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Growth and Reproduction in Harbour Porpoise (Phocoena phocoena) Inhabiting Hokkaido, Japan
Abstract: Growth and maturity parameters of harbour porpoises (Phocoena phocoena) around Japanese waters were summarized using samples and information from 214 individuals stranded and bycaught along the coast of Hokkaido from 2009 to 2019. We estimated ages from dental growth layer groups (GLGs), made more accurate by independently determining the mean date when layers are established. Gompertz growth curves were fitted, predicting asymptotic lengths of 136.9 cm for males and 158.5 cm for females. Sexual dimorphism was present from 3 years of age, with females larger than males as reported in other subpopulations. Length at sexual maturity (LSM) and age at sexual maturity (ASM) were estimated as 143.1 cm and 7.7 years, respectively, for males, and 154.4 cm and 7.3 years, respectively, for females. In comparison with other studies that examined stranded and bycaught harbour porpoises in other locations, foetuses and neonates comprised a very small proportion of samples. Differences from other populations in the age distributions of pregnant females also indicated that the coastal area of Hokkaido is not used as an area for parturition. This study uses data from the past 10 years to provide basic information on growth and reproduction of animals in and around Hokkaido, which is part of the North Pacific subpopulation of harbour porpoises.
Key Words: growth, maturity, western Pacific Ocean, harbour porpoise, Phocoena phocoena
Page Numbers: 185-195