No abstract

Right whales in Cape Cod Bay, Massachusetts, were studied to determine the relationship between their surface feeding behaviour and the density and composition of their planktonic prey. The swimming path characteristics of whales feeding, socializing, and travelling were compared. Zooplankton samples collected in the feeding path were contrasted with those from areas where whales were not present. Surface prey patches where right whales fed were dominated by Calanus finmarchicus (21 samples), Pseudocalanus minutus (n = 13), Centropages sp. (n = 3), and larval barnacles (n = 2). The zooplankton density in the feeding path of the whales tested significantly higher (Mann–Whitney U-test, P < 0.001) than at stations where whales were not present (mean total densities were 6.54 × 103 (SE = 1.03 × 103) and 0.87 × 103 (SE = 0.19 × 103) organisms/m3, respectively). Feeding was rarely observed in locations where the total zooplankton density was less than 1000 organisms/m3. The rate of change of direction in the feeding path (mean 19.3°/10 m of path) was significantly higher (P < 0.001) than for paths of whales travelling (mean 5.3°/10 m of path), reflecting area-restricted foraging behaviour.

During a 5–wk period beginning in late November, 1987, 14 humpback whales, Megaptera novaeangliae, died in Cape Cod Bay after eating Atlantic mackerel, Scomber scombrus, containing saxitoxin (STX), a dinoflagellate neurotoxin responsible for paralytic shellfish poisoning in humans. We propose a line of evidence to explain how whales, by virtue of their diving adaptations, may be particularly vulnerable to this systemic neurotoxin. Absence of STX in New England waters and shellfish during the episode suggests that the mackerel, representing the northern stock which spawns in the Gulf of St. Lawrence, accumulated the toxin there and delivered it to the Gulf of Maine and Cape Cod Bay in the fall of 1987. These findings challenge common perceptions of the manner in which planktonic toxins move through the food chain, and offer new insights into natural mortality and standings of marine mammals. It seems appropriate to search for STX and other phytotoxins when investigating marine mammal mortalities.

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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.