The research, published in Frontiers in Marine Science, relied on the doubly labeled water method, a technique that has been used for decades to measure energy expenditure in humans, birds and seals but has rarely been applied to cetaceans. The approach hinges on the different fates of two isotopes of water in the body: oxygen-18-labeled water leaves as both carbon dioxide and water, while deuterium-labeled water exits only as water. The difference in their turnover rates reveals how much carbon dioxide the animal produced — and therefore how much energy it burned — over the measurement period.

Applying this method to dolphins required a rare combination of circumstances. The Sarasota Bay community, roughly 170 animals, is one of the best-studied cetacean populations on Earth, with individuals of known age, sex and reproductive status. Researchers selected 14 dolphins aged 6 to 23 years — four females and ten males — that were not pregnant and were not nursing young calves. During routine health assessments, the animals were caught in a shallow-water net, dosed with isotopes via stomach tube, fitted with a small VHF radio tag on the dorsal fin, and released. Three to ten days later, the same animals were recaptured and resampled.

The results revealed a pronounced seasonal pattern. In summer, when water temperatures reached about 28 degrees Celsius, the dolphins burned energy at 5.66 watts per kilogram on average, compared with 3.98 watts per kilogram in winter, when water temperatures dropped to roughly 17 degrees. Statistical models confirmed the seasonal effect was robust, explaining nearly half the variation in metabolic rate. Total water influx followed the same pattern, averaging 207 milliliters per kilogram per day in summer versus 117 in winter — a difference that carries important clues about what the animals were eating.

Perhaps the most surprising finding was that the dolphins were heavier and fatter in winter. Their body fat content, estimated from total body water dilution, averaged about 22 percent in winter but only around 5 percent in summer, and mean body mass was slightly higher in the colder months. Because blubber serves as insulation, this makes sense: the animals build up energy reserves in autumn that help them weather the winter thermal gradient, when the temperature difference between their core and the surrounding water can reach 23 degrees Celsius.

Why would dolphins burn more energy in warm water than in cold? The authors consider several explanations. One possibility — increased swimming to shed heat — seems unlikely, because behavioral observations showed no significant seasonal difference in activity budgets. A more probable driver is skin biology. Dolphin skin cells proliferate rapidly in warmer water, and the cost of repairing and rejuvenating the epidermis rises with temperature. Thermal imaging studies show that dolphin skin temperature closely tracks ambient water, and in summer the animals’ bellies turn pink from increased peripheral blood flow, while in winter they appear pale as circulation is restricted to conserve heat.

Prey dynamics offer a third explanation. Winter dolphins had greater body mass, lower water influx and lower metabolic rates, suggesting they were foraging more efficiently on energy-dense fish. Striped mullet, a staple of the Sarasota dolphins’ diet, can range from about 3.8 to 8.4 kilojoules per gram depending on fat content, and local fishers report that mullet fatten in autumn before moving offshore to spawn. The data support this: dolphins with higher metabolic rates gained more mass or lost less, and the relationship between metabolic rate and preformed water intake indicates that individuals burning more energy were consuming more prey.

The water flux measurements also allowed the team to estimate seawater ingestion — a long-debated question in marine mammal physiology. By subtracting the water contained in prey and the water produced metabolically from total water influx, the researchers calculated that summer dolphins may have taken in roughly 16 liters of seawater per day and winter dolphins about 7 liters, representing 44 and 33 percent of their total water influx respectively. These estimates align with laboratory studies showing that dolphin skin is permeable to water, and that the animals can maintain water and salt balance thanks to their highly efficient, multi-lobed kidneys.

Placed in a broader context, the measurements suggest that bottlenose dolphins lead an energetically expensive lifestyle comparable to that of sea lions and fur seals — surface-swimming predators with high costs of transport. This contrasts sharply with the conservative energy strategies of deep divers such as beaked whales and elephant seals, which travel mostly underwater at low cost. The comparison underscores how lifestyle, not just body size, shapes metabolic intensity across marine mammals.

The findings also carry a warning for a warming ocean. If dolphin metabolic rates rise as waters warm — whether through direct thermal effects on skin and peripheral tissues or indirectly through changes in prey availability and quality — the animals may have limited capacity to compensate, especially when resident communities are constrained by the geography of bays and estuaries. Range shifts have already been documented for bottlenose dolphins during El Niño events and in the warming western North Atlantic. For the dolphins of Sarasota Bay, already operating at a high energetic baseline, climate change may leave little room to maneuver.

