Baleen Whales Research Articles

Blue whales not bothered by quake sounds

Our understanding of the prevalence of noise in our oceans has changed dramatically in recent years. We now know that the submarine environment is anything but Cousteau's ‘silent deep’. Shipping traffic, naval sonar and exploration for subsea resources, for example, all add to the underwater hubbub, leading to adverse impacts on the ability of marine animals to communicate, altered access to feeding grounds and elevated stress levels. And the largest animal in the world, the blue whale (Balaenoptera musculus), is not exempt from the effects of noise. When exposed to military sonar, they may swim faster, stop feeding and call less frequently; they are known to call louder when they hear shipping. And when airguns are discharged while probing for undersea oil, whales appear to call more frequently. Yet, humans are not responsible for all undersea noise. The waters around New Zealand are alive with deep rumbling of earthquakes as the tectonic plates shift and jar. So, what impact do these thunderous natural sounds have on the sensitive behemoths within earshot?Dawn Barlow at Oregon State University, USA, and colleagues from her home university and Cornell University, USA, listened to the blue whale undersea chorus recorded by five listening stations in the South Taranaki Bight, New Zealand. They used geological databases to identify individual earthquakes with Richter magnitudes greater than 3 originating within the study area and matched up blue whale calls at hourly intervals in the run up to and following each earthquake. The team kept track of two specific kinds of calls – the ‘D-call’, which is produced by both sexes when feeding and ‘song’, which is produced only by males – measuring how often and estimating how loud the D-calls were and measuring the intensity of song. In addition, the researchers examined the whales’ calls during periods when the earth's crust was silent, to capture seasonal variation in both soundscape and whale behaviour.To the surprise of Barlow and her colleagues, they found that the whales appeared to be unperturbed by seismic activity. The whales continued producing calls in the periods before and after earthquakes, and there was no difference in the animals’ calling rates. Specifically, no earthquake metrics (magnitude, depth, distance to the epicentre and relative received level) were useful predictors for estimating changes in blue whale calling rate. While the acoustic signature of an earthquake typically lasted less than a minute, these loud and natural occurrences did not seem to bother the blue whales. While the recording set-up did not allow the researchers to calculate the sound level that the whales would have heard, they were able to describe how loud the earthquakes were at the recorders and suspect that they all fell below the noise thresholds thought to disturb the whales’ behaviour.Scientists are chipping away at understanding how wild animals respond to disturbances by quantifying the responses of many species to specific acoustic disturbances, as individual intrusions can accumulate to impact the health and survival of a population. They are finding increasingly that the existing backdrop of both the animals’ behavioural state and its surrounding environment in which noises are heard matters a lot when it comes to predicting how they react. To contextualise whale responses to anthropogenic sounds, we also need to understand how they respond to natural noises. While the findings in Barlow's study are for a specific baleen whale in a specific region of the world, understanding how other whales respond to simultaneously occurring natural and anthropogenic noises can help to add context to their responses.

Effects of changing temperature phenology on the abundance of a critically endangered baleen whale

Incorporating the effects of climate change in species management strategies is one of today’s greatest conservation challenges. Mechanistic models can be used to address these challenges because they explain how climate change effects cascade through ecosystems and influence species distributions. We used structural equation models to test hypotheses about the cascading effects of climate change and basin-scale variables on the local abundance of North Atlantic right whales, a critically endangered species, in a historically important feeding habitat. We found that effects of the North Atlantic Oscillation, a basin-scale variable, on local right whale abundance occurred through a cascade of effects on other ecosystem variables, including chlorophyll a concentration, Calanus finmarchicus abundance, and zooplankton patchiness. These effects varied by month. We also found that the western Gulf of Maine spring thermal transition date (a proxy for climate change) is a major direct and indirect driver of variations in local right whale abundance. The indirect effect of earlier spring transition dates, through a pathway of prey abundance, suggested a decrease in local right whale abundance. However, right whale abundance increased because of the direct effect of regional spring transition date. The direct effect suggests that right whales may be using regional temperatures as a movement cue. The counter-acting direct and indirect effects of spring transition date suggest that right whales could face a mismatch with their prey, which could ultimately result in another large-scale distribution shift. Our causal modeling approach demonstrates that the influence of climate change on local right whale abundance in the Gulf of Maine cascades through a network of variables. These cascading effects make predicting local right whale abundance challenging and suggest that successful endangered species conservation requires identifying the mechanisms underlying species distributions.

