Lunar Cycle Research Articles

DETERMINING THE ROLE OF SPATIAL ABILITY IN PERFORMING LUNAR PHASE CHANGE TASK USING BRAIN ACTIVITY ANALYSIS

Many students have difficulty understanding the concept of lunar phase changes (LPCs) due to spatial ability problems such as perspective-taking (PT) and mental rotation (MR). Therefore, this study aimed to compare brain activity during PT and MR tasks while performing the LPC task to determine the involvement of PT and MR. This study measured brain waves using EEG in 20 participants while solving the 3 tasks. First, the power values in the theta band of all cortical areas showed a significant difference between MR and LPC tasks. Second, in the strategy execution section with a statistically significant difference, the occipital lobe and limbic system were mainly active during the PT task, whereas the frontal lobe was mainly active during the LPC task. Third, for strategy execution, during MR and LPC tasks, the frontal lobe, temporal lobe, and limbic system were all activated to significantly different degrees. Therefore, both PT and MR, particularly PT, are required to solve the LPC task. Moreover, for students who have difficulty learning LPC, it is necessary to recognize the need for spatial ability, such as PT ability, and establish an appropriate teaching strategy. Keywords: brain activation, electroencephalography, lunar phase change, mental rotation, perspective-taking

Estimation of nighttime PM2.5 concentrations over Seoul using Suomi NPP/VIIRS Day/Night Band

With rapid economic development and urban growth, Seoul experiences severe air pollution due to fine particulate matter with an aerodynamic diameter of ≤2.5 μm (PM2.5), which is detrimental to human health. Although recent studies have extensively focused on estimating daytime PM2.5 concentrations using various types of satellite data, there remains a significant lack of research on nighttime PM2.5 estimations. This study estimated nighttime PM2.5 in Seoul from December 2018 to November 2019 using multiple linear regression (MLR) and random forest (RF) models. These models, which incorporated data on radiance, moon illumination fraction, and terrain height from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) on board the Suomi National Polar-orbiting Partnership satellite covering all moon phases, also utilized meteorological data from the ERA5 reanalysis by the European Centre for Medium-Range Weather Forecasts (ECMWF). To address multicollinearity, seasonal models were developed using forward stepwise regression and variance inflation factor analysis. DNB radiance analysis indicates that the high intensity of artificial light sources in Seoul significantly reduces the impact of moonlight, leading to notable changes in the DNB radiation associated with PM2.5 concentrations. Consequently, this study estimated nighttime PM2.5 over Seoul across all moon phases. These estimates were then validated through 10-fold cross-validation. The RF model exhibited superior accuracy, with a coefficient of determination (R2) of 0.65–0.90, compared to MLR, with R2 of 0.15–0.50, reflecting seasonal fluctuations in the model performance. The developed models can be applied to estimate reliable nighttime PM2.5 concentrations in megacities with strong artificial light sources, utilizing a comprehensive dataset from satellite observations for all moon phases. Additionally, our findings can serve as scientific data for establishing environmental policies by providing valuable insights into understanding air pollution primarily caused by PM2.5.

Livestock guarding dogs shape activity patterns of sympatric mesocarnivores in sheep ranches of the Patagonia region

