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

72,000 fingerlings/ha), both among marshes and among years. The median
(2,717 fingerlings/ha) was used in the following calculations.
Survival of. fingerlings through adulthood is also highly variable.
Estimated survival of fingerling northern pike through their first summer was
6%, 22%, and 63% in three successive years (mean = 28°0) in a Michigan lake
(Beyerle and Williams 1972). Assuming 65°o annual mortality thereafter [which
seems reasonable for lakes in the conterminous United States, on the basis of
data compiled by Carlander (1970)], 9.8% of the fingerlings would survive to
age 1+, 3.4°o to age 2+, 1.2% to age 3+, and 0.4% to age 4+. Ages 2 through 4
usually account for most of the breeding stock for populations in the conter-
minous U.S. Assuming a stable age structure and that most mortality occurs
between autumn and spring, there would be a total of 0.034 + 0.012 + 0.004 =
0.050 adult fish in the population per fingerling produced in spawning habitat.
The minimum ratio of spawning to summer habitat can be calculated in the
following way:
spawning habitat area _ max. density of adults x 1
summer habitat area spawning habitat productivity
x fingerlings per adult
= 40 adults/ha summer habitat
x 1 ha spawning habitat/2,717 fingerlings
~~ x 1 fingerling/0.05 adults
= 0.29 ha spawning habitat/ha summer habitat

If it is assumed that most mortality .occurs between spring and autumn,
then the 1+ fish should be included in the calculation. There would be
0.098 + 0.034 + 0.012 + 0.004 = 0.148 adult fish in the population/fingerling
produced, and the minimum ratio of spawning to summer habitat would be 0.10.
Both values are similar to that obtained using the method based on spawn-
ing behavior (0.40). An intermediate value, 0.25, is used to develop a suit-
ability index curve. It is assumed that optimal northern pike habitat must
have at least 0.25 ha of spawning habitat for each ha of summer habitat.
Habitats in which the relative availability of spawning habitat is considerably
less than this can still have high suitability index ratings for V1 because of
the asymptotic shape of the suitability index curves.
Type of vegetation in spawning areas is also important. The probability
that fertilized eggs will settle on vegetation as they sink depends on vegeta-
tion density. Young northern pike also depend on vegetation for protective
cover and on the associated invertebrate fauna for food. Lush vegetative
cover is ideal; sparse cover is poor. The suitability index for V1 can be
maximal (1.0) only if proper vegetation is present.
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