The bottlenose dolphin Tursiops truncatus foraging around a fish farm：Effects of prey abundance on dolphins＇ behavior

The extent to which prey abundance influences both bottlenose dolphin foraging behavior and group size in the presence of human activities has not previously been studied.The primary aim of this study was to identify and quantify how wild bottlenose dolphins respond,individually and as groups,to the relative abundance of prey around a fish farm.Detailed views of dolphins＇ behavior were obtained by focal following individual animals whilst simultaneously collecting surface and underwater behavioral data.A total of 2150 dive intervals were analyzed,corresponding to 342 focal samples,lasting over 34 hours.Bottlenose dolphins remained submerged for a mean duration of 46.4 seconds and a maximum of 249 seconds.This study provides the first quantified data on bottlenose dolphin diving behavior in a marine fin-fish farm area.This study＇s results indicate that within a fish farm area used intensively by bottlenose dolphins for feeding,dolphins did not modify dive duration.Additionally,underwater observations confirmed that dolphins find it easier to exploit a concentrated food source and it appears that hunting tactic and not group size plays an important role during feeding activities.Thus,bottlenose dolphins appear capable of modifying their hunting tactics according to the abundance of prey.When top predators display behavioral responses to activities not directed at them,the task of studying all possible effects of human activities can become even more challenging.     

Observations of flipper rubbing in mother–calf pairs of captive bottlenose dolphins (Tursiops truncatus) suggest a body-surface care function

Journal of Ethology - Bottlenose dolphins perform flipper rubbing in which they rub their partners with their pectoral fins. Considered similar to social grooming in primates, which have social and...     

What’s occurring? Ultrasonic signature whistle use in Welsh bottlenose dolphins (Tursiops truncatus)

Animal communication signals are diverse. The types of sounds that animals produce, and the way that information is encoded in those sounds, not only varies between species but can also vary geographically within a species. Therefore, an understanding of the vocal repertoire at the population level is important for providing insight into regional differences in vocal communication signals. One species whose vocal repertoire has received considerable attention is the bottlenose dolphin. This species is well known for its use of individually distinctive identity signals, known as signature whistles. Bottlenose dolphins use their signature whistles to broadcast their identity and to maintain contact with social companions. Signature whistles are not innate, but are learnt signals that develop within the first few months of an animal’s life. It is therefore unsurprising that studies which have characterized signature whistles in wild populations of bottlenose dolphins have provided evidence of geographic variation in signature whistle structure. Here, we describe the occurrence of signature whistles in a previously unexplored wild population of bottlenose dolphins in Cardigan Bay, Wales. We present the first occurrence of a signature whistle with an ultrasonic fundamental frequency component (>30 kHz), a frequency band that was not thought to be utilized by this species for whistle communication. We also describe the occurrence of an ultrasonic non-signature whistle. Our findings highlight the importance of conducting regional studies in order to fully quantify a species’ vocal repertoire, and call into question the efficacy of those studies that use restricted sampling rates.     

Where to catch a fish? The influence of foraging tactics on the ecology of bottlenose dolphins (Tursiops truncatus) in Florida Bay,Florida

Observations of bottlenose dolphins ( Tursiops truncatus ) in Florida Bay, Florida, between 2002 and 2005 revealed the use of three distinct foraging tactics. The goal of this study was to identify ecological correlates with tactic use and describe the impact of foraging specializations on the overall habitat use and distribution patterns of this dolphin population. Foraging tactics showed strong association with contrasting environmental characteristics, primarily depth. Locations of two of these tactic groups were spatially repulsed. Analyses of sighting histories of individual dolphins observed at foraging events determined that dolphins which employed one tactic never employed the other, and vice versa . Although bottlenose dolphins have plastic foraging behaviors, dolphins in Florida Bay appear to specialize in one tactic and subsequently limit their overall distribution patterns to coincide with habitats that facilitate success using that foraging tactic. This study demonstrates how foraging behavior can be an ecological determinant of overall dolphin habitat use patterns and works to create spatial structure within a population due to consistent mapping of tactics onto environmental variation. These foraging specializations potentially impact the social and demographic patterns of this dolphin population. The possible evolutionary mechanisms behind this intraspecific variation, including resource limitation and social learning, are considered.     