Predation of livestock by wild carnivores is a source of human-wildlife conflict. Livestock Guarding Dogs (LGDs) are one of the most effective non-lethal methods used. LGDs could impact wildlife due to their possible top predator role; their effect on mesocarnivores has been studied mainly in terms of space use, however, temporal effects may also exist. Our study sought to determine the possible effects of LGD presence on the activity patterns of the native foxes Lycalopex griseus and L. culpaeus in southern Chile. Activity patterns were estimated from fox detections with camera traps set on ranches with and without LGDs in Isla Riesco, Magallanes region, Chile, between 2016 and 2018. We quantified the activity patterns of each fox species in presence/absence of LGDs, and under different conditions including breeding vs non-breeding season, moon phase and vegetation cover. Both species modified their daily activity pattern, avoiding times of day of high LGD activity; nevertheless, these modifications did not change the temporal interaction between the native foxes. Activity patterns of foxes without LGDs did not differ from those in natural areas. The effect of LGDs on fox activity patterns was stronger than other ecological variables (breeding season, moon phase or vegetation cover). Since LGDs change the activity patterns of foxes, they cannot be seen as a totally innocuous predation control tool; however, carnivores’ temporal avoidance of areas with a fear-evoking agent like LGDs would result in fewer livestock-predators encounters, thus reducing sheep predation risk. LGDs appear to exert non-lethal effects upon carnivores that would contribute to reduced predation rates and may help decrease producers’ economic losses, as well as the retaliatory hunting of wild carnivores. Thus, our results support that LGDs could be contributing to the co-existence with native predators in areas destined for livestock production.

Filling in Munk’s ‘orbital gap’ in climate and sea-level variability

Abstract This study explores the linkage between lunar precessions, solar activity, plus their interactions, and the interannual variability of climate indices and Australian sea level. The focus is on variability longer than the lunar nodal cycle (18.6 years), but shorter than millennia, also known as orbital gap. Climate indices include the Pacific Decadal Oscillation, El Niño-Southern Oscillation, the Southern Oscillation Index, the Indian Ocean Dipole, and the Southern Annular Mode. Long-term (> 100 years) sea-level data were examined at Fremantle (Western Australia) and Fort Denison (Sydney, Eastern Australia). Periodicities associated with gravitational and radiational forces were fitted to 3-yr- and 5-yr-filtered records of each climate index and of sea-level records. All fits, 10 for climate indices and 12 for sea level, explained the variance of all filtered records remarkably well (>60%). Findings suggest that lunar precessions and their interactions with solar activity may be connected to interannual variations in oceanic mixing. Mixing leads to climate variability through transport of heat, mass and solutes in the atmosphere and ocean, and ultimately relates to interannual sea-level variability. This study represents the possibility of astronomic effects on Earth’s environmental variables, beyond the internal variability of the ocean-atmosphere system.

Investigating Subsurface Properties of the Shallow Lunar Crust Using Seismic Interferometry on Synthetic and Recorded Data

AbstractIn the past few years, the remarkable progress of commercially operated spacecrafts, the success with reusable rocket engines, as well as the international competition to explore space, has led to a substantial acceleration of activities in the design and preparation of ambitious future lunar missions. In the search for ice and/or cavities imaging the shallow subsurface structure is of vital importance. Hereby, previous studies have shown that seismic interferometry is a promising method to investigate the subsurface properties from passive lunar data. In this study, we want to evaluate the potential of this method further by examining the required duration of seismic measurements and the influence of scattering on the Green's function retrieval. Therefore, we applied seismic interferometry to both measured Apollo 17 data and synthetic data. Our findings indicate that, under optimal conditions, a few hours of data are sufficient when using the method of time‐scaled phase‐weighted stack (ts‐PWS). However, this strongly depends on the inter‐station distance, the orientation toward the principal noise sources, and the timing of the measurement during the lunar cycle. Additionally, we were able to reproduce the measured data using numerical simulations in 2D. The synthetic results show that scattering effects clearly influence the Green's function extraction, especially for larger station distances.

