Lower Granite Transport Study Wild Yearling Chinook Travel Time

The Data

The fish were tagged and then released at Lower Granite just below the pittag observation site. The fish from these release groups were observed at Little Goose, McNary and John Day Dams. 13 cohorts (52 releases) were analyzed over the 2 year period 1995-1996. The migration period was mid April through early May.

Models

We applied four 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.

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 each of the four observation sites for all four models.

corresponds to observations at Little Goose Dam.

corresponds to observations at Lower Monumental Dam.

corresponds to observations at McNary Dam.

corresponds to observations at John Day Dam.

Tabular Results

Table 1 . Travel-time parameters for wild chinook from LGRRRR releases(1995-1996)

model	parameter estimates (std. error)							resid. ss	mult. R2
	MIN	MAX	FLOW		TINFL	2	2
1	12.7315 (1.3692)	-	-	-	-	-	82.8733 (6.4191)	529.223	-
2	0.0826 (0.2453)	-	1.4266 (.1158)	-	-	-	24.4373 (1.5563)	242.880	.5411
3	0.9221 (2.7306)	-	0.7813 (0.2991)	0.0742 (0.0600)	98.7280 (15.579))	-	28.2122 (1.6763)	182.610	.6549
4	.26837 (.3326)	12.5520 (3.0274)	0.3705 (.0950)	.0698 (.0810)	90.0053 (1.1234	.6100 (1.0496)	57.4549 (2.4992	53.126	.8996

Discussion

For the fish analyzed here, the most complex model is supported by the data. While the flow-dependent seasonal effect (model3) explains some of the variation, model4, with the experience effect, confers a considerable improvement in model fit over the simpler models. This is achieved by speeding up the fish as they move downstream - a difference in migration rate of more than 12 km per day in the non-flow related terms. (_MIN and _MAX).