Epidemiology of tattoo skin disease in captive common bottlenose dolphins (Tursiops truncatus): Are males more vulnerable than females?

Clinical and epidemiological features of tattoo skin disease (TSD) are reported for 257 common bottlenose dolphins held in 31 facilities in the Northern Hemisphere. Photographs and biological data of 146 females and 111 males were analyzed. Dolphins were classified into three age classes: 0–3 years, 4–8 years, and older than 9 years. From 2012 to 2014, 20.6% of the 257 dolphins showed clinical TSD. The youngest dolphins with tattoo lesions were 14 and 15 months old. TSD persisted from 4 to 65 months in 30 dolphins. Prevalence varied between facilities from 5.6% to 60%, possibly reflecting variation in environmental factors. Unlike in free-ranging Delphinidae, TSD prevalence was significantly higher in males (31.5%) than in females (12.3%). Infection was age-dependent only in females. Prevalence of very large tattoos was also higher in males (28.6%) than in females (11.1%). These data suggest that male T. truncatus are more vulnerable to TSD than females, possibly because of differences in immune response and susceptibility to captivity-related stress.     

Why do dolphins jump? Interpreting the behavioural repertoire of bottlenose dolphins (Tursiops sp.) in Doubtful Sound,New Zealand

Only a limited number of studies have tried to determine the purpose of surface behavioural events performed by dolphins. To date only one study has attempted to aggregate the behavioural events observed in a population in contextual groups using co-occurrence as the grouping factor. In the present study, I tried to characterise the behavioural repertoire of a bottlenose dolphin population (Tursiops sp.) present in Doubtful Sound, New Zealand. I first looked at the relationship between events performed by individuals depending on the behavioural state of their schools. I then assessed the likelihood for events to co-occur. Four main behavioural categories (orientation, travel, social displays and fights) emerged from this analysis. Aerial events (jumps) did not fall into one category, showing that different aerial behaviours play different roles. Moreover, it appears that dolphins used side-flopping and upside-down lobtailing to communicate motivation. Side-flops occurred when the focal schools finished a behavioural bout and started to travel, while upside-down lobtails occurred when the focal schools instigated a behavioural bout after travelling. This non-vocal communication can take place over a few meters to hundreds of meters. Having signals that are effective over very short ranges avoids unwanted signalling to prey, predators or conspecifics.     

Fine-scale sociality reveals female–male affiliations and absence of male alliances in bottlenose dolphins (Tursiops truncatus) in the Shannon Estuary,Ireland

Knowledge of social behavior at an individual level is central to our understanding of complex mammalian societies. In this study, we analyzed the fine-scale sociality of wild bottlenose dolphins in the Shannon Estuary, Ireland, by examining associations between members of the whole population and between specific female and male dolphins. We carried out 51 boat-based individual focal follows on 18 identifiable bottlenose dolphins over 90.8 hr (39 days) between 2014 and 2016. Additionally, we conducted 353 boat-based surveys (with 607 sightings) between 2012 and 2015, and identified 121 distinct adult/juvenile dolphins. The mean group size of focal dolphin groups was 7.2 ± 4.1 (range = 1–20) and the mean fission-fusion rate was 3.06 ± 1.35 changes/hr. The most frequent composition of within-group affiliate pairs was female–male. Focal males spent more time with female nearest-neighbors than male nearest-neighbors (p = .013). Differences between female and male activity budgets were not strongly supported (p = .13). There was no evidence for male alliance formation in the Shannon Estuary population, and all of the known-sex top-ranked associates (7) of known males (n = 10) were females. This research reveals a distinct bottlenose dolphin society with female–male affiliations and an absence of male alliances.     

