Echolocation in Marine Animals: How Whales and Dolphins See with Sound

Echolocation is an active biological sonar system used by toothed whales, dolphins, and porpoises to navigate, hunt, and interpret their underwater environment by emitting sound pulses and analyzing returning echoes. This article explains how marine mammals produce and receive sound underwater, how echolocation supports navigation, hunting, and communication, and how echolocation characteristics differ across marine species. The content is written for students, researchers, life-science professionals, and informed general readers who need a clear, evidence-based understanding of this sensory system.

What Is Echolocation in Marine Mammals

Echolocation is a form of biological sonar that uses high-frequency sound produced in the forehead and ultimately detected by the cochlea. Odontocetes, the toothed whale lineage, are the most species-rich marine mammal group, and echolocation is considered the catalyst for their evolutionary success. The system works by generating short, broadband sound pulses called clicks, which travel through water, reflect off objects, and return as echoes that the animal interprets to form an acoustic image of its surroundings.

The term active biosonar distinguishes echolocation from passive listening, where an animal simply detects sounds produced by other sources. Odontocete cetaceans have evolved a highly advanced system of active biosonar that supports foraging, navigation, and predator avoidance in environments where vision is limited by water clarity, depth, or darkness.

Echolocation is not universal among marine mammals. Pinnipeds, which include seals, sea lions, and walruses, do not echolocate. The accumulated evidence for pinniped echolocation is unconvincing, primarily because of constraints imposed by the obligate amphibious functioning of the pinniped auditory system. Pinnipeds have instead evolved enhanced visual, tactile, and passive listening skills to forage, navigate, and avoid predators underwater.

How Toothed Whales Produce and Receive Sound

Sound production in echolocating marine mammals occurs in the nasal region, not the larynx. Air is forced through phonic lips in the nasal passages, generating high-frequency clicks that are focused by the melon, a fatty structure in the forehead. The melon acts as an acoustic lens that shapes the sound beam and directs it forward into the water.

The returning echoes are received primarily through the lower jaw, which contains a fat-filled channel that conducts sound to the inner ear. The cochlea, the auditory portion of the inner ear, converts the mechanical vibrations of sound into neural signals. The cochlear morphology of toothed whales reflects the demands of echolocation, with convergent evolution of cochlear shape occurring across species that occupy similar acoustic environments.

The convergence of cochlear shape in sperm whales and beaked whales illustrates how the extreme acoustic environment of the deep ocean constrains auditory anatomy. Habitat type and dive type are significantly correlated with membership in this convergent regime, suggesting that the physical demands of deep diving and deep-water echolocation shape the auditory system in predictable ways.

The Mechanics of Dolphin Echolocation

Dolphins produce several categories of sound, including whistles, echolocation clicks, burst pulse sounds, and feeding buzzes. Echolocation clicks are short, broadband pulses with peak frequencies often in the ultrasonic range. Burst pulses are rapid sequences of clicks, and feeding buzzes are very rapid click trains emitted during prey capture attempts.

The vocalization patterns of dolphins are associated with environmental conditions and behavioral contexts. In captive bottlenose dolphins, click rates change during human-involved training activities, with click rate reduced by 41 percent and whistle production increased by 125 percent during training sessions. Rough-toothed dolphins showed no significant change in click emissions during training but significantly reduced whistles by 56 percent. These species-specific responses indicate that echolocation use is flexible and context-dependent.

The Indo-Pacific humpback dolphin produces a diverse range of emissions, including whistles and pulse trains categorized as echolocation clicks, burst pulses, and buzzes. Acoustic parameters measured from these signals provide insight into vocalization patterns and temporal variability in acoustic behavior, supporting conservation strategies for this endangered population.

Echolocation for Navigation and Hunting

Echolocation provides toothed whales with a continuous acoustic image of their environment, allowing them to detect prey, avoid obstacles, and orient themselves in three-dimensional space. The system is particularly valuable in deep water, where sunlight does not penetrate, and in turbid coastal waters where visual range is limited.

