Seasonal gain in body condition of foraging humpback whales along the Western Antarctic Peninsula

Abstract

Most baleen whales are capital breeders that use stored energy acquired on foraging grounds to finance the costs of migration and reproduction on breeding grounds. Body condition reflects past foraging success and can act as a proxy for individual fitness. Hence, monitoring the seasonal gain in body condition of baleen whales while on the foraging grounds can inform how marine mammals support the costs of migration, growth, and reproduction, as well as the nutritional health of the overall population. Here, we use photogrammetry from drone-based imagery to examine how the body condition of humpback whales (Megaptera novaeangliae) changed over the foraging season (November to June) along the Western Antarctic Peninsula (WAP) from 2017 to 2019. This population (IWC stock G) is recovering from past whaling and is growing rapidly, providing an opportunity to study how whales store energy in a prey-rich environment. We used a body area index (BAI) to estimate changes in body condition and applied a Bayesian approach to incorporate measurement uncertainty associated with different drone types used for data collection. We used biopsy samples to determine sex and pregnancy status, and a length-based maturity classification to assign reproductive classes (n = 228; calves = 31, juveniles = 82, lactating females = 31, mature males = 12, mature unknown sex = 56, non-pregnant females = 12, pregnant females = 3, pregnant & lactating females = 1). Average BAI increased linearly over the feeding season for each reproductive class. Lactating females had lower BAI compared to other mature whales late in the season, reflecting the high energetic costs of nursing a calf. Mature males and non-pregnant females had the highest BAI values. Calves and juvenile whales exhibited an increase in BAI but not structural size (body length) over the feeding season. The body length of lactating mothers was positively correlated with the body length of their calves, but no relationship was observed between the BAI of mothers and their calves. Our study establishes a baseline for seasonal changes in the body condition for this humpback whale population, which can help monitor future impacts of disturbance and climate change.

A surplus no more? Variation in krill availability impacts reproductive rates of Antarctic baleen whales

“…The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for the conservation and maintenance of ecosystem function, krill stocks, and commercial fishing, including implementing conservation measures defining and regulating the total allowable catch, spatial and temporal rules of the fishery, and monitoring of krill dependent species (CCAMLR, 2010(CCAMLR, , 2021. CCAMLR must utilize this along with other new knowledge on baleen whale foraging ecology and demography (i.e., Bierlich et al, 2022;Pallin, Bierlich, et al, 2022;Pallin, Botero-Acosta, et al, 2022;Reisinger et al, 2022), along with the impact that both We show significant variation in the pregnancy rates of humpback whales feeding along the WAP. Humpback whales are sentinel species of ecosystem health (Bengtson Nash et al, 2018).…”

“…The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for the conservation and maintenance of ecosystem function, krill stocks, and commercial fishing, including implementing conservation measures defining and regulating the total allowable catch, spatial and temporal rules of the fishery, and monitoring of krill dependent species (CCAMLR, 2010, 2021). CCAMLR must utilize this along with other new knowledge on baleen whale foraging ecology and demography (i.e., Bierlich et al, 2022; Pallin, Bierlich, et al, 2022; Pallin, Botero‐Acosta, et al, 2022; Pallin, Robbins, et al, 2018; Reisinger et al, 2022), along with the impact that both environmental variability and krill fishing have on this group of krill predators, to improve and modernize current ecosystem‐based management plans. This may help push forward CCAMLR's 2011 commitment to implement a Marine Protected Area system in the region (i.e., CCAMLR Conservation Measure 91‐04, see https://cm.ccamlr.org/en/measure-91-04-2011).…”

Defining a common language to assess external deformities in free‐ranging cetaceans

“…However, new technologies and sampling methods are already being used to evaluate the health status of cetaceans (e.g. Bierlich et al 2022). Monitoring of deformities can be employed alongside non‐invasive techniques and integrated into existing monitoring programmes and photo‐ID studies.…”

Downsizing a heavyweight: factors and methods that revise weight estimates of the giant fossil whale Perucetus colossus

“…Whales (or cetaceans) are particularly good examples of this dual phenomenon: living cetaceans, such as blue whales ( Balaenoptera musculus ) are perennial objects of popular fascination as the largest vertebrates ever; equally, studies on blue whale physiology, behavioral and feeding ecology have important implications for understanding broader trends among cetaceans and other mammals ( Abrahms et al, 2019 ; Goldbogen et al, 2019a , 2019b ). Recent improvements in animal-borne technology, including tags and aerial photogrammetry, have dramatically increased the precision for measuring the body sizes of living cetaceans in the field ( Christiansen et al, 2019 ; Bierlich et al, 2022 ). These improvements in data collection facilitate further studies in the macroecology of these extremely large organisms: in many cases, body size informs energetics, and models of the ecological impact that these top consumers have on ocean ecosystem health ( Savoca et al, 2021 ).…”