Why become speckled? Ontogeny and function of speckling in Shark Bay bottlenose dolphins (Tursiops sp.)1

To date, color patterns have been used to assess cetacean age and taxonomic status, but few studies have determined precise correlates of coloration with known age or investigated its function. Here, we examine the ontogeny of speckling in 88 bottlenose dolphins (Tursiops sp.) in Shark Bay, Australia, of known age, tracked from birth to age 34. Ventral speckles first appear in the genital area at a mean age of 10.2 ± 0.35 yr (range = 7.6–12.7 yr). Throughout their life span, speckles increase in number and density, particularly along the ventral and lateral sides. The timing of speckle onset does not significantly differ by sex but is related to sexual maturity in females. The age of speckle onset in the genital area correlates with the age of first known parturition. In terms of speckle function, we discuss two hypotheses commonly proffered to explain color variation, concealment, and communication. Concealment from predators or prey is unlikely to explain speckle development in Shark Bay Tursiops because the onset occurs long after peak predation risk and initial hunting success (at 3 mo of age). We suggest that speckle patterns offer reliable cues on reproductive status and/or condition and could, thus, serve a communicative or some other function.     

Feeding aggregation and aggressive interaction between bottlenose (Tursiops truncatus) and Commerson’s dolphins (Cephalorhynchus commersonii) in Patagonia,Argentina

We report the first recorded interactions between bottlenose dolphin (Tursiops truncatus) and Commerson’s dolphins (Cephalorhynchus commersonii). The diurnal behavioral patterns of bottlenose dolphins in Bahía Engaño, Argentina, were similar to those described for other coastal populations around the world. The majority of the feeding bouts were recorded near the mouth the Chubut River. When not feeding near the river, bottlenose dolphins generally swam along the coast, and interactions with Commerson’s dolphins were recorded very close to the shore on two occasions during a 3-year period. In the first event, both species were feeding on a fish school. The second interaction was aggressive in nature, involving one juvenile and three adult bottlenose dolphins with several Commerson’s dolphins. Two of the adult bottlenose dolphins attacked the Commerson’s dolphins. We propose that the observed behavior represented defense of the juvenile bottlenose dolphin.

     

Are two South-Western Atlantic wrasses involved in a case of social mimicry?

Journal of Ethology - We investigated whether two South-Western Atlantic wrasses [Halichoeres penrosei (models) and Thalassoma noronhanum (mimics)] were involved in social mimicry. In mixed shoals,...     

Were Multiple Stressors a ‘Perfect Storm’ for Northern Gulf of Mexico Bottlenose Dolphins (Tursiops truncatus) in 2011?

An unusual number of near term and neonatal bottlenose dolphin (Tursiops truncatus) mortalities occurred in the northern Gulf of Mexico (nGOM) in 2011, during the first calving season after two well documented environmental perturbations; sustained cold weather in 2010 and the Deepwater Horizon oil spill (DWHOS). Preceding the stranding event, large volumes of cold freshwater entered the nGOM due to unusually large snowmelt on the adjacent watershed, providing a third potential stressor. We consider the possibility that this extreme cold and freshwater event contributed to the pattern of perinatal dolphin strandings along the nGOM coast. During the 4-month period starting January 2011, 186 bottlenose dolphins, including 46% perinatal calves (nearly double the percentage for the same time period from 2003-2010) washed ashore from Louisiana to western Florida. Comparison of the frequency distribution of strandings to flow rates and water temperature at a monitoring buoy outside Mobile Bay, Alabama (the 4(th) largest freshwater drainage in the U.S.) and along the nGOM coast showed that dolphin strandings peaked in Julian weeks 5, 8, and 12 (February and March), following water temperature minima by 2-3 weeks. If dolphin condition was already poor due to depleted food resources, bacterial infection, or other factors, it is plausible that the spring freshet contributed to the timing and location of the unique stranding event in early 2011. These data provide strong observational evidence to assess links between the timing of the DWHOS, other local environmental stressors, and mortality of a top local predator. Targeted analyses of tissues from stranded dolphins will be essential to define a cause of death, and our findings highlight the importance of considering environmental data along with biological samples to interpret stranding patterns during and after an unusual mortality event.     

