Odontocetes Research Articles

Different developmental transformations underly blowhole orientation in a toothed whale (Odontoceti: Stenella attenuata) and a baleen whale (Mysticeti: Balaenoptera physalus)

Although the external bony nares have become posteriorly repositioned in the evolution of numerous groups of mammals (e.g. elephants, tapirs), reorientation of the nasal passage away from the anteroposterior axis has evolved rarely. In cetacean (whale, dolphin, porpoise) evolution, dorsoventral reorientation of the nasal passage along with extreme posteriad repositioning of the nares formed a “blowhole.” Despite the presence of a blowhole at birth, early cetacean fetuses exhibit head morphologies that resemble those of other mammals. Two distinct but non‐competing developmental models have been proposed for how the nasal passage reorients into a blowhole. In one model, which focused on external changes in the whole body, nasal passage reorientation was described in terms of dorsad rotation of the head during prenatal growth (Pilleri and Wandeler, 1962). A second, focusing on the nasal skull, noted that the nasal passage itself changes orientation relative to the palate and longitudinal axis of the skull (Klima, 1995, 1999). To integrate and revise these models, we used photos and CT scans of fetal growth series to characterize morphological, allometric, and angular changes within the head in representatives of the two extant cetacean suborders: a toothed whale, the pantropical spotted dolphin (Odontoceti: Stenella attenuata), and a baleen whale, the fin whale (Mysticeti: Balaenoptera physalus). In both fetal series, the angle between the nasal passage and the sagittal axis of the foramen magnum decreased with age, but this trend accompanied different morphological changes. In S. attenuata, the angle between the palate and basicranium flattened in association with facial lordosis and basicranial retroflexion in the region of the presphenoid. Basicranial retroflexion was not observed in B. physalus; rather, alignment of the nasal passage and the sagittal axis of foramen magnum accompanied anteriad tilting of the occipital bone. With these results, we propose a new developmental model, differing in its specifics for a toothed and a baleen whale, for the reorientations that produce the blowhole.

The Hydrodynamic Sensory System in the Skin of Cetaceans

The skin’s sensory afferents have a myriad of varieties, tactile functions and specialized end‐organ receptors enabling species to exploit ecological niches. In typical vertebrate skin, from fish to humans, axons innervate relatively small discreet receptive fields, providing fine‐scale discrimination of texture or location of a pin prick.The cetacean suborders of Mysticeti (baleen) and Odontoceti (toothed) whales are fully‐aquatic glabrous‐skinned mammals, descendants of terrestrial hairy‐skinned arteriodactyls. Shaped by dynamic forces of the marine environment, nerves in the skin of cetaceans (whales, dolphins and porpoises) have adapted to assess critical aquatic information including current flow, swim turbulence, fish movement and boundary layers, as well as tactile touch, temperature and nociceptive stimuli. The anatomy of this highly‐derived sensory system was investigated in the flank skin of humpback whales (Megaptera novaeangliae, NMFS permits 14809, 15240) using antibodies against highly‐conserved molecules of physiologically‐distinct afferents identified in other mammalian species.Humpback whales inherited a genomically‐diverse suite of cutaneous axons, including low‐threshold mechanoreceptors that sense innocuous environmental signals, as well as high‐threshold thermoreceptors, chemoreceptors and nociceptors. However, during their transition from terrestrial artiodactyls into obligate marine mammals, axon morphology and organization diverged. Unlike other vertebrates, heterogenous axons in whale skin assemble into thread‐like bundles. These ensembles divide into smaller bundles, follow circuitous trajectories that form unpredictable shapes, and lack structural endings. Developmental research has shown that axonal growth in vertebrates is guided by the skin’s signaling molecules and external physical stimuli. As environmental forces are transmitted through the epidermis they convey stretch at the dermal‐epidermal junction, a mechanically unstable boundary where mechanoreceptors typically reside. While lacking these receptor endings, the whale’s polymodal axon bundles are anatomically positioned at the dermal‐epidermal junction to transduce signals. Similar axon bundles innervation is found in the odontocete Tursiops truncatus (bottlenose dolphins), evidence that this trait is a cetacean synapomorphy. The polymorphic nature of these sensory ensembles may be a tuning mechanism that targets maximal signal strength, detects functionally diverse information (hydrostatic or hydrodynamic forces) or compares attenuation of signal properties at different locations in the skin (frequency, angular velocity or amplitude).Hallmarks of a hydrodynamically‐tuned system include the capacity to detect and integrate multiple signal properties. In becoming secondarily aquatic mammals, cetaceans have reconstructed the vertebrate somatosensory plan.Support or Funding InformationNOAA Award #NA10SEC4810008.

