Effects of duty cycle on passive acoustic monitoring metrics: The case of blue whale songs.

Long-term fixed passive acoustic monitoring of cetacean populations is a logistical and technological challenge, often limited by the battery capacity of the autonomous recorders. Depending on the research scope and target species, temporal subsampling of the data may become necessary to extend the deployment period. This study explores the effects of different duty cycles on metrics that describe patterns of seasonal presence, call type richness richness, and daily call rate of three blue whale acoustics populations in the Southern Indian Ocean. Detections of blue whale calls from continuous acoustic data were subsampled with three different duty cycles of 50%, 33%, and 25% within listening periods ranging from 1 min to 6 h. Results show that reducing the percentage of recording time reduces the accuracy of the observed seasonal patterns as well as the estimation of daily call rate and call call type richness. For a specific duty cycle, short listening periods (5-30 min) are preferred to longer listening periods (1-6 h). The effects of subsampling are greater the lower the species' vocal activity or the shorter their periods of presence. These results emphasize the importance of selecting a subsampling scheme adapted to the target species.

Redescription of three fossil baleen whale skulls from the Miocene of Portugal reveals new cetotheriid phylogenetic insights.

Cetotheriidae is a family of baleen whales that went nearly extinct during the Pleistocene (excluding Caperea marginata). For a long time, the Cetotheriidae family has been seen as a problematic clade, but in the past two decades there have been various studies trying to resolve the phylogeny of this group. In 1831, Alexandre Vandelli described three cetotheriid skulls, found during a gold exploration at Adiça beach (Portugal). These specimens constituted the first Portuguese vertebrate fossils ever published in the literature. Another skull was added to the "Vandelli skulls" by Jacinto Pedro Gomes, in 1914, during a survey of the Museu Nacional de História Natural collections without giving information on the origin of this skull. In 1941, Remington Kellogg states that one of the original "Vandelli skulls" is no longer present in the Museu Nacional de História Natural collections. Until today, there is no information on how, or exactly when, the fourth skull and one of the original three "Vandelli skulls" appeared and disappeared, respectively. Since their discovery, all the attempts to describe these specimens were not based on direct observations and no comprehensive phylogenetic analysis have included the three skulls. Here we provide a detailed anatomic description, a new phylogenetic analysis and a palaeoecological reconstruction of these specimens, clarifying their relationships within the Cetotheriidae family and fostering the importance of these historical specimens to the modern comprehension of fossil whale evolution. In addition, our results support that Cephalotropis nectus is a valid species with an emended diagnosis. We also concluded that two specimens belong to a new genus, forming two new fossil species (new combinations).

Application of a seismic network to baleen whale call detection and localization in the Panama basin-a Bryde's whale example.

Baleen whales use sounds of various characteristics for different tasks and interactions. This study focuses on recordings from the Costa Rica Rift, in the Eastern Tropical Pacific Ocean, made by 25 ocean-bottom seismographs and a vertical array of 12 hydrophones between January and February 2015. The whale calls observed are of two kinds: more commonly, repetitive 4-5 s-long signals separated into two frequency bands centered at ∼20 and ∼36 Hz; less commonly, a series of ∼0.5 to 1.0 s-long, lower amplitude signals with frequencies between 80 and 160 Hz. These characteristics are similar to calls attributed to Bryde's whales which are occasionally sighted in this region. In this study, the repetitive calls are detected using both the short-term average/long-term average approach and a network empirical subspace detector. In total, 188 and 1891 calls are obtained for each method, demonstrating the value of the subspace detector for highly similar signals. These signals are first localized using a non-linear grid search algorithm and then further relocalized using the double-difference technique. The high-resolution localizations reveal the presence of at least seven whales during the recording period, often crossing the instrument network from southwest to northeast.

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

Extremes in organismal size have broad interest in ecology and evolution because organismal size dictates many traits of an organism's biology. There is particular fascination with identifying upper size extremes in the largest vertebrates, given the challenges and difficulties of measuring extant and extinct candidates for the largest animal of all time, such as whales, terrestrial non-avian dinosaurs, and extinct marine reptiles. The discovery of Perucetus colossus, a giant basilosaurid whale from the Eocene of Peru, challenged many assumptions about organismal extremes based on reconstructions of its body weight that exceeded reported values for blue whales (Balaenoptera musculus). Here we present an examination of a series of factors and methodological approaches to assess reconstructing body weight in Perucetus, including: data sources from large extant cetaceans; fitting published body mass estimates to body outlines; testing the assumption of isometry between skeletal and body masses, even with extrapolation; examining the role of pachyostosis in body mass reconstructions; addressing method-dependent error rates; and comparing Perucetus with known physiological and ecological limits for living whales, and Eocene oceanic productivity. We conclude that Perucetus did not exceed the body mass of today's blue whales. Depending on assumptions and methods, we estimate that Perucetus weighed 60-70 tons assuming a length 17 m. We calculated larger estimates potentially as much as 98-114 tons at 20 m in length, which is far less than the direct records of blue whale weights, or the 270 ton estimates that we calculated for body weights of the largest blue whales measured by length.

