Decreasing body size is associated with reduced calving probability in critically endangered North Atlantic right whales

Enrico Pirotta*, Peter L. Tyack, John W. Durban, Holly Fearnbach, Philip Hamilton, Catriona M Harris, Amy Knowlton, Scott D. Kraus, Carolyn Miller, Michael Moore, Heather Pettis, Theoni Photopoulou, Rosalind Rolland, Robert Schick, Len Thomas

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Body size is key to many life-history processes, including reproduction. Across species, climate change and other stressors have caused reductions in the body size to which animals can grow, called asymptotic size, with consequences for demography. A reduction in mean asymptotic length was documented for critically endangered North Atlantic right whales, in parallel with declines in health and vital rates resulting from human activities and environmental changes. Here, we tested whether smaller body size was associated with lower reproductive output, using a state-space model for individual health, survival and reproduction that quantifies the mechanistic links between these processes. Body size (as represented by the cube of length) was strongly associated with a female's calving probability at each reproductive opportunity. This relationship explained 62% of the variation in calving among reproductive females, along with their decreasing health (20%). The effects of decreasing mean body size on reproductive performance are another concerning indication of the worsening prospects for this species and many others affected by environmental change, requiring a focus of conservation and management interventions on improving conditions that affect reproduction as well as reducing mortality.
Original languageEnglish
Article number240050
Number of pages8
JournalRoyal Society Open Science
Issue number2
Early online date28 Feb 2024
Publication statusPublished - 28 Feb 2024


  • Bayesian state-space model
  • Body size
  • Capital breeding
  • Eubalaena glacialis
  • Health
  • Length


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