Abstract

(…) Four newborn Dall’s porpoises were examined by the author during July of 1987 and 1988. All had muted color patterns, and some evidence of umbilical remnants, fetal folds, and fetal dorsal fin orientation. These four summer birth records prompted a re-examination of calving records for this species in the eastern North Pacific (Table 1). The literature was searched for records of fetuses, neonates, and other evidence of parturition. Approximate birth dates were computed for fetuses and calves, using a birth size of 100 cm (Mizue et al. 1966, Kasuya 1978), a fetal growth rate of 10 cm/mo (Kasuya 1978), and a first-year growth rate of 3.75 cm/mo-based on a length at one year of about 145 cm (Newby 1982). These parameters are based on large sample sizes from the western Pacific. The results indicate a large calving peak in summer (62% are from June through August), and a smaller peak in spring (15 % are from March). There is no evidence for any births during the winter months of November through January. All of the eight records that Morejohn (1979) presented are also shown in Table 1. These do not indicate year-round calving as he suggested, but are consistent with spring to summer parturition. (…)