Behavior Of Dolphins Research Articles

Occurrence, residency patterns and habitat use of the bottlenose dolphin, Tursiops truncatus truncatus, on two Marine Protected Areas in Southeastern Brazil.

The common bottlenose dolphin, Tursiops truncatus, is widely distributed. However, information about its ecology and behavior in Brazilian waters is scarce especially about the 'offshore' ecotype, an Evolutionarily Significant Unit in the Southwest Atlantic. We report for the first time the occurrence, behavior and habitat use of bottlenose dolphins Tursiops truncatus truncatus, in two Marine Protected Areas (MPA) in Cabo Frio coast, Brazil. There were fifteen sightings of different groups throughout the year. An overall of 429 individuals were photo-identified. 90.7% dolphins did not present a degree of residence, 1.4% dolphins were considered with high residency to the area, 5.8% medium and 2.1% low. Our habitat use map indicated dolphins were more common off ~10km from Cabo Frio municipality and between depths around 20-70m. Bottlenose dolphins on Cabo Frio coast were more frequently observed performing travelling, followed by foraging and socio-sexual behavior. Group sizes varied from three to 120 individuals. Larger groups were observed when travelling and foraging. Despite the existence of two local Marine Protected Areas, the fast human development in Cabo Frio may threaten this important area for bottlenose dolphins in terms of food resources and shelter from predators.

Is Enrichment Always Enriching and How Would You Know? Unintended Consequences and the Importance of Formal Assessment of Enrichment Programs in Bottlenose Dolphins (Tursiops truncatus)

Bottlenose dolphins (Tursiops truncatus) are viewed as a highly intelligent species, capable of complex behaviors, requiring marine parks to maintain dynamic environmental enrichment procedures in order to ensure their optimal psychological and physiological well-being in human care. In this study, two experiments were conducted to determine the effects of different forms of enrichment on the behavior of bottlenose dolphins. In Experiment 1, the most successful enrichment included highly novel items, which resulted in avoidance, but also what is frequently considered positive behavioral changes including a reduction in circle swimming and an increase in social behavior. In Experiment 2, the use of choice resulted in negative unintended social consequences. These two experiments together demonstrate that the results of deploying enrichment may not be as clear-cut as previously presumed. In order to maintain positive benefits of enrichment, the results of this study suggest that unique forms of enrichment should be implemented on a variable schedule that is offered several times a year and consistently evaluated for effectiveness.

Multi-robot Target Encirclement Control with Collision Avoidance via Deep Reinforcement Learning

The target encirclement control of multi-robot systems via deep reinforcement learning has been investigated in this paper. Inspired by the encirclement behavior of dolphins to entrap the fishes, the encirclement control is mainly to enforce the robots to achieve a capturing formation pattern around a target, and can be widely applied in many areas such as coverage, patrolling, escorting, etc. Different from traditional methods, we propose a deep reinforcement learning framework for multi-robot target encirclement formation control, combining the advantages of the deep neural network and deterministic policy gradient algorithm, which is free from the complicated work of building the control model and designing the control law. Our method provides a distributed control architecture for each robot in continuous action space, relying only on local teammate information. Besides, the behavioral output at each time step is determined by its own independent network. In addition, both the robots and the moving target can be trained simultaneously. In that way, both cooperation and competition can be contained, and the results validate the effectiveness of the proposed algorithm.

A biologging perspective to the drivers that shape gregariousness in dusky dolphins

