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Killer whales Orcinus orca are apex predators, and their health can indicate trophic dynamics in ecosystems that support them. We used aerial photogrammetry to estimate body lengths, to better understand size differences and food requirements, and widths, to infer current nutritional condition, of killer whales in the rapidly warming waters around the Antarctic Peninsula. A remotely controlled hexacopter drone was used to collect aerial images of 242 killer whales of 3 sympatric ecotypes (Type A, n = 34; Type B1, n = 19; and Type B2, n = 189) in the austral summers between 2015/2016 and 2018/2019. Total length (TL) varied between ecotypes, with B2s being diminutive in size, indicating large differences in energy requirements. The mean length for adult females ranged from 5.82 m (B2s) to 6.93 m (B1s), and the mean for adult males ranged from 6.44 m (B2s) to 7.80 m (As). We also found significant differences in head width (HW, proxy for body condition), with B2s being significantly leaner. Although this variation may reflect natural shape differences, we also estimated divergent regression lines of HW∼TL indicating that this difference was greater at larger body sizes, with some anomalously thin adult female B2s. We suggest that these dissimilarities may indicate a density-dependent response, with leaner body condition in adults with higher energetic requirements, as the abundance of B2s is almost an order of magnitude greater than that of B1s and As. We hypothesize that food limitation resulted from a decline in carrying capacity during recent reductions in sea ice and warmer ocean temperatures.

Killer whales ( Orcinus orca ) are apex marine predators in Antarctica, but uncertainty over their taxonomic and ecological diversity constrains evaluations of their trophic interactions. We describe two distinct, sympatric forms sharing the characteristic pigmentation of Type B, the most common around the Antarctic Peninsula. Laser photogrammetry revealed nonoverlapping size differences among adults: Based on a body length index (BLI: blowhole to dorsal fin) adult females of the larger form (“B1”) were 20 % longer than the smaller form (“B2”), and adult males were 24 % longer on average. Dorsal fins of B1 adult females were 19 % taller than B2 females, and adult males 32 % taller. Both types were strongly sexually dimorphic, but B1 more so, including for BLI (B1 males = 1.07× females; B2 = 1.05×) and especially for dorsal fin height (B1 male fins = 2.33× female; B2 = 2.10×). The characteristically large Type B eye patch was more extensive for B1 than B2, comprising 41 and 37 % of BLI, respectively. Average group size was also significantly different, with B1s in smaller groups (mean 7, range 1–14) and B2s more gregarious (mean 36, range 8–75). Stable isotope analysis of skin biopsies indicated dietary differences: a significantly lower nitrogen 15 N/ 14 N ratio in B2s supported observations of feeding primarily on krill consumers (e.g., pygoscelid penguins), while B1s prey mainly on predators of krill consumers (e.g., Weddell seals Leptonychotes weddellii ). These differences likely represent adaptations to distinct foraging niches, which has led to genetic divergence; their ecology now needs further study.

Identifying demographic changes is important for understanding population dynamics. However, this requires long-term studies of definable populations of distinct individuals, which can be particularly challenging when studying mobile cetaceans in the marine environment. We collected photo-identification data from 19 years (1992-2010) to assess the dynamics of a population of bottlenose dolphins ( Tursiops truncatus ) restricted to the shallow (<7 m) waters of Little Bahama Bank, northern Bahamas. This population was known to range beyond our study area, so we adopted a Bayesian mixture modeling approach to mark-recapture to identify clusters of individuals that used the area to different extents, and we specifically estimated trends in survival, recruitment, and abundance of a \"resident\" population with high probabilities of identification. There was a high probability ( p = 0.97) of a long-term decrease in the size of this resident population from a maximum of 47 dolphins (95% highest posterior density intervals, HPDI = 29-61) in 1996 to a minimum of just 24 dolphins (95% HPDI = 14-37) in 2009, a decline of 49% (95% HPDI = −5% to −75%). This was driven by low per capita recruitment (average ∼0.02) that could not compensate for relatively low apparent survival rates (average ∼0.94). Notably, there was a significant increase in apparent mortality (∼5 apparent mortalities vs. ∼2 on average) in 1999 when two intense hurricanes passed over the study area, with a high probability ( p = 0.83) of a drop below the average survival probability (∼0.91 in 1999; ∼0.94, on average). As such, our mark-recapture approach enabled us to make useful inference about local dynamics within an open population of bottlenose dolphins; this should be applicable to other studies challenged by sampling highly mobile individuals with heterogeneous space use.