Forest decline after a 15-year “perfect storm” of invasion by hemlock woolly adelgid,drought, and hurricanes

Invasions by introduced pests can interact with other disturbances to alter forests and their functions, particularly when a dominant tree species declines. To identify changes after invasion by the insect hemlock woolly adelgid (Adelges tsugae; HWA), coinciding with severe droughts and hurricanes, this study compared tree species composition of eastern hemlock (Tsuga canadensis) forests on 11 plots before (2001) and 15 years after (2016) invasion in the southern Appalachian Mountains, USA. Losses of hemlock trees after HWA invasion were among the highest reported, with a 90% decline in density, 86% decline in basal area, and 100% mortality for individuals ≥ 60 cm in diameter. In contrast to predictions of theoretical models, deciduous tree density declined after HWA invasion, while basal area changed little, at least during the initial 15 years after invasion. Overall, forest density declined by 58%, basal area by 25%, and tree species richness by 8%. Factors additional to HWA likely exacerbating forest decline included: droughts before (1999–2001) and after HWA invasion (2006–2008); tree uprooting from hurricane-stimulated winds in 2004; pest-related declines of deciduous tree species otherwise likely benefitting from hemlock’s demise; death of deciduous trees when large hemlocks fell; and competition from aggressive understory plants including doghobble (Leucothoe fontanesiana), rosebay rhododendron (Rhododendron maximum), and Rubus spp. Models of forest change and ecosystem function should not assume that deciduous trees always increase during the first decades after HWA invasion.     

Investigating a major assumption of predictive instream habitat models: is water velocity preference of juvenile Atlantic salmon independent of discharge?

The mean column velocity preference of juvenile Atlantic salmon Salmo salar (LF 30–55 mm) was investigated by observing their spatial pattern of habitat use in a laboratory flume while varying discharge (Q) over a 18‐fold range (Q=2·6–46·8l s^‐1). Based on 341 fish observations at three discharges (Q=2·6, 15·0 and 46·8l s^‐1), three separate velocity preference curves were developed using standard procedures. The mean column velocities measured at 0·6 depth for the fish positions at the set low, medium and high discharges had medians of 7, 10 and 24 cm s^‐1, respectively, and varied significantly between the discharges. Across the range of flows, the fish utilized mean column velocities between 0 and 56 cm s^‐1, but the three velocity preference curves differed. Differences between juvenile Atlantic salmon use of habitat, defined according to mean column velocities at different discharges, were greatest at the lower end of the available range of velocities (<20 cm s^‐1). Weighted usable area (WUA), the output of the instream flow model PHABSIM that is used to describe the available habitat at a given discharge, was calculated for the flume using the preference curves built at the three set discharges. The model was highly sensitive to differences between the three preference curves and WUA varied by up to a two‐fold difference. Furthermore, habitat‐discharge relationships derived from the three preference curves were very different. Predicted habitat losses across the modelled range of discharges varied by up to 150% depending upon which velocity preference curve was used in the model. Thus, the assumption that a single preference curve can be applied across a range of discharges is not valid and is likely to result in large errors when employing PHABSIM and other models that use similar principles.     

‘O father: where art thou?’— Paternity assessment in an open fission–fusion society of wild bottlenose dolphins (Tursiops sp.) in Shark Bay,Western Australia

