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

Type Article
Date 2021-03
Language English
Author(s) Kershaw Joanna L.ORCID1, 2, Ramp Christian A.1, 2, Sears Richard2, Plourde Stéphane3, Brosset Pablo3, 4, 5, Miller Patrick J. O.1, Hall Ailsa J.1
Affiliation(s) 1 : Sea Mammal Research Unit Scottish Oceans Institute University of St Andrews St Andrews, UK
2 : Mingan Island Cetacean Study Saint Lambert QC ,Canada
3 : Department of Fisheries and Oceans Canada Maurice Lamontagne Institute Mont‐Joli QC ,Canada
4 : Laboratoire de Biologie Halieutique Ifremer Plouzané ,France
5 : Laboratoire des Sciences de l'Environnement Marin ‐ IUEM Université de Brest ‐ UMR 6539 CNRS/UBO/IRD/Ifremer Plouzané,France
Source Global Change Biology (1354-1013) (Wiley), 2021-03 , Vol. 27 , N. 5 , P. 1027-1041
DOI 10.1111/gcb.15466
WOS© Times Cited 12
Keyword(s) biopsy, calving rates, endocrine profiling, environmental change, marine mammals, photo-identification, pregnancy rates
Abstract

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 ~37% and ~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.

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Kershaw Joanna L., Ramp Christian A., Sears Richard, Plourde Stéphane, Brosset Pablo, Miller Patrick J. O., Hall Ailsa J. (2021). Declining reproductive success in the Gulf of St. Lawrence’s humpback whales (Megaptera novaeangliae) reflects ecosystem shifts on their feeding grounds. Global Change Biology, 27(5), 1027-1041. Publisher's official version : https://doi.org/10.1111/gcb.15466 , Open Access version : https://archimer.ifremer.fr/doc/00665/77758/