Effects of Tour Boats on the Behavior of Bottlenose Dolphins: Using Markov Chains to Model Anthropogenic Impacts

Abstract:   Nature-based tourism activities have been developing over the last decade, but it is still difficult to manage these activities sustainably. This sector is increasingly focusing on whales and dolphins in coastal communities, but the exact effects of these tourism activities are unclear. Markov chain modeling may help researchers assess the effects of tourism activities on the behavioral budget of small cetaceans. Matrix models have been used widely in population ecology to provide successful management guidelines. From June 2000 to August 2001, I collected information on the behavioral state of bottlenose dolphin (  Tursiops spp.) schools from a population residing in Doubtful Sound, Fiordland, New Zealand. In addition, I recorded the occurrence of boat and dolphin interactions. I then calculated the transition probabilities of passing from one behavior to another by using a first-order, time-discrete Markov chain model. Behavioral transitions during which a boat-dolphin interaction occurred were compiled in an "impact" chain. All other transitions were tallied in a control chain. I then quantified the effect of boat-dolphin interactions during behavioral transitions by comparing the behavioral transition probabilities of both chains. Socializing and resting behaviors were disrupted by interactions with boats to a level that raises concern. Both the duration of bouts and the total amount of time spent in both these behavioral states were substantially decreased. Dolphins were significantly more likely to be traveling after an interaction with a boat. However, the overall behavioral budget of the population was not significantly affected. Therefore, the bottlenose dolphin population seems to be able to sustain the present level of boat interactions because of its low intensity. More effort is needed to develop prognosis analyses in order to understand how the effect of boat interactions on dolphins changes with variations in intensity.     

Behavioral games involving a clever prey avoiding a clever predator: An individual-based model of dusky dolphins and killer whales

Faced with an intermittent but potent threat, animals exhibit behavior that allows them to balance foraging needs and avoid predators and over time, these behaviors can become hard-wired adaptations with both species trying to maximize their own fitness. In systems where both predator and prey share similar sensory modalities and cognitive abilities, such as with marine mammals, the dynamic nature of predator-prey interactions is poorly understood. The costs and benefits of these anti-predator adaptations need to be evaluated and quantified based on the dynamic engagement of predator and prey. Many theoretic models have addressed the complexity of predator-prey relationships, but few have translated into testable mechanistic models. In this study, we developed a spatially-explicit, geo-referenced, individual-based model of a prototypical adult dusky dolphin off Kaikoura, New Zealand facing a more powerful, yet infrequent predator, the killer whale. We were interested in two primary objectives, (1) to capture the varying behavioral game between a clever prey and clever predator based on our current understanding of the Kaikoura system, (2) to compare evolutionary costs vs. benefits (foraging time and number of predator encounters) for an adult non-maternal dusky dolphin at various levels of killer whale-avoidance behaviors and no avoidance rules. We conducted Monte Carlo simulations to address model performance and parametric uncertainty. Mantel tests revealed an 88% correlation (426 × 426 distance matrix, km²) between observed field sightings of dusky dolphins with model generated sightings for non-maternal adult dusky dolphin groups. Simulation results indicated that dusky dolphins incur a 2.7% loss in feeding time by evolving the anti-predator behavior of moving to and from the feeding grounds. Further, each evolutionary strategy we explored resulted in dolphins incurring an additional loss of foraging time. At low killer whale densities (appearing less than once every 3 days), each evolutionary strategy simulated converged towards the evolutionary cost of foraging, that is, the loss in foraging time approached the 2.7% loss experienced by evolving near shore-offshore movement behavior. However, the highest level of killer whale presence resulted in 38% decreases in foraging time. The biological significance of these losses potentially incurred by a dusky dolphin is dependent on various factors from dolphin group foraging behavior and individual energy needs to dolphin prey availability and behavior.     

