APPENDIX E 



FETAL MORTALITY DURING THE LAST 

 6 MONTHS OF GESTATION 



by 

 Victor B. Scheffer and Ancel M. Johnson 



This section deals with the question: "Can 

 fetal nnortality be estinnated from study of the 

 pregnancy rates of seals taken at sea?" 



According to Niggol (1960), fetal mortality 

 between 11 January and 19 July is nearly 

 equal for the sexes. He tabulated sex ratios 

 by 10-day periods for 3,081 fetuses and found 

 that "no shift in mortality rate by either sex 

 was evident" (p. 428). 



We have now studied pregnancy rates by 

 month and by age of the pregnant female, 

 between January and June, in 8 years be- 

 tween 1952 and 1964 (table E-1). The sample 



includes 5,817 females, of which 4,321 (74.3 

 percent) were pregnant. ("Pregnant" means 

 that the female was carrying a live fetus; not 

 that she was recently post partum, an extended 

 meaning used by Abegglen and Roppel (1959).) 

 The study is based on three assumptions: 

 (1) that pregnancy rates are consistent from 

 year to year, (2) that pelagic sampling is 

 randonn, and (3) that a decrease in pregnancy 

 rate with time for each age class reflects the 

 loss of fetuses through absorption or abortion. 



Findings.-- The regressionof pregnancy rate 

 on time for each of the age classes indicated 

 by the nine columns of table E-1 is highly 

 variable, and the slope is not significant. 

 We concluded that fetal mortality cannot be 

 estimated from these data because their vari- 

 ability is too great. 



Table E-1. --Eight-year summary of pregnancy rates of seals collected pelagically by the U.S.A. 



from California to Alaska'"' 



■"" Samples taken in various months between January and June in years 1952, 1955, 1958-62, and 

 1964. N = number in sample; Np = number pregnant; percent = ^ of sample pregnant. 



^ Includes two seals taken in December 1960. 



MS. #1544 



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