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

This assumed relationship between suitability and spawning habitat avail-
ability must be sca]ed if it is to be used as the basis for a suitability
index curve. Two different scaling procedures were used, one based on spawning
behavior and a second based on what appeared to be representative values for
fingerling production from managed spawning marshes and subsequent survival
through adulthood.
Observations made by Fabricius and Gustafson (1958) under laboratory and
natural conditions provide a basis for estimating the area over which eggs of
a single "average" female are dispersed. These authors recorded the following
observations for pike (< 50 cm) spawning in an aquarium (bottom dimensions:
7.0 m x 0.8 m; depth: 0.4 to 0.5 m) at a temperature of 18° C:
mating frequency, within a series of mating acts: 1.5-2.6 mating acts/min
distance traveled between mating acts: 1 m
average duration of a series of mating acts: 5 min
average interval between successive series: 8 min
(At this time, the pike are at rest.)
Field observations of spawning pike indicated an average mating frequency of
1.7 acts/min, at a temperature of 12° C. This value corresponds to a net rate
of movement of 37.5 m/hr. If an average female carries 32,200 mature eggs
(Carbine 1944) and sheds an average of 60 eggs; spawning act [the upper limit
of the range reported by Svardson (1949)], 537 mating acts would be required
before all eggs were deposited. At a rate of 1.7 acts/min, spawning would
take at least 5.3 hr and cover a minimum distance of 200 m. If eggs are
scattered 0.5 m to either side of the spawning fish, a total area of 200 m2
(0.02 ha) would be involved. Assuming that spawning groups refrain from
spawning where eggs have already been deposited, the minimum ratio of spawning
habitat area to summer habitat area can be calculated as follows:
dawning habitat area = max. density x % females x minimum spawning area
summer habitat area female
_ 40 pike 1 female 0.02 ha spawning habitat
ha summer habitat x 2 pike x female
= 0.40 ha spawning habitat/ha summer habitat, for a
population with a balanced sex ratio.
The validity of this approach for estimating spawning habitat requirements
depends on the accuracy of several unproven assumptions about northern pike
$pawning behavior, the density at which crowding occurs on spawning grounds,
'and the consequences of crowding. An a]ternative procedure, based on esti-
mates of fingerling production and survival, was tried as a check.
Fingerling production data are available for a large number of managed
marshes (Fago 1977). These data show production to be highly variable (7 to
2z