Subject of Research: Seasonal field metabolic rates and water flux of free-ranging bottlenose dolphins measured with doubly labeled water

Article Title: Metabolic rates and water influx of free-ranging bottlenose dolphins in Sarasota Bay, Florida

Article References: Costa, D. P., Wells, R. S., Worthy, G. A. J., Holser, R. R., Waples, D. M., Read, A. J., Scott, M. D., & Irvine, A. B. (2026). Metabolic rates and water influx of free-ranging bottlenose dolphins in Sarasota Bay, Florida. Frontiers in Marine Science, 13, Article 1917705. https://doi.org/10.3389/fmars.2026.1917705

Image Credits: AI Generated

DOI: 10.3389/fmars.2026.1917705

Keywords: bottlenose dolphins, field metabolic rate, doubly labeled water, Sarasota Bay, marine mammal energetics, thermoregulation, blubber, seawater ingestion, climate change, cetacean physiology, water influx, body condition

The research, led by Giovanni Bearzi of Dolphin Biology and Conservation and OceanCare, together with Silvia Bonizzoni, Nathan B. Furey of the University of New Hampshire, and Randall R. Reeves, combined survey data collected between 2018 and 2025 with 17,755 kilometers of navigation effort from independent research boats. The team covered two study areas off the Italian regions of Veneto and Marche, spanning roughly 5,000 square kilometers of shallow coastal waters. Over 148 days of trawling activity, the researchers inspected 859 trawlers for dolphin presence or absence, photographing vessels and cataloguing gear types with high-resolution cameras and 20-megapixel digital equipment.

The results were stark. Dolphins were observed in the wake of 24.7 percent of all trawlers checked. But the proportion varied dramatically depending on the type of gear being towed. Bottom otter trawlers, which drag a single net kept open by two large boards across the seabed, were followed by dolphins 41.3 percent of the time. Midwater pair trawlers, in which two vessels tow a single net together, attracted dolphins 35.1 percent of the time. Beam trawlers, which tow narrow metal dredges fitted with teeth along the leading edge, were followed only 1.5 percent of the time—essentially ignored by the animals.

The regional contrast was even more surprising. Off Veneto, dolphins followed 25.9 percent of otter trawlers inspected. Off Marche, roughly 150 kilometers to the south, they trailed 75.9 percent of the same gear type. The difference was statistically significant, and the researchers note it is unlikely to be a sampling artifact given the robust number of inspections in both areas. Why dolphins in Marche associate with trawlers at triple the rate seen in Veneto remains difficult to explain, particularly since the two regions are so close together and share similar shallow, heavily fished waters.

Photo-identification data reinforce the picture of widespread reliance. The team compiled 47,261 high-quality photographs of individual dolphins, matching animals based on conspicuous dorsal fin markings. Of 490 marked adult individuals identified in Veneto, 85.9 percent were photographed at least once behind trawlers. In Marche, the figure rose to 90.3 percent of 308 marked adults. These numbers suggest that the large majority of bottlenose dolphins in both study areas forage regularly behind operating trawl gear, not merely as occasional opportunists but as consistent specialists targeting considerable proportions of the local trawl fleets.

The behaviour itself is technically sophisticated. Dolphins foraging behind towing trawlers normally surface between 20 and 200 meters behind the vessel’s stern, often splitting into subgroups: one cluster near the vessel, possibly feeding on organisms discarded from the deck; a second surfacing above the towed net; and a third behind the codend, the closed end of the net where catch accumulates. Dives typically last two to three minutes, with the longest recorded at about five minutes. During hauling, when trawlers are motionless or moving slowly backward, dolphins can approach the stern as the net is retrieved, surfacing as close as one to two meters from the vessel. The researchers tracked dolphin movements behind trawlers for a total of 86 hours and 1 minute, covering 525 kilometers of following.