Knowledge of proximate (causation and development) and ultimate (evolution and survival function) causes of gregariousness is necessary to advance our knowledge of animal societies. Delphinids are among the most social taxa; however, fine-scale understanding of their intra-specific relationships is hindered by the need for underwater observations on individuals. We developed a non-invasive animal-borne camera system with the goal of examining influences on gregariousness in dusky dolphins (Lagenorhynchus obscurus). We analyzed video and diving records from 11 individual dusky dolphins off Kaikoura, New Zealand. We examined the influence of biologger attachment on dolphin behavior and tested hypotheses regarding the effects of physiology, predation, and inter-individual variation on conspecific interactions. Dolphins did not exhibit increased rates of descent or ascent in the minutes immediately following biologger attachment, indicating a lack of behavioral response. Respiration rate was positively related to dive depth and duration, suggesting that diving is energetically expensive for this species. Gregariousness was negatively related to dive depth providing evidence that the physiological constraints of diving are likely to limit social behavior. Calves were not observed more frequently in infant (vs. echelon) position with increasing depth, highlighting the likelihood of other anti-predation strategies (e.g., dilution effect) in mother-calf pairs. We found that gregariousness differed between individuals within similar social groups, suggesting the importance of collecting data at the individual level. The evidence presented herein suggests that the further development of animal-borne camera systems will yield further insight into the mechanisms underlying delphinid social behavior. Dolphins are highly social and thus excellent model species for examining the cause and function of gregariousness. However, their cryptic nature poses a challenge to collecting the fine-scale data at the individual level required to conduct rigorous hypothesis tests. We overcame this obstacle by deploying a non-invasive cutting-edge biologger on free-ranging dusky dolphins to collect information on diving behavior, physiology, gregariousness, and mother-calf strategies. Results indicate that diving is energetically expensive, even to relatively shallow depths, and these costs likely hinder gregariousness at depth. Individual differences in gregariousness were apparent and as expected in this fission-fusion society. Unexpectedly, mother-calf pairs appeared to utilize strategies other than spatial positioning to minimize predation risk. This study advanced knowledge of dolphin social life and helps to improve the degree of data resolution in cetaceans to a level on par with terrestrial studies.

Interspecies pectoral fin contact between bottlenose dolphins and Atlantic spotted dolphins off Bimini, The Bahamas

Affiliative interspecies interactions are important to community structure within an ecosystem yet understudied relative to antagonistic relationships. Mixed-species associations provide important benefits via foraging, predator avoidance and social interactions. Tactile behaviours help with social bond formation and group establishment among conspecifics during social interactions, but little is known about the role of contact between heterospecific animals in mixed-species groups. Our objective was to quantify characteristics of pectoral fin contact between individuals of two sympatric species of wild dolphins, spotted dolphins, Stenella frontalis, and bottlenose dolphins, Tursiops truncatus, off Bimini, The Bahamas, in order to assess possible benefits of heterospecific interactions. Using underwater video recordings from mixed-species dolphin encounters from 2011 to 2017, we observed 74 pectoral fin contacts, of which 27 were between heterospecific animals. Encounters were either affiliative (61.5%) or sociosexual (38.5%). Conspecific and heterospecific dolphins had similar rates of initiating and receiving contacts. This suggests that during mixed-species groups, the cost-benefit trade-off in choosing a social partner is similar for conspecific and heterospecific individuals. Heterospecific contacts initiated by S. frontalis were primarily affiliative whereas heterospecific contacts initiated by T. truncatus were sociosexual. Both sociosexual behaviour and pectoral fin contact in dolphins have been suggested as mechanisms of bond formation. We conclude that mixed-species interactions with pectoral fin contact may be a mechanism for social bond formation between heterospecifics and that these bonds may help to re-establish groups, as needed, for predator avoidance.

Electrofishing as a potential threat to freshwater cetaceans

Electrofishing is an accepted practice for legal fish sampling and surveying, but its use for subsistence food and market fishing has long been illegal in most countries. Illegal use affects freshwater fish populations in many parts of the world, and has been cited as a cause of mortality for endangered freshwater cetaceans in China (Yangtze dolphins and finless porpoises) and Southeast Asia (Ayeyarwady, Mekong, and Mahakam dolphins in Myanmar, Cambodia, and Indonesia, respectively), although the extent of this threat to cetaceans is unclear. Given their threatened status, these populations can ill afford such mortality in addition to the other threats they face (e.g. entanglement in gillnets, habitat deterioration and loss, declines in prey). Here, we review the evidence that electrofishing is a serious threat to freshwater cetaceans. It may alter the behavior of dolphins and porpoises, and contact with electrical currents may even directly kill or injure these animals, although questions remain unanswered concerning the exact nature and scale of the impacts. While other threats may appear more certain and urgent, electrofishing could be playing a significant role in driving the declines of some critically endangered freshwater cetaceans in Asia. Due to ethical and logistical challenges to improving our understanding of the impacts of electrical currents on cetaceans, clear descriptions of lesions in dead animals found stranded are needed to characterize the damage caused by electrofishing, to be more certain about cause and effect beyond spatiotemporal associations, and to determine the extent of this threat. Mortality from electrofishing seems to be uncommon, but in face of the uncertainties and the numerous other threats to these small populations, high priority should be given to enforcing electrofishing bans in the freshwater habitat of dolphins and finless porpoises.