During foraging, dolphins modify their echolocation behavior to match the demands of the hunt. In a cooperative foraging interaction between artisanal fishers and wild dolphins, dolphins herded mullet schools toward the coast and modified their active foraging echolocation to match the time it took for fishing nets to sink and close over the mullets. This synchronization occurred only when fishers responded to the dolphins' foraging cues appropriately, demonstrating that echolocation behavior is adjusted in real time based on environmental feedback.

Killer whales also adjust echolocation use according to foraging context. Fish-eating killer whales and mammal-eating killer whales differ in sonar use, reflecting the different acoustic challenges of hunting fish versus marine mammals. Fish-eating northern resident killer whales reduced echolocation and performed rolling movements in the presence of Pacific white-sided dolphins, suggesting that the whales may eavesdrop on dolphin echolocation to scan broader areas for large Chinook salmon prey that are too big for dolphins to capture and swallow whole.

Echolocation for Communication and Social Coordination

Echolocation clicks serve dual functions of environmental sensing and social coordination. In cooperative foraging between killer whales and dolphins, the spatially and temporally coordinated behaviors suggest that echolocation signals from one species can be used by another to locate prey. The killer whales oriented toward the dolphins and followed them to depth, with no antagonistic interactions or avoidance behaviors observed.

The vocalization behavior of captive dolphins provides additional evidence for the social role of echolocation. Bottlenose dolphins and rough-toothed dolphins showed species-specific changes in click and whistle production during training and feeding activities. Rough-toothed dolphins shifted their predominant whistle type from constant to sinusoidal during feeding, while bottlenose dolphins changed from constant to upsweep. These shifts indicate that acoustic signals, including click trains, carry information relevant to social context and behavioral state.

Comparing Echolocation Across Marine Species

Different marine mammal species have evolved echolocation systems tailored to their ecological niches. The frequency, duration, intensity, and repetition rate of clicks vary among species, as do the acoustic properties of the sound beam and the sensitivity of the auditory system.

At a Glance: Echolocation Characteristics in Marine Mammals

The comparison table above summarizes key differences in echolocation characteristics among marine mammal groups. These differences reflect the acoustic demands of different habitats, prey types, and diving behaviors.

Convergent Evolution of Echolocation Systems

Convergent evolution has shaped the cochlear morphology of toothed whales that occupy similar acoustic environments. Three convergent regimes have been identified in odontocete cochlear shape. The first includes True's beaked whale and Cuvier's beaked whale. The second includes sperm whales and all other beaked whales sampled. The third includes pygmy and dwarf sperm whales and Dall's porpoise.

The first two regimes were significantly convergent, with habitat type and dive type significantly correlated with membership in the sperm whale plus beaked whale regime. The extreme acoustic environment of the deep ocean likely constrains cochlear shape, causing the cochlear morphology of sperm and beaked whales to converge. This finding supports the use of cochlear morphology to predict the ecology of extinct cetaceans.

Interestingly, the river dolphins, a group known for convergent morphologies and riverine ecologies, do not have convergent cochlear shapes. This suggests that the acoustic demands of riverine environments do not impose the same constraints on cochlear form as deep ocean habitats.

High-Frequency Echolocation and the Marine-Freshwater Transition

The transition between marine and freshwater environments has influenced the evolution of high-frequency echolocation and ear morphology in toothed whales. Comparative studies of extant and extinct toothed whales examine how ear morphology changes across this ecological boundary. Freshwater environments present different acoustic challenges than marine environments, including differences in sound propagation, background noise, and prey distribution.

Passive Acoustic Monitoring of Echolocation

Passive acoustic monitoring uses hydrophones to detect and record the echolocation clicks and other vocalizations of marine mammals. This approach is non-invasive and provides continuous data over long durations, making it valuable for studying animal behavior, population status, and the impact of human activities on marine ecosystems.

Estimating Population Density from Echolocation Clicks

Passive acoustic monitoring with widely dispersed hydrophones has been suggested as a cost-effective method to monitor population densities of echolocating marine mammals. This approach requires an estimate of the effective detection area around each receiver over which vocalizations are detected. In the absence of auxiliary measurements, the effective detection area can be modeled.