Influences on dusky dolphin (<Emphasis Type="Italic">Lagenorhynchus obscurus</Emphasis>) fission-fusion dynamics in Admiralty Bay,New Zealand

In societies characterized by a high degree of fission-fusion dynamics, individuals adjust their grouping patterns according to the shifting balance of costs and benefits associated with grouping. This study examines influences on fission-fusion dynamics for dusky dolphins (Lagenorhynchus obscurus) in Admiralty Bay, New Zealand. This area is an important foraging habitat for dusky dolphins during the winter and spring. Admiralty Bay has little predation risk, but nearshore mussel farms may infringe on available habitat. I used generalized estimating equations to determine the influences of coordinated foraging, predation risk, and presence of mussel farms on party size, rate of fission-fusion, and behavioral state. I conducted 168 boat-based group focal follows totaling 168 h. The proportion of individuals observed foraging was positively related to party size and rate of party fusion. Resting had no effect on party size and did not vary according to location. Near mussel farms, traveling decreased, and rate of party fission decreased. I conclude that (1) coordinated foraging strategies are a primary influence on fission-fusion dynamics within this population, (2) dolphins may respond to decreased predation risk by not adjusting party size or location during resting, and (3) areas near mussel farms are not used for traveling.     

Effects of Urbanization on Occupancy of Stream Salamanders

Abstract: Urban development is the most common form of land conversion in the United States. Using a before–after control‐impact study design, we investigated the effects of urbanization on larval and adult stages of southern two‐lined salamanders (Eurycea cirrigera) and northern dusky salamanders (Desmognathus fuscus). Over 5 years, we estimated changes in occupancy and probabilities of colonization and survival in 13 stream catchments after urbanization and in 17 catchments that were not urbanized. We also examined effects of proportion of urbanized area in a catchment and distance of the salamander population to the nearest stream on probabilities of colonization and survival. Before urbanization, adult and larval stages of the two salamander species occupied nearly all surveyed streams, with occupancy estimates ranging from 1.0 to 0.78. Four years after urbanization mean occupancy of larval and adult two‐lined salamanders had decreased from 0.87 and 0.78 to 0.57 and 0.39, respectively. Estimates of mean occupancy of larval northern dusky salamanders decreased from 1.0 to 0.57 in urban streams 4 years after urbanization; however, adult northern dusky salamander occupancy remained close to 1.0 in urban streams over 5 years. Occupancy estimates in control streams were similar for each species and stage over 5 years. Urbanization was associated with decreases in survival probabilities of adult and larval two‐lined salamanders and decreases in colonization probabilities of larval dusky salamanders. Nevertheless, proportion of impervious surface and distance to nearest stream had little effect on probabilities of survival and colonization. Our results imply that in the evaluation of the effects of urbanization on species, such as amphibians, with complex life cycles, consideration of the effects of urbanization on both adult and larval stages is required.     

Marine aquaculture and bottlenose dolphins’ (<Emphasis Type="Italic">Tursiops truncatus</Emphasis>) social structure

In this study, we investigate association patterns of 249 bottlenose dolphin feeding groups off Sardinia Island (Italy) from January 2000–May 2007 and describe how their association behaviour is related to their response to food patches created by a marine fin fish farm. We also tested the hypothesis that dolphins have different social structures with different feeding activities: Associations should decrease during opportunistic feeding behaviours as it is easier to capture prey, and cooperation is not as necessary. Sixteen individually identified bottlenose dolphins were observed participating in both opportunistic and not opportunistic feeding activities, with a mean of 30 ± 8 times and 9.6 ± 1 times, respectively. Bottlenose dolphins show non-random social behaviour during feeding and this behaviour differs depending on their specific foraging activity. Dolphin associations during feeding can be divided into three categories: acquaintances, affiliates, and feeding associates. Association behaviour during fish farm feeding is consistent with our hypothesis that during opportunistic behaviours, benefits from cooperation decrease, as it is easier to capture prey. Group size homogeneity in both feeding activities demonstrates that the number of dolphins engaging in foraging is not necessarily related with cooperation levels. Moreover, an adult dolphin may prefer to associate with a specific individual, independent of the sex, who shares the same foraging priorities. This study is the first to show how aquaculture is not only directly affecting marine predators but could also indirectly affect their social structure and behaviour.     

