Rock Island Spring Chinook Travel Time

The Data

The fish were tagged and released at Rock Island and observed at McNary Dam. 86 cohorts were analyzed over the 8 year period 1989-1996. The migration period was mid April through late May.

Models

We applied three nested models of increasing complexity to the data:

• Model 1 uses a constant migration rate.
• Model 2 incorporates a linear flow relationship.
• Model 3 adds a seasonal/flow interaction - fish use more of the flow for migration as the season progresses.
• Model 4 adds an experience factor - flow independent migration speed increases the longer the fish have been in the river. However, since these fish only passed through one reach, (RIS to MCN), this model is inappropriate.

Model details are provided by Zabel, et al. (1996).

Graphical Results

The plots below show observed average travel times versus modeled average travel times to the McNary observation site for the three models.

corresponds to observations at McNary Dam.

Tabular Results

Table 1 . Travel-time parameters for spring chinook from RIS releases (1989-1996). *(Vvar is fixed at 200 to overcome the problems of small samples, long reach, and single observation site.)

model	parameter estimates (std. error)							resid. ss	mult. R2
	MIN	MAX	FLOW		TINFL	2	2*
1	9.7148 (2.3075)	-	-	-	-	-	200*	2810.587	-
2	4.303 (4.0232)	-	0.4906 (0.4032)	-	-	-	200*	2705.058	.0375
3	7.7454 (5.1844)	-	0.0961 (0.3302)	0.0481 (1.7307)	80.8280 (1077.8)	-	200*	2734.495	.0271

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Discussion

The small cohort size creates some problems in the analysis of the data. As the fish travel downriver, their arrival times at McNary are very spread out. As a result. The VVar term is large and it distorts the predicted average travel time. To prevent this affect on predicted travel times, we have fixed Vvar at 200. However, the more complex models are not successful at predicting more of the variation in travel times than model 1. We are currently looking at the model and datasets to determine why this is the case.

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