Pseudopregnancy in harp seals (Phoca groenlandica).

Concentrations of circulating progesterone were monitored in a captive breeding group of harp seals. Five females were monitored for 2 years, over which time they either became pregnant (four instances) or displayed an overt pseudopregnancy (five instances). Only one female exhibited consecutive pseudopregnancies. In all pseudopregnancies, serum progesterone values were high and remained high until July, which is close to the time when implantation normally occurs. After this time progesterone concentrations remained high, gradually declining to baseline values over the following four months. In the three females that were pregnant one year and pseudopregnant in the other year, the average progesterone concentration during pseudopregnancy was lower than that exhibited during pregnancy (P < 0.05). All females (except one) increased their mass, girth and condition index over the normal gestation period whether they were pregnant or pseudopregnant. The potential consequences of such a high rate of pseudopregnancy on the use of ovarian scars for estimating reproductive rates and population size are discussed.