Whakapapa, Mauritau, and Placefulness to Decolonise Indigenous Minds

This article explores the relationship between genealogy and the environment as a pathway towards decolonising indigenous minds. In Māori worldviews, everything is categorised, organised, and understood through whakapapa, or genealogy. Whakapapa resides within the land and water, safeguarding ancestral stories as they weave through time, space, and place. The environment serves as a powerful tool for maintaining, reclaiming, and reinforcing indigeneity. Strengthening the connections between whakapapa and the environment offers significant avenues for decolonising Indigenous minds, by recalibrating and releasing colonised ways of being to embody mauritau (mindfulness) through whenua kura (placefulness). Unlike Cartesian dualism, which separates the body and mind, the Māori conception of the mind is multifaceted and embodied. The mind is thought to be situated in the solar plexus, emotions in the gut, and connection to spirit in the head, all of which are deeply rooted in whakapapa and the enduring ties to ancestors and place. Whakapapa’s connections to the land, water, animals, and spiritual entities are imbued with narratives that aid in recollection and provide profound cultural context to place. These narratives offer pathways for communion with the land and water, enabling sensitivity to environmental cues, such as changing seasons, solstices, moon phases, star cycles, and natural rhythms within our inner landscapes of body, heart, and mind, fostering a sense of placefulness.

The moon's influence on the activity of tropical forest mammals.

Changes in lunar illumination alter the balance of risks and opportunities for animals, influencing activity patterns and species interactions. We examined if and how terrestrial mammals respond to the lunar cycle in some of the darkest places: the floors of tropical forests. We analysed long-term camera trapping data on 86 mammal species from 17 protected forests on three continents. Conservative categorization of activity during the night revealed pronounced avoidance of moonlight (lunar phobia) in 12 species, compared with pronounced attraction to moonlight (lunar philia) in only three species. However, half of all species in our study responded to lunar phases, either changing how nocturnal they were, altering their overall level of activity, or both. Avoidance of full moon was more common, exhibited by 30% of all species compared with 20% of species that exhibited attraction. Nocturnal species, especially rodents, were over-represented among species that avoided full moon. Artiodactyla were more prominent among species attracted to full moon. Our findings indicate that lunar phases influence animal behaviour even beneath the forest canopy. Such impacts may be exacerbated in degraded and fragmented forests. Our study offers a baseline representing relatively intact and well-protected contexts together with an intuitive approach for detecting activity shifts in response to environmental change.

Environmental and ecological factors associated with stinging jellyfish at a tourism hotspot in the Gulf of Thailand

The waters of Thailand are associated with some of the most severe cases of envenomation from jellyfish in Asia, often attributed to the extensive marine recreational tourism industry it supports. The western Gulf of Thailand in particular has been shown to host among the highest abundances of box jellyfish, while also being home to some of the highest marine recreational tourism, such as along the Koh Samui archipelago. Here we utilise aspects of the same tourism industry to develop a deeper understanding of stinging jellyfish population dynamics, by combining citizen science at the island of Koh Tao, with dedicated in-situ surveys and remote sensing data. Our analyses of 170 box jellyfish sightings and 81 blooms of Pelagia sp. across a six-year period revealed a strong seasonal trend, with both groups being most abundant between July and December. Decision tree analysis of the complete observation dataset and multiple environmental variables revealed a combination of precipitation and lunar cycle to be the strongest predictors of the assessed stinging jellyfish at Koh Tao. Furthermore, blooms of Pelagia sp. were associated with extensive medusivory by a large diversity of predators, including reef building corals. These observations add to the growing literature showing that scleractinian corals are readily able to ingest larger prey items, either by solitary or protocooperative feeding strategies. Meanwhile, no consumption of box jellyfish medusae was recorded during the study. These findings may allow for improved tourism management practices while also supporting a wider biogeographic assessment of stinging jellyfish in south-east Asia.

Exploring Indigenous Knowledge Systems Integrated in Natural Sciences Practical Work in Selected South African Schools

This study used the nature of indigenous knowledge (NOIK) framework to explore indigenous knowledge systems (IKS) practices that were integrated when practical work in natural sciences was facilitated. In this interpretive explorative case study, data were collected by semistructured interviews, lesson observations and a focus group interview conducted with three purposively selected natural sciences teachers and two natural sciences district officials in the province of KwaZulu-Natal in South Africa. Thematic analysis techniques were used to analyze the data that were collected. Three findings on ways to integrate IKS in science practical work are the following. First, IKS was integrated in practical work through teaching of applied science and including the learners’ lived experiences of local technologies to solve problems. Second, practical work that integrated IKS was conducted as empirical observations of natural phenomena, which included genetic variation of plants and animals, including human beings, animal behavior, using moon cycles and the movement of the sun to guide day-to-day, cultural and agricultural activities. Third, some of the IKS included myths and superstitions that distorted the public understanding of science but were nevertheless used to persuade people to uphold certain cultural practices. The study recommends comparing NOIK and the nature of science when integrating IKS in the classroom to enable learners to distinguish myths from scientific facts.

