The relationship between body condition and the timing of implantation in pregnant Grey seals (Halichoerus grypus)

Adult female Grey seals were sampled from the Farne Islands, Northumbria at monthly intervals during 1980 and 1981. The mean date of implantation was 7 April and most females implanted between 11 March and 5 May. Sculp, core and total body weights declined most at the time of lactation in November and were lowest during February. These weights increased most rapidly during March and April; at the same time as implantation occurred. The pectoral blubber depth followed a similar pattern. Females in which the spring increase in body condition occurred earliest also had the earliest implantation. The study demonstrates a correlation between body condition and the time of implantation.