FISHERY BULLETIN: VOL. 69, NO. 1 



body length and number of young, calculated 

 by the method of Bartlett ( 1949) , was: number 

 of young = 4.8 (body length, mm) -10.4. This 

 is represented by the lower, unbroken straight 

 line in Figure 10. 



This relationship gives estimates of fecundity 

 that are about 1.5 to 2 young per female higher 

 than the relationship calculated from preserved 

 animals. But this is not quite a maximum esti- 

 mate of fecundity because it does not include 

 the reduction from mortality that occurs during 

 incubation. 



As already demonstrated, we can assume a 

 brood pouch mortality rate of 0.013 per day. 

 The relative survival of young in the brood 

 pouch during the 10 days between the extrusion 

 of eggs and the release of larvae was therefore 

 estimated to be 0.87. The number of young 

 released per female was adjusted to the equiv- 

 alent number of eggs extruded per female by 

 multiplying the number of young by 1/0.87 = 

 1.15. The relationship (Fig. 10) then becomes: 

 number of eggs = 5.5 (body length, mm) -11.9, 

 which is shown in Figure 10, as the upper, 

 dashed line. 



This relationship gives estimates of fecundity 

 that are about four eggs per female higher than 

 the minimum estimates calculated from pre- 

 served animals. We consider this to be the max- 

 imum estimate of fecundity. It is the same as 

 that used by Fager and Clutter (1968). 



COPULATION AND FERTILITY 



The fecundity estimates given above apply 

 only to the females that engage in copulation 

 and are fertilized. Mature females that are not 

 fertilized apparently extrude some eggs, but only 

 about one-half the usual number. 



Many observations of copulation were made 

 in the laboratory (Clutter, 1969). It occurs in 

 artificial light as well as in the dark, but only at 

 night, between about 2000 and 2400 hr. It oc- 

 cui-s within only 2 to 3 min after the mature 

 females molt, and apparently only when the fe- 

 male exudes a pheromone to attract adult males 

 of the same species. 



Ten females were captured immediately after 



they were observed in copulo and kept in sep- 

 arate chambers for 10 days. Impregnation had 

 been successful and the usual number of eggs 

 were extruded in every instance. Some adult 

 females that molt do not stimulate males to at- 

 tend them. Ten adult females were captured 

 after they had been observed to be unattended 

 by males during molting and recovery. They 

 later extruded only about one-half of the normal 

 number of eggs, which eventually disappeared 

 from the brood pouch, presumably because they 

 were infertile. Therefore, the unfertilized fe- 

 males expended only about half the amount of 

 energy in eggs that the fertilized females ex- 

 pended. 



Since the mature females are subject to fertil- 

 ization for only a few minutes following molting, 

 and they apparently do not always attract males 

 during the time, copulation does not always oc- 

 cur. Therefore, not all produce young every 

 10 days. In a large number of field collections 

 during all seasons, the observed fraction of ma- 

 ture females carrying eggs or larvae in their 

 brood pouches varied from 18 ^r to 78 Sr I the 

 mean was 51 '}r . We are not certain of the 

 source of this variability; there is some evi- 

 dence that it could be related to population den- 

 sity (Clutter, 1969) . We have assumed an aver- 

 age value of 50 fr for the purpose of calculating 

 the amount of energy used in reproduction. 



On the average, mature females extrude the 

 usual number of eggs about one-half of the time, 

 and they otherwise extrude only one-half of the 

 usual number of eggs. Therefore, the effective 

 average fecundity, in terms of energy used in 

 reproduction (but not in terms of the number 

 of viable young produced), is 0.5 + (0.5) (0.5) 

 = 75 % of the fecundity estimated from counts 

 of young produced/female. For the purpose of 

 calculating the amount of energy used in repro- 

 duction the fecundity equations are: 



minimum — number of eggs = 4.1 (body length, 



mm) - 12.0 



maximum — number of eggs = 4.1 (body length, 



mm) -8.9 



The second of these relationships is used in the 

 ensuing energy budget calculations. 



102 



