Reproduction and recruitment of individually identified humpback whales, Megaptera novaeangliae, observed in Massachusetts Bay, 1979–1985

Abstract

Humpback whale mother–calf pairs from a currently unexploited population were observed in Massachusetts Bay between 1979 and 1985. During this period, 44 individually identified mature females were observed, with a total of 72 calves. Of the 20 mothers observed with more than one calf during the study period, 12 had two calves and 8 had three calves. The observed calving intervals were 1 year (n = 1), 2 years (n = 16), 3 years (n = 10), and 4 years (n = 1). The crude birth rate varied from a low of 0.045 in 1981 to a high of 0.103 in 1983 (mean = 0.075). An alternative calculation of reproductive rate yielded a range of 0.30–0.43 calves per mature female per year. Mature females were observed significantly more frequently in years when they had a calf than in years when they did not. Females with calves associate with other whales less frequently than females without calves. Observations of calves feeding suggest that weaning may begin when calves are 5–6 months of age. Forty-five of the 49 calves born before 1985 separated from their mothers during the calf's second winter, while 37 of the 49 were observed to return to the study area in 1 or more years after separation from their mothers. One calf is known to have died. Two females born during the study period returned with calves of their own in later years. The high return rate of calves in years after separation strongly suggests that the composition of a humpback whale feeding stock is determined matrilineally.

Against the current: an inter-oceanic whale migration event

“…The largest number of alleles (21) An inter-oceanic whale migration event C. Pomilla & H. C. Rosenbaum 477 In Madagascar, this individual was accompanied by a female and analyses of genotypes putatively identified her as his mother (relationship log(ratio)Z1.673, p!0.001; table 1; and see electronic supplementary material for kinship analyses). Other behavioural data show that humpback whale calves remain with their mother for their first year, and occasionally for their second year (Glockner-Ferrari & Ferrari 1984;Baker et al 1987;Clapham & Mayo 1987). Therefore, when sighted in Gabon two years later, this individual could have been a three-or four-year-old juvenile, as the mean age at attainment of sexual maturity in male humpback whales is five years (Clapham 1992;Chittleborough 1955).…”

Age determination of humpback whales Megaptera novaeangliae through blubber fatty acid compositions of biopsy samples

“…Calves were classified in the field based on their physical size, stereotypical behaviours and close (consistent) association with an adult (its mother). Calves encountered on the feeding range were assumed to range in age from 3 to 9 mo when first observed, and typically remained dependent until at least October of their first year (Clapham & Mayo 1987, Baraff & Weinrich 1993. Thus, the ages of EKA whales were simply computed as the number of intervening years between first observation and when re-encountered and biopsy sampled.…”

Global diversity and oceanic divergence of humpback whales (Megaptera novaeangliae)

“…Despite an absence of geographical barriers to dispersal, populations show significant genetic structure between and within ocean basins [1][2][3][4][5][6][7], with the strongest restrictions to maternal gene flow across the equatorial boundary [1,8]. Observations of naturally marked and genotyped individuals suggest that maternally directed fidelity to both breeding and feeding grounds may be responsible for this population structure [9][10][11][12][13][14]. Some population structure has also been identified in the nuclear genome; a recent study using multiple nuclear introns to survey Atlantic diversity [15] found evidence of population structuring between the North Atlantic and Southern Hemisphere, but not among breeding and feeding grounds within the North Atlantic.…”