Reproduction of the dog snapper Lutjanus jocu in captivity, linking ecological, and production observations

Snappers’ domestication for reproductive purposes is a first step to allow future offering of high quality, more sustainable fish products, generating ecological advantages to the marine ecosystem such as the reduction on the pressure of current stocks. The dog snapper Lutjanus jocu is a very important species with very little information on its capability for domestication. For that reason, dog snappers were collected in the coastal area and maintained in laboratory to verify their capacity to be domesticated and achieve reproductive success. A specific protocol was designed for their maintenance in recirculating aquaculture systems and is presented in the methods section. The domestication of wild specimens until they achieved reproductive success and produced viable eggs in captivity took approximately 2.5 years. Spawning events produced an average of about 25,000 eggs, or about 2,100 eggs·kg-1 of broodstock, with an average of three events per week. During new and full moon, the viability of eggs was higher, showing a strong influence of the lunar cycle in their reproduction. Spawning activities only happened during the night, and embryo development took about 535 degree-hours. Our results concluded that the dog snapper L. jocu can be conditioned in captivity for reproductive purposes, with consistent production of eggs in a weekly basis, enabling the possibility of a large-scale production to help reduce the pressure on the natural stocks.

No effects of abiotic and anthropogenic factors on reef-associated neonate shark abundance within a shark nursery-area system

Context Coastal habitats function as shark nursery areas; however, coastal habitats can experience extreme variation in abiotic conditions and are susceptible to human disturbances. Aims Drivers of abundance were tested within a shark nursery-area system in two populations of reef-associated neonate sharks, namely, blacktip reef sharks (Carcharhinus melanopterus) and sicklefin lemon sharks (Negaprion acutidens). Methods Catch data from a fisheries-independent gill-net survey (n = 90 sets from October 2018 to March 2019) at 10 sites around Moorea, French Polynesia, were used to test for associations between shark abundance and abiotic conditions (temperature, oxygen, pH, salinity, lunar phase and depth). Historical levels of fin-fish fishing effort, trampling (i.e. human movement through habitat), and coastal artificialisation (i.e. walls and embankments) estimated for each site were used to test for anthropogenic effects on shark abundance. Key results There were no effects of any abiotic or anthropogenic factor on abundance of either species. Conclusions Previous work corroborates our findings by demonstrating neonate sharks’ physiological tolerance to extreme abiotic conditions and high survival in response to anthropogenic stressors. Alternatively, populations are already degraded from decades of coastal development. Implications These data can aid in predicting the use of coastal habitats as shark nursery areas.