Identifying demographic changes is important for understanding population dynamics. However, this requires long-term studies of definable populations of distinct individuals, which can be particularly challenging when studying mobile cetaceans in the marine environment. We collected photo-identification data from 19 years (1992-2010) to assess the dynamics of a population of bottlenose dolphins ( Tursiops truncatus ) restricted to the shallow (<7 m) waters of Little Bahama Bank, northern Bahamas. This population was known to range beyond our study area, so we adopted a Bayesian mixture modeling approach to mark-recapture to identify clusters of individuals that used the area to different extents, and we specifically estimated trends in survival, recruitment, and abundance of a \"resident\" population with high probabilities of identification. There was a high probability ( p = 0.97) of a long-term decrease in the size of this resident population from a maximum of 47 dolphins (95% highest posterior density intervals, HPDI = 29-61) in 1996 to a minimum of just 24 dolphins (95% HPDI = 14-37) in 2009, a decline of 49% (95% HPDI = −5% to −75%). This was driven by low per capita recruitment (average ∼0.02) that could not compensate for relatively low apparent survival rates (average ∼0.94). Notably, there was a significant increase in apparent mortality (∼5 apparent mortalities vs. ∼2 on average) in 1999 when two intense hurricanes passed over the study area, with a high probability ( p = 0.83) of a drop below the average survival probability (∼0.91 in 1999; ∼0.94, on average). As such, our mark-recapture approach enabled us to make useful inference about local dynamics within an open population of bottlenose dolphins; this should be applicable to other studies challenged by sampling highly mobile individuals with heterogeneous space use.

Blubber biopsy samples from eastern North Pacific killer whales Orcinus orca were analyzed for fatty acids, carbon and nitrogen stable isotopes and organochlorine contaminants. Fatty acid profiles were sufficiently distinct among the 3 reported ecotypes (resident,' transient' or offshore') to enable individual animals to be correctly classified by ecotype and also by mitochondrial DNA (mtDNA) haplotype. Profiles of PCBs also enabled unambiguous classification of all 3 killer whale ecotypes, but stable isotope values lacked sufficient resolution. Fatty acid, stable isotope and PCB profiles of the resident and transient ecotypes were consistent with those expected for these whales based on their reported dietary preferences (fish for resident whales, marine mammals for transients). In addition, these ecotype profiles exhibited broad similarity across geographical regions, suggesting that the dietary specialization reported for resident and transient whales in the well-studied eastern North Pacific populations also extends to the less-studied killer whales in the western Gulf of Alaska and Aleutian Islands. Killer whales of the same ecotype were also grouped by region of sample collection. The mean stable isotope ratios of various regional groups differed considerably, suggesting that the prey preferences of these North Pacific killer whales may be both region and ecotype specific. Furthermore, 3 specific ecotypes of killer whales were found to have measured stable isotope values that were consistent with dietary preferences reported in the literature. Finally, although the offshore population had blubber fatty acid profiles implicating fish as its primary prey, contaminant and stable isotope results were equally congruent with predation on marine mammals.

