Acceleration Data Loggers Research Articles

Variable post-release mortality in common shark species captured in Texas shore-based recreational fisheries.

The practice of catch and release fishing is common among anglers but has been shown to cause unintended mortalities in some species. Current post-release mortality estimates used in coastal shark stock assessments are typically derived from boat-based shark fisheries, which differ from shore-based operations that expose sharks to potentially more stressful environmental and handling conditions. Recreational post-release mortality rates in shore-based fisheries must be quantified to improve stock assessment models and to create guidelines that protect species from overexploitation. Here, we partnered with experienced anglers acting as citizen scientists to deploy pop-up satellite archival transmitting tags (PSAT, n = 22) and acceleration data loggers (ADLs, n = 22). on four commonly caught sharks including the blacktip shark (Carcharhinus limbatus, n = 11), bull shark (Carcharhinus leucas, n = 14), tiger shark (Galeocerdo cuvier, n = 6), and great hammerheads (Sphyrna mokarran, n = 2). Mortality occurred within minutes to hours post-release. If evidence of mortality occurred after normal diving behavior had been re-established for 10 days, then the mortality was considered natural and not related to the catch-and-release process. Post-release mortality estimates ranged from 0% for bull and tiger sharks to 45.5% for blacktip sharks. Of the two great hammerheads, one died within 30 minutes post-release while the other exhibited mortality characteristics 14 days after release. Moribund blacktip sharks experienced on average 3.4-4.9°C warmer water compared with survivors. Recovery periods were estimated for survivors of each species and were highly variable, differing based on duration of tag deployment. High variability in responses to capture and release between species demonstrates the need for species-specific assessments of post-release mortality in shore-based recreational fisheries.

Forage particle size and forage preservation method modulate lying behaviour in dairy cows

It has been suggested that reducing forage particle size as well as feeding hay compared to silage may improve forage intake. Little is known, however, how such ration characteristics affect other aspects of cattle behaviour. Therefore, this study investigated the lying behaviour of cows in response to particle size reduction (LONG versus SHORT; Trial 1) and preservation method (SILAGE versus HAY; Trial 2) of forages which constituted ≥ 80% of the rations’ dry matter. Two feeding groups with 10 (Trial 1) and 9 Holstein cows each (Trial 2) received the experimental rations for approximately 5 weeks. Cows were housed in a free-stall barn with straw-bedded cubicles and rubberized floor in the alleys. Lying behaviour was recorded using HOBO Pendant® acceleration data loggers during the last 3 weeks of the experimental period as well as for 3 consecutive days during the week preceding the experiment, the latter serving as a baseline covariate to consider individual cow lying behaviour.SHORT-fed cows (Trial 1) had a longer daily lying time (+ 1.1 h/d; P = 0.003) and tended to have more lying bouts (+ 3.1; P = 0.090) than cows fed the LONG ration. In both groups, a preference towards the left lying side (57.4%) was observed. A similar pattern was observed for both groups with regard to rumination time while lying. Cows fed SILAGE or HAY (Trial 2) did not differ with regard to lying times (12.8 h/d). However, cows on HAY tended to lie less on the left side (- 1.1 h/d; P = 0.098) and had less lying bouts per day (- 2.5 bouts/d; P = 0.039). Consequently, these cows showed nearly an equal preference for the left and right lying side with 49.1% and 51.6%, respectively; whereas cows on SILAGE tended to prefer the left lying side (55.6%), also when ruminating. In contrast, cows on HAY tended to reduce rumination time on the left lying side (- 0.61 h/d; P = 0.079).Effects observed may be attributed to changes in eating behaviour as well as the amount of feed ingested in a given time period. Under the conditions investigated, time budgets for lying may be limited and changes of the forage characteristics (e.g. particle size reduction) could mitigate these constraints.

Temporal niche partitioning as a novel mechanism promoting co-existence of sympatric predators in marine systems.

Niche partitioning of time, space or resources is considered the key to allowing the coexistence of competitor species, and particularly guilds of predators. However, the extent to which these processes occur in marine systems is poorly understood due to the difficulty in studying fine-scale movements and activity patterns in mobile underwater species. Here, we used acceleration data-loggers to investigate temporal partitioning in a guild of marine predators. Six species of co-occurring large coastal sharks demonstrated distinct diel patterns of activity, providing evidence of strong temporal partitioning of foraging times. This is the first instance of diel temporal niche partitioning described in a marine predator guild, and is probably driven by a combination of physiological constraints in diel timing of activity (e.g. sensory adaptations) and interference competition (hierarchical predation within the guild), which may force less dominant predators to suboptimal foraging times to avoid agonistic interactions. Temporal partitioning is often thought to be rare compared to other partitioning mechanisms, but the occurrence of temporal partitioning here and similar characteristics in many other marine ecosystems (multiple predators simultaneously present in the same space with dietary overlap) introduces the question of whether this is a common mechanism of resource division in marine systems.

