Lewis Evans

North Pacific humpback whales are a celebrated conservation success, rebounding from extensive commercial whaling. Yet they remain vulnerable to the impacts of climate change, a multifaceted stressor that can exacerbate existing threats. During 2013–2016, a Northeast Pacific marine heatwave severely reduced forage availability in their feeding grounds, concurrent with diminished whale recruitment and increased mortality. We analyzed photo‐identification data of whales that visited the Main Hawaiian Islands from 2002 to 2023 to estimate apparent survival, abundance, and distinct population segment (DPS) growth rates. Survival was high prior to (0.987; SE = 0.003), low during (0.684; SE = 0.022), and higher, but still reduced, after (0.956; SE = 0.006) the heatwave. Annual breeding season abundance estimates averaged 11,617 (SD = 1914) and included a striking 37% decrease from 2014/15 to 2021/22. While the average annual DPS growth rate was stable (1.00) over 20 breeding seasons, shorter periods included high growth (1.09) and steep decline (0.783). Depressed survival and abundance estimates may signal lingering heatwave effects or adjustment to current carrying capacity. Climate change predictions include more frequent, intense, and longer heatwaves; thus, this DPS serves as a crucial ecosystem‐health indicator. Continued research and monitoring are essential to support resiliency against future climate perturbations.

Movement is energetically expensive, and locomotor efficiency depends on body size and morphology. Humpback whales Megaptera novaeangliae exhibit a remarkable ontogenetic size range and experience periods of intense fasting coinciding with energetically demanding migration, lactation, and growth. To quantify how propulsive costs scale with body size, we combined accelerometry data and aerial photogrammetry collected from 62 humpback whales ranging from calves to adults (4.4-14.1 m) on their Hawaiian breeding ground. Using a hydrodynamic model incorporating swimming kinematics and morphology, we found that mass-specific propulsive costs declined with increasing body length, representing a 62% reduction between a 4 m calf and a 14 m adult. Elevated activity levels and higher mass-specific propulsive costs in calves energetically burden lactating females, whose energy reserves must support both calf activity and rapid somatic growth. These energetic demands are buffered by the female’s own reduced activity and mass-specific propulsive costs. We estimate that propulsion accounts for approximately 21% of a lactating female’s daily energetic expenditure while on the breeding grounds. Our approach highlights the disproportionately higher cost of displacement in smaller individuals, ranging from approximately 4 kJ m ^-1 in calves to 25 kJ m ^-1 in adults, providing a scalable framework to quantify the energetic consequences of disturbance. These findings underscore the importance of large body size in baleen whales, refine understanding of how activity costs scale across body size in humpback whales on their breeding grounds, and provide an energetic baseline to predict consequences of environmental and anthropogenic disturbance.

Diving is one of the most important behaviors undertaken by marine mammals. Pilot whales (Globicephala spp.) are oceanic dolphins that regularly forage at extreme depths (∼600–1000 m) and maintain body sizes similar to beaked whales. They are also listed as data deficient, with little known about their population dynamics. To help fill this knowledge gap, we estimated their energetic demands through a combination of multiple data streams (e.g. unoccupied aerial systems photogrammetry, high-resolution accelerometry tag data, stomach content analysis and long-duration dive data from satellite tags) from short-finned pilot whales (Globicephala macrorhynchus) in Hawaiian waters. We estimated and compared pilot whale field metabolic rates from breathing frequency against a more granular cost of transport method developed from morphometrics and swimming kinematics, finding that these methods gave similar estimates of energetic expenditure during foraging dives. We then combined expenditure and intake estimates into an exploratory model of daily net energetic balance. Using an estimate of prey size derived from squid beaks collected from a stranded animal, we found that an average of 142±59.8 squid day−1 (52,000±21,800 squid year−1) is enough for an average adult short-finned pilot whale to reach a neutral net energetic balance. This species has an estimated population abundance of ∼8000 individuals in Hawaiian waters, suggesting that the population as a whole would require 416±175 million squid (at an average of 559±126 kJ squid−1) or approximately 88,000±37,000 tonnes of squid annually, assuming similar energetic requirements for each animal.

