5. Extensions of the travel time model
5.1. Introduction

In this chapter I expand the model to make it more realistic. In section 5.2 mortality is no longer considered to be equal within the cohorts but is dependent upon the amount of time spent in the river. In section 5.3 I incorporate migrational delay into the model. In the last section of this chapter, section 5.e, I explore factors related to migration rate and attempt to use these factors to predict model parameters. In addition, in chapter 6 I allow for population heterogeneity and attempt to determine how various factors affect migratory behavior.

I use some of the travel time data from the previous chapter to test for the appropriateness of the added features. Since I do not want to use the same data in several treatments (to avoid multiple comparisons), I have divided the Snake River trap chinook and steelhead data into treatment groups. To randomly place the cohorts into 5 treatment groups, I used the following procedure. I started by dividing the cohorts in a year into blocks of 5 or 6 in a chronological sequence; the blocks with 6 members were randomly assigned so that all the extra cohorts didn't come at the end of the season. From each of these blocks, 5 cohorts were randomly assigned to each of the treatment groups. This ensured that cohorts were randomly assigned to the treatment groups and that the yearly chronological sequence of cohorts was represented in each treatment group. For the mid- Columbia fall chinook, I assigned cohorts into two treatment groups because of the smaller number of cohorts.