Strandings in St Vincent Gulf Bioregion, South Australia: 12-Year Study Monitors Biology and Pathology of Cetaceans

The semi-enclosed environment of the St Vincent Gulf Bioregion and its fauna are impacted by many human activities. Long-term monitoring of cetaceans is vital. Records of collected specimens (173) and those not examined by the South Australian Museum (98 non-specimens) from 2009–2020 were analyzed. Necropsies were carried out on most carcasses using gross, histopathological, and diagnostic assessment of pathogens, organs, and skin lesions. The relative age and circumstance of death were assigned. Baleen whales (five species) and odontocetes (eight species) were studied. Indo-Pacific bottlenose dolphins (Tursiops aduncus) and common dolphins (Delphinus delphis) were frequently recorded and analyzed in detail. Anthropogenic cases were prevalent (21%). Many dolphins (62%) were immature males. Disease (73%) was the most frequently recorded circumstance of death. The most common pathological change was inflammatory disease, including infectious pneumonia. In Indo-Pacific bottlenose dolphins, infectious disease was more prevalent in the greater St Vincent Gulf Bioregion than in the Adelaide Dolphin Sanctuary. Microbe testing confirmed 32 species of bacteria, 2 fungi, and 1 virus. Nematodes and trematodes were recorded throughout the study, sometimes in association with microbes. Toxoplasma gondii was observed in an Indo-Pacific bottlenose dolphin. Severe traumatic injury was recorded in many dolphins, including anthropogenic cases. A tumor (leiomyoma) was described from a single common dolphin. This study provides an important baseline for the future monitoring of emerging infectious and chronic diseases, and anthropogenic threats in the region.

"Playing the beat": Occurrence of Bio-duck calls in Santos Basin (Brazil) reveals a complex acoustic behaviour for the Antarctic minke whale (Balaenoptera bonaerensis).

The Antarctic minke whale (Balaenoptera bonaerensis) (AMW) is one of the smallest species among baleen whales, occurring in the southern hemisphere from Antarctica to near the equator, and performing seasonal migrations from polar to tropical waters. Information about (AMW) occurrence in the winter breeding grounds is scarce, mostly coming from old records from whaling stations before the 1960’s international moratorium, such as Costinha Station in Northeastern Brazil (6° S / 34° W) and some sightings from few dedicated visual surveys. Acoustic methods can provide important data on the occurrence and distribution of migratory species. This work describes the occurrence of the Antarctic minke whale through acoustic detections of their “Bioduck” vocalisations in the Santos Basin, South-Southeastern Brazil (22° and 28° S / 42° and 48° W). Data was recorded between November 12 and December 19, 2015. AMW calls were detected for 12 days. We detected and classified 9 different Bio-duck calls in Brazilian coastal waters, evidencing a highly diverse acoustic behavior for the minke whale breeding ground. This is the first attempt to describe the acoustic diversity of AMW vocalizations in lower latitudes, contributing important information for future conservation efforts and management of AMW populations and their habitat. Therefore, our study presents the foremost acoustic evidence of the Antarctic minke whale in Brazilian coastal waters.