Anisakis pegreffii

Anisakis pegreffii belongs to the Anisakis simplex species complex that causes anisakiasis, an important fish-borne zoonosis worldwide. The parasite typically reproduces in the gastric chambers of toothed whales (final hosts). Larvae hatch from the eggs that are expelled in seawater; the larvae are ingested by crustaceans and small fish (intermediate hosts). Many fish and cephalopod species (paratenic hosts) that prey upon them transport infective third-stage larvae (L3) to the final host. Humans are accidentally infected by L3 through consumption of uncooked seafood. Anisakiasis is characterised by four main types: gastric, intestinal, ectopic, and gastroallergic that elicit mostly mild, only occasionally severe symptoms. Recently, a fifth type has been proposed based on many asymptomatic Anisakis-IgE seropositive subjects, predominately in countries with high per capita fish consumption. In humans, L3 fails to develop into the adult stage, dies, and decomposes in infected tissues, evoking a local proinflammatory response characterized by eosinophilic granulomatosis.

Extensive Diversity and Disparity of the Early Miocene Platanistoids (Cetacea, Odontoceti) in the Southeastern Pacific (Chilcatay Formation, Peru).

Several aspects of the fascinating evolutionary history of toothed and baleen whales (Cetacea) are still to be clarified due to the fragmentation and discontinuity (in space and time) of the fossil record. Here we open a window on the past, describing a part of the extraordinary cetacean fossil assemblage deposited in a restricted interval of time (19–18 Ma) in the Chilcatay Formation (Peru). All the fossils here examined belong to the Platanistoidea clade as here redefined, a toothed whale group nowadays represented only by the Asian river dolphin Platanista gangetica. Two new genera and species, the hyper-longirostrine Ensidelphis riveroi and the squalodelphinid Furcacetus flexirostrum, are described together with new material referred to the squalodelphinid Notocetus vanbenedeni and fragmentary remains showing affinities with the platanistid Araeodelphis. Our cladistic analysis defines the new clade Platanidelphidi, sister-group to Allodelphinidae and including E. riveroi and the clade Squalodelphinidae + Platanistidae. The fossils here examined further confirm the high diversity and disparity of platanistoids during the early Miocene. Finally, morphofunctional considerations on the entire platanistoid assemblage of the Chilcatay Formation suggest a high trophic partitioning of this peculiar cetacean paleocommunity.

Skeletal pathologies track body plan evolution in ichthyosaurs

Changing predator-prey interactions during the Mesozoic Marine Revolution (MMR) profoundly altered the trajectory of marine tetrapod evolution. Here, we assess potential signatures of this landmark transition through the fossil record of skeletal pathologies in ichthyosaurs — iconic marine reptiles that developed increasingly ‘fish-like’ body plans over time. We surveyed a stratigraphically constrained sample of 200 Middle Triassic ichthyosaur specimens and compared the type, distribution and prevalence of pathologies with an approximately equivalent assemblage of Early Jurassic age. Overall, skeletal pathologies were equally prevalent in these groups, and most often manifested in species >4 m long. However, pathological bones were found to be concentrated in the hind limbs and tail of Triassic ichthyosaurs, whereas the jaws, forelimbs, and ribcage were preferentially affected in Jurassic taxa. We posit that the occurrence of ankylosed zygapophyses in the caudal peak of Triassic ichthyosaurs could represent a functional by-product of their primitive ‘eel-like’ swimming. Conversely, increased instances of broken ribs in Jurassic ichthyosaurs may infer ramming or tail strike behaviours that characterise morphologically ‘fish-like’ marine tetrapods, such as modern toothed whales. Different categories of skeletal pathologies thus evidently reflect structural modifications in the ichthyosaur body plan, and indirectly coincide with ecological turnover during the MMR.