Common simplifying model assumptions include approximating the spectrum of clicks by flat energy spectra and neglecting the frequency dependence of sound absorption within the click bandwidth. These assumptions render the problem amenable to solution using the sonar equation. However, these approximations can bias estimated density. For Blainville's beaked whales, the effective detection area differed by up to a factor of 2 depending on the spectral energy distribution of echolocation clicks. Both modeling methods predicted relative density bias due to narrowband assumptions ranging from 5 percent to more than 100 percent, depending on species, detector settings, and noise conditions.

Automatic Detection and Classification of Echolocation Signals

Automatic algorithms for the detection and classification of sound are essential to the analysis of acoustic datasets with long duration. Metrics for performance evaluation include receiver-operating-characteristic curves, detection-error-trade-off curves, precision-recall curves, and cost curves. These metrics have been applied to detectors for blue whale D calls and click-clustering neural network algorithms for Cuvier's beaked whale echolocation click detection.

Detection class imbalance, particularly the situation of rare occurrence, is common for long-term passive acoustic monitoring datasets and affects the performance of receiver-operating-characteristic and detection-error-trade-off curves with regard to the impact of false positive detections. Precision-recall curves overcome this shortcoming when calculated for individual detections and do not rely on the reporting of true negatives. Cost curves provide additional insight on the effective operating range for the detector based on the a priori probability of occurrence. Use of more than a single metric is helpful in understanding the performance of a detection algorithm.

Classification of Dolphin Vocalizations Using Machine Learning

Convolutional neural networks have been applied to classify dolphin vocalizations from passive acoustic monitoring recordings. Four types of common bottlenose dolphin vocalizations can be identified from underwater recordings: whistles, echolocation clicks, burst pulse sounds, and feeding buzzes. Edge-detection filters applied to spectrograms remove unwanted noise components and enhance classification performance.

In one study using nearly 10,000 spectrograms, a convolutional neural network achieved an average accuracy of 95.2 percent and an F1-score of 87.8 percent. Class-specific accuracy was highest for whistles at 97.9 percent, followed by echolocation clicks at 94.5 percent, feeding buzzes at 94.0 percent, and burst pulse sounds at 92.3 percent. This method provides a promising step toward improving passive acoustic monitoring of dolphins, contributing to both species conservation and the mitigation of conflicts with fisheries.

Bio-Inspired Sonar and Acoustic Technology

The echolocation systems of marine mammals have inspired technological innovations in sonar design, underwater communication, and robotic positioning. These applications demonstrate the practical value of understanding biological echolocation.

Covert Active Sonar Using Sperm Whale Calls

The covertness of active sonar is an important issue in naval and underwater applications. Many marine mammals produce call pulses for communication and echolocation, and existing interception systems typically classify these biological signals as ocean noise and filter them out. A bio-inspired covert active sonar strategy uses true sperm whale call pulses as sonar waveforms to ensure camouflage ability.

A range and velocity measurement combination was designed using two true sperm whale call pulses that had excellent range resolution and large Doppler tolerance. The range and velocity estimation methods were developed based on this combination. In the sonar receiver, correlation technology confirms the start and end time of sonar signals and their echoes, and the range and velocity of the underwater target are obtained. The range and velocity measurement combination is embedded into the true sperm whale call train to improve the camouflage ability of the sonar signal train.

Cooperative Positioning of Underwater Robots

The collaborative echolocation mechanisms of dolphin pods have inspired algorithms for cooperative positioning of clusters of unmanned underwater vehicles. Cooperative positioning systems typically rely on acoustic ranging information to correct positional errors. However, the propagation characteristics of underwater acoustic signals are susceptible to environmental disturbances, often resulting in non-Gaussian, heavy-tailed distributions of ranging noise.

A factor graph based adaptive cooperative positioning algorithm was designed for heavy-tailed noise environments. The method constructs a factor graph model for unmanned underwater vehicle cooperative positioning to represent the probabilistic dependencies between system states and observed variables. A factor graph estimation mechanism integrating adaptive weights with the product algorithm dynamically adjusts the fusion weights of different measurements by conducting online assessment of residual information. Experimental results demonstrated that this method reduces positioning errors by 22.31 percent compared to the traditional algorithm.