Localization of peptide hormones in the placentas of Bryde's (Balaenoptera brydei), sei (B. borealis), and common minke (B. acutorostrata) whales.

In this study, we examined the morphological features of the placentas from 3 species of rorqual whales (Balaenopteridae), namely Bryde's (Balaenoptera brydei), sei (B. borealis), and common minke (B. acutorostrata) whales, and verified the secretion of 2 placental-specific peptide hormones, placental lactogen (PL) and chorionic gonadotropin (CG). The placentas were collected in the second phase of the Japanese Whale Research Program under a special permit in the North Pacific (JARPN II) between 2009 and 2010. For all three species of rorqual whales, as the fetus grew, the interdigitation between the maternal endometrial folds and chorionic villi became more complicated, and many blood capillaries of chorionic villi and endometrium became larger and infiltrated the trophoblast cells and endometrial epithelial cells, respectively. In the immunohistochemical examination, the trophoblast cells (except for areolar trophoblast cells) showed immunoreactivities for the PL and luteinizing hormone (LH) antibodies, and this phenomenon was similar in the placentas of all 3 rorqual whale species. Our results suggest that PL and LH-like CG play roles in regulating pregnancy in the placenta of cetacean.

Estimating distances to baleen whales using multipath arrivals recorded by individual seafloor seismometers at full ocean depth.

Ocean bottom seismometer networks can record opportunistic data sets of 20-Hz fin whale calls. Because networks are often too sparse for multi-station tracking, single-station methods are needed to estimate call density. We investigated a method to range to singing fin whales at full ocean depths using the spacing of water column multiples. Calls were detected by cross-correlating a spectrogram with a template call. To enhance multipath signals, we considered 20-min windows and either summed the spectrograms of all calls aligned on the strongest detection before measuring the multipath spacing or measured the spacing directly from the autocorrelation of the cross correlation time series. We evaluated the methods at five sites with contrasting seafloor and subsurface properties, bathymetric relief, and water depths of 4000-6000 m, using fin whale songs at four sites and a sei whale song at the fifth. The autocorrelation method works best, and ranges can be obtained to >15 km. Ranging at sedimented sites requires careful accounting for subsurface reflections. Ranges have considerable uncertainty in regions of bathymetric relief. The method requires that the time between calls is different from that of the multipaths and does not work reliably when more than one whale is singing nearby.

A High-Quality Blue Whale Genome, Segmental Duplications, and Historical Demography.

The blue whale, Balaenoptera musculus, is the largest animal known to have ever existed, making it an important case study in longevity and resistance to cancer. To further this and other blue whale-related research, we report a reference-quality, long-read-based genome assembly of this fascinating species. We assembled the genome from PacBio long reads and utilized Illumina/10×, optical maps, and Hi-C data for scaffolding, polishing, and manual curation. We also provided long read RNA-seq data to facilitate the annotation of the assembly by NCBI and Ensembl. Additionally, we annotated both haplotypes using TOGA and measured the genome size by flow cytometry. We then compared the blue whale genome with other cetaceans and artiodactyls, including vaquita (Phocoena sinus), the world's smallest cetacean, to investigate blue whale's unique biological traits. We found a dramatic amplification of several genes in the blue whale genome resulting from a recent burst in segmental duplications, though the possible connection between this amplification and giant body size requires further study. We also discovered sites in the insulin-like growth factor-1 gene correlated with body size in cetaceans. Finally, using our assembly to examine the heterozygosity and historical demography of Pacific and Atlantic blue whale populations, we found that the genomes of both populations are highly heterozygous and that their genetic isolation dates to the last interglacial period. Taken together, these results indicate how a high-quality, annotated blue whale genome will serve as an important resource for biology, evolution, and conservation research.

Investigation of organic contaminants in the blubber of a blue whale (Balaenoptera musculus) first stranded on the coast of Taiwan.

