produces reasonably similar results across species. Data from other years could also be used to produce estimates of transport survival, but in most years estimates are based on very small sample sizes and are of dubious value.

At first glance it may seem impossible to have transport survivals greater than 100%, but bear in mind this fraction represents the total difference in survival between transported and non-transported fish, a difference which may include differential post-transport survival. For example, if transport survival is 100% and in-river survival is 50%, but in-river fish also experience twice the mortality of transported fish in their first year at sea, the TBR will be 4:1, and if we only examine the in-river survival we would estimate transport survival of 200% (4 x 50%). High TBR values, therefore, probably reflect not only high transport survivals, but also improved early ocean survival as well.

Transportation schedule

The schedule of transporting fish from each transport dam depends on the flow, number of each species passing the dam, and the efficiency of separating fish for return back into the river. The schedules for transportation, compiled from FTOT annual reports, for the historical years are given in Table 56.

Transportation Separation

The above table indicates conditions under which fish are separated and returned to the river. While it is assumed that transportation always benefits steelhead juveniles, many people believe that smaller migrants (chinook, coho, sockeye) benefit from transportation when flows are low, but are better off in the river when flows are higher and conditions are presumably better.

If a dam has a Separation Trigger, when flows exceed that value, smaller fish are separated from the larger steelhead smolts and are returned to the river. This separation continues according to the Criterion given in the table. For example, if the criterion is "full transport at 80% yearlings", this means that fish are separated under high flow conditions until it is estimated that 80% of yearlings have already passed the dam. After that point, all collected fish are transported regardless of flow condition.

There is great variability in separator efficiency: the idea is to retain steelhead for transport and return other fish to the river. As a rule of thumb, CRiSP uses the "80/20" criterion (Table 57), which means that 80% of steelhead are successfully retained, and 80% of smaller fish are successfully returned to the river, but 20% of steelhead also escape to the river, and 20% of smaller fish are retained for transport.

Flow-based transport model calibration

The most recent versions of CRiSP include the capacity to vary transport survival as a function of water particle travel time (WPTT). This was put in place at the request of members of the FLUSH modeling team to provide similar functionality found in the spring FLUSH model used by the State and Tribal Agencies (described in ANCOOR 1994). In their "transport model 3" they hypothesize that transportation mortality is related to flow such that:

• For flows equal to or greater than those in 1986, the TBR from Little Goose tailrace is 1.01 to 1,
• For flows equal to or less than those in 1977, the TBR from Little Goose tailrace is 3 to 1, and
• For flows between these conditions, transport survival is determined by linear interpolation between the two end points.

Determination of mortality levels for these conditions is exactly the same as described above and the reach defined for determining WPTT is Lower Granite Pool to below Bonneville Dam. The resulting parameters are given below in Table 58.