Encryption Using Dolphin Vocalizations

Bionic covert underwater acoustic communication is increasingly important for military and underwater telemetry applications. A text information encryption and hiding mechanism was designed using real bottlenose dolphin vocalizations. A chaotic encryption scheme, spread spectrum technology, and a modified chaotic Hénon map were integrated into the mechanism.

Four bottlenose dolphin vocalizations and four test text information samples were employed to demonstrate performance. When the correct encryption and decryption parameters were used, the test text information was completely recovered and could be recognized by humans. When the encryption and decryption parameters were not identical, the test text information was unrecoverable and could not be recognized by the human eye. The average modified amplitude correlation coefficient was 0.99995924 and the average unified average amplitude change intensity was 3.84 times 10 to the negative 6.

On-Board Acoustic Recording of Echolocation Behavior

Technological advances have enabled researchers to develop miniature devices that record animal behavior directly on the animals themselves. On-board audio recordings have become common following pioneering work in marine mammal research. These recordings address questions about vocal behavior, including when animals call, how they adjust their behavior, and what acoustic parameters they change.

On-board acoustic recordings also address topics like foraging behavior, social interactions, and environmental acoustics. The approach is particularly useful for echolocating animals because their active sensing lifestyle allows many approaches to a multifaceted acoustic assessment of behavior. The general ideas and concepts are applicable to many animals, demonstrating the versatility of on-board acoustic recordings.

Biologgers equipped with video, acoustic, and inertial sensors have been used to record interactions between fish-eating northern resident killer whales and Pacific white-sided dolphins. These recordings revealed reduced echolocation and rolling movements by the killer whales in the presence of dolphins, suggesting eavesdropping on dolphin echolocation to scan broader areas for prey.

Echolocation in Human-Dolphin Cooperation

The interaction between artisanal fishers and wild dolphins provides a unique window into the flexibility of echolocation behavior. By tracking fine-scale behavioral interactions between fishers and dolphins targeting migratory mullets, researchers revealed that foraging synchrony is key to benefiting both predators.

Dolphins herd mullet schools toward the coast, increasing prey availability within the reach of net-casting fishers, who gain higher foraging success when matching their casting behavior with the dolphins' foraging cues. When dolphins approach the fishers' nets closely and cue fishers in, they dive for longer and modify their active foraging echolocation to match the time it takes for nets to sink and close over mullets. This modification occurs only when fishers respond to the dolphins' foraging cues appropriately.

Long-term demographic surveys show that cooperative foraging generates socioeconomic benefits for net-casting fishers and approximately 13 percent survival benefits for cooperative dolphins by minimizing spatial overlap with bycatch-prone fisheries. Recent declines in mullet availability threaten these benefits by reducing the foraging success of fishers and increasing the exposure of dolphins to bycatch in alternative fisheries. A numerical model parameterized with empirical data predicts that environmental and behavioral changes are pushing this traditional human-dolphin cooperation toward extinction.

Why Pinnipeds Do Not Echolocate

The absence of echolocation in pinnipeds provides a useful contrast for understanding the evolutionary requirements of active biosonar. Despite sporadic investigation over the past 30 years, the accumulated evidence in favor of the pinniped echolocation hypothesis is unconvincing. An advanced echolocation system is unlikely to have evolved in pinnipeds primarily because of constraints imposed by the obligate amphibious functioning of the pinniped auditory system.

As a result of these constraints, pinnipeds have not developed the highly acute, aquatic, high-frequency sound production or reception systems required for underwater echolocation. Instead, pinnipeds have evolved enhanced visual, tactile, and passive listening skills. The evolutionary refinement of alternative sensory systems allows pinnipeds to effectively forage, navigate, and avoid predators underwater despite the lack of active biosonar capabilities.

Limitations of Echolocation Research

Research on marine mammal echolocation faces several limitations that affect the interpretation of acoustic data. The frequency dependence of sound absorption within click bandwidths can bias population density estimates when ignored. Detection class imbalance in long-term passive acoustic monitoring datasets affects the performance of detection metrics. The acoustic environment, including background noise and propagation conditions, influences the detectability of echolocation signals.