The emergence of unshared consensus decisions in bottlenose dolphins

Unshared consensus decision-making processes, in which one or a small number of individuals make the decision for the rest of a group, are rarely documented. However, this mechanism can be beneficial for all group members when one individual has greater knowledge about the benefits of the decision than other group members. Such decisions are reached during certain activity shifts within the population of bottlenose dolphins residing in Doubtful Sound, New Zealand. Behavioral signals are performed by one individual and seem to precipitate shifts in the behavior of the entire group: males perform side flops and initiate traveling bouts while females perform upside-down lobtails and terminate traveling bouts. However, these signals are not observed at all activity shifts. We find that, while side flops were performed by males that have greater knowledge than other male group members, this was not the case for females performing upside-down lobtails. The reason for this could have been that a generally high knowledge about the optimal timing of travel terminations rendered it less important which individual female made the decision. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau and R. James).     

Prey dynamics affect foraging by a pelagic predator (Stenella longirostris) over a range of spatial and temporal scales

Studies have shown that pelagic predators do not overlap with their prey at small scales. However, we hypothesized that spinner dolphin foraging would be affected by the spatio-temporal dynamics of their prey at both small and large scales. A modified echosounder was used to simultaneously measure the abundance of dolphins and their prey as a function of space and time off three Hawaiian islands. Spinner dolphin abundance closely matched the abundance patterns in the boundary community both horizontally and vertically. As hypothesized, spinner dolphins followed the diel horizontal migration of their prey, rather than feeding offshore the entire night. Spinner dolphins also followed the vertical migrations of their prey and exploited the vertical areas within the boundary layer that had the highest prey density. Cooperative foraging by pairs of dolphins within large groups was evident. The geometric and density characteristics of prey patches containing dolphins indicate that dolphins may alter the characteristics of prey patches through this cooperative foraging. The overlap of Hawaiian spinner dolphins and their prey at many temporal and spatial scales, ranging from several minutes to an entire night and 20 m to several kilometers, indicates that the availability of truly synoptic data may fundamentally alter our conclusions about pelagic predator-prey interactions.     

Decline in Relative Abundance of Bottlenose Dolphins Exposed to Long-Term Disturbance

Abstract:  Studies evaluating effects of human activity on wildlife typically emphasize short-term behavioral responses from which it is difficult to infer biological significance or formulate plans to mitigate harmful impacts. Based on decades of detailed behavioral records, we evaluated long-term impacts of vessel activity on bottlenose dolphins ( Tursiops sp.) in Shark Bay, Australia. We compared dolphin abundance within adjacent 36-km² tourism and control sites, over three consecutive 4.5-year periods wherein research activity was relatively constant but tourism levels increased from zero, to one, to two dolphin-watching operators. A nonlinear logistic model demonstrated that there was no difference in dolphin abundance between periods with no tourism and periods in which one operator offered tours. As the number of tour operators increased to two, there was a significant average decline in dolphin abundance (14.9%; 95% CI =−20.8 to −8.23), approximating a decline of one per seven individuals. Concurrently, within the control site, the average increase in dolphin abundance was not significant (8.5%; 95% CI =−4.0 to +16.7). Given the substantially greater presence and proximity of tour vessels to dolphins relative to research vessels, tour-vessel activity contributed more to declining dolphin numbers within the tourism site than research vessels. Although this trend may not jeopardize the large, genetically diverse dolphin population of Shark Bay, the decline is unlikely to be sustainable for local dolphin tourism. A similar decline would be devastating for small, closed, resident, or endangered cetacean populations. The substantial effect of tour vessels on dolphin abundance in a region of low-level tourism calls into question the presumption that dolphin-watching tourism is benign.     