Group sizes behind trawlers averaged 9.0 individuals, ranging from 1 to 70. Adults were present in all 212 groups followed, while juveniles appeared in 51.4 percent, calves in 29.2 percent, and newborns in 7.1 percent. Critically, dependent newborns and small calves were routinely observed surfacing and diving in synchrony with adults above towed nets, performing dives as long as those of the adults. The youngest animals did not approach vessels as closely as adults, but by observing the behaviour of mature foragers, immature dolphins are likely to learn this specialised tactic and become trawler-followers themselves as they mature—a pattern consistent with cultural transmission of foraging behaviour documented in other odontocete populations worldwide.

The researchers frame this adaptation against a backdrop of severe ecological degradation. The Adriatic Sea has one of the world’s highest regional intensities of bottom trawling and, by far, the poorest seabed condition compared to 23 other trawled regions worldwide. Trawling has helped drive a major regime shift in the basin, flattening rich three-dimensional habitats into sedimentary plains and depleting natural prey for apex predators. Elasmobranchs declined by more than 94 percent between 1948 and 2005. Short-beaked common dolphins, once abundant throughout the Adriatic, have virtually disappeared. In this context, the dolphins’ turn to trawlers may simply reflect exploitation of the resources that remain available to them—a pattern paralleled in terrestrial carnivores such as polar bears, which become reliant on human food sources when natural prey is scarce.

Whether this reliance ultimately helps or harms the dolphins is unknown. Foraging behind trawlers could augment food intake in the short term, and in other species, association with fishing gear has been linked to higher survival and calving rates. But any advantages may be offset by chronic exposure to vessel noise, trawl-related pollutants, occasional injury or death in trawl gear, and the continued deterioration of the ecosystems on which the animals depend. Culture-driven foraging specialisation can also fragment populations into separate social clusters, making them more vulnerable to further environmental change. When the targeted niche depletes, the behavioural trait becomes maladaptive—an evolutionary trap in which short-term benefits mask long-term costs.

The authors argue that promoting the continued use of trawlers is inadvisable, not only to protect dolphins but to conserve Adriatic marine biodiversity more broadly. They point to spatial restrictions on trawl fisheries and the adoption of less destructive fishing methods as sensible approaches consistent with obligations under the Convention on Biological Diversity, the Convention on Migratory Species, and the Barcelona Convention. The Jabuka/Pomo Pit Fisheries Restricted Area, established in 2017 in the Adriatic, offers a compelling example of how spatial management can benefit both the marine environment and fisheries. Yet compliance there was high while fishers maintained similar overall effort by trawling elsewhere. The northern Adriatic has been classified as an Important Marine Mammal Area for bottlenose dolphins, and appropriately large no-take zones would allow researchers to investigate whether dolphins, over time, reduce their dependence on trawlers and return to catching prey the natural way—potentially opening the door for common dolphins to return to waters they once dominated.

Subject of Research: Bottlenose dolphin reliance on trawlers in the prey-depleted Adriatic Sea

Article Title: Bottlenose dolphin reliance on trawlers in prey-depleted Adriatic Sea regions

Article References: Bearzi, G., Bonizzoni, S., Furey, N. B., & Reeves, R. R. (2026). Bottlenose dolphin reliance on trawlers in prey-depleted Adriatic Sea regions. Frontiers in Mammal Science, 5, Article 1855890. https://doi.org/10.3389/fmamm.2026.1855890

Image Credits: AI Generated

DOI: 10.3389/fmamm.2026.1855890

Keywords: bottlenose dolphins, Adriatic Sea, trawling, prey depletion, cultural transmission, marine conservation, Frontiers in Mammal Science, Bottlenose, dolphin, reliance, trawlers, prey-depleted

For decades, researchers probing animal creativity have relied on trained paradigms, in which an animal is cued to produce a novel behavior and rewarded for originality. Dolphins have excelled in such studies, famously inventing new tricks on command, but critics have noted a limitation: those tasks measure creativity only under stimulus control, shaped by human expectations and reinforcement schedules. The new study took a different route. Instead of asking dolphins to perform, the team examined object play, a naturally occurring, self-initiated behavior, and asked whether it displayed two key features associated with creative cognition: fluency, meaning the diversity and frequency of behaviors produced, and elaboration, meaning the sequential organization of those behaviors into increasingly complex chains.