The vocalization patterns of dolphins are associated with environmental conditions and behavioral contexts, particularly in captive populations. Studies of captive dolphins provide baseline information for acoustic assessment of welfare but may not fully represent the echolocation behavior of wild populations. The Indo-Pacific humpback dolphin dataset from Xiamen Bay addresses data gaps regarding vocalizations of this endangered population and supports population connectivity research through acoustic comparisons between populations across different geographic regions.

Welfare and Conservation Context

Echolocation is central to the welfare and conservation of marine mammals. Mammals are threatened worldwide, with approximately 26 percent of all species included in IUCN threatened categories. For marine mammals, the primary threats include pollution, open net fishing, climate change, and prey depletion. Information on species distribution is crucial to delineate and support conservation actions.

Passive acoustic monitoring of echolocation signals contributes to conservation by providing continuous data on species presence, behavior, and population status. The MAMMALS IN PORTUGAL data set includes 105,026 georeferenced occurrence records of 92 terrestrial, volant, and marine mammals, with vocalization and echolocation records representing one of 13 record types. Bioacoustics surveys account for 4 percent of the data collection methods.

Acoustic monitoring also supports the mitigation of conflicts with fisheries. The classification of dolphin vocalizations from passive acoustic monitoring recordings contributes to both species conservation and the mitigation of conflicts with fisheries. The cooperative foraging between dolphins and fish-eating killer whales highlights the need for further investigation into the ecological implications of interspecific encounters.

Professional Escalation Criteria

Researchers and practitioners working with marine mammal acoustic data should escalate to specialized expertise under specific conditions. If passive acoustic monitoring data show unexpected changes in echolocation click rates, species composition, or acoustic behavior that cannot be explained by normal environmental variation, consult a marine bioacoustician or cetacean biologist. If population density estimates derived from echolocation click monitoring differ substantially from independent estimates, review the modeling assumptions, including spectral energy distribution and narrowband approximations.

If automated detection and classification algorithms produce inconsistent results across datasets, evaluate the performance metrics, including precision-recall curves and cost curves, and consider the impact of detection class imbalance. If captive dolphin vocalization patterns change during training or feeding activities in ways that suggest distress, consult a veterinary professional with expertise in marine mammal welfare.

If cooperative foraging interactions between humans and dolphins show signs of breakdown, such as reduced foraging success or increased bycatch exposure, engage with local fisheries management authorities and conservation organizations to implement protective measures.

Frequently Asked Questions

How do dolphins use echolocation to find prey?

Dolphins emit high-frequency clicks that travel through water and reflect off objects. The returning echoes provide information about the location, size, shape, and movement of prey. Dolphins adjust their click rates and patterns during foraging, producing rapid click trains called feeding buzzes as they close in on prey. In cooperative foraging with human fishers, dolphins modify their active foraging echolocation to match the time it takes for nets to sink and close over fish.

What animals use echolocation in the ocean?

Toothed whales, dolphins, and porpoises use echolocation. This includes bottlenose dolphins, rough-toothed dolphins, Indo-Pacific humpback dolphins, killer whales, sperm whales, beaked whales, and porpoises. Pinnipeds such as seals and sea lions do not echolocate, having instead evolved enhanced visual, tactile, and passive listening skills.

How is echolocation different from communication sounds in dolphins?

Echolocation clicks are short, broadband pulses used for active sensing of the environment. Whistles are tonal sounds used primarily for communication. Burst pulses and feeding buzzes are rapid click sequences that serve both sensing and social functions. Dolphins produce all four categories of sound and adjust their production based on behavioral context, as shown by species-specific changes in click and whistle rates during training and feeding activities.

Why do some whales have convergent cochlear shapes?

Convergent evolution of cochlear shape occurs when species occupy similar acoustic environments. Sperm whales and beaked whales have convergent cochlear morphology because the extreme acoustic environment of the deep ocean constrains cochlear shape. Habitat type and dive type are significantly correlated with membership in this convergent regime. River dolphins, despite their convergent morphologies, do not have convergent cochlear shapes.