Occurrence of cetaceans and seabirds along the Indian Ocean 110°E meridian from temperate to tropical waters

The first extensive physical and biological observations of the Indian Ocean were made from 1959 to 1965, during a ship-based International Indian Ocean Expedition (IIOE-1). Decades later in 2019, the 110°E meridian was revisited during the second International Indian Ocean Expedition (IIOE-2). The aim of this study, as part of a large number of related studies, was to examine the occurrence of cetaceans and seabirds along the 110°E meridian from temperate to tropical waters (39.5–11.5°S). Cetaceans and seabirds were actively scanned for across a four-week period spanning austral autumn to winter. Acoustic recordings of vocalising cetaceans were made using directional and omnidirectional sonobuoys (n = 87 deployments). In total, seven cetacean sightings (six baleen whale, one toothed whale), 186 seabird sightings and 225 cetacean acoustic detections were recorded. The baleen whale species detected acoustically were assigned to Antarctic blue whales (Balaenoptera musculus intermedia; Z-calls), pygmy blue whales (B. m. brevicauda; south east Indian Ocean 3-component calls, D-calls), fin whales (B. physalus; 20 Hz-pulses), southern right whales (Eubalaena australis; upcalls), Antarctic minke whales (B. bonaerensis; bio-duck calls) and an unknown signal; a “spot call”. The toothed whale species detected acoustically were Kogia sperm whales (Kogia sp.) and delphinids (from whistles).. Pygmy blue whales were detected across Subantarctic to Tropical Surface Waters, and were the most commonly detected cetacean. There was some delineation in other cetaceans: the spot call was detected in Subantarctic and Subtropical Surface Water (south of 23°S); fin whales in Subtropical Surface Water (between 23° and 30.5°S); and Antarctic minke whales in Tropical Surface Water (between 14° and 23°S). Data were not collected on cetaceans during IIOE-1, so data here represent baseline occurrence along 110°E for future studies. A total of 22 seabird species were sighted, including, petrels, albatrosses, tropicbirds, terns, shearwaters, boobies, frigatebirds, gannets, gulls, skuas and prions. Soft-plumaged petrels (Pterodroma mollis) were observed across all water masses and were the most commonly sighted seabird. There was some delineation of seabird species; albatrosses were sighted south of the Subtropical Front (south of 32°S); flesh-footed shearwaters (Ardenna carneipes) in Subantarctic and Subtropical Surface Waters (south of 27°S); and tropicbirds in Tropical Surface Water (north of 20°S). The occurrence of highly mobile species is particularly important to investigate as the waters in the eastern Indian Ocean have been warming faster than in the Pacific and Atlantic Oceans.

Sam Houston Ridgway 1936–2022

Sam Houston Ridgway 1936–2022

Oligocene-Miocene marine mammals from Belgrade Quarry, North Carolina

A diverse but fragmentary assemblage of fossil cetaceans is reported from the Oligocene-Miocene Belgrade Formation of North Carolina. This assemblage preserves many odontocetes including four xenorophids (Albertocetus, Echovenator sp., cf. Cotylocara, and Xenorophus sp.), a possible waipatiid (cf. Waipatiidae), a giant agorophiid-grade dolphin (Ankylorhiza), a shark-toothed dolphin (cf. Squalodon), longirostrine “swordfish” dolphins (Eurhinodelphinidae), a longirostrine eoplatanistid dolphin (cf. Eoplatanista), a longirostrine squalodelphinid dolphin, a possible early delphinidan (Kentriodontidae), as well as an eomysticetid baleen whale (Eomysticetus sp.) and sirenian fragments. Most of these taxa are characteristic of or unique to Oligocene deposits (Xenorophidae, cf. Waipatiidae, Ankylorhiza, Eomysticetus) whereas others are more typical of early or middle Miocene deposits (cf. Eoplatanista, Eurhinodelphinidae, cf. Squalodon, Squalodelphinidae, Kentriodontidae). The Belgrade Formation at Belgrade Quarry is dated to 25.95–21.12Ma, approximating the Oligocene-Miocene transition. The transitional composition of the Belgrade cetacean assemblage suggests gradual changes between Oligocene to Miocene cetacean faunas, to be verified by the discovery of more complete remains from the poorly sampled earliest Miocene (Aquitanian).

