Stephanie H. Stack

Growth curves provide critical biological context for understanding life history, population dynamics, and responses to environmental change, yet our understanding of age–length relationships for humpback whales ( Megaptera novaeangliae ) remains largely based on measurements collected during commercial whaling operations from the mid‐20th century. These measurements may not reflect the growth trajectories of present‐day populations that have undergone substantial recovery and ecological change. Here, we establish contemporary, population‐specific, growth curves for eastern Australian humpback whales (breeding stock E1) using noninvasive aerial photogrammetry coupled with photo‐identification sighting histories. Total length measurements were collected from 865 individually identified whales between 2021 and 2024 and for a subset of these individuals, minimum age estimates were derived from long‐term photo‐identification sighting histories. Bayesian growth models were fitted to evaluate age–length relationships across multiple growth functions and age formulations. Growth was rapid during early life and approached an asymptotic adult length consistent with historical estimates for humpback whales in Australia. Predicted length at age 5 (median 10.93 m) and the age at which whales reached 90% of asymptotic length (median 6.58 years) indicated faster juvenile growth and earlier attainment of near‐adult size than reported elsewhere for contemporary Northern Hemisphere populations. The growth parameters and length‐at‐age estimates provide a baseline for demographic inference. Further, they support long‐term monitoring of growth and energetic constraints in a humpback whale population that has undergone one of the most rapid recoveries documented in a large whale species and is experiencing ongoing environmental change.

Cetacean epibionts offer noninvasive insights into host health, physiology, and spatial ecology, yet quantitative assessments in wild populations remain scarce. Although vessel‐based observations may be limited by field of view and analyst input, unoccupied aerial vehicles (UAVs; drones) are increasingly used to monitor cetacean health indices, enhancing observational availability and reproducibility. However, the suitability of drones for quantifying epibiota has not been thoroughly evaluated. Implementing a standardized workflow, we compared dorsal proportional epibiont coverage estimates derived from drone‐based imagery and traditional vessel‐based techniques across reproductive classes of humpback whales ( Megaptera novaeangliae ). We analyzed 32 paired datasets using pixel‐based methods, incorporating semiautomated graph‐cut segmentation and iterative color‐thresholding. Drone‐derived estimates of epibiont coverage consistently exceeded vessel‐based measures, which averaged 58% of the relative coverage estimated from corresponding drone imagery, partly attributable to variable lighting during image capture. Nevertheless, 94% of paired observations differed by less than 5% in absolute coverage, indicating strong agreement. While refinement of flight parameters, image resolution, and further validation are recommended, we demonstrate that drones can provide a reliable source of quantitative epibiont data, with potential applicability across diverse epibiont–host systems, benefiting cetacean population health monitoring programs and informing conservation strategies, particularly for elusive or understudied species.

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.

Body condition is a critical indicator of health and nutritional status in cetaceans, particularly for small, endangered populations facing ecological stressors. We used aerial photogrammetry to evaluate body size and condition of the endangered false killer whale Pseudorca crassidens population resident in the main Hawaiian Islands. From 2019 to 2025, 68 individuals were assessed across 142 photogrammetric measurements. Relative body width declined with age class, particularly across the mid-body region, indicating early-life lipid accumulation followed by increased energetic demands in adulthood. Photogrammetric volume estimates were validated against 3D-scanned individuals, providing estimates within 3% of scanned volumes. Standardized major axis regression revealed significant differences in the body length-volume relationship across social clusters. Body condition index (BCI) varied across years, with the lowest values in 2020, coinciding with the largest single-year population decline and record sea surface temperatures from a marine heatwave, suggesting that environmental stressors may have contributed to reduced body condition during this period. Individual-level trajectories further highlighted substantial fluctuations in BCI, including one case of 28% estimated body mass loss over a 2.5 mo period, and pronounced variability within one cluster, potentially reflecting higher energetic costs and nutritional stress associated with broader ranging behavior. These findings underscore the influence of spatial ecology and local prey availability on the health of this declining population, while providing a foundation for long-term monitoring of the energetic stressors shaping their viability.

Movements between humpback whale (Megaptera novaeangliae) breeding stocks are exceedingly rare, and exchange between distant breeding grounds in both directions has not previously been documented between eastern Australia and Brazil. Using 19 283 curated photo-identification images from eastern Australia (breeding stock E1 (BSE1)) and Brazil (breeding stock A (BSA)) collected between 1984 and 2025, we identified two individuals photographed in both areas, representing the first recorded exchange in both directions between BSE1 and BSA. The breeding grounds are separated by minimum great-circle distances of 14 200 km and 15 100 km, respectively, distances that reflect the separation between sighting locations rather than actual distances travelled, as photo-identification records only the endpoints of each individual’s travel. Resighting intervals of 6 and 22 years suggest that these are rare, possibly single-lifetime events rather than regular migratory shifts. These findings extend the known spatial limits of inter-basin connectivity for Southern Hemisphere humpback whales and support the ‘Southern Ocean Exchange’ hypothesis, whereby population recovery and environmental variability may create opportunities for exceptional exchange between ocean basins. Although such events occurred in only 0.01% of identified whales, continued global collaboration through photo-identification platforms will be essential for detecting and quantifying these rare exchanges.