Morphological Evidence for the Sensitivity of the Ear Canal of Odontocetes as shown by Immunohistochemistry and Transmission Electron Microscopy

The function of the external ear canal in cetaceans is still under debate and its morphology is largely unknown. Immunohistochemical (IHC) analyses using antibodies specific for nervous tissue (anti-S100, anti-NSE, anti-NF, and anti-PGP 9.5), together with transmission electron microscopy (TEM) and various histological techniques, were carried out to investigate the peripheral nervous system of the ear canals of several species of toothed whales and terrestrial Cetartiodactyla. This study highlights the innervation of the ear canal with the presence of lamellar corpuscles over its entire course, and their absence in all studied terrestrial mammals. Each corpuscle consisted of a central axon, surrounded by lamellae of Schwann receptor cells, surrounded by a thin cellular layer, as shown by IHC and TEM. These findings indicate that the corpuscles are mechanoreceptors that resemble the inner core of Pacinian corpuscles without capsule or outer core, and were labelled as simple lamellar corpuscles. They form part of a sensory system that may represent a unique phylogenetic feature of cetaceans, and an evolutionary adaptation to life in the marine environment. Although the exact function of the ear canal is not fully clear, we provide essential knowledge and a preliminary hypothetical deviation on its function as a unique sensory organ.

Evidence of Echolocation in the Common Shrew from Molecular Convergence with Other Echolocating Mammals.

Along with sophisticated echolocation found in bats and toothed whales, the common shrew (Sorex araneus) was confirmed to possess echolocation ability based on behavioral and experimental evidence such as high-frequency twittering and close-range spatial orientation. However, whether echolocation in the common shrew is convergent with bats and dolphins at the molecular level remains poorly understood. In this study, we gathered the coding region sequences of 11 hearing-related genes from genome data and previous studies. Convergent evolutionary analyses identified 13 amino acid residues (seven in CDH23, five in OTOF, and one in PRESTIN) under strong convergent evolution shared among the common shrew and other echolocating mammals (bats and dolphins). Furthermore, a phylogenetic tree was constructed based on the combined amino acid dataset of convergent/parallel substitutions, sites with parallel radical property changes, and sites supporting echolocator-convergence; it supported the converged topology of the simple echolocator Sorex araneus and sophisticated echolocating bats with high posterior probability. This study gives evidence at the molecular level that the common shrew echolocate and provides novel insights into the convergent evolution between the common shrew and bats and dolphins.

Behaviorally measured tactile sensitivity in the common bottlenose dolphin, Tursiops truncatus

AbstractLittle research has been conducted on the somatosensory system of toothed whales and it remains uncertain how tactile sensitivity varies about their bodies. In this study, tactile sensitivity to high‐frequency (250‐Hz) displacement of the skin was quantified in three trained adult common bottlenose dolphins (Tursiops truncatus) using a vibratory device (tactor). The magnitude of skin displacement was controlled by varying the voltage to the tactor held against the skin surface with a constant force. Tactile thresholds were determined using an adaptive method of limits in which dolphins reported perception of the tactile stimulus by producing a whistle. Displacement thresholds ranged from 2.4 to 40 μm, with the greatest sensitivity found along the rostrum, melon, and blowhole. Sensitivity decreased caudally along the body, with the dorsal fin and tip of the fluke being the least sensitive locations tested. The results support hypotheses that the follicles on the dolphin rostrum are particularly important for perception. The reduction in tactile sensitivity at the appendages is consistent with their primary role in stabilization and locomotion compared to exploration or environmental sensing.