Natural and anthropogenic drivers of foraging behaviour in bottlenose dolphins: Influence of shellfish aquaculture

Abstract In the coastal environment, marine mammals are exposed to one of the fastest growing food production sectors; namely, the shellfish farming industry. Identification of critical habitats, such as foraging grounds in highly human‐impacted areas, is essential to species conservation. Therefore, understanding the variables that influence a species' foraging behaviour is important for their conservation, especially for long‐lived mammals such as cetaceans. The aims of this study were (a) to identify and quantify the environmental and anthropogenic drivers of wild bottlenose dolphin (Tursiops truncatus) foraging behaviour, and (b) to investigate whether the shellfish farming industry influences the behaviour of this species. Behavioural observations were conducted along the north‐western coast of Spain, an area affected by intensive human activities, particularly the shellfish aquaculture industry. A multi‐modelling approach highlighted the importance of shellfish farm areas as a foraging ground for bottlenose dolphins. Dolphins were predicted to be more likely found foraging inside shellfish farm areas than outside (57% vs. 43%). Variability in bottlenose dolphin behaviour is likely a result of the interactions of environmental and anthropogenic drivers with prey availability and the physiological needs of the dolphins. Although shellfish farm areas provide high prey density for dolphins, they can also pose threats in a number of ways (i.e. collisions with vessels, entanglement with ropes, habitat loss, noise and water pollution). From a conservation perspective, aquaculture management should consider the presence of dolphins foraging and minimize the associated risks that this industry may pose to these coastal cetaceans.

Modelling the spatial dynamics of Maui dolphins using individual-based models

The current anthropogenic impacts on nature necessitate more research for nature conservation and restoration purposes. To answer ecological and conservation questions concerning endangered species, individual-based modelling is an obvious choice. Individual-based models can provide reliable results that may be used to predict the effects of different future conservation strategies, once calibrated correctly. Here, we calibrate an individual-based model of Maui dolphin movement, which generates Maui dolphin probability distribution maps. We used sighting data for calibration of the chosen parameter combinations; for each simulation run, collected simulated data was compared to the empirical survey data, resulting in cost (Badness-of-Fit) estimates. Using costs of four different aspects of dolphin behaviour, we estimated the most likely parameter combinations. With optimized parameter values, Maui dolphin probability distribution maps were created, resulting in distributions that fall well outside of the current protection zones where either gillnets or trawling or both are prohibited. With these results, protected areas can be properly adjusted to the estimated distribution of this critically endangered species and so aid in their conservation.

Fine scale spatial variability in the influence of environmental cycles on the occurrence of dolphins at coastal sites

Environmental cycles often influence the presence of animals, creating patterns at different temporal scales, which may mean that their effects overlap and/or interact. Interactions between diel and seasonal cycles have been reported to influence fish behaviour but little is known about such interactions in marine top predators. Here, we studied the combined effect of seasonal, tidal and diel cycles on the occurrence of bottlenose dolphins (Tursiops truncatus) within a Marine Protected Area in Scotland. Our analyses were based on echolocation detections from passive acoustic devices (CPODs) deployed at three coastal sites between 2010 and 2016. We described patterns of dolphins’ occurrence using circular statistics and then used generalised additive mixed models to explore the relative importance of each cycle and any interactions between them. We found site-specific cyclical patterns of presence that remained constant across years. There was a highly significant interaction between seasonal and diel cycles at two sites around deep channels, where occurrence was diurnal in summer but became nocturnal in autumn. The study demonstrates the highly plastic behaviour of bottlenose dolphins and shows a previously unreported behaviour that has management implications for this and other marine protected areas.

Common bottlenose dolphin (Tursiops truncatus) behavior in an active narrow seaport.