Millions of social oceanic delphinids are exposed to and presumably affected by military sonar annually; however, empirically measuring its impact on their behavior is challenging. Consequently, no study has experimentally tested the effects of mid-frequency (3-4 kHz) active sonar (MFAS) on dolphins. We integrated drone-based photogrammetry and focal group movement, passive acoustics, and broad-scale visual observations to measure behavioral responses of short- and long-beaked common, bottlenose, and Risso's dolphins to controlled exposure experiments (CEEs) of military MFAS. Fifty CEEs were conducted across all species, yielding hundreds of hours of acoustic and group sampling data, hundreds of thousands of spatially explicit photogrammetry measurements, and nearly 200 biopsy samples. In our initial analysis of short- and long-beaked common dolphins, we used Bayesian hidden Markov models to evaluate response probability and persistence during CEEs. We commonly detected changes in subgroup movement and aggregation during MFAS exposures but not in controls. In short-beaked common dolphins, a direct relationship between response probability and received level (RL) was observed. Longbeaked common dolphins showed less consistent responses, although contextual differences in some CEEs may have limited which movement responses could be detected. These results represent the first experiments on the effects of MFAS on social delphinids and indicate that these species may be more sensitive to military sonar than previously presumed.

Synopsis Species ecology and life history patterns are often reflected in animal morphology. Blue whales are globally distributed, with distinct populations that feed in different productive coastal regions worldwide. Thus, they provide an opportunity to investigate how regional ecosystem characteristics may drive morphological differences within a species. Here, we compare physical and biological oceanography of three different blue whale foraging grounds: (1) Monterey Bay, California, USA; (2) the South Taranaki Bight (STB), Aotearoa New Zealand; and (3) the Corcovado Gulf, Chile. Additionally, we compare the morphology of blue whales from these regions using unoccupied aircraft imagery. Monterey Bay and the Corcovado Gulf are seasonally productive and support the migratory life history strategy of the Eastern North Pacific (ENP) and Chilean blue whale populations, respectively. In contrast, the New Zealand blue whale population remains in the less productive STB year-round. All three populations were indistinguishable in total body length. However, New Zealand blue whales were in significantly higher body condition despite lower regional productivity, potentially attributable to their non-migratory strategy that facilitates lower risk of spatiotemporal misalignment with more consistently available foraging opportunities. Alternatively, the migratory strategy of the ENP and Chilean populations may be successful when their presence on the foraging grounds temporally aligns with abundant prey availability. We document differences in skull and fluke morphology between populations, which may relate to different feeding behaviors adapted to region-specific prey and habitat characteristics. These morphological features may represent a trade-off between maneuverability for prey capture and efficient long-distance migration. As oceanographic patterns shift relative to long-term means under climate change, these blue whale populations may show different vulnerabilities due to differences in migratory phenology and feeding behavior between regions. Spanish abstract La ecología y patrones de historia de vida de las especies a menudo se reflejan en la morfología animal. Las ballenas azules están distribuidas globalmente, con poblaciones separadas que se alimentan en diferentes regiones costeras productivas de todo el mundo. Por lo tanto, brindan la oportunidad de investigar cómo las características regionales de los ecosistemas pueden impulsar diferencias morfológicas dentro de una especie. Aquí, comparamos la oceanografía física y biológica de tres zonas de alimentación diferentes de la ballena azul: (1) Bahía de Monterey, California, EE. UU., (2) Bahía del sur de Taranaki (BST), Nueva Zelanda, y (3) Golfo de Corcovado, Chile. Adicionalmente, comparamos la morfología de las ballenas azules de estas regiones utilizando imágenes de aeronaves no tripuladas. La Bahía de Monterey y el Golfo de Corcovado son estacionalmente productivos y apoyan la estrategia migratoria de la historia de vida de las poblaciones de ballena azul chilena y del Pacífico Norte Oriental (PNO), respectivamente. Por el contrario, la población de ballena azul de Nueva Zelanda permanece en la menos productiva BST durante todo el año. Las tres poblaciones eran indistinguibles en cuanto a la longitud corporal total. Sin embargo, las ballenas azules de Nueva Zelanda tenían una condición corporal significativamente mayor a pesar de una menor productividad regional, potencialmente atribuible a su estrategia no migratoria que facilita un menor riesgo de desalineación espaciotemporal con oportunidades de alimentación disponibles de manera más consistente. Alternativamente, la estrategia migratoria de las poblaciones de ballenas PNO y chilena puede tener éxito cuando su presencia en las zonas de alimentación se alinea temporalmente con la abundante disponibilidad de presas. Documentamos diferencias en la morfología del cráneo y la aleta caudal entre poblaciones, que pueden estar relacionadas con diferentes comportamientos de alimentación adaptados a las características de hábitat y presas específicas para cada región. Estas características morfológicas pueden representar una compensación entre la maniobrabilidad para la captura de presas y una migración eficiente a larga distancia. A medida que los patrones oceanográficos cambian en términos de mediano a largo plazo debido al cambio climático, estas poblaciones de ballenas azules pueden mostrar diferentes vulnerabilidades debido a diferencias en la fenología migratoria y el comportamiento de alimentación entre regiones.