An autonomous hydrophone array to study the acoustic ecology of deep-water toothed whales

For vocal animals with distinctive calls, passive acoustic monitoring can be used to infer presence, distribution, and abundance provided that the calls and calling behaviour are known. Key to enabling quantitative acoustic surveys are calibrated recordings of identified species from which the source parameters of the sounds can be estimated. Obtaining such information from free-ranging aquatic animals such as toothed whales requires multi-element hydrophone arrays, the use of which is often constrained by cost, the logistical challenge of long cables, and the necessity for attachment to a boat or mooring in order to digitise and store multiple channels of high-sample rate audio data. Such challenges are compounded when collecting recordings or tracking the diving behaviour of deep-diving animals for which the array must be deployed at depth. Here we report the development of an autonomous drifting deep-water vertical passive acoustic array that uses readily available off-the-shelf components. This lightweight portable array can be deployed quickly and repeatedly to depths of up to 1000 m from a small boat. The array comprises seven ST-300 HF SoundTrap autonomous recorders equally spaced on an 84 m electrical-mechanical cable. The single-channel digital sound recordings were configured to allow for synchronisation in post-processing using an RS-485 timing signal logged by all channels every second. We outline how to assemble the array, and provide software for time-synchronising the acoustic recorders. To demonstrate the utility of the array, we present an example of short-finned pilot whale clicks localised on the deep-water (700 m) array configuration. This array method has broad applicability for the cost-effective study of source parameters, acoustic ecology, and diving behaviour of deep diving toothed whales, which are valuable not only to understand the sensory ecology of deep-diving cetaceans, but also to improve passive acoustic monitoring for conservation and management.

Assessing the impact of toothed whale depredation on socio-ecosystems and fishery management in wide-ranging subantarctic fisheries

Marine predators feeding on fisheries catches directly on the fishing gear, a behaviour termed “depredation”, has emerged as a major human-wildlife conflict globally, often resulting in substantial socio-economic and ecological impacts. This study investigated the extent of this conflict in commercial Patagonian toothfish (Dissostichus eleginoides) fisheries across subantarctic waters where both killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) feed on toothfish caught on longline hooks. Using long-term datasets from six major fishing areas, from southern Chile to the Indian Ocean sector of the Southern Ocean, statistical models were developed to quantify the catch removals due to whale depredation interactions. The results indicated that these removals were large, totalling more than 6600 t of toothfish between 2009 and 2016 with an annual mean of 837 t [95% CI 480–1195 t], comprised of 317 t [232–403 t] and 518 t [247–790 t] removed by killer whales and sperm whales, respectively. Catch removals greatly varied between areas, with the largest estimates found at Crozet, where on average 279 t [179–379 t] of toothfish per year, equivalent to 30% [21–37%] of the total catches. Together, these findings provide metrics to assess the impacts of depredation interactions on the fishing industry, whale populations, fish stocks and associated ecosystems. With an estimated $15 M USD worth of fish depredated every year, this study highlights the large geographic scale and economic significance of the depredation issue and its potential to compromise the viability of some toothfish fisheries which are the primary socio-economic activity in subantarctic regions.

Fear of Killer Whales Drives Extreme Synchrony in Deep Diving Beaked Whales

Fear of predation can induce profound changes in the behaviour and physiology of prey species even if predator encounters are infrequent. For echolocating toothed whales, the use of sound to forage exposes them to detection by eavesdropping predators, but while some species exploit social defences or produce cryptic acoustic signals, deep-diving beaked whales, well known for mass-strandings induced by navy sonar, seem enigmatically defenceless against their main predator, killer whales. Here we test the hypothesis that the stereotyped group diving and vocal behaviour of beaked whales has benefits for abatement of predation risk and thus could have been driven by fear of predation over evolutionary time. Biologging data from 14 Blainville’s and 12 Cuvier’s beaked whales show that group members have an extreme synchronicity, overlapping vocal foraging time by 98% despite hunting individually, thereby reducing group temporal availability for acoustic detection by killer whales to <25%. Groups also perform a coordinated silent ascent in an unpredictable direction, covering a mean of 1 km horizontal distance from their last vocal position. This tactic sacrifices 35% of foraging time but reduces by an order of magnitude the risk of interception by killer whales. These predator abatement behaviours have likely served beaked whales over millions of years, but may become maladaptive by playing a role in mass strandings induced by man-made predator-like sonar sounds.