The Galveston Ship Channel (GSC) is a narrow, congested waterway that supports large-scale shipping, commercial fishing, dolphin tourism, and recreation. Human activity and common bottlenose dolphins (Tursiops truncatus) converge in the GSC with potentially negative consequences on the dolphins. Elevated land-based tracking and behavioral observation of dolphins and vessels were conducted along the GSC in June-August 2013 using a digital theodolite. Positional information was used to calculate dolphin movement patterns and proximity to vessels. Log-likelihood ratio and Chi-square contingency tests were used to assess behavioral states, and generalized additive models were used to analyze movement patterns (i.e., swimming speed, reorientation rate, and linearity) relative to endogenous and exogenous factors and vessel presence. Dolphins regularly use the GSC to forage (57% of observed behavioral states) and socialize (27%), and it is not a travel corridor for accessing other favorable sites (traveling = 5%). Dolphin behavior varied significantly based on time of day, group size, calf presence, and general boat presence. When boats were present, the proportion of time dolphins spent socializing and foraging was significantly less than expected by chance. Swimming speeds increased significantly in the presence of small recreational boats, dolphin-watching tour boats, shrimp trawlers, and when tour boats and shrimp trawlers were both present. Reorientation rate increased significantly in the presence of tour boats and trawlers. Dolphin behavioral responses to vessel presence may result in decreased energy consumption due to disrupted foraging activity. Without proper management, the observed behavioral changes may be detrimental to individuals within this population in the short term, with potential long-term consequences to health and survivorship.

Pre and post session behaviour of captive bottlenose dolphins Tursiops truncatus involved in "swim-with-dolphin" events.

Pre and post session behaviour of captive bottlenose dolphins Tursiops truncatus involved in "swim-with-dolphin" events.

“Hot deals at sea”: responses of a top predator (Bottlenose dolphin,Tursiops truncatus) to human-induced changes in the coastal ecosystem

The main response of top predators to human-induced environmental changes is often behavioral. Although human activities regularly impose a disturbance on top predators, they can also be a source of reliable and concentrated food resources for species with a high degree of behavioral plasticity. This study represents the first assessment of the influence of these resources on migratory patterns and social interaction of a marine top predator, the common bottlenose dolphin, Tursiops truncatus. Pollock’s closed robust design models and association analyses were applied to data collected over 9 consecutive years of research in a coastal area subject to significant use and pressure by humans. Photo-identification data were collected year-round during 955 boat-based surveys, resulting in 1638 common bottlenose dolphin group encounters. Results of this study revealed a significant upward trend in density of bottlenose dolphins, preferences for a coastal area with higher human pressure, and a reduction of the social interactions associated to a temporal switch to the food sources provided by human activities. The observed link between human activities and changes in common bottlenose dolphin behavior aim to contribute to a better understanding of the ecology of a marine top predator and provide some of the needed baseline data, from which effective management and conservation strategies can be designed.

Risk versus reward: interactions, depredation rates, and bycatch mitigation of dolphins in demersal fish trawls

An improved understanding of interaction dynamics between dolphins and trawlers is essential for improving bycatch mitigation strategies. In-situ observations using video at increasing distances from the net opening during 50 commercial fish trawls, recorded 5908 common bottlenose dolphin (Tursiops truncatus (Montagu, 1821)) interactions and provided details on their duration, depredation rates, and behaviours. Dolphin interactions with trawls were very common (98% of day-trawls, 118 ± 16 interactions per trawl), with durations and prey consumption positively correlated with the distances ventured into the net. Acoustic deterrents (pingers) had no effect on interaction numbers or durations. Based on in-situ observations, the factors that contribute toward dolphin bycatch in demersal fish trawls were likely associated with (i) risky dolphin behaviour (i.e., entering net during hauling, residing deep within trawl for extended periods or social aggression) and (or) (ii) instability of fishing gear resulting in entrapment. Given the high level of dolphin attendance during most day-trawls, mitigation strategies that focus on improving and monitoring the stability of trawl gear would be more effective than current acoustic deterrent devices aimed at modifying dolphin behaviour.