Sexually mature male bottlenose dolphins in Shark Bay cooperate by pursuing distinct alliance strategies to monopolize females in reproductive condition. We present the results of a comprehensive study in a wild cetacean population to test whether male alliance membership is a prerequisite for reproductive success. We compared two methods for inferring paternity: both calculate a likelihood ratio, called the paternity index, between two opposing hypotheses, but they differ in the way that significance is applied to the data. The first method, a Bayesian approach commonly used in human paternity testing, appeared to be overly conservative for our data set, but would be less susceptible to assumptions if a larger number of microsatellite loci had been used. Using the second approach, the computer program cervus 2.0, we successfully assigned 11 paternities to nine males, and 17 paternities to 14 out of 139 sexually mature males at 95% and 80% confidence levels, respectively. It appears that being a member of a bottlenose dolphin alliance is not a prerequisite for paternity: two paternities were obtained by juvenile males (one at the 95%, the other at the 80% confidence level), suggesting that young males without alliance partners pursue different mating tactics to adults. Likelihood analyses showed that these two juvenile males were significantly more likely to be the true father of the offspring than to be their half-sibling (P < 0.05). Using paternity data at an 80% confidence level, we could show that reproductive success was significantly skewed within at least some stable first-order alliances (P < 0.01). Interestingly, there is powerful evidence that one mating was incestuous, with one calf apparently fathered by its mother's father (P < 0.01). Our study suggests that the reproductive success of both allied males, and of nonallied juveniles, needs to be incorporated into an adaptive framework that seeks to explain alliance formation in male bottlenose dolphins.     

Interspecific hybridization, a matter of pioneering? Insights from Atlantic salmon and brown trout

Interspecific hybridization may occur in situations of recent contact between a colonizer and a resident species, being more intense in the colonization front. Atlantic salmon Salmo salar and brown trout S. trutta have been sympatric species since their origin and they share spatial and temporal spawning niches, exhibiting low levels of bidirectional interspecific hybridization and introgression throughout their distribution range. Different causes have been identified for increased hybridization, from escapes or deliberate releases of domesticated fish to sneaking male behavior. We have examined hybridization rates and direction in different situations of advance of one of these species into a territory formerly inhabited by the other (247 samples were analyzed in northern Spain and 487 in Kerguelen Islands). In all cases, hybrids found in the colonization front were offspring of colonizer females and resident males. We hypothesize that these findings are the result of adaptive relaxed mate choice of colonizing females, regardless of the relative abundance of each species.     

Where have all the weta gone? Results after two decades of transferring a threatened New Zealand giant weta, Deinacrida mahoenui

There have been numerous transfers of the large-bodied orthopteran, the Mahoenui giant weta (Family Anostostomatidae: Deinacrida mahoenui), over the past 19 years but there has been limited follow-up monitoring to ascertain establishment and breeding of transferred populations. Recent surveys carried out at all the locations where this weta were transferred, found weta at four of the seven transferred sites. The most important factor determining the success of past transfers is the absence of introduced mammalian predators, particularly rats, at a site. At two sites, Mahurangi Island Scenic Reserve and Warrenheip, weta appeared to be flourishing and have successfully established new populations in the absence of rats. If mammals are present at a site, the occurrence of dense prickly gorse to protect giant weta from predation is another important factor in their survival. Weta were found at very low densities (only single specimens were captured) at Mangaokewa Scenic Reserve and Tikikaru (private land) and it is likely their populations are not viable in the long term. Further efforts to establish Mahoenui giant weta populations should be in mammal-free sanctuaries containing native forest. More intensive post-transfer monitoring using radio-transmitters would enable better understanding of their behaviour after transfer. In addition, long-term regular monitoring of transferred populations is required, particularly those where the likelihood of rat re-invasion is high.     

Hydra and Niccolo Paganini (1782–1840)—two peas in a pod? The molecular basis of extracellular matrix structure in the invertebrate,Hydra

The body wall of Hydra is organized as an epithelial bilayer with an intervening extracellular matrix (ECM). Molecular and biochemical analyses of Hydra ECM have established that it contains components similar to those seen in more complicated vertebrates such as human. In terms of biophysical parameters, Hydra ECM is highly flexible; a property that facilitates continuous movements along the organism's longitudinal and radial axis. A more rigid ECM, as in vertebrates, would not be compatible with this degree of movement. The flexible nature of Hydra ECM can now be explained in part by the unique structure of the organism's collagens. Interestingly, some aspects of the structural features of Hydra collagens mimic what is seen in Ehlers-Danlos syndrome, an inherited condition in humans that results in an abnormally flexible ECM that can be debilitating in extreme cases. This review will focus on structure-function relationships of the ECM of Hydra.