Accelerometry to study fine-scale activity of invasive Burmese pythons (Python bivittatus) in the wild

BackgroundThe establishment of Burmese pythons (Python bivittatus) in Everglades National Park, Florida, USA, has been connected to a > 90% decline in the mesomammal population in the park and is a major threat to native reptile and bird populations. Efforts to control this population are underway, but are hampered by a lack of information about fine-scale activity cycles and ecology of these cryptic animals in the wild. We aimed to establish a technique for monitoring the activity of Burmese pythons in the wild using acceleration data loggers (ADLs), while attempting to identify any behavioral patterns that could be used to help manage this invasive species in the Greater Everglades and South Florida.ResultsWe obtained continuous acceleration and temperature data from four wild snakes over periods of 19 to 95 days (mean 54 ± 33 days). Snakes spent 86% of their time at rest and 14% of their time active, including transiting between locations. All snakes showed at least one period of continuous transiting lasting 10 h or more, with one animal transiting continuously for a period of 58.5 h. Acceleration data logger-derived transiting bout duration was significantly correlated with the distance snakes traveled per hour for two snakes that also carried GPS loggers. Snakes were most active in midday or early-night depending on individual and time of year, but all snakes were least likely to be active in the early mornings (0400–0700 h local time). Very little movement took place at temperatures below 14 °C or above 24 °C, with most movement taking place between 15° and 20 °C. One animal showed a highly unusual rolling event that may be indicative of a predation attempt, but this could not be confirmed.ConclusionsFine-scale activity and some behaviors were apparent from ADL data, making ADLs a potentially valuable, unbiased tool for monitoring large-bodied snakes in the wild. Snakes spent the majority of their time resting, but also moved continuously for several hours at a time during bouts of transiting. Results suggest that individuals may shift their diel activity pattern based on season. Understanding seasonal differences in activity levels can improve the accuracy of population estimates, help detect range expansion, and improve managers’ ability to find and capture individuals.

Feature Extraction, Selection, and K-Nearest Neighbors Algorithm for Shark Behavior Classification Based on Imbalanced Dataset

This paper presents the feature extraction, selection and K-Nearest Neighbors (K-NN) algorithm to classify behaviors of sharks based on the data collected by tri-axial acceleration data loggers (ADLs). Because these behaviors are hard to observe in the wild and do not occur frequently, being able to adequately classify them is extremely challenging. In the proposed scheme, we first employ several transformations to enrich the static and dynamic acceleration data. Then, the enhanced data is converted from time to the frequency domain through the fast Fourier transform (FFT) for noise removal. A modified K-NN approach integrated with feature selection is developed and conducted on the frequency domain data to improve the F1-score for minority classes. The acceleration data of California horn sharks ( Heterodontus francisci ) gathered through ADLs mounted on the first dorsal fin is used to demonstrate our algorithm. A comparison study shows that the features extracted and selected by our proposed scheme can significantly improve the performance of classification on the imbalanced dataset.

Active acoustic telemetry tracking and tri-axial accelerometers reveal fine-scale movement strategies of a non-obligate ram ventilator

