Seasonal and interannual correlations between right-whale distribution and calving success and chlorophyll concentrations in the Gulf of Maine, USA

The North Atlantic right whale Eubalaena glacialis is one of the most endangered species of large whales, Although human-caused mortality is the primary factor contributing to poor recovery of E. glacialis, variability in reproductive success may also play a role. The present study evaluates the idea that seasonal distributions and reproductive success in E. glacialis are linked to food availability or related environmental conditions that can be assessed by treating satellite-derived sea-surface chlorophyll (chl) concentration as a proxy. Sea-surface chl time series in the major high-use feeding habitats and whale-sightings data were compared. Whale transition between habitats reflects a pattern in the seasonal distribution of peak concentration in satellite-derived chl. A regionally and seasonally weighted chl index was calculated to reflect aspects of average potential food condition. We found a significant correlation between the number of whale calves born and the weighted chl averaged over the prior 2 yr. These findings are consistent with the view that food availability during and just before the gestation period may be a critical factor regulating reproductive success, with low food years contributing to delays in conception. Longer time series are necessary to examine the predictive relationship between weighted chl concentration and calf production. Although ecological interactions and whale reproductive biology are certainly more complex than can be encompassed by emphasizing only food availability, analysis of satellite-derived surface chl concentrations provides a practical means to monitor a level of ecosystem variability that affects right-whale distributions and productivity.