Declining reproductive success in the Gulf of St. Lawrence's humpback whales (Megaptera novaeangliae) reflects ecosystem shifts on their feeding grounds

• Published in: Global Change Biology
• Main Authors: Kershaw, Joanna L., Ramp, Christian A., Sears, Richard, Plourde, Stephane, Brosset, Pablo, Miller, Patrick J. O., Hall, Ailsa J.
• Other Authors: Sea Mammal Research Unit University of St Andrews (SMRU), School of Biology University of St Andrews, University of St Andrews Scotland -University of St Andrews Scotland -Natural Environment Research Council (NERC), Maurice Lamontagne Institute, Laboratoire de Biologie Halieutique, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), University of St Andrews Scotland
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: ACL; climate-change; dynamics; mortality; environmental change; panorama; Ifremer; northern gulf; marine mammals; atlantic right whale; balaenoptera-physalus; biopsy; blubber; calving rates; cetaceans; endocrine profiling; photo-identification; pregnancy; pregnancy rates; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; Canada; Balaenoptera physalus; Megaptera novaeangliae; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-03246764; https://doi.org/10.1111/gcb.15466

WOS:000601403400001 Climate change has resulted in physical and biological changes in the world's oceans. How the effects of these changes are buffered by top predator populations, and therefore how much plasticity lies at the highest trophic levels, are largely unknown. Here endocrine profiling, longitudinal observations of known individuals over 15 years between 2004 and 2018, and environmental data are combined to examine how the reproductive success of a top marine predator is being affected by ecosystem change. The Gulf of St. Lawrence, Canada, is a major summer feeding ground for humpback whales (Megaptera novaeangliae) in the North Atlantic. Blubber biopsy samples (n = 185) of female humpback whales were used to investigate variation in pregnancy rates through the quantification of progesterone. Annual pregnancy rates showed considerable variability, with no overall change detected over the study. However, a total of 457 photo-identified adult female sightings records with/without calves were collated, and showed that annual calving rates declined significantly. The probability of observing cow-calf pairs was related to favourable environmental conditions in the previous year; measured by herring spawning stock biomass, Calanus spp. abundance, overall copepod abundance and phytoplankton bloom magnitude. Approximately 39% of identified pregnancies were unsuccessful over the 15 years, and the average annual pregnancy rate was higher than the average annual calving rate at similar to 37% and similar to 23% respectively. Together, these data suggest that the declines in reproductive success could be, at least in part, the result of females being unable to accumulate the energy reserves necessary to maintain pregnancy and/or meet the energetic demands of lactation in years of poorer prey availability rather than solely an inability to become pregnant. The decline in calving rates over a period of major environmental variability may suggest that this population has limited resilience to such ecosystem change.