Harbour Porpoise

1School of Biological Sciences (Zoology), University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ, UK, 2Facultade de Ciencias do Mar, Campus Universitario Lagoas-Marcosende, 36200 Vigo, Spain, 3Instituto Espan˜ol de Oceanografıa, Centro ...

In this study,we analyse some aspects of the macro- and microscopical appearance of gonads of harbour porpoises (Phocoena phocoena) from Icelandic coastal waters. Sampling of animalsbycaught in gillnets took place in the years 1991 to 1997 and covered the months from Septemberto June. The differences in diameter of seminiferous tubules between samples from the peripher-al and central parts of the testis indicate that histological changes associated with maturity beginin the core of the testis. The average tubule diameter was 49,78 and 118 µm in immature,puber-tal and mature animals respectively. The tubule size increased from 55 to 95 µm,coinciding withcombined testis weight of 75 to 150 g,indicating the onset of puberty within this range of tubulesize and testis weight. The estimated average diameter of tubules when an animal reaches matu-rity is 82.2 µm or 86.15 µm depending on the method used. The diameter of seminiferous tubulesof mature and pubertal animals varies seasonally with a steady increase in the spring. However,lack of samples after mid-June makes estimation of the exact timing of mating impossible. Infemales,the follicle size of mature and immature animals of age 2 years and older shows seasonalvariation,increasing in late winter or spring. The corpus luteum
increases in size during the latepregnancy. The average size of the corpus albicans
as a function of the total number of corpora albicantiafor each animal,diminishes following the logarithmic equation  y = 4.49 – 0.447 · lnx ( y = corpus size, x = number of corpora albicantia) but apparently they never disappear completely from the ovary. Ovarian activity was almost confined to the left ovary. Our results indi-cate parturition and copulation in the summer months from late June to August.

Reports of violent interactions between bottlenose dolphins (Tursiops truncatus) and harbour porpoises (Phocoena phocoena) in the coastal waters of the UK are well documented. Examination of stranded cetaceans by the Cornwall Wildlife Trust Marine Strandings Network and the UK Cetacean Strandings Investigation Programme has indicated that seven animals, of four other species, found stranded in south-west England, had pathology consistent with bottlenose dolphin interaction, including two juvenile and two adult common dolphins (Delphinus delphis), one juvenile pilot whale (Globicephala melas), one juvenile Risso's dolphin (Grampus griseus) and one adult striped dolphin (Stenella coeruleoalba). Although recorded traumatic lesions were often not as severe as those found in harbour porpoises, it is probable that the interactions did contribute to stranding and/or death in all four of the juvenile animals examined. Furthermore, analysis of photographs taken before establishment of th...

Identification of periods of high and low cod production, and the reasons for these periods, can increase understanding of variability in populations and ecosystems. In this study we investigate the multi-decadal and multi-century scale variations in the cod population in the eastern ...