The sexual development and reproductive seasonality in testicular activity in male harbour
porpoises (Phocoena phocoena) from the North-East Atlantic were investigated during this study.
The study area comprised three management/assessment units: the Greater North Sea, Celtic and
Irish Sea, and western Scotland and Ireland. Harbour porpoises have relatively large testes
compared to body size, and it requires an enormous amount of energy to maintain these testes.
Sexual maturity was determined based on histological assessment of testis tissue. Significant
differences between sexually immature and sexually mature animals were found for most
parameters assessed. Sexually immature porpoises did not display any seasonal differences in
parameters. During the summer, a period of high activity was observed for sexually mature
animals, characterised by an increase in combined testes weight and mean seminiferous tubule
diameter, a decrease in the proportion of interstitial tissue, and higher production of germinal
cells. Body length, ASM and LSM differed between management/assessment units. In contrast to
the North-west Atlantic population, harbour porpoises from the North-east Atlantic display signs
of activity (i.e. spermatozoa production) all year round.
Managing Thesis and Internship Exchanges