Modeling population effects of the Deepwater Horizon oil spill on a long-lived species

The 2010 Deepwater Horizon (DWH) oil spill exposed common bottlenose dolphins (Tursiops truncatus) in Barataria Bay, Louisiana to heavy oiling that caused increased mortality and chronic disease and impaired reproduction in surviving dolphins. We conducted photographic surveys and veterinary assessments in the decade following the spill. We assigned a prognostic score (good, fair, guarded, poor, or grave) for each dolphin to provide a single integrated indicator of overall health, and we examined temporal trends in prognostic scores. We used expert elicitation to quantify the implications of trends for the proportion of the dolphins that would recover within their lifetime. We integrated expert elicitation, along with other new information, in a population dynamics model to predict the effects of observed health trends on demography. We compared the resulting population trajectory with that predicted under baseline (no spill) conditions. Disease conditions persisted and have recently worsened in dolphins that were presumably exposed to DWH oil: 78% of those assessed in 2018 had a guarded, poor, or grave prognosis. Dolphins born after the spill were in better health. We estimated that the population declined by 45% (95% CI 14–74) relative to baseline and will take 35 years (95% CI 18–67) to recover to 95% of baseline numbers. The sum of annual differences between baseline and injured population sizes (i.e., the lost cetacean years) was 30,993 (95% CI 6607–94,148). The population is currently at a minimum point in its recovery trajectory and is vulnerable to emerging threats, including planned ecosystem restoration efforts that are likely to be detrimental to the dolphins’ survival. Our modeling framework demonstrates an approach for integrating different sources and types of data, highlights the utility of expert elicitation for indeterminable input parameters, and emphasizes the importance of considering and monitoring long-term health of long-lived species subject to environmental disasters. Article impact statement: Oil spills can have long-term consequences for the health of long-lived species; thus, effective restoration and monitoring are needed.     

Functional mechanisms underlying cetacean distribution patterns: hotspots for bottlenose dolphins are linked to foraging

Many studies have shown that the distribution of cetaceans can be closely linked to habitat, but the underlying function of the preferred habitats often remains unclear. Only when behavioural observations are made in relation to habitat types can functional mechanisms behind the habitat use be revealed. Within the range of a bottlenose dolphin (Tursiops truncatus) population off NE Scotland, dolphins show clear preferences for several discrete areas. If the observed patterns of distribution are related to foraging, we predict that behaviour patterns shown by dolphins would reflect this relationship. In this study we identify behaviours of dolphins at the water surface that were related to feeding events, evaluate whether the patterns of distribution were related to foraging and whether they were related the local submarine habitat characteristics. To investigate whether visible surface evidence of foraging behaviour varied spatially, we analysed data collected from 104 regular boat-based surveys made within the Moray Firth, NE Scotland, between 1990 and 2000. To determine whether underlying bathymetry had any influence on the surface behaviour of dolphins, a land-based observation study was carried out in the populations core region of use. The results of this study show that feeding behaviour by dolphins was significantly higher in areas used intensively by dolphins. Furthermore, there were clear relationships between feeding events and the submarine habitat characteristics; certain forms of feeding occur primarily over steep seabed gradients, and in deeper waters during June and July. These results quantitatively support the hypothesis that the distinctive patterns of distribution shown by these dolphins are related to foraging behaviour or opportunities, and that submarine habitat characteristics may be a significant factor in the foraging efficiency of dolphins. Future work should focus on collecting detailed information on the distribution patterns of prey within the study area to allow direct comparisons between predator and prey distributions.Communicated by J.P. Thorpe, Port Erin     

Latency to resume calling after disturbance in the field cricket,<Emphasis Type="Italic"> Teleogryllus oceanicus</Emphasis>, corresponds to population-level differences in parasitism risk

A possible parasitoid-evasion behavioral adaptation is examined in male field crickets, Teleogryllus oceanicus, from three Hawaiian islands where parasitoid prevalence varies naturally among islands. Ormia ochracea, the parasitoid fly that parasitizes T. oceanicus on these islands, uses male calling song to locate its hosts. We used laboratory-reared males from three Hawaiian islands to determine if there are population differences in the time it takes for calling males to resume calling after a standardized disturbance. Males follow the expected pattern; males from the island with the greatest risk of parasitism have the longest latency to resume calling, and males from the island with the least risk of parasitism have the shortest latency to resume calling. Results are discussed in the context of behavioral adaptations to differing parasitism levels, and trade-offs between natural and sexual selection.Communicated by D. Gwynne     

Analysis of behavioral changes of zebrafish (Danio rerio) in response to formaldehyde using Self-organizing map and a hidden Markov model

