Report on Habitat Quality and Calving Rates

Survival of the endangered northern right whale might be linked to the abundance and caloric richness of plankton, collectively called zooplankton, that are found in Cape Cod Bay. In a scientific paper just released to federal and state officials, PCCS Senior Scientist Dr. Charles “Stormy” Mayo, reported that there is a “very strong correlation” between the quantity and quality of zooplankton sampled during the winter and early spring and the calving rates of right whales that winter in Cape Cod Bay. On the other hand, the correlation is not significant for whales that do not use the near-shore waters of the Gulf of Maine.

Recent surveys and statistical analysis of data have led scientists to conclude that right whales have experienced negative population growth in the past five years. The causes of this decline have been thought to be principally due to collisions with ships and entanglement in fishing gear. Recently, however, detailed studies of the individual composition of the population have shown that a more insidious process may be at work, that of a declining rate of calving. The causes for such a decline have confounded scientists, because reproduction is supported by a variety of basic ecological and biological processes that cannot be simply investigated for cause and effect. One of the potential influences on reproduction is nutrition.

“There is ample evidence that poor nutrition results in reduced fecundity and poor prognosis for newborns among a variety of species,” said Mayo. “This led us to explore the potential that poor nutrition is suppressing the natural rates of reproduction among right whales. Our hypothesis was that the calving success of the right whales of the western North Atlantic reflects the quality of the Cape Cod Bay food resource.” Mayo admits in retrospect, that the hypothesis at first seemed “a bit far-fetched.”

To test the hypothesis, Mayo, PCCS Associate Scientist Edward Lyman, and Research Assistant Amy DeLorenzo generated an annual measurement of the food energy of the bay and compared it with historic calving data of the population. The habitat data was drawn from 15 years of plankton and oceanographic sampling of the bay and observations and measurements of right whale foraging. The calving data was drawn from official population surveys maintained by the New England Aquarium.

Their analysis showed a strong correlation between the richness of Cape Cod Bay and calving rates. Specifically, the research team discovered a recurring pattern of high zooplankton counts followed two years later by high calving rates. “The two-year lag,” said Mayo, “is probably linked in some way to basic reproductive cycles.” If the correlation holds, Mayo and his colleagues predict that calving among right whales that feed in Cape Cod Bay will increase this winter to at least 3 calves, and in 2002 to at least 5 to 8 calves, due to substantial increases in the food resource quality in Cape Cod Bay recorded during the winters of 1999 and 2000.

The foundation of PCCS's research on the right whale’s habitat is thousands of samples of zooplankton that make up the right whale’s primary source of food. Calculations are then made of the amount of food the animal was able to filter and of its caloric value, resulting in what an annual measurement called the caloric capture factor. The researchers have found that if the food density of the bay drops below a certain minimum level, the whales will exit the bay; sometimes within a matter of hours.

As Mayo explains, “Making a living in the bay is what it is all about. Cape Cod Bay is critical to their survival. When the food is here in abundance they do well. When it is not, they leave. But now we have reason to believe that when feeding conditions are not good, the population as a whole is impacted. This suggests, among other things, that we must do everything we can to avoid any manmade alterations to their habitat.”

“This intriguing discovery would not have been possible,” said PCCS Executive Director Peter Borrelli, “were it not for the fact that Stormy and his colleagues have sampled Cape Cod Bay every winter for the past 15 years, making it the most complete habitat database of its kind in the world. We are especially grateful to the Massachusetts Environmental Trust and Massachusetts Division of Marine Fisheries for their recent financial support of this research. It may unlock some of the mysteries of the right whale and guide us toward ways of protecting them from extinction.”

PCCS's findings are reported in a scientific paper entitled, “Comparison of the Yearly Caloric Availability in Cape Cod Bay with North Atlantic Right Whale Calving Rates: 1984-2000,” which is available by contacting PCCS.