Mammalia (1997)

DOI: 10.1515/mamm.1997.61.1.65


We collected testes from 62 male harbor porpoise (Phocoena phocoena) incidentally caught in gillnets of commercial fisheries in the Gulf of St-Lawrence, in June-July- August. In adults (≥4 years), both testes weight and seminiferous tubules diameter declined from June to August, suggesting that breeding is seasonal. For the 7 adults captured at the presumed peak of the rut, in early July, combined testes weight (2 115 ± 296 g) represented 4.1 ± 1.8 % of those males’ body weight. Since the harbor porpoise has no secondary sexual characters, is almost monomorphic, and has such large testes, sperm competition probably is the most salient feature of its reproductive strategy.