Two computational methods were applied to classification of movement patterns of zebrafish (Danio rerio) to elucidate Markov processes in behavioral changes before and after treatment of formaldehyde (0.1 mg/L) in semi-natural conditions. The complex data of the movement tracks were initially classified by the Self-organizing map (SOM) to present different behavioral states of test individuals. Transition probabilities between behavioral states were further evaluated to fit Markov processes by using the hidden Markov model (HMM). Emission transition probability was also obtained from the observed variables (i.e., speed) for training with the HMM. Experimental transition and emission probability matrices were successfully estimated with the HMM for recognizing sequences of behavioral states with accuracy rates in acceptable ranges at central and boundary zones before (77.3-81.2%) and after (70.1-76.5%) treatment. A heuristic algorithm and a Markov model were efficiently combined to analyze movement patterns and could be a means of in situ behavioral monitoring tool.     

Influences of divergent behavioral strategies upon risk allocation in juvenile flatfishes

Animals balance feeding and anti-predator behaviors at various temporal scales. When risk is infrequent or brief, prey can postpone feeding in the short term and temporally allocate feeding behavior to less risky periods. If risk is frequent or lengthy, however, prey must eventually resume feeding to avoid fitness consequences. Species may exhibit different behavioral strategies, depending on the fitness tradeoffs that exist in their environment or across their life histories. North Pacific flatfishes that share juvenile rearing habitat exhibit a variety of responses to predation risk, but their response to risk frequency has not been examined. We observed the feeding and anti-predator behaviors of young-of-the-year English sole (Parophrys vetulus), northern rock sole (Lepidopsetta polyxystra), and Pacific halibut (Hippoglossus stenolepis)—three species that exhibit divergent anti-predator strategies—following exposure to three levels of predation risk: no risk, infrequent (two exposures/day), and frequent (five exposures/day). The English sole responded to the frequent risk treatment with higher feeding rates than during infrequent risk, following a pattern of behavioral response that is predicted by the risk allocation hypothesis; rock sole and halibut did not follow the predicted pattern, but this may be due to the limited range of treatments. Our observations of unique anti-predator strategies, along with differences in foraging and species-specific ecologies, suggest divergent trajectories of risk allocation for the three species.     

Dominance rank differences in the energy intake and expenditure of female Bwindi mountain gorillas

Socioecological models predict that contest competition for clumped foods can lead to higher energy intake and lower energy expenditure for higher-ranking individuals. Here, we examine the relationships between dominance rank and energy intake and expenditure of female mountain gorillas in Bwindi Impenetrable National Park, Uganda (Gorilla beringei beringei). Bwindi gorillas have weak dominance relationships, feed on nonreproductive plant parts throughout the year, and consume fruit when it is seasonally available. We used behavioral observations on one group of gorillas and nutritional analysis of their major food items to calculate energy intake rates and estimated energy expenditure. Using linear mixed models, we found a significant positive relationship between dominance rank and energy intake rates, due to higher-ranking females having faster ingestion rates, rather than consuming foods with higher energy concentrations. Lower-ranking females did not spend significantly more time feeding to compensate for their lower energy intake rates. Lower-ranking females spent significantly more time traveling than higher-ranking females, leading to a negative relationship between dominance rank and energy expenditure. The combined results revealed a significant positive relationship between dominance rank and energy balance. Higher-ranking females did not spend longer feeding on fruit than lower-ranking ones, and the relationship between dominance rank and energy intake rates was not stronger when fruit was available. According to socioecological models, these results suggest that contest competition may be occurring with both fruit and nonreproductive plant parts, which would be consistent with growing evidence that nonreproductive plant parts can be contestable.     