This study presents a comprehensive assessment of persistent organic pollutants (POPs) in the blubber of a stranded blue whale found on the coast of Taiwan. The analysis included polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), Hexachlorobenzene (HCB), and polybrominated diphenyl ethers (PBDEs). The whale exhibited evident signs of emaciation, including low body weight, reduced blubber fat content, and thin blubber thickness. The dominant fatty acid type detected in the blubber was short-chain monounsaturated fatty acids (SC-MUFA), known to aid in thermoregulation. Stable isotope ratios indicated that the blue whale occupied a lower trophic position compared to a fin whale, suggesting its proximity to krill habitats in the Southern Ocean for feeding. The average concentrations of DDTs (1089.2 ± 4.7 ng/g lw; ΣDDT) and PCBs (1057.1 ± 49.8 ng/g lw) in the blubber were almost one order of magnitude higher than PAHs (41.7 ± 10.0 ng/g lw), HCB (70.6 ± 2. ng/g lw), and PBDEs (7.2 ± 1.2 ng/g lw). Pollutant concentrations in this individual blue whale were comparable to levels found in Norway, higher than those found in Chile, and notably lower than those found in Canada and Mexico. Calculating the biomagnification factor (BMF) for the POPs from krill (Euphausia superba) to the blue whale revealed significant bioaccumulation of pollutants in this particular whale. Additional research is imperative to achieve a thorough comprehension of bioaccumulation of POPs and their potential toxicological impacts on whale health.

Characteristics and spatiotemporal variation of sei whale (Balaenoptera borealis) downsweeps recorded in Atlantic Canada.

The call characteristics and vocal behaviour of sei whales (Balaenoptera borealis) off eastern Canada, including potential spatiotemporal variation, is poorly understood. Such information can improve the performance of automated detector-classifiers, enhancing the accuracy and efficiency of identifying sei whales in large acoustic datasets. Ultimately, these data can be used to understand the occurrence, distribution, and population structure of sei whales in Atlantic Canada. We measured sei whale downsweep characteristics recorded from six locations off Nova Scotia (NS) and Newfoundland and Labrador (NFLD), Canada over a two-year period (2015-2017), and examined variation between call subtypes (singlets, doublets, triplets+), and seasons (Spring, Summer, Fall, Winter). We found that downsweeps had a mean duration of 1.58 s, sweeping from 75.66 to 34.22 Hz, with a peak frequency of 43.89 Hz and an intra-call interval of 2.22 s. Most call characteristics did not vary between location, subtype, or season; however, significantly longer downsweeps occurred off NS, within doublet calls, and in fall months. We also found that NFLD had a higher proportion of doublets (70%) than NS (52%). This variation may be evidence of acoustically diverging sei whale populations, as well as useful for improving detector-classifiers of sei whales in the region.

Acoustic recording tags provide insight into the springtime acoustic behavior of sei whales in Massachusetts Bay.

The acoustic ecology of sei whales (Balaenoptera borealis) is poorly understood due to limited direct observation of the behavioral context of sound production and individual behavior. Suction cup-attached acoustic recording tags were deployed on sei whales to unambiguously assign call types and explore the acoustic behavior of this endangered species. Twelve tag deployments resulted in ∼173 h of acoustic data and 1030 calls. Sound types included downsweeps and three previously undescribed call types. Knocks were short duration (<1 s), with an average peak frequency of 330 Hz. Pulse type 1 and pulse type 2 calls, typically produced in sequences, were short in duration (0.08 and 0.28 s) and low in average peak frequency (50 and 26 Hz), with relatively high received levels. Average call rates for all call types combined were three calls per hour, but increased during twilight. Sex differences in call type usage included a higher use of pulses by females and knocks by males. Calls were almost exclusively produced at depths <10 m, although whales rarely dove deeper in this study. These data provide a more comprehensive picture of the acoustic and behavioral ecology of sei whales than previously possible, which can inform future conservation efforts for this endangered species.

Kinematics and energetics of foraging behavior in Rice's whales of the Gulf of Mexico.