Sex- and age-specific migratory strategies of blue whales in the northeast Pacific Ocean

Migration is a complex behavior that has evolved in multiple taxonomic groups as a means of accessing productive foraging grounds and environmentally stable areas suitable for reproduction. For migratory whales that forage throughout the year because of their high energetic demands, changes in the abundance of prey in different areas along their migratory route(s) can have serious implications for individual fitness and population viability. Thus, identifying the regions these species use to forage and breed while evaluating their migratory plasticity at the individual level can provide key information for their management and conservation. Serial stable isotope analysis of whale baleen, a continuously growing but metabolically inert tissue, has proven useful in generating individual migratory and foraging records over several years prior to death. We measured carbon (δ13C) and nitrogen (δ15N) isotope values along the length of baleen plates collected from thirteen blue whales of different sex and age classes, representing the largest collection analyzed to date in the northeast Pacific Ocean. Adult females exhibited relatively stable seasonal movements between temperate latitude foraging grounds and subtropical breeding grounds, although two skipped migration one year and subsequently moved to the same subtropical breeding ground near the Costa Rica Dome, potentially to give birth. Adult males exhibited two movement strategies with most remaining at temperate latitudes for 3-4 years before death, while two migrated to subtropical breeding grounds. In contrast, movement patterns in juveniles were erratic. These results are potentially driven by the energetic requirements during pregnancy and nursing in adult females, intra-specific competition among adult males, and inexperience in locating prey in juveniles. We also describe baleenδ15N patterns in recently weaned whales (<16.5m) that reflect switching from the consumption of milk to solid food (krill). In addition, baleenδ13C data suggest that weaned whales continue to use stored nutrients (blubber) acquired during the nursing period long after they are weaned. These results broaden our understanding of habitat selection in this species, highlight the importance of nursing for the critical period after weaning, and indicate that the Costa Rica Dome is an important calving region for this endangered population.

Occurrence of baleen whales in the New York Bight, 1998–2017: insights from opportunistic data

AbstractThe New York Bight is undergoing rapid anthropogenic change amidst an apparent increase in baleen whale sightings. Though survey efforts have increased in recent years, the lack of published knowledge on baleen whale occurrence prior to these efforts impedes effective assessments of distributional or behavioural shifts due to increasing human activities. Here we synthesize opportunistic sightings of baleen whales from 1998–2017, which represent the majority of sightings data prior to recent survey efforts, and which are largely unpublished. Humpback and fin whales were the most commonly sighted species, followed by North Atlantic right whales and North Atlantic minke whales. Important behaviours such as feeding and nursing were observed, and most species (including North Atlantic right whales) were seen during all seasons. Baleen whales overlapped with multiple anthropogenic use areas, and all species, but of particular importance North Atlantic right whales, were sighted outside the spatial and temporal bounds of the Seasonal Management Areas for North Atlantic right whales. These opportunistic data are vital for providing a baseline and context of baleen whales in the New York Bight prior to broad-scale efforts and facilitate interpretation of current and future observations and trends, which can more accurately inform effective management and mitigation efforts.

A wave glider-based, towed hydrophone array system for autonomous, real-time, passive acoustic marine mammal monitoring.

An autonomous surface vehicle known as a wave glider, instrumented with a low-power towed hydrophone array and embedded digital signal processor, is demonstrated as a viable low-noise system for the passive acoustic monitoring of marine mammals. Other key design elements include high spatial resolution beamforming on a 32-channel towed hydrophone array, deep array deployment depth, vertical motion isolation, and bandwidth-efficient real-time acoustic data transmission. Using at-sea data collected during a simultaneous deployment of three wave glider-based acoustic detection systems near Stellwagen Bank National Marine Sanctuary in September 2019, the capability of a low-frequency towed hydrophone array to spatially reject noise and to resolve baleen whale vocalizations from anthropogenic acoustic clutter is demonstrated. In particular, mean measured array gain of 15.3 dB at the aperture design frequency results in a post-beamformer signal-to-noise ratio that significantly exceeds that of a single hydrophone. Further, it is shown that with overlapping detections on multiple collaborating systems, precise localization of vocalizing individuals is achievable at long ranges. Last, model predictions showing a 4× detection range, or 16× area coverage, advantage of a 32-channel towed array over a single hydrophone against the North Atlantic right whale upcall are presented for the continental shelf environment south of Martha's Vineyard.