The researchers analyzed video footage of bottlenose dolphins (Tursiops truncatus) housed at the Roatan Institute for Marine Sciences in Honduras and wild Atlantic spotted dolphins (Stenella frontalis) studied near Bimini in the Bahamas. Data collection at both sites was funded and organized through the Dolphin Communication Project, and all observations were non-invasive, relying on footage rather than direct interference with the animals. Trained coders, using the event-logging software BORIS, marked each object play event and broke it down into its component behaviors, the type of object involved, and the social context in which it occurred. That granular coding allowed the team to apply quantitative measures of fluency and elaboration rather than relying on anecdotal impressions of playfulness.

The results revealed striking patterns that differed between the two populations. Among the managed-care bottlenose dolphins, object play varied significantly by sex and age. Males accounted for 66.2 percent of recorded play events, and their interactions were dominated by jawing, a mouthing behavior. Females, by contrast, showed greater behavioral diversity, with high proportions of carrying and pushing behaviors. Age mattered as well: younger dolphins showed higher frequencies of jawing, while older individuals engaged in more complex manipulation behaviors. The objects themselves were used differently across the sexes, with males primarily interacting with a single object category and females more frequently engaging with leaves and seagrass. These differences hint that play may serve different developmental and social functions across demographic groups.

The wild Atlantic spotted dolphins told a different story. In this population, the researchers found no significant differences in object play across sex or age, and interactions were overwhelmingly dominated by seaweed, which featured in at least 81 percent of play events across all groups. The contrast between the two species is intriguing: the managed-care bottlenose dolphins, living in an environment with access to a wider variety of objects, displayed a richer and more differentiated play repertoire, while the wild spotted dolphins converged on a single favored material. Whether that reflects ecological opportunity, species differences, or the different social structures of the two populations remains an open question that the authors frame as a direction for future work.

Perhaps the most technically significant finding came from lag sequential analysis, a statistical method that examines whether one behavior reliably predicts the next in a sequence. The analysis revealed structured, non-random behavioral organization in the object play of both populations. In other words, dolphins were not simply grabbing objects and doing whatever came next; their play followed discernible patterns of transitions from one action to another. The bottlenose dolphins exhibited more diverse behavior transitions than the spotted dolphins, suggesting a broader repertoire of possible play sequences. This kind of sequential structure is precisely what the elaboration criterion requires: evidence that play behaviors are chained together in organized ways rather than emitted as isolated, disconnected actions.

Going a step further, the team applied higher-order analyses that looked beyond immediate transitions to identify behavioral associations spanning longer stretches of the play sequence. These analyses identified associations beyond the immediate next-step level, supporting the interpretation that dolphins elaborate on their play, building extended, organized sequences rather than repeating simple two-step patterns. In the framework of creative cognition, elaboration is considered a marker of generative thinking, the capacity to take an initial idea or action and develop it into something more complex. Finding that signature in spontaneous play, without any training or prompting, strengthens the argument that object play can serve as a proxy for creativity in dolphins.

The study, which formed part of the lead author’s master’s thesis at Nova Southeastern University, contributes to a growing body of work suggesting that innovative and flexible behaviors in non-human animals are indicators of cognitive sophistication. Dolphins have long been candidates for such claims, given their large brains, complex social lives, and documented vocal and behavioral innovations. But demonstrating creativity rigorously requires more than charm; it requires measurable structure. By quantifying fluency and elaboration in an unprompted behavior, the researchers provided exactly that, and they did so across two ecologically distinct populations, which adds weight to the conclusion that structured object play is a real feature of dolphin behavior rather than an artifact of captivity or human interaction.

There are caveats worth keeping in mind. The managed-care sample lived in an environment where humans provide objects and where the dolphins’ daily experience differs profoundly from that of wild animals, and the wild data came from a single study site with a narrow range of available materials. Play itself remains notoriously difficult to define, and inferring internal states such as creativity from external behavior is inherently an interpretive act. The authors are careful to describe object play as a window into spontaneous creativity rather than definitive proof of it. Still, the demonstration that play in both populations is statistically non-random and elaborated moves the conversation forward in a way that purely observational anecdotes cannot.