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.

The drivers of animal social structures remain poorly understood, particularly in species such as cetaceans that are wide‐ranging and challenging to study. Understanding the factors shaping sociality can shed light on population ecology, gene flow, and information transmission. Here, we investigated variation in social structure among three independent island‐associated stocks of common bottlenose dolphins ( Tursiops truncatus ) around the main Hawaiian Islands. We generated social networks for each stock using photo‐identification data from 2002 to 2022. We calculated modularity, density, degree centralization, and betweenness centralization to assess network structure. We measured the stocks' available habitat and calculated their population densities. We also quantified association strength with the half‐weight association index (HWI) and compared it within‐ and between‐clusters, and by sex for each stock. HWIs revealed that within‐cluster associations were much stronger than between‐cluster in all stocks. Network modularity and HWI showed the lowest fragmentation into distinct clusters and the strongest associations in the smallest of the three habitats (Kaua‘i‐Ni‘ihau). We found no conclusive evidence of sex differences in HWI. Our findings suggest that denser populations might drive social network fragmentation. Our study highlights the importance of further investigating the drivers of sociality.

Anthropogenic impacts on marine systems are increasing in frequency, geographic range and severity. While changes in climate will likely lead to the greatest impacts at the system-level, for marine megafauna, entanglement in marine debris also constitutes a pernicious threat. For baleen whales, in regions where high productivity and prolific fisheries overlap, entanglement is emerging as a component of their life history: In some of these regions, entanglement comprises the leading cause of serious injury and mortality. Additionally, up to 80% of whales carry scars indicative of entanglement, and associated declines in long-term health are reducing fecundity. Here, we describe behavioral traits seen in humpback whales during entanglement incidents. Specifically, we focus on reports of humpback whales that have remained in association with entangled whales during these incidents and apply the term “companion whales” in reference to these whales. Reports reviewed include a detailed account of a recent incident observed in Hawaiian waters, a compilation of 62 accounts of similar behavior extracted from 414 reports of entanglement events provided by regional entanglement response networks, and a series of six reports associated with whaling activities. The similarities between the current behavior of companion whales and behaviors observed during whaling activities suggest that this may be an example of behavioral plasticity, underscoring the expanding behavioral repertoire exhibited by baleen whales, and highlighting their potential resilience as they respond to the changing marine environment.

Humpback whale (Megaptera novaeangliae) mothers and their calves predominantly avoid social interactions with conspecifics. However, observations from East Australia indicate that mother–calf pairs occasionally associate with other mother–calf pairs. We investigated the prevalence, composition, and behaviour of multiple-mother-calf (multi-MC) groups in East Australia from 2009 to 2023. In 2009 and 2010, data were collected from two tropical breeding areas (Port Douglas and the Whitsunday Islands) and two coastal migratory locations (Hervey Bay and Eden). No multi-MC groups were detected in Port Douglas out of 15 calf groups observed. Only one (4%) of 23 calf groups encountered in the Whitsunday Islands was a multi-MC group. In Hervey Bay, seven (4%) multi-MC groups were recorded out of 180 calf groups; while in Eden, seven (11%) out of 63 calf groups were multi-MC groups. Between 2009 and 2023, 978 calf groups were encountered in Hervey Bay over 12 years, including 56 (6%) multi-MC groups; while 39 (13%) out of 293 calf groups encountered in Eden over six years were multi-MC groups. Multi-MC groups exhibited more social behaviours compared to single MC groups. Social behaviour was common in both Hervey Bay and Eden; however, groups in Hervey Bay displayed lower arousal behaviours, consistent with the area’s importance as a resting habitat for whales. We did not detect behavioural differences in multi-MC groups with or without escort whales. These findings suggest that humpback whale mothers may gradually socialise their calves by forming multi-MC groups, with an increasing prevalence along the southerly migration route as calves mature. While multi-MC groups have only been detected in Australia to date, it is possible that they occur elsewhere, particularly if social development is a key driver of the phenomenon. Our results enhance our understanding of humpback whale mother–calf sociality and highlight the importance of migration routes for calf social development.

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.