Monitoring cetacean occurrence and variability in ambient sound in Scottish offshore waters

The characterisation of marine soundscapes allows observation of spatiotemporal distribution of vocalising species and human activities, which can inform an assessment of their interactions. Such data are important for monitoring the ecological status of marine habitats. The Scottish Atlantic Frontier is an important habitat for a variety of cetacean species. Historic whaling has heavily impacted several species inhabiting these waters and current comprehensive information about seasonal occurrence and distribution is lacking for all species. This study presents year-round passive acoustic monitoring data from ten sites in this understudied region. The three most offshore sites were examined for baleen whale vocalisations, and four species were regularly detected. Fin whale detections peaked from October to January and were at their lowest during May and June. Humpback whale song was detected as early as January but showed a strong seasonal peak in March and April. In contrast, minke whales were detected regularly throughout the year but with a peak in detections from October to November, when sei whales were also detected. All monitoring sites showed frequent occurrence of odontocete echolocation clicks and whistles. Comprised mainly of delphinid vocalisations, whistles and clicks were detected on an almost-daily basis among the offshore sites, with a slight reduction in detections from May to July particularly among the more inshore sites. Ambient sound levels (root-mean-square sounds pressure level; SPL) varied by site and season in relation to species presence, anthropogenic contributions, and environmental conditions. Monthly median SPL across the array varied up to 18 dB within 1/3-octave bands. Throughout the year, variability in median SPL was lowest in the higher frequency bands (>10 kHz), while highest variability was found between January to July in specific lower frequency bands (<1 kHz). Results from this study demonstrate the value of passive acoustic data in providing novel baseline information about cetacean occurrence and distribution in Scottish offshore habitats where data are limited and outdated. The results will feed into statutory reporting on underwater noise, support the identification and designation of future marine protected areas for cetaceans, and help guide management of future human-marine mammal interactions in Scottish offshore waters.

Comparing the social signaling behavior of humpback whales in three group types on the Hawaiian breeding grounds using acoustic tags

Humpback whales (Megaptera novaeangliae) are exceptionally vocal among baleen whale species. While extensive research has been conducted on humpback whale songs, gaps remain in our understanding of other forms of communication, particularly non-song calls. Here, we compare the spectral features and temporal parameters of non-song calls recorded from AcousondeTM tagged humpback whales in three commonly observed group types in the breeding grounds: adult dyads (N = 3), singly escorted mother-calf pairs (N = 4), and competitive groups (N = 4). Recordings were collected off Maui, Hawai’i during the winter breeding seasons of 2019–2021. Individual calls were identified based on visual and aural inspection of spectrograms using Raven Pro 1.6 software, with a total of 842 calls isolated from 47.6 h of acoustic recordings. Competitive groups produced the most calls (N = 358); however, after adjusting for the differences in recording hours and the number of individuals, the call rate (calls/hour/whale) was not significantly different between group compositions. The temporal parameters and frequency measures of calls did not vary significantly across the groups. However, interesting patterns of calling behavior were observed (e.g., competitive groups had the shortest inter-call intervals and the highest frequency calls, and escorted mother-calf pairs had the longest inter-call intervals) and it is possible the lack of statistical significance could be attributed to the small sample size of tag deployments. This study provides new insights into humpback whale vocal communication behavior in the Hawaiian Islands breeding grounds.