BackgroundCalifornia horn sharks (Heterodontus francisci) are nocturnally active, non-obligate ram ventilating sharks in rocky reef habitats that play an important ecological role in regulating invertebrate communities. We predicted horn sharks would use an area restricted search (ARS) movement strategy to locate dense resource patches while minimizing energetic costs of travel and nighttime activity. As ectotherms, we predicted environmental temperature would play a significant role in driving movement and activity patterns.MethodsContinuous active acoustic tracking methods and acceleration data loggers were used to quantify the diel fine-scale spatial movements and activity patterns of horn sharks. First passage time was used to identify the scale and locations of patches indicative of ARS. Activity was assessed using overall dynamic body acceleration (ODBA) as a proxy for energy expenditure. Behavior within a patch was characterized into three activity patterns: resting, episodic burst activity, and moderate, consistent activity.ResultsAfter resting in daytime shelters, individuals travelled to multiple reefs throughout the night, traversing through depths of 2–112 m and temperatures of 10.0–23.8 °C. All sharks exhibited area restricted search patch use and arrived at their first patch approximately 3.4 ± 2.2 h (mean ± SD) after sunset. Sharks exhibited moderate, consistent activity in 54% of the patches used, episodic burst activity in 33%, and few (13%) were identified as resting at night. ODBA peaked while sharks were swimming through relatively deeper (~ 30 m), colder channels when traversing from one patch to the next. There was no consistent pattern between ODBA and temperature.ConclusionsWe provide one of the largest fine-scale, high-resolution paired data sets for an elasmobranch movement ecology study. Horn sharks exhibited ARS movement patterns for various activity patterns. Individuals likely travel to reefs known to have profitable and predictable patches, potentially tolerating less suitable environmental temperatures. We demonstrate how gathering high-resolution information on the movement decisions of a community resident enhances knowledge of community structure and overall ecosystem function.

Stroke effort and relative lung volume influence heart rate in diving sea lions.

The dive response, bradycardia (decreased heart rate) and peripheral vasoconstriction, is the key mechanism allowing breath-hold divers to perform long-duration dives while actively swimming and hunting prey. This response is variable and modulated by factors such as dive duration, depth, exercise and cognitive control. This study assessed the potential role of exercise and relative lung volume in the regulation of heart rate (fH) during dives of adult female California sea lions instrumented with electrocardiogram (ECG), depth and tri-axial acceleration data loggers. A positive relationship between activity (minimum specific acceleration) and fH throughout dives suggested increased muscle perfusion associated with exercise. However, apart from late ascent, fH during dives was still less than or equal to resting fH (on land). In addition, the activity-fH relationship was weaker in long, deep dives consistent with prioritization of blood oxygen conservation over blood oxygen delivery to muscle in those dives. Pulmonary stretch receptor reflexes may also contribute to fH regulation as fH profiles generally paralleled changes in relative lung volume, especially in shallower dives and during early descent and late ascent of deeper dives. Overall, these findings support the concept that both exercise and pulmonary stretch receptor reflexes may influence the dive response in sea lions.

Fine-scale behavior and habitat use of the endangered smalltooth sawfish (Pristis pectinata): insights from accelerometry

Determining movement, behavior, and activity patterns is of central importance to conservation efforts for threatened and endangered species because this knowledge is crucial for prioritizing management actions. In this study, we used acceleration data loggers (ADLs) concurrently with passive acoustic monitoring to examine behavior, activity patterns, and habi¬tat use of juvenile smalltooth sawfish (Pristis pectinata) in a Florida nursery. Data from the ADLs indicate that small¬ tooth sawfish were more active and that more burst events indicative of foraging occurred during the evening and night than during the day. Smalltooth sawfish were also most active at depths <1 m and during low tides. The locations of individuals derived from acoustic mon¬itoring techniques indicate that they were less active while in mangrove creek habitats and were more active and more likely to engage in burst activity in habitats within the main stem of the Peace River. This study is the first one to deploy ADLs on smalltooth sawfish, and results describe their fine scale activity and behavior, clarifying patterns of habitat use by this endangered species in one of their few remaining nurseries.

Development of a method for classifying and transmitting high-resolution feeding behavior of fish using an acceleration pinger

BackgroundMonitoring the feeding behavior of animals in the wild is key to understanding their energetics and the influence of the environment on their survival. Recently, a novel acceleration transmitter that processes acceleration data onboard and outputs identification results has been developed by AquaSound Inc. (Kobe, Japan) to investigate feeding biology in fish. To date, few attempts have been made to identify the feeding behavior of fish using transmitters, and none of these attempts accomplished classification of alternative feeding behaviors according to prey items. The objective of this study was to develop an algorithm that can be incorporated in the acceleration transmitter and can identify alternative feeding behaviors in fish, using red-spotted grouper (Epinephelus akaara) as a model species.ResultsMost of the identification algorithms describing feeding behavior in fish developed in previous studies used a combination of acceleration and angular velocity. In this study, we constructed an algorithm based on three-axis accelerometry data alone, since a gyroscope consumes much more electricity and would shorten the battery life of the transmitter. Acceleration data were obtained in tank experiments. Feeding behaviors, induced by feeding three types of live prey (Trachurus japonicus, Metapenaeus ensis and Hemigrapsus sanguineus), as well as other behaviors (routine and escape movements), were simultaneously recorded at 200 Hz by acceleration data loggers, implanted in the abdominal cavities of fish, and by a video camera. A decision tree, including a three-dimensional lookup table, was constructed to classify the behaviors into four behavior classes: shrimp-eating, fish-eating, crab-eating and other behaviors. The classification accuracy was estimated to be 0.77 (F-measure) for shrimp-eating, 0.73 for fish-eating, 0.71 for crab-eating and 0.78 for other movements, using fivefold cross-validation.ConclusionsThe algorithm developed in this study could be incorporated into the transmitter, which would record acceleration data at high frequency (200 Hz), process the data onboard and output classification results of behaviors. This method would reveal more aspects of fish biology, such as individual feeding strategies.

