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

Temperatures at which development is most rapid are also associated with j
reduced embryonic and larval survival. Mortality of eggs is high at incubation
temperatures greater than 16° C (Swift 1965). Larvae from eggs exposed to
temperatures greater than 18° C early in development appear unhealthy
(Lillelund 1966). Lillelund (1966) reported maximum hatching success for
incubation temperatures between 9 and 15° C and noted that the tolerance of
embryos to temperatures outside of this range increases quickly after fertili-
zation. Hokanson et a1. (1973) gave an optimal range for incubation of 6.4 to
17.7° C. Most eggs die when temperatures drop to, or remain near, 5° C, but
embryos can tolerate dies temperature fluctuations of up to 4° C provided the
temperature stays in the suitable range (Hassler 1970).
~. The habitat of the embryos becomes the initial habitat of the fry
(Franklin and Smith 1963). Dense vegetative cover provides several advantages
to larval northern pike (Frost and Kipling 1967). Yolk sac fry have small
papillae on the front of their heads with which they can attach to vegetation
and remain suspended above the sediments. This keeps the fry removed from
dangerously low levels of oxygen, and high levels of H2S, on the bottom.
Hydrogen sulfide concentrations greater than 0.004 to 0.006 ppm (96-hour
exposure) decrease growth and survival of sac fry (Adelman and Smith 1970a).
Once the yolk sac is absorbed and the fry are ready to feed, approximately
10 days after hatching in Minnesota (Franklin and Smith 1963), the invertebrate
fauna associated with the vegetation provides a suitable food base. Thick
vegetation also provides refuge from potential predators. Young northern pike
are vulnerable to predation from a variety of fishes, including other northern
pike (Hunt and Carbine 1951; Al t 1968) .
.Immediately after hatching, fry are very active (Frost and Kipling 1967;
Howard and Thomas 1970). Within the first day, however, most attach to vegeta-
tion, where they remain for several days while the yolk sac is being absorbed
(Frost and Kipling 1967). In hatchery jars, with no vegetation, fry became
quiescent after the initial burst of activity and sank to the bottom (Howard
and Thomas 1970).
Fry average 7 to 9 mm in length at hatching (Frost and Kipling 1967;
Forney 1968). They begin to emigrate from spawning sloughs when 15 to 20 mm
long (Carbine 1942; Franklin and Smith 1963; Forney 1968). The time required
to grow to this size is variable. Emigration began 10 to 13 days after hatch-
ing in New York (Forney 1968) and 16 to 24 days after hatching in Minnesota
(Franklin and Smith 1963).
Emigration may be concentrated or prolonged. Forney (1968) reported that
82, 99, and 37% of the fry left a controlled marsh within 20 days after emigra-
tion started, in 3 successive. years. Data of Franklin and Smith (1963) indi-
cate similar variability in the length of time for emigration. Most young-of-
the-year pike emigrated from a Saskatchewan marsh within a 1-week period,
6 weeks after the completion of spawning (Koshinsky 1979). The reasons for
this variability are unclear. Emigration is inhibited by low light intensity;
prolonged periods of overcast weather might extend the emigration period
(Franklin and Smith 1963; Forney 1968). Other factors, such as water level
and food supply, may also determine when the fry depart (Royer 1971).
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