Coexistence of Fisheries with River Dolphin Conservation

Abstract: Freshwater biodiversity conservation is generally perceived to conflict with human use and extraction (e.g., fisheries). Overexploited fisheries upset the balance between local economic needs and endangered species’ conservation. We investigated resource competition between fisheries and Ganges river dolphins (Platanista gangetica gangetica) in a human‐dominated river system in India to assess the potential for their coexistence. We surveyed a 65‐km stretch of the lower Ganga River to assess habitat use by dolphins (encounter rates) and fishing activity (habitat preferences of fishers, intensity of net and boat use). Dolphin abundance in the main channel increased from 179 (SE 7) (mid dry season) to 270 (SE 8) (peak dry season), probably as a result of immigration from upstream tributaries. Dolphins preferred river channels with muddy, rocky substrates, and deep midchannel waters. These areas overlapped considerably with fishing areas. Sites with 2–6 boats/km (moderately fished) were more preferred by dolphins than sites with 8–55 boats/km (heavily fished). Estimated spatial (85%) and prey–resource overlap (75%) between fisheries and dolphins (chiefly predators of small fish) suggests a high level of competition between the two groups. A decrease in abundance of larger fish, indicated by the fact that small fish comprised 74% of the total caught, may have intensified the present competition. Dolphins seem resilient to changes in fish community structure and may persist in overfished rivers. Regulated fishing in dolphin hotspots and maintenance of adequate dry season flows can sustain dolphins in tributaries and reduce competition in the main river. Fish‐stock restoration and management, effective monitoring, curbing destructive fishing practices, secure tenure rights, and provision of alternative livelihoods for fishers may help reconcile conservation and local needs in overexploited river systems.     

Use of Acoustic Tools to Reveal Otherwise Cryptic Responses of Forest Elephants to Oil Exploration

Abstract: Most evaluations of the effects of human activities on wild animals have focused on estimating changes in abundance and distribution of threatened species; however, ecosystem disturbances also affect aspects of animal behavior such as short‐term movement, activity budgets, and reproduction. It may take a long time for changes in behavior to manifest as changes in abundance or distribution. Therefore, it is important to have methods with which to detect short‐term behavioral responses to human activity. We used continuous acoustic and seismic monitoring to evaluate the short‐term effects of seismic prospecting for oil on forest elephants (Loxodonta cyclotis) in Gabon, Central Africa. We monitored changes in elephant abundance and activity as a function of the frequency and intensity of acoustic and seismic signals from dynamite detonation and human activity. Elephants did not flee the area being explored; the relative number of elephants increased in a seasonal pattern typical of elsewhere in the ecosystem. In the exploration area, however, they became more nocturnal. Neither the intensity nor the frequency of dynamite blasts affected the frequency of calling or the daily pattern of elephant activity. Nevertheless, the shift of activity to nocturnal hours became more pronounced as human activity neared each monitored area of forest. This change in activity pattern and its likely causes would not have been detected through standard monitoring methods, which are not sensitive to behavioral changes over short time scales (e.g., dung transects, point counts) or cover a limited area (e.g., camera traps). Simultaneous acoustic monitoring of animal communication, human, and environmental sounds allows the documentation of short‐term behavioral changes in response to human disturbance.     

Travel duration,energetic expenditure,and patch exploitation in the parasitic wasp <Emphasis Type="Italic">Venturia canescens</Emphasis>

Foraging animals usually keep track of how costly it is to reach new resource patches and adjust patch residence time and exploitation rate accordingly. There are at least two potential factors, which are not necessarily closely linked, that animals could measure to estimate costs of traveling: the time the forager needs to reach the next patch and the amount of energy it has to invest until arrival. In the parasitoid wasp Venturia canescens, females forage for hosts from which their offspring can develop. Two different types of this parasitoid exist. The thelytokous type lives in anthropogenic habitats where flight is not necessarily linked with foraging. The arrhenotokous type lives under field conditions and shows frequent flight activity. We tested whether the wasps would use time or energy needed to assess patch availability, by either confining them into vials or letting them travel actively in a flight mill between patch visits. Our results show that in thelytokous lines, time is a sufficient cue influencing patch exploitation and an additional effect of the energy needed was not visible. In the arrhenotokous wasps, however, only the number of rounds flown in the mill influenced subsequent behavior, while mere time spent traveling did not. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of surrounding land use and water depth on seagrass dynamics relative to a catastrophic algal bloom