Short-term effects of tagging on activity and movement patterns of Eurasian beavers (Castor fiber)

Bio-logging is becoming increasingly popular amongst wildlife researchers, providing a remote way of monitoring free-ranging animals in their natural habitats. However, capturing and tagging can be stressful and may alter animal behaviour. In this study, we investigated whether tagging altered activity and movement patterns of Eurasian beavers (Castor fiber) during the first week after release, predicting that beavers would be less active, travel shorter distances and stay closer to the lodge in the first nights after the tagging event. We captured 29 dominant free-ranging beavers (12 females, 17 males) in Telemark county, Norway, and tagged them with GPS units (n = 23; 12 males, 11 females) and tri-axial acceleration data loggers (n = 14; 9 males, 5 females). Accelerometer data was used to investigate activity levels (using mean overall dynamic body acceleration ODBA and principal activity periods), while GPS data was used to determine movement patterns (using distance moved and lodge displacement rate). Tagging effects were apparent only in activity levels of beavers, where we found lower mean ODBA values after release although the small effect size (Cohen’s d = 0.17) indicates only a minimal difference in activity. Neither principal activity periods nor distances moved or lodge displacement rate changed within the first week after release, which indicates that beavers were active and post-release space use within the territory was not affected by the tagging event in this respect.

A novel method for determining post-release mortality, behavior, and recovery period using acceleration data loggers

Recent declines in global fish stocks have raised questions regarding the sustainability of both extractive and catch-and-release fishing activities, and prompted efforts to quantify the total impact of fishing pressure. While at-vessel mortality rates are relatively easy to obtain, accurately assessing post-release mortality and sub-lethal behavioral effects has proven difficult. Acceleration data loggers (ADLs) represent a useful tool in post-release studies, but have yet to be fully utilized. The goal of this paper is to demonstrate the utility of ADLs in identifying mortality events, and to provide an example of recovery period quantification methods using acceleration-based swimming metrics. To illustrate the application of this method, we use sample data from blacktip sharks (Carcharhinus limbatus) captured and released in the Florida recreational shark fishery. Mortality events were inferred from stationary depth traces and the eventual cessation of all tailbeat activity, while posture information confirmed that the tag was still attached to the animal. We also detail how ADL data from surviving individuals were used to calculate 58 metrics of fine-scale swimming behavior. Using nonlinear mixed modeling, we found 19 of these metrics displayed a significant logistic relationship with time post-release, indicative of a recovery period. Calculated recovery periods ranged from 5.1 to 19.5h, with a mean of 10.54±3.78h. The low cost of ADLs and their capacity for multiple deployments allows for relatively large sample sizes at a fraction of the cost of satellite tag studies. ADLs provide definitive evidence of post-release mortality, and also allow for the quantification of sub-lethal effects which can be used to measure the impact of different gear types or handling methods, even in species for which mortality events are rare.

Validation of HOBO Pendant® data loggers for automated step detection in two age classes of male turkeys: growers and finishers

