WWRC 97-05pp
Development of an Individual-Based Model to Assess the Instream Flow
Requirements of Stream Salmonids
Abstract
Individual-based modeling is a recent technique that
is fast becoming an established discipline separate
from more classical population models. Individual-based
models (IBM's) incorporate 3 distinguishing
characteristics. First, they reflect real life cycle
complexity including mortality, fecundity, and
spawning migrations that depend upon the age or size
of individuals. Second, resources are explicitly
modeled. Physical habitat availability, food
abundance, temperature, and water quality are
modeled using actual measurements at high,
intermediate, and low flows. Third, and most
important, is accounting for differences among
individuals within a population. Rather than assume
that mortality, growth, reproduction, movement,
spatial distribution, and the effects of interference
competition is the same for an average trout, IBM's
model differences between individuals (e.g. size)
providing a realistic prediction of the stream flows
required to maintain salmonid populations. The instream
flow incremental methodology (IFIM), is a
straightforward technique of estimating potential fish
abundance from field observations. Although IFIM
is widely used, it is increasingly viewed as an
inadequate oversimplification. A new approach
(IBM's) will incorporate increased biological realism
by considering how environmental factors influence
fish energetics and growth.
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