The broader implications reach beyond dolphins. If spontaneous object play can be rigorously analyzed for fluency and elaboration, the same toolkit could be applied to other species, from primates to corvids to cetaceans yet unstudied, offering a common metric for comparing creative capacities across the animal kingdom. For dolphins specifically, the study suggests that the playful dolphin twirling seaweed at the surface may be exercising a form of behavioral innovation that parallels, in its structure, the creative processes psychologists study in humans. As the authors conclude, object play offers a way to better understand dolphin cognitive capacity in novel situations, and it does so on the dolphins’ own terms, in behavior they choose freely, without a trainer, a cue, or a reward in sight.

Subject of Research: Spontaneous object play as a measure of creativity in bottlenose and Atlantic spotted dolphins

Article Title: Fluency and elaboration in dolphin object play: evidence for creativity in behavioral exchanges?

Article References: Adams, A. H., Themelin, M., Manitzas Hill, H., Yeater, D. B., Walker, R. T., Hirons, A. C., & Dudzinski, K. M. (2026). Fluency and elaboration in dolphin object play: evidence for creativity in behavioral exchanges?. Animal Cognition. https://doi.org/10.1007/s10071-026-02117-6

Image Credits: AI Generated

DOI: 10.1007/s10071-026-02117-6

Keywords: dolphins, object play, creativity, animal cognition, bottlenose dolphins, Atlantic spotted dolphins, fluency, elaboration, behavioral sequences, play behavior, cetacean cognition, lag sequential analysis

The significance of the new method lies in the sampling matrix itself. Historically, urine has been considered the gold standard for assessing phthalate exposure in humans, because metabolism renders these compounds hydrophilic and readily excreted. After ingestion, inhalation or dermal absorption, phthalate diesters are hydrolyzed in the liver and small intestine into monoester metabolites, then conjugated into water-soluble glucuronides that are flushed from the body. But collecting urine from a wild dolphin requires catheterization during a catch-and-release health assessment, a logistically demanding and stressful procedure. Blubber, by contrast, can be obtained from free-swimming animals using remote biopsy dart sampling, a technique already used worldwide to measure persistent organic pollutants and trace metals in cetaceans.

Blubber is a biologically compelling target for contaminant surveillance. Composed of 80 to 90 percent lipid, it serves roles in buoyancy, thermal insulation and energy storage, and acts as a reservoir for lipophilic anthropogenic chemicals. High-molecular-weight phthalates such as DEHP, DINP and DIDP carry high octanol-water partition coefficients, meaning they preferentially partition into fatty tissues. Moreover, evidence from human breast milk, which shares lipid-rich characteristics with blubber, has long shown that monoester metabolites can be retained in such matrices. The research team reasoned that blubber might capture metabolites too hydrophobic to be efficiently excreted in urine, potentially extending the detectable window of exposure in a way urine cannot.

To build the protocol, the researchers adapted existing methods that had extracted phthalate metabolites from roach muscle tissue and harbor porpoise liver. They validated the technique using a single full-depth blubber sample collected during necropsy from a bottlenose dolphin stranded near Charleston, South Carolina. The finalized workflow is technically precise: approximately 200 milligrams of blubber is placed in methanol-rinsed amber glass vials, submerged in ammonium acetate buffer, and spiked with isotopically labeled internal standards. The mixture undergoes two 20-minute rounds of sonication, followed by an enzymatic deglucuronidation step using beta-glucuronidase from E. coli K12, incubated at 37 degrees Celsius for 90 minutes.

The extracts are then cleaned up and concentrated using solid-phase extraction on Bond Elut NEXUS cartridges, conditioned with acetonitrile and phosphate buffer, rinsed with formic acid and HPLC-grade water, and eluted with ethyl acetate followed by acetonitrile. After evaporation to dryness under nitrogen at 50 degrees Celsius, samples are reconstituted in water and analyzed by high-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry with negative electrospray ionization. Separation is achieved in just 11 minutes using a water-acetonitrile gradient. Twelve phthalate metabolites, spanning both low- and high-molecular-weight compounds, were targeted, with calibration curves required to achieve correlation coefficients of at least 0.995 for every analytical batch.

