Reproductive seasonality in harbour porpoises, Phocoena phocoena, from the Bay of Fundy

• Published in: Canadian Journal of Zoology
• Main Author: Read, Andrew J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1990
• Subjects: Phocoena phocoena
• Online Access: http://dx.doi.org/10.1139/z90-042; http://www.nrcresearchpress.com/doi/pdf/10.1139/z90-042

I examined the reproductive tracts from 244 harbour porpoises, Phocoena phocoena, captured incidentally in commercial fishing operations in the Bay of Fundy during June to September, 1985–1988. Evidence from follicular growth and the development of corpora lutea suggests that ovulation and conception occur in late June. This interpretation is supported by subtracting the duration of gestation from estimated mean birth date, and also by seasonal changes in testicular mass. Six or 7 weeks of preimplantation pregnancy follows conception and foetuses are first detectable in early August. Gestation lasts for approximately 10.6 months and parturition occurs during mid-May. Females that fail to conceive during the breeding season must wait 12 months for another opportunity to mate. Estimates of pregnancy rate must account for the seasonal nature of reproduction. The observed pattern of reproductive seasonality may reflect seasonal variation in prey quality, and perhaps availability.