7143

• UCREFRP Catalog Number: 7143
• Author: Inskip, P. D.
• Title: Habitat Suitability Index Models
• USFW Year: 1982.
• USFW - Doc Type: Northern Pike.
• Copyright Material: NO

i ,
The user must decide what part of a body of water is to qualify as "summer
j habitat". To this point, it .has been implied that the entire area would be
( used. This is not necessarily so. In the case of a large, stratified lake,
for example, only that area shallower than the depth of the bottom of the
thermocline might be included as as "available habitat". In a river, areas
where the velocity exceeds some threshold value might be excluded. If such a
preliminary screening step is taken, the decision about limiting the area used
j as available habitat applies for all model variables. The area included as
summer habitat for V1 should also be used as the total area (that is, the
divisor) for V3 and V8i the model output (HSI) applies only to this area.
Interpreting Model Outputs
The model described above can generate HSI's to any. desired number of
decimal places, but it would be misleading to present results to a level of
precision greater than ±0.1. The model cannot be expected to discriminate
among different habitats with high resolution at this stage of development.
It depends on a series of untested assumptions and known oversimplifications.
Interactions among model variables and species interactions both play a role
in determining habitat quality for northern pike, but these influences are
ignored. I recommend interpreting HSI outputs as indicators (or predictors)
of excellent (0.8-1.0}, good (0.5-0.7), fair (0.2-0.4), or poor (0.0-0.1)
habitat.
Habitats with high HSI's would, on average, be expected to have higher
standing crops of northern pike than habitats with low HSI's, but a close
correlation between population size and HSI is unlikely. Factors not included
in this habitat model can also limit northern pike populations.
ADDITIONAL HABITRT MODELS
Aggus and Bivin (in press) used angler harvest as the criterion of habitat
suitability and calculated a regression equation relating harvest to reservoir
habitat variables for 37 impoundments in the conterminous United States:
Loglo harvest = 3.7882 - 0.0177 (growing season) - 0.8447 (Log,o outlet depth)
RZ = 0.67
Units are kg/ha (harvest), days (growing season), and feet below a specified
elevation (outlet depth). These authors discuss procedures for converting
measured or predicted harvest values to HSI's.
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