Welsh Journals

TABLE II Selected live recoveries of immature seals near where ringed in West Wales Ring Place of Date of Place of Date of Age at No. Birth Birth Recovery Recovery Recovery 1074 Ramsey 22/9/55 Alive Ramsey (where ringed) 26/9/56 12 months 1138 Ramsey 26/10/56 Skomer 8/9/57 10 months 1197 Ramsey 21/9/56 N. Pembs. 16/2/57 5 months 1220 N. Pembs. 7/10/56 N. Pembs. (where ringed) 16/3/57 5 months 1225 Skomer 8/10/56 N. Pembs. 10/2/57 4 months 1233 N. Pembs. 13/10/56 "Grassholm 16/6/57 8 months 1242 Ramsey 5/10/56 N. Pembs. 10/2/57 4 months These recoveries show that after being marked at their birth- place in West Wales in September and October, some young seals are present in the region in February, March, June and September while others of the same age are absent in November and December (Table I) and March (203 born Ramsey 18/9/54 recovered in fishing net Ballycotton, Co. Cork, 14/3/55). OUT OF SEASON BIRTHS In every year a certain number are born out of the normal autumn calving season. We have records of Atlantic seals born in every month except January. This tendency is reviewed by H. R. Hewer (Proc. Zool. Soc. London 128 593-595). I mentioned these out of season births in Seals and the Curragh and surmised they might be associated partly with delayed implantation, which is now proved for this as for other species of seal recently studied histologically. Both sexes, in our observation, are sexually active for a longer period than has hitherto been recorded. Harem bulls become spent in October and November, but some adult bulls are active again in December and onwards to May, although with few calves about there is no territorial struggle between males, and in fact they are often friendly--even with some homosexual behaviour. But mating takes place freely in the first four months of the year, at the favourite assembly grounds, both on the beach and in the sea hard by. The cow is often more importunate at this season than the bull. These spring matings could result in the birth of spring calves after the normal term of 11 t months, including the 41 months of delay in implantation of the fertilised egg (known in its free state as the blastocyst) or they could be the result of autumn matings followed by no delay in the development of the ovum (i.e. followed by a 7 months undelayed pregnancy). Virgin cows mated in the autumn, with no calf to feed at that season, would be physically robust and able to support immediately a growing embryo whereas older nursing cows, which mate normally a fortnight after parturition in the autumn, and lose about 6 lbs. a day over the 12-16 days of lactation, need a period of several months' rest over the winter before supporting a normal pregnancy. The convenience of delayed implantation for physically exhausted mothers is obvious.