Understanding how closely related, sympatric species distribute themselves relative to their environment is critical to understanding ecosystem structure and function and predicting effects of environmental variation. The Antarctic Peninsula supports high densities of krill and krill consumers; however, the region is warming rapidly, with unknown consequences. Humpback whales Megaptera novaeangliae and Antarctic minke whales Balaenoptera bonaerensis are the largest krill consumers here, yet key data gaps remain about their distribution, behavior, and interactions and how these will be impacted by changing conditions. Using satellite telemetry and novel spatial point-process modeling techniques, we quantified habitat use of each species relative to dynamic environmental variables and determined overlap in core habitat areas during summer months when sea ice is at a minimum. We found that humpback whales ranged broadly over continental shelf waters, utilizing nearshore bays, while minke whales restricted their movements to sheltered bays and areas where ice is present. This presents a scenario where minke whale core habitat overlaps substantially with the broader home ranges of humpback whales. While there is no indication that prey is limiting in this ecosystem, increased overlap between these species may arise as climate-driven changes that affect the extent, timing, and duration of seasonal sea ice decrease the amount of preferred foraging habitat for minke whales while concurrently increasing it for humpback whales. Our results provide the first quantitative assessment of behaviorally based habitat use and sympatry between these 2 krill consumers and offers insight into the potential effects of a rapidly changing environment on the structure and function of a polar ecosystem.

We used photographic mark-recapture methods to estimate the number of mammal-eating “transient” killer whales using the coastal waters from the central Gulf of Alaska to the central Aleutian Islands, around breeding rookeries of endangered Steller sea lions. We identified 154 individual killer whales from 6,489 photographs collected between July 2001 and August 2003. A Bayesian mixture model estimated seven distinct clusters (95% probability interval = 7-10) of individuals that were differentially covered by 14 boat-based surveys exhibiting varying degrees of association in space and time. Markov Chain Monte Carlo methods were used to sample identification probabilities across the distribution of clusters to estimate a total of 345 identified and undetected whales (95% probability interval = 255-487). Estimates of covariance between surveys, in terms of their coverage of these clusters, indicated spatial population structure and seasonal movements from these near-shore waters, suggesting spatial and temporal variation in the predation pressure on coastal marine mammals.

We propose a continuous-time version of the correlated random walk model for animal telemetry data. The continuous-time formulation allows data that have been nonuniformly collected over time to be modeled without subsampling, interpolation, or aggregation to obtain a set of locations uniformly spaced in time. The model is derived from a continuous-time Ornstein-Uhlenbeck velocity process that is integrated to form a location process. The continuous-time model was placed into a state—space framework to allow parameter estimation and location predictions from observed animal locations. Two previously unpublished marine mammal telemetry data sets were analyzed to illustrate use of the model, by-products available from the analysis, and different modifications which are possible. A harbor seal data set was analyzed with a model that incorporates the proportion of each hour spent on land. Also, a northern fur seal pup data set was analyzed with a random drift component to account for directed travel and ocean currents.