On the behaviour of an under-studied population of bottlenose dolphins in the Southern Adriatic Sea

AbstractPerhaps the world's best-known cetacean, the bottlenose dolphin shows considerable variation in behaviour between and within populations in relation to differences in natural and anthropogenic conditions. Drivers of behavioural variation need to be identified to understand the dynamics of wild dolphin populations. Little research has been published on the bottlenose dolphin population found in the Southern Adriatic Sea. Using a set of spatial, temporal and social predictors, we aimed to investigate what variables are related to the behaviour of an under-studied population of bottlenose dolphins along the coastline of Montenegro. We present the results of a year-long study monitoring the behaviour of bottlenose dolphins along coastal Montenegro. We considered the effect of topography, seasonality and group size. A large proportion of travelling (55%) small groups (mean 4, range 1–9) in shallow waters (<50 m) was observed. We showed that seasonality alone explained behaviour best, with surface-feeding and socializing-resting increasing in autumn and winter. Group size was found to be a result of behavioural choice. We suggest seasonal changes in environmental conditions and anthropogenic pressure may explain the recorded behavioural pattern. This research points to the necessity of increased collaboration in the region to help understand complex patterns in behaviour and habitat use of local dolphin populations if effective conservation measures are to be developed.

The ocean has music for those who ping AND listen

Sound is a key sense for animals in the ocean, including humans. The integration of passive and active acoustics in behavioral and ecosystem studies has revealed much about how ocean systems work. Here, I will discuss how the integration of echosounders with various passive acoustic approaches has contributed to our understanding to the biology and ecology of marine mammals. For example, explaining the habitat selection of beaked whales, the foraging ecology, behavior, and communication of spinner dolphins, and the ability of dolphin sonar to discriminate fish species. Careful integration of passive and active acoustics has also contributed to sonar signal design and processing approaches. A recent study of Risso’s dolphins using passive acoustic recording tags on the dolphins themselves and echosounders deployed from a ship and an underwater vehicle provided new insights into how these animals make foraging decisions, what information is available to them and when, and how changes in their prey over space and time affect their foraging behavior. The combination of passive and active acoustics is providing insight into the ecology and dynamics of predator and prey at the scale of the individual and the population.Sound is a key sense for animals in the ocean, including humans. The integration of passive and active acoustics in behavioral and ecosystem studies has revealed much about how ocean systems work. Here, I will discuss how the integration of echosounders with various passive acoustic approaches has contributed to our understanding to the biology and ecology of marine mammals. For example, explaining the habitat selection of beaked whales, the foraging ecology, behavior, and communication of spinner dolphins, and the ability of dolphin sonar to discriminate fish species. Careful integration of passive and active acoustics has also contributed to sonar signal design and processing approaches. A recent study of Risso’s dolphins using passive acoustic recording tags on the dolphins themselves and echosounders deployed from a ship and an underwater vehicle provided new insights into how these animals make foraging decisions, what information is available to them and when, and how changes in their prey over spac...

Potential impacts of shipping noise on Indo-Pacific humpback dolphins and implications for regulation and mitigation: a review.

Shipping noise is a widespread and relatively loud sound source among human-induced underwater sounds. The impacts of shipping noise are of special concern for Indo-Pacific humpback dolphins (Sousa chinensis), as they inhabit shallow and nearshore habitats and are highly dependent on sound for survival. This study synthesizes our current understanding of the potential impacts of shipping noise on Indo-Pacific humpback dolphins combined with knowledge on sound production and hearing of these animals and the impacts of noise on other whales and dolphins. For further protection and management of Indo-Pacific humpback dolphins and their habitats, shipping noise should be regulated and mitigated to modify sound from ships, to reduce overall noise levels, and to set more marine protected areas (MPAs) covering most Indo-Pacific humpback dolphin habitats with seasonal and geographical restrictions to avoid ensonification of shipping noise. The emphasis for future research should be on obtaining more baseline information about the population distribution, sound production, hearing capabilities at the population level, behavior, and stress hormones of the humpback dolphins under different noise conditions or under different noise-producing activities, and/or in high-noise areas compared with relatively quiet areas, and the noise characteristics of ships of different types, sizes and speeds.

Conflict between Dolphins and a Data-Scarce Fishery of the European Union

Fisheries depredation by marine mammals is an economic concern worldwide. We combined questionnaires, acoustic monitoring, and participatory experiments to investigate the occurrence of bottlenose dolphins in the fisheries of Northern Cyprus, and the extent of their conflict with set-nets, an economically important metier of Mediterranean fisheries. Dolphins were present in fishing grounds throughout the year and were detected at 28% of sets. Net damage was on average six times greater where dolphins were present, was correlated with dolphin presence, and the associated costs were considerable. An acoustic deterrent pinger was tested, but had no significant effect although more powerful pingers could have greater impact. However, our findings indicate that effective management of fish stocks is urgently required to address the overexploitation that is likely driving depredation behaviour in dolphins, that in turn leads to net damage and the associated costs to the fisheries.

