Environmental Engineering Reference
In-Depth Information
important thing is that we test not only within a model (for example, by
including a range of variables and then simplifying the model by removing
non-significant variables in a step-wise fashion), but also consider models
with different fundamental structures. For example, we might test a set of
models containing different relationships between CPUE and population size
(linear and non-linear), and within each model we also have variables for
spatial location, habitat type and the gear type used by the hunter.
●
Confronting these models with data, and assessing how well each of them per-
forms.This basically means carrying out regression analyses, but the emphasis
is on
hypothesis testing
. We first need hypotheses for how the world works
(the important factors that affect our dependent variable) and then we can test
our predictions using data (Box 4.5).
Box 4.5
Why are Steller's sea lions declining?
The Steller sea lion (
Eumetopias jubatus
, Figure 4.3) has declined dramatically
since the late 1970s. There have been many research programmes devoted to
Fig. 4.3
Steller sea lions on Yamski Island, Russia. The western Pacific
population of this species declined by 75% between 1976 and 1990.
Photo
©
Tracey Goldstein, the Marine Mammal Centre.
