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

typically had TP levels <_ 0.10 ppm (Moyle 1956). Moyle noted that temperature
may also explain patterns of fish distribution in Minnesota and cautioned
against overemphasis on edaphic factors alone.
Ionic concentrations appear to be directly limiting to northern pike only
in coastal and arid environments. Ryder et al. (1974) noted that TDS levels
are rarely so low that ions essential for fish metabolism and growth are
limiting; these authors speculated that such a limit is near or below 3 ppm,
and very few natural waters are that dilute. Waters with high ionic concentra-
tions apparently do limit the distribution of northern pike, but the critical
concentration is unknown. Northern pike apparently do not utilize brackish
habitats in North America, but there are reports of pike occurring in the
Baltic Sea at salinities of 10 ppt and reproducing at salinities of 7 ppt
(Svardson, personal communication cited in Toner and Lawler 1969), and pike
have been commercially harvested from brackish waters in Finland (Lind 1977).
Rawson and Moore (1944) found northern pike in saline Saskatchewan lakes only
where TDS levels were less than about 3,500 ppm (roughly equivalent to a
salinity of 3.5 ppt). Northern pike are said to have "some tolerance" to TDS
levels of 2,200 to 3,800 ppm in alkaline Nebraska lakes (Schoenecker 1970),
but pike did not spawn in a Nebraska lake with a TDS level of 1,024 ppm
(McCarraher 1962). High concentrations of particular ions may be harmful at
salinities which do not cause general .osmoregulatory stress.' For example,
mortality of northern pike embryos and fry is extensive when total alkalinity
exceeds 950 mg/1 (McCarraher 1971). Until effects of individual ions are
clarified, it seems reasonable to assume an upper TDS limit of 3,500 ppm.
Self-sustaining populations of northern pike can persist at pH's as low
as 5.0 (Harvey 1980). Lower pH's are damaging to fry. Cumulative mortality
of fry held at a pH of 4.2 (range 4.0 to 4.3) was 96.5%, compared to 25.6%
mortality at a pH of 5.2 (4.7 to 6.0), and 17% mortality at a pN of 6.8 (6.5
to 7.2) (Johansson and Kihlstrom 1975). Towards the opposite extreme, northern
pike occur in lakes with a pH of 8.9 (Rawson and Moore 1944; Priegel and Krohn
1975). Fingerling and large r.northern pike can survive pH's in the 9.0 to 9.5
range, but it is not clear whether successful reproduction can occur at the
upper limit of this range (McCarraher 1962).
Northern pike grow through a broad size range; tolerances, requirements,
and preferences change as they grow. Although most developmental changes are
gradual, it is useful to describe habitat requirements for northern pike in
terms of four stages: spawning/embryo; fry; juvenile; and adult. These life
stages, for purposes of this discussion, are defined as follows:
1. Spawning/embryo. Includes spawning requirements and requirements of
the developing embryo.
2. Fry. Immediately after hatching to size .at which they assume adult
proportions; i.e., approximately 6.5 cm, according to Franklin and
Smith (1960).
3. Juvenile. From 6.5 cm to onset of sexual maturity (beginning of
gonadal maturation).
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