| Summary: | Harbour porpoises stranded around the Scottish coast throughout the year, with fatal attacks by bottlenose dolphins and pathological conditions being the main causes of death, there has been an apparent increase in the number of porpoises dying due to pathological conditions and starvation in recent years, although there was no evidence of any overall trend in the annual number of stranded porpoises. Reproductive seasonality was found to occur and the mating and calving periods were estimated to take place between May and August, with gestation lasting approximately 11 months. Lactation appears to last 9-10 months, with weaning taking place in March/April. Age at sexual maturity for female and male porpoises was approximately 5 and 6 years, respectively. The maximum age for both male and female proposes was 20 years. The pregnancy rate was estimated to be 0.42. The presence of two pregnant and lactating females suggests that female harbour porpoises in Scottish waters can give birth annually, however it is more likely that many females only give birth every two years. Cause of death, body length, season and year stranded, all had significant effects on blubber thickness, with an apparent decrease in blubber thickness in recent years. The fatty acid profile of the inner blubber layer was significantly affected by blubber thickness, cause of death, body length, season, year and area stranded. The main prey species of porpoises from Scottish and adjacent waters, could be distinguished based on their fatty acid profile. Despite the current limitations of the model, seasonal and geographical variations were detected in the diet of harbour porpoises using quantitative fatty acid signature analysis (QFASA).
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