Reproductive ecology of fire corals in the northern Red Sea

AbstractScleractinian corals, the principal architects of coral reefs, face substantial threats from ongoing and anticipated climate change and other anthropogenic disturbances. This underscores the significance of investigating alternative reef-building organisms and their contribution to reefs’ resilience. Among these alternatives, colonial hydrozoans of the genus Millepora, commonly called ‘fire corals’, play substantial roles in contributing to coral reef structure and functionality by depositing calcareous exoskeletons. Despite the ecological importance of fire corals, fundamental knowledge gaps remain regarding their biology and reproductive ecology. Here, we present a comprehensive study on the population dynamics, reproductive ecology, phenology, and sex ratio of the three Red Sea fire corals—Millepora dichotoma, M. exaesa, and M. platyphylla—in the Gulf of Aqaba and Eilat. The abundance of M. dichotoma and M. exaesa seems to have remained consistent over the last 50 years across two of the three depth zones surveyed, indicating their potential resistance or resilience. However, at the third depth surveyed, their abundance appears to have decreased. Our extensive in-situ monitoring of breeding events over six consecutive years has revealed a previously undetected relationship between Millepora species breeding events and the lunar cycle. Histological analyses indicated remarkably short reproductive cycles of only 2–3 weeks, recurring multiple times within a single season, in both M. dichotoma and M. exaesa, which is a unique reproductive aspect compared to other reef-building corals. These results highlight the high reproductive and resilience potential of Millepora species. Consequently, fire corals could assume a more substantial role as keystone species in changing environments and future reefs, emphasizing their importance in reef conservation and management.

Monitoring aerosol optical depth during the Arctic night: Instrument development and first results

Moon-photometric measurements were made at two locations in the Arctic during winter nights using two different modified Sun photometers; a Carter Scott SP02 and a Precision Filter Radiometer (PFR) developed at PMOD/WRC. Values of aerosol optical depth (AOD) were derived from spectral irradiance measurements made at four wavelengths for each of the devices. The SP02 was located near Barrow, Alaska and recorded data from November 2012 to March 2013, spanning five lunar cycles, while the PFR was deployed to Ny-Ålesund, Svalbard each winter from February 2014 to February 2019 for a total of 56 measurement periods. A methodology was developed to process the raw data, involving calibration of the instruments and normalizing measured spectral irradiance values in accordance with site-specific determinations of the extraterrestrial atmospheric irradiance (ETI) as Moon phase cycled. Uncertainties of the derived AOD values were also evaluated and found to be in the range, 0.006–0.030, depending on wavelength and which device was evaluated.The magnitudes of AOD determined for the two sites were in general agreement with those reported in the literature for sunlit periods just before and after the dark periods of Arctic night. Those for the PFR were also compared with data obtained using star photometers and a Cimel CE318-T, recently deployed to Ny-Ålesund, showing that Moon photometry is viable as a means to monitor AOD during the Arctic night. Such data are valuable for more complete assessments of the role aerosols play in modulating climate, the validation of AOD derived using various remote sensing techniques, and applications related to climate modeling.

Unearth the Facts and Fiction of “The Influence of Moon Phases on Living Beings”

The moon, Earth's most constant companion, it is a satellite of our planet. Being the closest cosmic body to Earth, the moon has given rise to numerous myths worldwide throughout the years. The lunar phases are a result of the moon orbiting Earth while Earth orbit the sun. Everything is in motion. Essentially, what we observe from Earth is different parts of the moon being illuminated by the sun as the moon follows its orbit. The relationship between Earth and the Moon is characterized by mutual gravitational attraction and interdependence. The moon significantly influences various aspects of Earth's environment and behavior. While human biology has often been disregarded as a myth, recent studies have suggested a connection between lunar phases and human behavior. Some researchers propose that humans may be responding to subtle changes in Earth's magnetic field that concur with the moon's phases. Today, the moon continues to hold many fascinating mysteries for scientists to investigate. This article aims to uncover the facts and myths surrounding the impact of Lunar phases on humans on Earth.

Learning About Lunar Phases: Exploring Taiwanese University Students’ Conceptions of and Approaches to Learning by Holographic Projection

Extant literature has preliminarily confirmed the potential benefits of holographic projections for educational purposes. Yet, students’ experiences of learning by holographic projection have rarely been addressed. The main purpose of this study was therefore to explore students’ conceptions of and approaches to learning by holographic projection. A holographic projection system was devised to assist students in learning the concept of lunar phases. This study also investigated the relationships between students’ conceptions and approaches, and determined if there were any variations based on students’ learning gains. Phenomenographic analysis was adopted to analyze 30 university students from Taiwan, and a multiple-choice conceptual test was conducted to assess their learning achievements. The main findings indicated that students with conceptions of learning by holographic projection as increasing the presence of a scene or mapping 2D images to 3D structures tended to adopt surface approaches, such as only observing the changes presented in the holographic projection, repetitively operating the system functions without intended purposes, or simply following the instruction guidelines to meet the minimal requirements. However, this study unexpectedly found that students who utilized surface approaches had significantly higher learning gains on the conceptual test than their counterparts did.