Humpback whale (Megaptera novaeangliae) sonar: Ten predictions.

Bats and dolphins echolocate ultrasonically while foraging, an active mode of perception that is effective for intercepting small, fast-moving targets, but less so for tracking large targets from long distances. Unlike toothed whales, humpback whales and other baleen whales are widely assumed not to echolocate. Echoes generated by humpback whale vocalizations often have been viewed either as low-level background noise that minimally affects acoustic communication between whales or as indirect cues to large environmental features. An additional possibility is that vocalizing humpback whales (and perhaps other whales) produce sonic sounds to actively generate echoes that they localize and interpret. Animals attempting to echolocate using lower frequency sounds underwater face some of the same signal processing challenges faced by ultrasonic echolocators, as well as some unique challenges. The extent to which listening whales can meet these challenges largely determines what they can actively perceive by monitoring self-generated echoes. In the absence of psychophysical experiments with baleen whales, comparisons with auditory processing by echolocating species provide the best indications of what humpback whales may echoically perceive. Empirical tests of key predictions derived from the hypothesis that humpback whales echolocate are also critical to understanding how they use sound. Recognizing that sonic echolocation by whales may differ substantially from ultrasonic echolocation in smaller species is an important step toward clarifying the role that active auditory perception plays in whale behavior. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Why don’t long-finned pilot whales have a widespread postreproductive lifespan? Insights from genetic data

AbstractIn a handful of mammals, females show an extended postreproductive lifespan (PRLS), leading to questions over why they spend a substantial portion of their lifespan nonreproductive. Theoretical and empirical studies suggest that PRLS may evolve when 1) demographic patterns lead to increasing local relatedness as females age, and 2) females come into reproductive competition with their daughters, as these conditions lead to high relative benefits of helping kin versus reproducing in later life. However, evolutionary pathways to PRLS are poorly understood and empirical studies are scarce. Here, we use a dataset of 1522 individuals comprising 22 pods to investigate patterns of reproduction and relatedness in long-finned pilot whales Globicephala melas; a toothed whale without species-wide PRLS. We find a similar relatedness structure to whales with PRLS: pods appear composed of related matrilines, and relatedness of females to their pod increases with age, suggesting that this species could benefit from late-life help. Furthermore, females with a large number of philopatric adult daughters are less likely to reproduce, implying intergenerational reproductive competition between females. This suggests that individuals may display a plastic cessation of reproduction, switching to investing in existing offspring when they come into competition with their daughters. To the best of our knowledge, this is the first time such a relationship has been described in relation to PRLS, and it raises questions about whether this represents a step towards evolving PRLS or is a stable alternative strategy to widespread postreproductive periods.

Lateralized sound production in the beluga whale (Delphinapterus leucas).

Like other toothed whales, belugas produce sound through pneumatic actuation of two phonic lip pairs, but it is unclear whether both pairs are actuated concurrently to generate a single sound (the dual actuation hypothesis) or laterally in the production of their rich vocal repertoires. Here, using suction cup hydrophones on the head of a trained beluga whale, we measured seven different communication signal types and echolocation clicks in order to test the hypothesis that belugas produce distinct sounds unilaterally. We show that, like other delphinoids, belugas produce echolocation clicks with the right phonic lips and tonal sounds from the left. We also demonstrate for the first time that the left phonic lips are responsible for generating communication signals other than tonal sounds. Thus, our findings provide empirical support for functionalized laterality in delphinoid sound production, in keeping with the functional laterality hypothesis of vocal-motor control in toothed whales.

