Population Structure and Dynamic of Humpback Whales ( Megaptera novaeangliae ) in the Gulf of St Lawrence, Canada

Two humpback whale aggregations can be found in the Gulf of St. Lawrence in eastern Canada. The first is located mainly in the Mingan/Anticosti area (MA) and forms the St Lawrence stock while the second one is situated in the Northeast Gulf (NEGU) and is part of the Newfoundland/Labrador stock. In 26 years of research 223 animals were photo-identified in the Mingan area and 501 in the Northeast Gulf. Fifty-four animals were observed in both areas. The sex ratio was 1.4 females to 1 male. Altogether 70 females were seen with 129 calves. Mean calving interval for females with consecutive sightings was 3.5 years. Very few males observed as calves were seen a second time, while half of the females returned, suggesting a higher site fidelity for females. Only two females seen as calves returned with their own offspring, after 9 and 11 years respectively. The high number of individuals seen only once (both calves and adults) created an age structure in the mark recapture analysis. Different models (CJS, Barker’s, Pradel’s and Multi State) yielded estimates of adult survival rate ranging from 0.974 to 0.986. No significant difference in survival was observed between the two stocks or between sexes. The dataset was analyzed in increasing time spans, backwards and forwards. Results show that longer data sets provide more precise survival estimates at first, but very long datasets could potentially hide short-term trends or between-year differences.