Ecological interactions between Antarctic krill (Euphausia superba) and baleen whales in the South Sandwich Islands region – Exploring predator-prey biomass ratios

Following the cessation of whaling, the southwest Atlantic humpback whale (Megaptera novaeangliae) population is thought to be close to pre-exploitation size, reversing 20th century changes in abundance. Using a model-based approach applied to concurrently collected data on baleen whale abundance and Antarctic krill (Euphausia superba) biomass in the South Sandwich Islands (SSI) region, we explore ecological interactions between these taxa. Krill biomass and baleen whale density were highest to the north and northeast of the SSI, where the Antarctic Circumpolar Current (ACC) is deflected around the island chain. Humpback whale density was elevated at locations of krill biomass density >150 gm-2. Krill consumption by baleen whales was estimated at 19–29% of the available krill standing stock. We used historic whaling data to confirm the plausibility of these consumption rates and found evidence of rapid weight gain in humpback whales, such that blubber depleted during the breeding season could be restored in a much shorter period than previously assumed. Little is known about krill replenishment rates in the flow of the ACC, or about niche separation between recovering baleen whale populations; both factors may affect species carrying capacities and further monitoring will be required to inform the management of human activities in the region.

Energy absorption of multilayer aluminum foam-filled structures under lateral compression loading

This article proposes a biomimetic multilayer foam-filled structure (BMFS) that mimics the microstructural characteristics of biological structures such as human bone and whale baleen. The lateral compression performance of such structures is investigated using experimental and numerical analyses. The proposed structure consists of three layers of aluminum foam with different densities filled in several concentric circular aluminum tubes. The test includes a solid design (Design-1) and a hollow design (Design-2). A series of quasi-static compression tests and finite element simulations are conducted, and the results show that BMFS exhibits a more advantageous sequential collapse deformation pattern for practical use. An energy absorption analysis of each layer shows that the energy absorption ratio of the foam layer reaches 85%. Comparing Models 1–3 of the two designs shows that the energy efficiency decreases, and the work efficiency increases, as the foam density increases. In addition, the interaction between the tubes and foams enhances the energy absorption properties of the structure. The parameter study shows that the energy absorption characteristics of Design-2 are insensitive to the diameter of the tube. The SEA of Design-1 increases with the thickness of Tube-1.

Fast and Furious: Energetic Tradeoffs and Scaling of High-Speed Foraging in Rorqual Whales.

SynopsisAlthough gigantic body size and obligate filter feeding mechanisms have evolved in multiple vertebrate lineages (mammals and fishes), intermittent ram (lunge) filter feeding is unique to a specific family of baleen whales: rorquals. Lunge feeding is a high cost, high benefit feeding mechanism that requires the integration of unsteady locomotion (i.e., accelerations and maneuvers); the impact of scale on the biomechanics and energetics of this foraging mode continues to be the subject of intense study. The goal of our investigation was to use a combination of multi-sensor tags paired with UAS footage to determine the impact of morphometrics such as body size on kinematic lunging parameters such as fluking timing, maximum lunging speed, and deceleration during the engulfment period for a range of species from minke to blue whales. Our results show that, in the case of krill-feeding lunges and regardless of size, animals exhibit a skewed gradient between powered and fully unpowered engulfment, with fluking generally ending at the point of both the maximum lunging speed and mouth opening. In all cases, the small amounts of propulsive thrust generated by the tail were unable to overcome the high drag forces experienced during engulfment. Assuming this thrust to be minimal, we predicted the minimum speed of lunging across scale. To minimize the energetic cost of lunge feeding, hydrodynamic theory predicts slower lunge feeding speeds regardless of body size, with a lower boundary set by the ability of the prey to avoid capture. We used empirical data to test this theory and instead found that maximum foraging speeds remain constant and high (∼4 m s–1) across body size, even as higher speeds result in lower foraging efficiency. Regardless, we found an increasing relationship between body size and this foraging efficiency, estimated as the ratio of energetic gain from prey to energetic cost. This trend held across timescales ranging from a single lunge to a single day and suggests that larger whales are capturing more prey—and more energy—at a lower cost.

