Reproduction in the Female Sea Otter

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Abstract
The morphology, histology, and field reports of 136 sexually mature female sea otters yielded information on the reproductive cycle. Free blastocytes were removed from 9 tracts and judged to be present in 44 others. Two blastocytes from Jan. and July were near implantation and 28 others were implanted pregnancies. It is concluded that sea otters breed throughout the year, having no distinct breeding season. Pups are born in every month of the year and litter size is normally one. The total period of gestation is not known but it includes a long period of delayed implantation. The tract is that of a typical carnivore. Interstitial glandular cells from the theca interna of degenerating (atretic) follicles are abundant during estrus. The corpora lutea of the free blastocyte stage are smaller and apparently less active than those of implanted pregnancy. Corpora lutea of implanted pregnancies show secondary cavities of various sizes. These vary markedly in different animals. The secondary cavities are not remnants of an antrum and are fluid filled. Histological changes in the uterus correlate with the ovarian cycle. The histological changes described for both ovary and uterus would be useful in identifying stages in the reproductive cycle for studies of productivity of sea otters.

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