Amyloid-beta peptide and phosphorylated tau in the frontopolar cerebral cortex and in the cerebellum of toothed whales: aging versus hypoxia.

ABSTRACTHypoxia could be a possible risk factor for neurodegenerative alterations in cetaceans’ brain. Among toothed whales, the beaked whales are particularly cryptic and routinely dive deeper than 1000 m for about 1 h in order to hunt squids and fishes. Samples of frontal cerebral and cerebellar cortex were collected from nine animals, representing six different species of the suborder Odontoceti. Immunohistochemical analysis employed anti-β-amyloid (Aβ) and anti-neurofibrillary tangle (NFT) antibodies. Six of nine (67%) animals showed positive immunolabeling for Aβ and/or NFT. The most striking findings were intranuclear Aβ immunopositivity in cerebral cortical neurons and NFT immunopositivity in cerebellar Purkinje neurons with granulovacuolar degeneration. Aβ plaques were also observed in one elderly animal. Herein, we present immunohistopathological findings classic of Alzheimer's and other neurodegenerative diseases in humans. Our findings could be linked to hypoxic phenomena, as they were more extensive in beaked whales. Despite their adaptations, cetaceans could be vulnerable to sustained and repetitive brain hypoxia.

Le dauphin à dents de requin Squalodon (Cetacea: Odontoceti) du remarquable assemblage de vertébrés marins de Montagna della Majella (Formation de Bolognano, Italie centrale).

The extinct family Squalodontidae consists of heterodont, medium-sized odontocetes, featuring a long rostrum that houses large, procumbent incisors and heavily ornamented postcanine teeth carrying accessory denticles, hence their vernacular name, dolphins. These longirostrine toothed whales are often seen as bridging the anatomical gap between archaic Oligocene odontocetes and their late Miocene to Holocene relatives. Possibly among the major marine predators of their time, the shark-toothed dolphins are important components of several lower Miocene marine-mammal assemblages from the North Atlantic and Mediterranean/Paratethysian realms. In the present work, a partial skull of Squalodontidae is described from the strata of the Bolognano Formation cropping out in the northeastern sector of the Montagna della Majella massif (Abruzzo, central Italy), which has previously yielded a rich lower Miocene marine-vertebrate assemblage, including eleven taxa of elasmobranchs as well as subordinate teleosts and very fragmentary remains of marine reptiles and mammals. The specimen consists of the anterodorsal portion of a rostrum, preserving parts of both premaxillae and left maxilla, and the anteriormost seven upper left teeth. This partial skull is here identified as belonging to the genus Squalodon, whose presence in the Montagna della Majella vertebrate assemblage had already been tentatively proposed on the basis of two fragmentary teeth. The paleontological significance of this find is discussed in the broader framework of the Euromediterranean record of Squalodon.

A critical review about neurotoxic effects in marine mammals of mercury and other trace elements.

Marine mammals are more exposed to mercury (Hg) than any others animals in the world. As many trace elements, Hg it is able to impair the brain function, which could be a cause of population decline. Nevertheless, these issues have been scarcely studied because of the technical and ethical difficulties. We conducted a systematic review about marine mammals' brain exposition to Hg and other trace elements, and their neurotoxic effects. Information was scarce and the lack of standardization of nomenclature of brain structures, sample collecting and results presentation made it difficult to obtain conclusions. Hg was the most studied metal and toothed whales the most studied group. Despite being its target organ, brain accumulates lesser concentrations of Hg than other tissues as liver. We found a significant positive correlation between both organs' burden (rho=0.956 for cetaceans; rho=0.756 for pinnipeds). Reported Hg values in brain of cetaceans (median 3.00ppm ww) surpassed by one or two orders of magnitude those values found in other species as pinnipeds (median 0.33ppm ww) or polar bears (median 0.07ppm ww). Such values exceeded neurotoxicity thresholds. Although marine mammals ingest mostly the organic and more toxic form MeHg, different fractions of inorganic mercury can appear in brain, which could suggest some detoxification mechanisms. Other suggested mechanisms include Se-Hg interaction and liver sequestration. Although other elements are subjected to a rigid homeostatic control, appear in low concentrations or do not exert an important neurotoxic effect, they should be more studied to elucidate their neurotoxicity potential.