Photo‐identification (photo‐ID) is a widely used, non‐invasive method for monitoring individual animals, including humpback whales ( Megaptera novaeangliae ; HBWs), and has provided valuable insights into their population dynamics, movement patterns, and social structures. Traditional identification relies on the trailing edge and ventral pigment patterns of the tail fluke (fluke‐ID); however, not all whales present their flukes, limiting identification and re‐sighting opportunities. We developed a novel aerial‐identification (aerial‐ID) approach using drone imagery to identify individual HBWs based on the arrangement of two features, tubercles (TB) and cookiecutter shark scars (CCS). Between January and March 2022, we sampled 1498 HBWs, including repeated individuals, capturing fluke‐ID images for 772 and aerial‐ID images for 1437. Fluke‐ID yielded 164 re‐sightings (76 lactating females, 88 others), while aerial‐ID yielded 372 (249 and 123, respectively), representing a 227% increase for lactating females and 40% for others. We extended this approach to a multi‐year, cross‐regional dataset (2018–2025) of 54 individuals verified with fluke‐ID. All were matched using aerial‐ID, with the longest re‐sight spanning 2737 days (6.5 years), representing the maximum interval within our study period. Aerial‐ID thus offers a powerful complement to fluke‐ID, expanding demographic coverage, increasing re‐sighting rates, and enabling long‐term, cross‐regional monitoring.

Given recent declines in North Pacific humpback whale (Megaptera novaeangliae) reproductive output and calf survival, there is additional urgency to better understand how mother–calf pairs allocate energy resources across their migratory cycle. Here, unoccupied aerial system (UAS; or drone) photogrammetry was used to quantify the body size and condition (BC) of humpback whales on their Hawaiʻi (HI) breeding and Southeast Alaska (SEAK) feeding grounds. Between 2018 and 2022, we collected 2410 measurements of 1659 individuals. Rates of change in body volume (BV) and length (BL) were quantified using 803 repeat measurements of 275 individuals. On average, HI mothers lost 0.106 m³ or 96.84 kg day⁻¹ while fasting, equivalent to 2641 MJ day⁻¹ or 830 kg of krill and 424 kg of Pacific herring daily. HI calf BV and BL increased by 0.035 m³ and 2.6 cm day⁻¹, respectively. In SEAK, maternal BV increased by 0.015 m³ or 14.54 kg day⁻¹ (367 MJ day⁻¹), while calf BV and BL increased by 0.039 m³ and 0.93 cm day⁻¹, respectively. Maternal investment in calf growth correlated with both female BL and BC, with larger females producing larger, faster‐growing calves. Finally, using 330 measurements from 156 females, we quantified differences in BC increase over four feeding seasons. Lactating females exhibited an average BC increase of 6.10%, half that of unclassified females (13.51%) and six times lower than pregnant females (37%). These findings represent novel insights into the life history of humpback whales across their migratory cycle, providing key baseline data for bioenergetic models elucidating the effects of anthropogenic disturbance and rapidly changing ocean ecosystems. image Key points: On average, Hawaiʻi (HI) mothers lost 0.106 m³ or 96.84 kg day⁻¹, equivalent to 2641 MJ day⁻¹. Over a 60 day period, this corresponded to an estimated mean energetic cost of 158 GJ, or ≈50 tons of krill or ≈25 tons of Pacific herring, surpassing the total energetic cost of gestation estimated for humpback whales of similar length. In Southeast Alaska (SEAK), maternal body volume (BV) increased by just 0.015 m³ or 14.54 kg day⁻¹ (367 MJ day⁻¹). Further, SEAK lactating females showed the slowest rates of growth in body width and condition over a 150 day period compared to non‐lactating females. Maternal investment in calf growth correlated with both maternal length and body condition, with larger females producing larger, faster‐growing calves. In HI, however, the ratio between maternal BV lost and calf BV gained (conversion efficiency) was relatively low compared to other mammals.