Growth and reproduction in the harbor porpoise, Phocoena phocoena (L.), from eastern Newfoundland

Richardson, Shelly Faye (1992) Growth and reproduction in the harbor porpoise, Phocoena phocoena (L.), from eastern Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Growth and reproduction characteristics were described for 94 porpoises incidentally caught in gillnets during the summers of 1990 and 1991. Most porpoises (56%) were below five years of age. The oldest female was nine; the oldest male was twelve. Growth rates were similar for males and females until one year of age, at which time females grew longer and weighed more than males of similar ages. Using the Gompertz growth model, asymptotic values for body length were 142.9 cm for males and 156.3 cm for females and asymptotic values for weight were 49.1 kg and 61.6 kg for males and females respectively. -- The majority of mature females were pregnant (76%); a high proportion were simultaneously pregnant and lactating (35%). Mean age at sexual maturity for females was 3.1 years at a mean length of 146.4 cm. Younger females appear to have multiple ovulations or an increased proportion of luteinized follicles. Parturition occurred before the sampling period (before late June) and ovulation and conception were estimated to occur from early to late July. -- Sexual activity in males as indicated by spermatogenic activity was high during July, supporting estimates for the timing of ovulation and conception. On average, sexual maturity in males was estimated to occur at 3.0 years of age and at a length of 135.1 cm. There was a dramatic increase in testes weight, testes volume, and seminiferous tubule diameter at the onset of age three. -- Female porpoises from Newfoundland matured earlier and were larger than females from other areas. Dentinal deposition patterns in the teeth of harbor porpoises from Newfoundland were very different from those of the Bay of Fundy and suggest a new method of stock discrimination.

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