The Bay of Fundy is a known area of concentration of Phocoena phocoena during the summer months. In this study, 698 females with calves and 5 473 porpoises of other social status were sighted during 1 858 hours of observation from July–September 1970–1977. It was noted that segregation of mother-calf pairs occurred in certain sectors of the study area. To evaluate habitat utilization by mother-calf pairs, a numerical index was developed which evaluated information on 12 physical and biological factors such as water temperature, current velocity, bottom depth and food availability as indicated by the level of secondary productivity. Statistical analysis revealed a significant (p < 0.001) relationship between uncorrected sightings per unit effort (S/UE) for mother-calf pairs and the habitat index. It is suggested that a complex interaction of physical and biological factors influences the distribution of mother-calf pairs. There were no strong correlations between S/UE values and individual index components, with the exception of significant (p < 0.05) correlations with increase in bottom depth and Calanus density. Females with calves appear to seek out areas of warm, stable water with high secondary productivity. Since such areas occur both inshore and offshore, the concept of a protected inshore nursery area does not seem valid for the Deer Island region.