Harbour porpoises (Phocoena phocoena) in the North Atlantic: Biological parameters

• Published in: NAMMCO Scientific Publications
• Main Author: Lockyer, Christina
• Format: Article in Journal/Newspaper
• Language: English
• Published: Septentrio Academic Publishing 2003
• Subjects: harbour porpoises; biological parameters; North Atlantic; Phocoena phocoena
• Online Access: https://septentrio.uit.no/index.php/NAMMCOSP/article/view/2740; https://doi.org/10.7557/3.2740

Biological parameters for harbour porpoises are reviewed throughout their range in the NorthAtlantic. Most information is based on studies of a combination of directed catches, bycatchesand strandings. All these sources are valuable for providing biological information, but each carriessome bias when it comes to interpretation of parameters, especially those involving age structure.Information on age-related parameters, reproduction and growth is presented and assessed byregion and/or population, of which there may be 14 throughout the North Atlantic. Among age relatedparameters, maximum longevity recorded is 24 years; maximal rate of population growth is probably 9.4% but in the range 5-10%; mortality is highest in year 1, and <5% of the populationlive beyond 12 years; an estimate of 0.867 with a maximum age of 23 years has been givenfor survival. Among reproductive parameters, age at sexual maturation falls between 3-4 yearsfor both sexes; age at first parturition is probably 4-5 years; age at first ovulation is >3 years; ovulationrates fall in the range 0.64 - 0.988 corpus per year, and reproductive interval is 1.01-1.57years; pregnancy rates are generally in the range 0.74 - 0.986 per year, meaning that not all femalesproduce a calf every year; there is seasonal breeding/mating in the period June–August; gestationlasts 10-11 months; parturition generally occurs between mid-May to mid-July; duration oflactation is uncertain, but is probably at least 8 months; size at birth is usually in the range 65-75 cm with a maximum size of about 80 cm. Sex ratio is biased to males throughout life: 1.1-1.2males : 1.0 females in the foetal stage, and 1.1-1.7 males : 1.0 females post-natal. Growth parametersindicate an asymptotic length and weight that varies with population, but usually falls inthe range 153-163 cm and 55-65 kg for females and 141-149 cm and 46-51 kg for males. Growthmodels used for length and weight are typically based on von Bertalanffy and Gompertz models.Length at sexual maturity also varies with population, but is usually in the range138-147 cm for females and 127-135 cm for males. There is no information based on vertebralepiphyseal fusion to indicate age at physical maturity. Foetal growth appears normal, but there isuncertainty about the existence of embryonic diapause. Size/age at weaning are uncertain, but sizemay be <115 cm and at an age >8 months; however, entirely independent feeding may not occuruntil about 10 months.