Postreproductive killer whale grandmothers improve the survival of their grandoffspring.

Understanding why females of some mammalian species cease ovulation prior to the end of life is a long-standing interdisciplinary and evolutionary challenge. In humans and some species of toothed whales, females can live for decades after stopping reproduction. This unusual life history trait is thought to have evolved, in part, due to the inclusive fitness benefits that postreproductive females gain by helping kin. In humans, grandmothers gain inclusive fitness benefits by increasing their number of surviving grandoffspring, referred to as the grandmother effect. Among toothed whales, the grandmother effect has not been rigorously tested. Here, we test for the grandmother effect in killer whales, by quantifying grandoffspring survival with living or recently deceased reproductive and postreproductive grandmothers, and show that postreproductive grandmothers provide significant survival benefits to their grandoffspring above that provided by reproductive grandmothers. This provides evidence of the grandmother effect in a nonhuman menopausal species. By stopping reproduction, grandmothers avoid reproductive conflict with their daughters, and offer increased benefits to their grandoffspring. The benefits postreproductive grandmothers provide to their grandoffspring are shown to be most important in difficult times where the salmon abundance is low to moderate. The postreproductive grandmother effect we report, together with the known costs of late-life reproduction in killer whales, can help explain the long postreproductive life spans of resident killer whales.

A Bioinspired Twin Inverted Multiscale Matched Filtering Method for Detecting an Underwater Moving Target in a Reverberant Environment.

To this day, biological sonar systems still have great performance advantages over artificial sonar systems, especially for detection in environments with clutter, strong reverberation, and a low signal to noise ratio (SNR). Therefore, mammal sonar systems, for instance, bats and toothed whales, have many characteristics worth learning from. This paper proposes a bioinspired twin inverted multiscale matched filtering method to detect underwater moving targets. This method can be mainly divided into three parts. Firstly, a hyperbolic frequency modulation (HFM) continuous wave (CW) multiharmonic detection signal was adopted after analyzing signals from bats and dolphins. This signal combines the advantages of CW and HFM signals and has excellent time measurement and speed measurement performance when detecting a moving target. Secondly, the twin inverted waveform was introduced to suppress strong linear reverberation and highlight moving targets. The pulse interval was determined by assessing the reverberation reduction time. Thirdly, when processing echoes, a multiscale matched filtering method was proposed to make use of multiharmonic information and improve detection performance. Finally, a channel pool experiment was carried out to test the performance of the proposed method. The experimental result demonstrates that the proposed method has better performance when detecting a moving target in a reverberant environment compared to the conventional matched filtering method. Related results can be applied to small underwater platforms or sensor network platforms for target detection and coastal defense applications.

Seismic surveys reduce cetacean sightings across a large marine ecosystem

Noise pollution is increasing globally, and as oceans are excellent conductors of sound, this is a major concern for marine species reliant on sound for key life functions. Loud, impulsive sounds from seismic surveys have been associated with impacts on many marine taxa including mammals, crustaceans, cephalopods, and fish. However, impacts across large spatial scales or multiple species are rarely considered. We modelled over 8,000 hours of cetacean survey data across a large marine ecosystem covering > 880,000 km2 to investigate the effect of seismic surveys on baleen and toothed whales. We found a significant effect of seismic activity across multiple species and habitats, with an 88% (82–92%) decrease in sightings of baleen whales, and a 53% (41–63%) decrease in sightings of toothed whales during active seismic surveys when compared to control surveys. Significantly fewer sightings of toothed whales also occurred during active versus inactive airgun periods of seismic surveys, although some species-specific response to noise was observed. This study provides strong evidence of multi-species impacts from seismic survey noise on cetaceans. Given the global proliferation of seismic surveys and large propagation distances of airgun noise, our results highlight the large-scale impacts that marine species are currently facing.