Movement and diving behavior of satellite-tagged male sperm whales in the Gulf of Alaska

Male sperm whales (Physeter macrocephalus) are known to interact with and depredate from commercial longline fishing vessels targeting sablefish (Anoplopoma fimbria) in the Gulf of Alaska (GOA). This study aims to better understand their movement patterns and diving behavior in this region, and in relation to depredation behavior. Between 2007 and 2016 a total of 33 satellite tags were deployed on sperm whales interacting with fishing vessels in the eastern GOA. A subset of these tags also collected dive characteristics. We used state space models to interpolate hourly positions from tags and estimate behavioral state from 29 usable tag records, 14 of which had associated dive information. Whales exhibited slower horizontal movement (1.4 km/hr) within GOA waters compared to south of the GOA (5.5 km/hr), indicating tagged whales sped up when they left the region. Behavioral states indicated primarily foraging behavior (82% of locations) in the GOA and primarily transiting behavior (74% of locations) when whales left the GOA. Dive data showed average ( ± Standard Deviation) maximum dive depths of 396 m ( ± 166), and dive durations of 32 min (± 9). Generalized additive models indicated that dives were significantly deeper and longer during the daytime than dawn, dusk, or nighttime, and dives were significantly deeper and shorter during quarter moons, when tidal currents are weakest. Maximum dive depth decreased in areas of higher sablefish CPUE, suggesting a potential link between the sablefish fishery and depredation behavior. As seafloor depth increased, up to 800 m, dives became deeper, indicating that whales were likely targeting both bathypelagic and mesopelagic prey. This highlights the importance of the GOA continental slope as a foraging ground for male sperm whales. This enhanced understanding of sperm whale foraging ecology informs management and conservation efforts in high latitude foraging grounds.

Induced sexual reproduction ex situ reveals bidirectional sex change of the coral Montastraea cavernosa

Induction of gonad maturation and synchronized spawning of corals ex situ has been mostly used to propagate corals for restoration, but it also provides a unique opportunity to study the reproductive biology of species. We present, for the first time, the induction of gonad maturation and synchronous spawning of the coral Montastraea cavernosa in a laboratory. This was achieved by mimicking the annual temperature, sun and moon cycles experienced in the northern portion of Florida’s Coral Reef. Similarly to field observations, peak spawning of M. cavernosa colonies in the laboratory occurred 5–10 nights after the full moons of July, August, and/or September, 75–125 min after sunset. This coral species was known as gonochoric, meaning colonies are either females (release eggs) or males (release sperm). Yet, three consecutive years observing the same colonies ex situ revealed that these corals are capable of changing sexes annually, and they can do so in both directions. Spawning observations and histology showed corals shifting from male to female, others shifting from female to male, and several changing sex one year and reverting to their original sex in the following year. The sex change was not related to size, nor likely socially driven. A greater number of colonies was observed to shift from female to male when food provision was reduced. Further studies are required to determine if food availability drives sex change in this species.

