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COI Funded Project: Health Assessment of the Northern Right Whale

Project Duration: 6/1/97-12/31/00
Key Words: Right Whales, Bay of Fundy, biological indicator, endangered species

Progress Report

Relationship between acoustic measurements of blubber thickness and age, sex and reproductive history in free-ranging Northern right whales.

Presented at the Biennial Meeting of the Society for Marine Mammalogy, in Maui, December 1st, 1999.
Carolyn Miller, Michael Morss, Marylin Marx and Michael Moore
Biology Department
Woods Hole Oceanographic Institution, MA 02543
New England Aquarium, Central Wharf, Boston MA 02110

The small size and slow growth rate of the North Atlantic right whale population has made it highly vulnerable. Although substantive efforts are underway to reduce mortality from ships and fishing gear, less attention has been given to the reduced reproductive rate, which is half that of southern right whales. Insufficient body fat may be one of the factors influencing reproductive failure, as body fat and fertility co-vary in many terrestrial mammalian species. To evaluate body condition we used amplitude-mode ultrasound to measure dorsal blubber thickness. Relationships between blubber thickness and demographic factors were examined in 31 live free-ranging right whales during 6 days in August 1998 in the Bay of Fundy, Canada. Concurrent photo-identification of individual animals allowed comparison of blubber thickness with catalogued age, sex and reproductive history. Measurements taken from 5 to 30 % of the body length from the blowholes to the fluke notch did not differ on animals touched more than once; therefore, measurements from this area only were compared. Among females, blubber was 1.4 times thicker in adults than in juveniles and blubber thickness increased with age. Similar trends were absent in males. There was no difference in blubber thickness between reproductively successful and unsuccessful females. However, blubber thickness appeared to increase with increasing time since last calf. These results, whilst needing verification with a larger sample size, indicate that age and amount of time since last calf may be important factors affecting female blubber thickness. The results also suggest that measurements of blubber thickness may allow prediction of both calving interval and critical level of blubber thickness necessary for successful reproduction. Further investigation into blubber thickness, girth and length are needed to determine if body condition is an important factor in the reproductive failure of the NW Atlantic right whale. (Office of Naval Research)

Cruise Report Summary:
The North Atlantic Right Whale is an endangered species: the population numbers less than 300 animals, a number that is growing slowly if at all. In addition to ship-strike and gear-entanglement mortalities, many females never calve. In this project we are gathering acoustic measurements of blubber thickness, to look for differences in body condition between animals that breed successfully and those that do not. These data will allow a better appraisal of the potential significance of nutrition to the apparent reproductive failure of the northern species. We have recently successfully deployed a custom-engineered field probe on a 40-foot long pole in a large congregation of right whales east of Grand Manan in the Bay of Fundy. We had six days at sea, working 15 miles East of Grand Manan. Each day we laid our probe on 20 to30 animals, often repeatedly during a surfacing interval. The boat, pole, probe, crew, and whales worked harmoniously most of the time. The final tally of usable data awaits analysis of data tapes, but a conservative assessment is that we acquired blubber thickness data on at least 50 animals. This kind of data has never been collected from free-ranging large whales before. We have thus initiated, and with further funding will continue, a novel long term study of body condition and reproductive success in this endangered species. This project was initiated with support from the Massachusetts Environmental Trust and the recent field work was supported by the Rinehart Coastal Research Center of the Woods Hole Oceanographic Institution.

Originally published: January 1, 1997