Rorqual foraging behavior varies with species, prey type and foraging conditions, and can be a determining factor for their fitness. Little is known about the foraging ecology of Rice's whales (Balaenoptera ricei), an endangered species with a population of fewer than 100 individuals. Suction cup tags were attached to two Rice's whales to collect information on their diving kinematics and foraging behavior. The tagged whales primarily exhibited lunge-feeding near the sea bottom and to a lesser extent in the water-column and at the sea surface. During 6-10 min foraging dives, the whales typically circled their prey before executing one or two feeding lunges. Longer duration dives and dives with more feeding-lunges were followed by an increase in their breathing rate. The median lunge rate of one lunge per dive of both animals was much lower than expected based on comparative research on other lunge-feeding baleen whales, and may be associated with foraging on fish instead of krill or may be an indication of different foraging conditions. Both animals spent extended periods of the night near the sea surface, increasing the risk for ship strike. Furthermore, their circling before lunging may increase the risk for entanglement in bottom-longline fishing gear. Overall, these data show that Rice's whale foraging behavior differs from other lunge feeding rorqual species and may be a significant factor in shaping our understanding of their foraging ecology. Efforts to mitigate threats to Rice's whales will benefit from improved understanding of patterns in their habitat use and fine-scale ecology.

Critically endangered Rice's whales (Balaenoptera ricei) selectively feed on high-quality prey in the Gulf of Mexico.

Determining the drivers of prey selection in marine predators is critical when investigating ecosystem structure and function. The newly recognized Rice's whale (Balaenoptera ricei) is one of the most critically endangered large whales in the world and endemic to the industrialized Gulf of Mexico. Here, we investigated the drivers of resource selection by Rice's whales in relation to prey availability and energy density. Bayesian stable isotope (δ13C, δ15N) mixing models suggest that Rice's whales feed primarily on a schooling fish, Ariomma bondi (66.8% relative contribution). Prey selection using the Chesson's index revealed that active prey selection was found to be positive for three out of the four potential prey identified in the mixing model. A low degree of overlap between prey availability and diet inferred from the mixing model (Pianka Index: 0.333) suggests that prey abundance is not the primary driver of prey selection. Energy density data suggest that prey selection may be primarily driven by the energy content. Results from this study indicate that Rice's whales are selective predators consuming schooling prey with the highest energy content. Environmental changes in the region have the potential to influence prey species that would make them less available to Rice's whales.

A New Acoustical Autonomous Method for Identifying Endangered Whale Calls: A Case Study of Blue Whale and Fin Whale.

In this paper, we study to improve acoustical methods to identify endangered whale calls with emphasis on the blue whale (Balaenoptera musculus) and fin whale (Balaenoptera physalus). A promising method using wavelet scattering transform and deep learning is proposed here to detect/classify the whale calls quite precisely in the increasingly noisy ocean with a small dataset. The performances shown in terms of classification accuracy (>97%) demonstrate the efficiency of the proposed method which outperforms the relevant state-of-the-art methods. In this way, passive acoustic technology can be enhanced to monitor endangered whale calls. Efficient tracking of their numbers, migration paths and habitat become vital to whale conservation by lowering the number of preventable injuries and deaths while making progress in their recovery.

An unknown nocturnal call type in the Mariana Archipelago.

In spring/summer of 2018 and 2021, the Pacific Islands Fisheries Science Center Cetacean Research Program deployed drifting acoustic recorders in the U.S. Exclusive Economic Zones surrounding the Mariana Archipelago. Manual assessments revealed a low-frequency (median 473-554 Hz), short-duration (median 0.596 s), stereotypic tonal nocturnal call throughout the Mariana Archipelago. Based on time of year, spatiotemporal patterns, clear division among calls (i.e., no chorusing), comparisons with known vocalizations of whales, turtles, and fish, and presence of Bryde's whale calls, and because the call has not been detected elsewhere, we hypothesize this 500-Hz pulsed call is produced by Bryde's whales (Balaenoptera brydei).

A novel expert-driven methodology to develop thermal response curves and project habitat thermal suitability for cetaceans under a changing climate.

Over the last decades, global warming has contributed to changes in marine species composition, abundance and distribution, in response to changes in oceanographic conditions such as temperature, acidification, and deoxygenation. Experimentally derived thermal limits, which are known to be related to observed latitudinal ranges, have been used to assess variations in species distribution patterns. However, such experiments cannot be undertaken on free-swimming large marine predators with wide-range distribution, like cetaceans. An alternative approach is to elicit expert's knowledge to derive species' thermal suitability and assess their thermal responses, something that has never been tested in these taxa. We developed and applied a methodology based on expert-derived thermal suitability curves and projected future responses for several species under different climate scenarios. We tested this approach with ten cetacean species currently present in the biogeographic area of Macaronesia (North Atlantic) under Representative Concentration Pathways 2.6, 4.5 and 8.5, until 2050. Overall, increases in annual thermal suitability were found for Balaenoptera edeni, Globicephala macrorhynchus, Mesoplodon densirostris, Physeter macrocephalus, Stenella frontalis, Tursiops truncatus and Ziphius cavirostris. Conversely, our results indicated a decline in thermal suitability for B. physalus, Delphinus delphis, and Grampus griseus. Our study reveals potential responses in cetaceans' thermal suitability, and potentially in other highly mobile and large predators, and it tests this method's applicability, which is a novel application for this purpose and group of species. It aims to be a cost-efficient tool to support conservation managers and practitioners.