Linkage of El Niño-Southern Oscillation to astronomic forcing

Abstract Deciphering the causes of El Niño-Southern Oscillation (ENSO) represents one of the greatest scientific and societal challenges because ENSO impacts people’s safety, food, water, health, and economy. Traditionally, ENSO has been considered a phenomenon that is mostly influenced by the interactions between oceanic and atmospheric processes, i.e. by the internal variability in Earth’s ocean-atmosphere system. However, dendrochronological records of climate indices, ENSO among them, have statistically significant variance at periodicities related to solar activity (sunspots) and lunar precessions. Other studies indicate a modulation by the lunar nodal cycle of ocean’s mixing and its implications on water and air temperatures, steric sea levels, coastal flooding, rain, river discharge and heat transport. Those findings suggest that astronomic forces may influence ENSO. In fact, this study shows that a fit to well-established periodicities from lunar precessions, solar activity and their interactions explains 91% of the variance of an ENSO index smoothed at 5 years, and 67% of a 3 yr filtered ENSO index. Provided that the future Earth’s ocean-atmospheric system remains roughly within historical bounds under a changing climate in the next 2–3 decades, one can venture a projection into the future of 3- and 5 yr smoothed ENSO variability. Such projection is given here and might help in preparations for adaptation and mitigation measures caused by ENSO-related coastal hazards.

Patterns of spawning and settlement of reef fishes as strategic responses to post-settlement competition

Settlement is a critical transition in the life history of reef fish, and the timing of this event can have a strong effect on fitness. Key factors that influence settlement timing are predictable lunar cyclic variation in tidal currents, moonlight, and nocturnal predation risk as larvae transition from pelagic to benthic environments. However, populations typically display wide variation in the arrival of settlers over the lunar cycle. This variation is often hypothesized to result from unpredictable conditions in the pelagic environment and bet-hedging by spawning adults. Here, we consider the hypothesis that the timing of spawning and settlement is a strategic response to post-settlement competition. We use a game theoretic model to predict spawning and settlement distributions when fish face a tradeoff between minimizing density-independent predation risk while crossing the reef crest vs. avoiding high competitor density on settlement habitat. In general, we expect competition to spread spawning over time such that settlement is distributed around the lunar phase with the lowest predation risk, similar to an ideal free distribution in which competition spreads competitors across space. We examine the effects of overcompensating density dependence, age-dependent competition, and competition among daily settler cohorts. Our model predicts that even in the absence of stochastic variation in the larval environment, competition can result in qualitative divergence between spawning and settlement distributions. Furthermore, we show that if competitive strength increases with settler age, competition results in covariation between settler age and settlement date, with older larvae settling when predation risk is minimal. We predict that competition between daily cohorts delays peak settlement, with priority effects potentially selecting for a multimodal settlement distribution.

Temporal patterns in dolphin foraging activity in the Mediterranean Sea: insights from vocalisations recorded during the ACCOBAMS Survey Initiative

Marine organisms continually adapt their physiology and behaviour to temporal variations in their environment, resulting in diurnal rhythmic behaviour, particularly when foraging. In delphinids, these rhythms can be studied by recording echolocation clicks, which can provide indicators of foraging activity. The foraging rhythms of delphinids and their relationship to temporal parameters are poorly documented and most studies so far have used moored passive acoustic systems. The present study provides, for the first time, information on the activity rhythms of delphinids investigated in relation with temporal variables at a basin scale from a moving platform, in the western and central Mediterranean Sea. We used passive acoustic recordings collected by hydrophones towed along transect lines during the ACCOBAMS Survey Initiative in the summer 2018. We extracted variables that may influence daily and monthly rhythms, including time of day, lunar cycle, lunar illumination and sea state and fitted generalised additive models. The nycthemeral and lunar cycles were the two main factors influencing dolphin activity rhythms. Echolocation activity was predominant at night, with a maximum of 0.026 acoustic events per minute at 21:00/22:00 compared to as few as 0.0007 events per minute at 11:00. These events were also more frequent during the third quarter of the moon; 0.033 acoustic events on day 22 of the lunar cycle as opposed to 0.0008 on day 8 of the lunar cycle, corresponding to the first quarter of the moon. Variations in the echolocation activity of delphinids in the Mediterranean Sea could reflect variation in their foraging effort and be related to prey density, composition, accessibility and catchability within dolphin foraging depth range. These results should also improve interpretation of passive acoustic monitoring data.