Song recordings suggest feeding ground sharing in Southern Hemisphere humpback whales

The Atlantic sector of the Southern Ocean (ASSO) has one of the highest densities of Antarctic krill (Euphausia superba) compared to other polar and subpolar regions, which attracts migratory baleen whale species to aggregate in this area for feeding. Humpback whales (Megaptera novaeangliae) also sing extensively while on the Southern Ocean feeding grounds which allows for the exploration of song similarity between feeding grounds and breeding populations which helps to understand population mixing. The results of comparative song analyses between the ASSO and the Ecuadorian and Brazilian breeding populations and recordings from the Chilean, South African and Namibian migration routes/mid-latitude feeding grounds revealed that individuals from at least three humpback whale breeding populations most likely migrate to shared feeding grounds in the ASSO. Humpback whales from different populations potentially mix at different times (i.e., years) at feeding hotspots in variable locations. The ASSO seems to provide sufficient prey resources and seems to present an important area for both cultural and maybe even genetic exchange between populations supporting the maintenance of large gene pools. Assuming that multi-population feeding hotspots are also suitable habitat for krill and other krill-dependent predators, these areas in the ASSO should be carefully managed integrating population, ecosystem and fisheries management.

Cetacean acoustic occurrence on theUSAtlantic Outer Continental Shelf from 2017 to 2020

AbstractLong‐term distribution data for cetaceans are lacking, inhibiting the ability of management bodies to assess trends and react appropriately. Such is true even along the US Atlantic Outer Continental Shelf (OCS) where previous passive acoustic monitoring programs have laid the groundwork for monitoring cetacean occurrence over a multidecadal scale. Here, we continue and expand the scope of previous acoustic programs, providing a synopsis of the monthly cetacean acoustic occurrence from late 2017 to late 2020. Acoustic data were collected using bottom‐mounted autonomous recorders located at seven stations along the OCS in depths of 212–900 m. Automated cetacean vocalization detector‐classifiers were applied, and the resulting automated detections directed the manual review of a subset of the data by analysts. Only manual detections informed the occurrence results. Six baleen whale species and at least eight toothed whale species occurred in the region with diversity increasing in winter. In considering previous monitoring program results, we found evidence that some mysticete whales are spending less time in the region annually, confirmed that some species occur farther offshore than previously reported, and identified two previously unreported areas utilized by beaked whales. For effective species management, these findings must be considered, and monitoring programs continued.

Detection of baleen whale species using kernel dynamic mode decomposition-based feature extraction with a hidden Markov model

The negative effects of human activities within the ecological space of whales remains an issue of concern to marine ecologists. The accurate detection and subsequent classification of whale species are vital in mitigating these negative effects. Automatic detection techniques have come in handy for the efficient detection of the various whale species without human error. Hidden Markov model (HMM) remains one the most efficient detectors of whale species. However, its performance efficiency is greatly influenced by the feature vectors adapted with it. In this work, we propose the use of the kernel dynamic mode decomposition (kDMD) algorithm as a tool to extract features of baleen whale species, which are then adapted with HMM for their detection. Dynamic mode decomposition (DMD) is an eigendecomposition-based algorithm that is capable of extracting latent underlying features of non-linear signals such as those vocalised by whales. However, the underlying cost of DMD is the singular value decomposition (SVD), which adds significant complexity to the modes derivation steps. Thus, this work is introducing the kernel method into the DMD, in order to find a more efficient way of computing DMD without explicitly using the SVD algorithm. Furthermore, the feature formation steps in the original DMD was modified (mDMD) in this work, to make it more generic for datasets with sparse whale sound samples. The performance of the detectors was tested on datasets containing sounds of southern right whales (SRWs) and humpback whales. The results obtained show a high true positive rate (TPR), high precision (PREC) and low error rate (ERR) for both species. The performance of the three DMD-based feature-extraction methods were compared. The kDMD-HMM generally performed better than the mDMD-HMM and DMD-HMM detectors. The methods proposed here can be tailored for the automatic detection and classification of other vocalising animal species through their sounds.