Another dolphin in peril? Photo‐identification, occurrence, and distribution of the endangered Indian Ocean humpback dolphin (Sousa plumbea) in Algoa Bay

Abstract In South Africa, the humpback dolphin (Sousa plumbea) has been recognized as the most endangered marine mammal, with a low abundance, a discontinuous distribution, and numerous threats. This research was initiated in 2008 to estimate the number of individual humpback dolphins in Algoa Bay, as well as studying their residency patterns and distribution. The last boat‐based study on humpback dolphins, conducted 24 years ago, formed an important reference against which to compare current findings. This study reveals that since the 1990s the number of identified animals decreased from 70 to 50 individuals, and the mean group size of humpback dolphins has also decreased, from seven to three animals. Humpback dolphin behaviour was predominantly that of foraging and travelling, although the overall frequency of foraging still seems to have decreased since early 1990s. Although the species was seen almost all year round, the number of sightings per survey was lowest in January, March, and April. The number of sightings per kilometre surveyed substantially decreased from 0.018 sightings per kilometre in 2008 to 0.004 in 2011, and the number of animals per kilometre also decreased from 0.042 to 0.009. The re‐sighting rates were low, ranging from one to eight times, with 52% of identified dolphins seen only once throughout the study period. Only 6% of the individuals were seen more than three times. Reduced humpback dolphin numbers and sighting rates could be indicative of the rise in anthropogenic activities, such as shipping and recreational boating, as well as a rise in pollution from vessels and urban development. Conservation strategies, such as a Biodiversity Management Plan for the species, are urgently needed in Algoa Bay, especially in the south‐west part of the bay, between Cape Recife and the Port Elizabeth Harbour, where the species occurs most frequently.

Calf age and sex affect maternal diving behaviour in Shark Bay bottlenose dolphins

Maternal care varies across taxa from brief, minimal care to long-term, intensive care. Mammalian mothers provide extensive and energetically expensive care by definition through pregnancy and lactation, which can extend for years, resulting in behavioural trade-offs between resource acquisition and direct care. In marine environments, mammalian mothers face unique challenges, such as the inability to cache or den their offspring while diving for prey. Dolphin newborns are precocious, accomplishing shallow dives in the first few weeks of life, however, fully mature diving and breath-holding capabilities take years to develop. Consequently, mothers are faced with a trade-off between diving and foraging or remaining close to and protecting their calves at the surface. Here we examined this trade-off, specifically by investigating whether mothers change their dive durations, especially during foraging, as a function of calf age. We used a longitudinal (1988–2014) data set on wild bottlenose dolphins, Tursiops aduncus, in Shark Bay, Western Australia, which included 27 388 dive bouts from mothers (N = 26) and calves (N = 41). Our results show that maternal diving behaviour changes in response to calf age and sex. While both male and female calves increased their dive durations with age as expected, mothers were more likely to adjust their diving behaviour to accommodate female but not male calves, especially when daughters were in close proximity. This is consistent with findings that vertical social learning is more critical for daughters than for sons, and may reflect the sex-specific foraging and social tactics of the males and females more generally.

Hybrid Improved Dolphin Echolocation and Ant Colony Optimization for Optimal Discrete Sizing of Truss Structures

This paper presents a robust hybrid improved dolphin echolocation and ant colony optimization algorithm (IDEACO) for optimizing the truss structures with discrete sizing variables. The dolphin echolocation (DE) is inspired by the navigation and hunting behavior of dolphins. An improved version of dolphin echolocation (IDE), as the main engine, is proposed and uses the positive attributes of ant colony optimization (ACO) to increase the efficiency of the IDE. Here, ACO is employed to improve the precision of the global optimization solution. In the proposed hybrid optimization method, the balance between exploration and exploitation process was the main factor to control the performance of the algorithm. IDEACO algorithm performance is tested on several problems of benchmarks discrete truss structure optimization. The results indicate the excellent performance of the proposed algorithm in optimum design and rate of convergence in comparison with other metaheuristic optimization methods, so IDEACO offers a good degree of competitiveness against other existing metaheuristic methods.