. The Canadian field-naturalist. 380 The Canadian Field-Naturalist Vol. 102 were linked in the media to various toxic substances, including pesticides, PCBs, heavy metals, and wood preservatives (Knox 1985). However, no conclusive evidence has been published linking the whales' deaths to the effects of pollutants. Life History Age and Growth: The ear plugs of Gray Whales, when longitudinally bisected, reveal growth layers assumed to be deposited annually (Rice and Wolman 1971; Blokhin and Tiupeleyev 1987). Because the laminae laid down in the earliest years of life may "disappear" in
. The Canadian field-naturalist. 380 The Canadian Field-Naturalist Vol. 102 were linked in the media to various toxic substances, including pesticides, PCBs, heavy metals, and wood preservatives (Knox 1985). However, no conclusive evidence has been published linking the whales' deaths to the effects of pollutants. Life History Age and Growth: The ear plugs of Gray Whales, when longitudinally bisected, reveal growth layers assumed to be deposited annually (Rice and Wolman 1971; Blokhin and Tiupeleyev 1987). Because the laminae laid down in the earliest years of life may "disappear" in mature whales (Rice and Wolman 1971: 39-40), readings from ear plugs may underestimate absolute age. Adult females can be aged more reliably by reference to corpora in the ovaries. Asymptotic lengths were estimated at m for females (n = 68) and m for males (n=100) (Rice and Wolman 1971). Maximal length in females is about 15 m; in males, about m. Gray Whales continue growing until about 40 years of age. One male specimen examined by Rice and Wolman (1971) had 70 growth layers in the ear plugs. As would be expected, the major growth spurt occurs during the first year, when calves grow from a birth length of about m to about 7 m at the time of weaning in August and 8 m by one year of age (Sumich 1986). The mean age at sexual maturity is 8 years (Rice and Wolman 1971) or 6 to 7 years (Blokhin and Tiupeleyev 1987) for both sexes. Reproduction: The Gray Whale is the only mysticete for which good specimen material is available representing the early embryonic phase and the perinatal period (Rice 1983). Although sexual behaviour by Gray Whales has been observed year-round, the period of conception is well defined on the basis of the condition of ovaries and the length distribution of fetuses. The mean date of conception has been calculated as 5 December (Rice and Wolman 1971). Thus, the peak of effective mating occurs in late November and early December, while th
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