CLUTTER and THEILACKER: PELAGIC MYSID SHRIMP 



not investigate this in Metamysidopsis, there- 

 fore, our estimate of total catabolism could be 

 slightly low because it includes only losses of 

 heat energy. 



NET ECOLOGICAL EFFICIENCY 

 Mortality and Generation Time 



Estimates of natural mortality in the field 

 population were made during the same period 

 that the laboratory growth experiments were 

 done (Fager and Clutter, 1968). 



Brood pouch mortality rate was estimated to 

 be 0.013/ day (maximum of 0.017/day). Mor- 

 tality rates for juveniles, immatures, and adults 

 were estimated from consecutive series of field 

 collections. The field mortality rates varied 

 during the year. Survival curves (Ix = proba- 

 bility of being alive at age x) for periods of 

 at least mortality, median mortality, and great- 

 est mortality are shown in Figure 14. The mor- 

 tality rates that we used to calculate these Ix 

 curves are shown in Table 5. The greatest 

 mortality rate results in a declining population; 

 at the median mortality rate the population size 

 remains about constant; and at the least mor- 

 tality rate the population increases. 



An average female first reproduces at about 

 age 53 days. The generation length for the 

 population is somewhat longer because the fe- 

 males reproduce more than once. The gener- 

 ation length for the field population varied be- 

 tween 67 days and 71 days; the median was 68 

 days (Fager and Clutter, 1968). 



Figure 14. — Age specific survival (l^ = probability of 

 being alive at age x) of Metamysidopsis calculated from 

 estimates of greatest, median, and least mortality in the 

 field population (Table 5). 



Table 5. — Mortality rates (per day) used to calculate 

 Ir schedules for the Metamysidopsis field population. 



Relative Energy Use by Individuals 



We determined the calories of energy used 

 by average individual female and male mysids, 

 and the fractions used for growth, molting, re- 

 production, and respiration from the estimates 

 of cumulative energy use (shown in part in 

 Figures 12 and 13). The amounts and the per- 

 centage distributions required to reach selected 

 stages of development are shown in Table 6. 



Table 6. — Energy used by individual Metamysidopsis to reach selected 

 stages of development. 



* Approximate age at which l^ = 0.01 in a nearly stable population (r-».0). 



Ill 