Quality assurance was rigorous. Reagent blanks, field blanks, reagent spikes and matrix spikes accompanied every batch of six samples, and blank-derived contamination was subtracted from sample values. Mean recoveries for most analytes fell comfortably within the 70 to 130 percent range accepted by the U.S. Environmental Protection Agency, and solid-phase extraction recoveries in validation matrix spikes exceeded 90 percent for all compounds. MEHP proved the exception, with a lower but consistent mean recovery of roughly 60 to 90 percent, a pattern the authors attribute to possible binding to matrix components, incomplete cartridge elution, ion suppression, and pervasive background contamination from DEHP in laboratory materials, a well-documented problem given DEHP’s ubiquity.

Once validated, the method was applied to blubber samples from 27 bottlenose dolphins captured and released during health assessments in Sarasota Bay, Florida, in 2016, 2017, 2022 and 2023. The Sarasota Bay community of roughly 170 dolphins has been studied continuously for more than 50 years, making it one of the best-characterized marine mammal populations in the world and an ideal proving ground for a new exposure biomarker. The sampled animals included 13 males and 14 females aged 2 to 34 years, with 67 percent classified as sexually immature.

The results revealed detectable concentrations of three metabolites. MEHP, the monoester of the plasticizer DEHP, was found in six dolphins at 5.2 to 12.4 nanograms per gram wet weight. MEP, the metabolite of diethyl phthalate used in personal care products, appeared in two animals at 39.7 to 50.1 nanograms per gram. MIDP, the metabolite of the industrial plasticizer diisodecyl phthalate, was detected in three dolphins at 26.0 to 27.4 nanograms per gram. Overall, at least one metabolite was detectable in 37 percent of sampled dolphins, and a single two-year-old female carried detectable levels of two metabolites simultaneously. The oldest sampled dolphin, a 34-year-old female, had the highest concentration of any analyte.

Compared with earlier urine-based studies in the same population, which found multiple phthalate compounds in roughly 75 percent of dolphins tested, the blubber detection rate was lower, and the authors interpret this through the lens of chemical partitioning. Low-molecular-weight phthalates and their metabolites are more hydrophilic and are preferentially excreted in urine rather than stored in lipid, whereas high-molecular-weight parent compounds may partition into blubber before or after metabolism. Elevated limits of detection, driven by the deliberately small 200-milligram sample mass needed to avoid clogging extraction cartridges with co-extracted lipids, also likely suppressed detection rates. Larger samples introduced excessive lipid material that overwhelmed the cleanup process, forcing a trade-off between extraction practicality and analytical sensitivity.

The study’s authors emphasize that this is the first analysis of phthalate metabolites in blubber from live, healthy dolphins, filling a critical gap in marine mammal health surveillance. Remote biopsy darts typically yield full-thickness blubber samples of 0.05 to 0.8 grams, comparable to the tissue mass used here, suggesting the method could be deployed on remotely collected samples in future work. That capability would allow phthalate exposure assessments in at-risk or remote populations where catch-and-release assessments are infeasible, increase sampling efficiency, and reduce stress on protected animals. While blubber remains a less reliable indicator of total exposure than urine, particularly for low-molecular-weight compounds from personal care products, it offers a powerful complementary tool for high-molecular-weight compounds from plastics. As researchers begin to trace the trophic transfer of phthalates from microplastics through prey to dolphins, this new blubber-based protocol provides a standardized foundation for expanding chemical surveillance across the world’s coastal oceans, with direct implications for marine conservation and, given dolphins’ role as sentinels for ecosystem and human health, for people who share the same contaminated waters.

Subject of Research: Development of a blubber-based detection protocol for phthalate ester metabolites in bottlenose dolphins

Article Title: Development and application of a blubber-based detection protocol for phthalate ester metabolites in bottlenose dolphins (Tursiops truncatus)

Article References: Knight, M. A., Pisarski, E. C., Wells, R. S., Dziobak, M. K., Wirth, E. F., Sandifer, P. A., Moors, A. J., & Hart, L. B. (2026). Development and application of a blubber-based detection protocol for phthalate ester metabolites in bottlenose dolphins (Tursiops truncatus). Environmental Science and Pollution Research, 33(30), 15553-15567. https://doi.org/10.1007/s11356-026-38215-8

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38215-8

Keywords: bottlenose dolphins, phthalates, blubber, marine mammals, endocrine disruptors, plastic pollution, LC-MS/MS, Sarasota Bay, environmental monitoring, contaminant exposure, biopsy sampling, ecotoxicology