Childress and Price estimated time per instar for Gnathophausia in three ways:(^1) In the laboratory, newly molted individuals stay soft for 12 days. In a
large field collection, 11 of 149 individuals were soft, so the intermolt
period approximately equals (12 × 149/11) + 6 = 168 days. [A problem for
you: why did Childress and Price add 6 days?]
2 Seventy individuals in a sample molted before dying, and a cumulative
distribution indicated that 63 days were required for half to molt. So, the
intermolt period approximately equals (2 × 63) + 12 = 138 days (+12
because soft individuals were removed from the sample at capture).
3 Duration of intermolt for individuals that molted twice in the laboratory
was a function of size and temperature, with a range from 120 days at 20
mm carapace length and 7.5°C to 200 days at 40 mm and 5.5°C.
(^) Total life span based on all this information is of the order of 6.4 to 8 years. Typical
benthic shrimp of comparable size on temperate continental shelves live only 2 years.
(^) Mauchline (1988) has studied size–frequency distributions of various mid-water
shrimps collected over a 5-year period from the Rockall Trough in the northeast
Atlantic. He grouped collections by month of the year, and showed (Fig. 12.14) that
the implied growth pattern is intermittent. Mid-water shrimp, at least at this high-
temperate site, grow faster in late summer and fall (some cases) or in spring (other
cases) than they do in winter.
Fig. 12.14 Growth curves for (a) Boreomysis microps, a mysid, (b) female and (c)