Can echolocation clicks be used to estimate whale population density?

Yes, passive acoustic monitoring with widely dispersed hydrophones can monitor population densities of echolocating marine mammals. This requires an estimate of the effective detection area around each receiver. Modeling assumptions, such as flat energy spectra and narrowband approximations, can bias density estimates by 5 percent to more than 100 percent depending on species, detector settings, and noise conditions.

How do killer whales use echolocation differently from dolphins?

Fish-eating and mammal-eating killer whales differ in sonar use. Fish-eating northern resident killer whales reduced echolocation and performed rolling movements in the presence of Pacific white-sided dolphins, suggesting that the whales may eavesdrop on dolphin echolocation to scan broader areas for large Chinook salmon prey. This behavior reflects the different acoustic challenges of hunting fish versus marine mammals.

Why do pinnipeds not echolocate?

Pinnipeds have not evolved echolocation primarily because of constraints imposed by the obligate amphibious functioning of their auditory system. They have not developed the highly acute, aquatic, high-frequency sound production or reception systems required for underwater echolocation. Instead, pinnipeds have evolved enhanced visual, tactile, and passive listening skills.

How is dolphin echolocation used in technology?

Dolphin echolocation has inspired covert active sonar strategies using true sperm whale call pulses as sonar waveforms, cooperative positioning algorithms for underwater robots based on dolphin pod collaborative mechanisms, and encryption mechanisms using bottlenose dolphin vocalizations for covert underwater acoustic communication. These applications demonstrate the practical value of understanding biological echolocation.

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References and Further Reading

• NCBI Literature Resources. National Center for Biotechnology Information.
• PubMed. National Library of Medicine.
• Modelling the broadband propagation of marine mammal echolocation clicks for click-based population density estimates.. The Journal of the Acoustical Society of America, 2018.
• Performance metrics for marine mammal signal detection and classification.. The Journal of the Acoustical Society of America, 2022.
• Bio-Inspired Covert Active Sonar Strategy.. Sensors (Basel, Switzerland), 2018.
• MAMMALS IN PORTUGAL: A data set of terrestrial, volant, and marine mammal occurrences in Portugal.. Ecology, 2022.
• Why pinnipeds don't echolocate.. The Journal of the Acoustical Society of America, 2000.
• Foraging synchrony drives resilience in human-dolphin mutualism.. Proceedings of the National Academy of Sciences of the United States of America, 2023.
• Convergent evolution in toothed whale cochleae.. BMC evolutionary biology, 2019.
• Using on-board sound recordings to infer behaviour of free-moving wild animals.. The Journal of experimental biology, 2019.
• Acoustic recordings of underwater vocalizations of Indo-Pacific humpback dolphins in Xiamen Bay, China.. 2025.
• Cooperative foraging between dolphins and fish-eating killer whales.. 2025.
• Vocalization behaviors in captive bottlenose dolphins (Tursiops truncatus) and rough-toothed dolphins (Steno bredanensis).. 2025.
• First Report on the Acoustic Signals of Lahille’s Bottlenose Dolphins in Argentina. 2026.
• Multiclass CNN Approach for Automatic Classification of Dolphin Vocalizations.. 2025.
• Research on Adaptive Cooperative Positioning Algorithm for Underwater Robots Based on Dolphin Group Cooperative Mechanism.. 2026.
• Modified Chaotic Hénon Map-Based Text Information Encryption and Hiding Mechanism Using Bottlenose Dolphin Vocalizations.. 2026.
• From looking to echolocation. Posthumanist rhetorics of marine mammal welfare. Res Rhetorica, 2026.
• The mixed blessing of echolocation: Differences in sonar use by fish-eating and mammal-eating killer whales. Animal Behaviour, 1996.
• Echolocation. Encyclopedia of Marine Mammals Third Edition, 2017.
• High frequency echolocation, ear morphology, and the marine-freshwater transition: A comparative study of extant and extinct toothed whales. Palaeogeography Palaeoclimatology Palaeoecology, 2014.

This article is educational and does not replace institutional policy, professional advice, or applicable safety and regulatory requirements.