FISHERY BULLETIN: VOL. 69. NO. 1 



The indicated age at which the probability of 

 being alive reaches 0.01 applies to the stable 

 population (median death rates). 



The males require less energy to reach ma- 

 turity than females, but relatively more of this 

 energy goes into molting and respiration and 

 less is incorporated. Two-thirds of the energy 

 used in reproduction remains in the population; 

 one-third is lost as unfertilized eggs. 



The estimates of relative use of assimilated 

 food by Metamysidopsis females during a life 

 span are compared with estimates for a copepod 

 and a euphausid (Corner, Cowey, and Marshall, 

 1967) in Table 7. The mysids apparently use 

 a fraction of assimiliated energy for growth that 

 is intermediate between the other two species, 

 a lower fraction for metabolism, and a higher 

 fraction for producing eggs. 



Table 7. — Use of assimilated food by Metamysidopsis 

 females (life span 103 days) compared with the copepod 

 Calanus finmarchicus^ (life span 10 weeks) and the 

 euphausid Euphausia pacifica' (life span 20 months). 



* From Corner, Cowey, and Morshcll (1967). 

 - From Losker (1966), revised in Corner et al. 



Relative Energy Use by the Population 



The values of relative energy use given in 

 Tables 6 and 7 apply to individuals, or to pop- 

 ulations wherein all members live a full life 

 span. They do not apply to the natural popu- 

 lation, because some die during all stages of 

 growth. 



We have estimated the relative amounts of 

 energy that would be lost by populations in res- 

 piration, production of infertile eggs, molting, 

 and mortality at the observed minimum, median 

 and maximum mortality rates shown in Table 5. 

 This was done by calculating the fraction of 

 the population that died during each intermolt 

 period (A/^), and multiplying this times: (1) 

 the mean body energy content for the midpoint 

 of that period, (2) the quantity of cumulative 

 energj' lost in infertile eggs \x\) to the midpoint 



of that period, and (4) the quantity of cumula- 

 tive energj' used in respiration up to the mid- 

 point of that period. The product values for 

 each of these loss categories (mortality, molting, 

 etc.) were then summed over all ages (to Zx ^ 

 0.001). The relative energy use values were 

 calculated as fractions of the overall sum for 

 all categories combined. We excluded fertilized 

 eggs because this reproduction energy is retained 

 in the population. 



The age specific distribution of energy use 

 (representing energy loss, because fertilized 

 eggs are excluded) by a population (females 

 and males) of Metamysidopsis at the median 

 mortality rate is illustrated in Figure 15. All 

 the curves are plotted with reference to the base 

 line, zero. The rate of energy loss is low among 

 eggs and larvae, and much higher among the 

 juveniles that have just emerged from the 

 brood pouch and begun to swim. In the larger 

 animals, the respiration per unit weight is low- 

 er, but the respiration per animal is higher, so 

 that the respiration rate per day is highest 

 among the animals that are about 25 days old. 

 The loss of energy per day from all causes is 

 highest among the animals that are about 30 

 days old. After this the curve declines because 

 the effect of larger size becomes less than the 

 effect of smaller numbers. 



The estimated relative amounts of energy 

 lost by the population of females, males, and 

 both sexes combined, for each loss category and 



Ao* Id 



Figure 15. — Age specific distribution of energy loss by 

 a Metamysidopsis population at the median mortality 

 rate. Production of fertilized eggs is excluded. 



112 