Spatiotemporal Overlap of Baleen Whales and Krill Fisheries in the Western Antarctic Peninsula Region

In Antarctica, abundant consumers rely on Antarctic krill for food, but krill are also the subject of a commercial fishery. The fishery overlaps in time and space with the foraging areas of these consumers, thus potential competition between krill fisheries and krill consumers is a major management concern. The fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources with an ecosystem approach, according to which fishing should not interfere with either the population growth of krill, or krill-dependent consumers. Krill catches have become increasingly spatially concentrated in a small number of hotspots, raising concerns about how local depletion of krill impacts consumers. Such concentrated fishing demonstrates that there is a mismatch between the spatial and temporal scale at which krill fisheries are currently managed, and that at which fisheries operate and consumers forage. Information on the seasonal dynamics of predator abundance and their foraging behaviour is fundamental to future precautionary management of the krill fishery. We analysed the spatiotemporal distribution of two major krill consumers – humpback and minke whales – and that of krill fishing, off the Western Antarctic Peninsula. We used whale tracking data (58 humpback whale tracks and 19 minke whale tracks) to develop spatial random forest models predicting the monthly distribution of whale foraging areas from January-July. Using these predictions, we calculated spatiotemporally-explicit geographic overlap between whales and fisheries, the latter represented by krill fishing effort and catch data. Over the krill fishing season, fishing effort and catch hotspots shifted to the southwest, into the Bransfield Strait where effort and catch was highest. Predicted humpback whale foraging areas increased in the Bransfield Strait over the same period, while predicted minke whale foraging areas showed an opposite trend. For both we predicted a whale-fishing interaction hotspot in the Bransfield Strait, strongest in April and May. Our results illustrate the fine spatial scale of likely interactions between baleen whales and the krill fishery, and their concentration over the season, underlining the need for fishery management more closely aligned to the spatiotemporal scale of likely predator-fishery interactions.

Dive Behavior and Activity Patterns of Fin Whales in a Migratory Habitat

Efficient use of the energy budget is of fundamental importance for long-distance migrants, which must cope with seasonal energy demands and environmental conditions. Time-activity budgets can provide information on how animals balance energy use and acquisition over their annual cycle, and on the costs and benefits of different migratory strategies. Baleen whales, such as the fin whale, perform long migrations between feeding and breeding grounds. Although there are now a handful of studies describing the diving and foraging behavior of fin whales, most were carried out at their high-latitude foraging grounds, and very little is known about their behavior in wintering habitats or during migration. We analyzed time-depth recorder data to describe the diving behavior and activity patterns of fin whales in a migratory habitat. Using a hierarchical cluster analysis based on a set of dive variables, we identified six dive types. Four of these dive types (shallow exploratory, shallow active, deep exploratory and deep active) were likely associated to foraging. The other two comprised long non-active dives and dives of variable shape, which may represent resting, traveling or even vocalizing behavior. Shallow exploratory dives were the most frequent dive type (23%) and shallow active were the least frequent (5%). The two deepest dive types, deep active and exploratory, were predominantly carried out during the day, and night dives were significantly shallower than daylight dives, suggesting that fin whales tracked the vertical migration of prey. Whales spent 60% of their dive time engaged in dives associated with feeding and/or prey searching, suggesting they prioritized energy intake over energy conservation. Finally, we found that whales spent more time at or close (<15 m depth) to the surface at night (73%) than during the day (55%), indicating a higher vulnerability to ship strikes during this period. Our study provides novel information on the behavioral patterns and time-activity budgets of fin whales in a migratory habitat. This information is essential for bioenergetic analyses and to predict how fin whales respond to human activities and ongoing environmental changes.