Seagrasses are the foundation of many coastal ecosystems and are in global decline because of anthropogenic impacts. For the Indian River Lagoon (Florida, U.S.A.), we developed competing multistate statistical models to quantify how environmental factors (surrounding land use, water depth, and time [year]) influenced the variability of seagrass state dynamics from 2003 to 2014 while accounting for time‐specific detection probabilities that quantified our ability to determine seagrass state at particular locations and times. We classified seagrass states (presence or absence) at 764 points with geographic information system maps for years when seagrass maps were available and with aerial photographs when seagrass maps were not available. We used 4 categories (all conservation, mostly conservation, mostly urban, urban) to describe surrounding land use within sections of lagoonal waters, usually demarcated by land features that constricted these waters. The best models predicted that surrounding land use, depth, and year would affect transition and detection probabilities. Sections of the lagoon bordered by urban areas had the least stable seagrass beds and lowest detection probabilities, especially after a catastrophic seagrass die‐off linked to an algal bloom. Sections of the lagoon bordered by conservation lands had the most stable seagrass beds, which supports watershed conservation efforts. Our results show that a multistate approach can empirically estimate state‐transition probabilities as functions of environmental factors while accounting for state‐dependent differences in seagrass detection probabilities as part of the overall statistical inference procedure.     

Minimizing the cost of translocation failure with decision‐tree models that predict species’ behavioral response in translocation sites

The high number of failures is one reason why translocation is often not recommended. Considering how behavior changes during translocations may improve translocation success. To derive decision‐tree models for species’ translocation, we used data on the short‐term responses of an endangered Australian skink in 5 simulated translocations with different release conditions. We used 4 different decision‐tree algorithms (decision tree, decision‐tree parallel, decision stump, and random forest) with 4 different criteria (gain ratio, information gain, gini index, and accuracy) to investigate how environmental and behavioral parameters may affect the success of a translocation. We assumed behavioral changes that increased dispersal away from a release site would reduce translocation success. The trees became more complex when we included all behavioral parameters as attributes, but these trees yielded more detailed information about why and how dispersal occurred. According to these complex trees, there were positive associations between some behavioral parameters, such as fight and dispersal, that showed there was a higher chance, for example, of dispersal among lizards that fought than among those that did not fight. Decision trees based on parameters related to release conditions were easier to understand and could be used by managers to make translocation decisions under different circumstances. Minimizar el Costo del Fracaso de la Reubicación con Modelos de Árboles de Decisión que Predigan la Respuesta Conductual de la Especie en los Sitios de Reubicación     

Prey caloric value and predator energy needs: foraging predictions for wild spinner dolphins

Spinner dolphins (Stenella longirostris) feed on individual small (2–10 cm long) prey that undergo diel vertical migrations, presumably making them inaccessible to dolphins during the day. To examine how time, prey behavior, prey distribution, and energy needs constrain dolphin foraging, a calorimeter was used to measure the caloric content of prey items. These data were combined with information on prey distribution in the field and the energetic needs of dolphins to construct basic bioenergetic models predicting the total prey consumption and mean feeding rates of wild dolphins as well as potential prey preferences. The mean caloric density of mesopelagic animals from Hawaii was high (2,837 cal/g wet weight for shrimps, squids, and myctophid fishes). Their total caloric content, however, was low because of their small size. Energy value of prey and energetic needs of spinner dolphins were used to examine the effect of time and energy constraints on dolphin foraging. The results predict that spinner dolphins need to consume an estimated minimum of 1.25 large prey items per minute to meet their maintenance energy needs. If the additional energy costs of foraging are considered, the estimated necessary foraging rate is predicted to increase only slightly when large prey are consumed. If smaller prey are consumed, the total energy demand may be twice the basic maintenance value. Prey density and size are predicted to be important in determining if dolphins can forage successfully, meeting their energetic needs. The prey size predictions compare well with results from previous gut content studies and from stomach contents of a recently stranded spinner dolphin that had enough prey in its stomach to meet its estimated basic maintenance energy needs for a day. Finally, the results suggest that spinner dolphins are time and therefore efficiency limited rather than being limited by the total amount of available prey. This may explain the diel migration exhibited by spinner dolphins that allows them to follow the movements of their prey and presumably maximizes their foraging time.Communicated by P.W. Sammarco, Chauvin