REPRODUCTION AND REPRODUCTIVE SEASONALITY IN DANISH HARBOR PORPOISES,PHOCOENA-PHOCOENA

The reproduction and reproductive seasonality of 365 Danish harbour po rpoises (Phocoena phocoena (L.)), incidentally caught in various gill nets or stranded, was studied. The animals were collected from all Dan ish waters throughout the year from 1985 to 1991. Ovulations were only found in the left ovary whilst the right was permanently submature. L arge vesicular follicles are found in July, with the largest size (14 mm) in the end of July. Developing corpora lutea with mean diameters o f 13.5 mm were found in early August. These findings suggest that ovul ation and conception occur in late July and early August. Testicular m ass and spermatogenic activity peak in July. Foetuses are first detect able in early September. Gestation lasts for approximately 10.5 months and parturition occurs in the middle of June and early July. Age at s exual maturity (ASM) was estimated by the sum of fraction immature met hod for both females and males. The average age at attainment of sexua l maturity for females was 3.64 yrs and for males 2.93 yrs. Pregnancy rate was estimated using two methods. By considering the entire sample and using the presence of a corpus luteum as indicative of pregnancy, and by considering the sample collected after implantation and using the foetus as the criterion of pregnancy. Estimated pregnancy rate usi ng these two methods were 0.61 and 0.73, respectively.