Occurrence of emerging brominated flame retardants and organophosphate esters in marine wildlife from the Norwegian Arctic.

To understand the exposure and potential sources of emerging brominated flame retardants (EBFR) and organophosphate esters (OPEs) in marine wildlife from the Norwegian Arctic, we investigated concentrations of EBFRs in 157 tissue samples from nine species of marine vertebrates and OPEs in 34 samples from three whale species. The samples, collected from a wide range of species with contrasting areal use and diets, included blubber of blue whales, fin whales, humpback whales, white whales, killer whales, walruses and ringed seals and adipose tissue and plasma from polar bears, as well as adipose tissue from glaucous gulls. Tris(2-ethylhexyl) phosphate (TEHP) and tris(2-chloroisopropyl) phosphate (TCIPP) ranged from <0.61 to 164 and < 0.8-41 ng/g lipid weight, respectively, in blue whales and fin whales. All other EBRFs and OPEs were below the detection limit or detected only at low concentration. In addition to the baseline information on the occurrence of EBFRs and OPEs in marine wildlife from the Arctic, we provide an in-depth discussion regarding potential sources of the detected compounds. This information is important for future monitoring and management of EBFRs and OPEs.

Oceanic giants dance to atmospheric rhythms: Ephemeral wind-driven resource tracking by blue whales.

Trophic transfer of energy through marine food webs is strongly influenced by prey aggregation and its exploitation by predators. Rapid aggregation of some marine fish and crustacean forage species during wind-driven coastal upwelling has recently been discovered, motivating the hypothesis that predators of these forage species track the upwelling circulation in which prey aggregation occurs. We examine this hypothesis in the central California Current Ecosystem using integrative observations of upwelling dynamics, forage species' aggregation, and blue whale movement. Directional origins of blue whale calls repeatedly tracked upwelling plume circulation when wind-driven upwelling intensified and aggregation of forage species was heightened. Our findings illustrate a resource tracking strategy by which blue whales may maximize energy gain amid ephemeral foraging opportunities. These findings have implications for the ecology and conservation of diverse predators that are sustained by forage populations whose behaviour is responsive to episodic environmental dynamics.

Blue whales increase feeding rates at fine-scale ocean features.

Marine predators face the challenge of reliably finding prey that is patchily distributed in space and time. Predators make movement decisions at multiple spatial and temporal scales, yet we have a limited understanding of how habitat selection at multiple scales translates into foraging performance. In the ocean, there is mounting evidence that submesoscale (i.e. less than 100 km) processes drive the formation of dense prey patches that should hypothetically provide feeding hot spots and increase predator foraging success. Here, we integrated environmental remote-sensing with high-resolution animal-borne biologging data to evaluate submesoscale surface current features in relation to the habitat selection and foraging performance of blue whales in the California Current System. Our study revealed a consistent functional relationship in which blue whales disproportionately foraged within dynamic aggregative submesoscale features at both the regional and feeding site scales across seasons, regions and years. Moreover, we found that blue whale feeding rates increased in areas with stronger aggregative features, suggesting that these features indicate areas of higher prey density. The use of fine-scale, dynamic features by foraging blue whales underscores the need to take these features into account when designating critical habitat and may help inform strategies to mitigate the impacts of human activities for the species.

Mathematical models of long term evolution of blue whale song types' frequencies.

The linear decrease in the frequency of blue whale songs around the world is, to date, an unexplained phenomenon. We show it can be reproduced by a mathematical model considering two antagonistic behavioral trends: first, a bias towards conformity in the song, and second, a tendency to try and sing lower than the other whales. We check the robustness of our model by considering some more complex premises. First, different hierarchical relations between the singers are explored, adapting methods used in the flocking motion studies. Then a population-dependant simulation shows that even considering the gradual addition of new whales, the evolution is still globally linear. Finally, we show that intra-annual variations surging from different causes can be naturally incorporated into the model. We then conclude that, unlike other explanations, a cultural hypothesis seems compatible with the observed linearity of the blue whales's songs frequency shift.