Activity levels can be used as a predictor of health status, physical condition, feed efficiency, and coping style in animals. Small, portable data loggers have been validated as an inexpensive and effective alternative to video or live observation for automated activity detection in several livestock species. Our study aimed to validate the use of Onset HOBO Pendant® G acceleration data loggers for automated step detection in two age classes of male turkeys: growers and finishers. The loggers were attached to one leg in an elastic harness and programmed to record each turkey’s leg accelerations every 0.1s. For the grower turkeys, the activities of 60 males were recorded in a runway twice per week from 9–11 weeks of age. In the finisher trial, the loggers were attached to eight 14 week old male turkeys to record their stepping activities in a trial pen over 54min. Simultaneous video observation allowed for logger suitability to be determined for reporting walking activity. The 0.1s data points were identified as either: true positives, false positives, false negatives, or true negatives then the logger sensitivity, false discovery rate, specificity, precision, and accuracy were calculated for each turkey run. Over the 309 grower turkey runs, 4364 steps were observed in the video while the loggers detected 4865 steps. The grower logger results showed a mean sensitivity of 96.02±6.82%, specificity of 99.10±0.86%, and an average false discovery rate of 12.41±10.13% for step detection (mean±standard deviation). For the grower turkey loggers, the mean precision and accuracy for step detection were 87.59±10.13% and 98.95±0.77%. For the eight finisher turkeys, a total of 2420 steps were seen by the video and the loggers recorded 2691 data points as steps. The finisher turkey logger data showed a mean sensitivity of 89.58±11.75%, mean false discovery rate of 14.73±10.66%, and average specificity of 99.81±0.19%. The finisher logger results had a mean precision of 85.27±10.66% and a mean accuracy of 99.73±0.13%. Although the loggers showed high sensitivity for detecting turkey steps under research settings, future research should try to reduce the loggers’ susceptibility to background noise, which would improve their performance for application in commercial conditions.

Trading shallow safety for deep sleep: juvenile green turtles select deeper resting sites as they grow

To better protect endangered green sea turtles Chelonia mydas, a more thorough understanding of the behaviors of each life stage is needed. Although dive profile analyses obtained using time-depth loggers have provided some insights into habitat use, recent work has shown that more fine-scale monitoring of body movements is needed to elucidate physical activity patterns. We monitored 11 juvenile green sea turtles with tri-axial acceleration data loggers in their foraging grounds in Dry Tortugas National Park, Florida, USA, for periods ranging from 43 to 118 h (mean ± SD: 72.8 ± 27.3 h). Approximately half of the individuals (n = 5) remained in shal- low (overall mean depth <2 m) water throughout the experiment, whereas the remaining individ- uals (n = 6) made excursions to deeper (4 to 27 m) waters, often at night. Despite these differences in depth use, acceleration data revealed a consistent pattern of diurnal activity and nocturnal rest- ing in most individuals. Nocturnal depth differences thus do not appear to represent differences in behavior, but rather different strategies to achieve the same behavior: rest. We calculated over- all dynamic body acceleration (ODBA) to assess the relative energetic cost of each behavioral strategy in an attempt to explain the differences between them. Animals in deeper water experi- enced longer resting dives, more time resting per hour, and lower mean hourly ODBA. These results suggest that resting in deeper water provides energetic benefits that outweigh the costs of transiting to deep water and a potential increased risk of predation.

Take-off performance of flying fish Cypselurus heterurus doederleini measured with miniature acceleration data loggers

Flying fish (Teleostei: Exocoetidae) glide at a speed considerably faster than they can travel in water. This phenomenon has been investigated and examined from taxonomic, anatom- ical, aerodynamic and biological standpoints through field observations. However, direct meas- urements of the flight performance of flying fish at the moment of leaping from the water surface have not previously been performed, due to the difficulty of monitoring gliding behavior. In the present study, we used recently developed data loggers capable of recording acceleration on a 3- dimensional axis to directly examine the gliding behavior of the flying fish Cypselurus heterurus doederleini under controlled conditions. Gliding behavior was assessed with the data logger fixed to the fish in 1 of 2 different positions, and positioning was not found to seriously affect leaping performance, as no effects on pitch angle, amplitude of fluctuation in swaying acceleration, stroke cycle frequency, or the duration of acceleration were observed. Pitch angle (20.0 ± 3.3°) and stroke cycle frequency (21.2 ± 4.6 Hz) were found to be lower in the present study than in previous stud- ies that examined gliding behavior in the field. Additionally, the flying fish were estimated to leap from the water surface at speeds of 3.9 to 5.2 m s �1 in our study, which is 38.7 to 51.5% of previ- ously reported maximum swimming speeds determined using stroboscopic filming. Our results suggest that the flying fish in our study may have recognized the capacity of the experimental space and regulated swimming performance before leaping from the water surface.

Tri-axial accelerometers tease apart discrete behaviours in the common cuttlefish Sepia officinalis

Acceleration data loggers can be used to construct time–energy budgets or identify specific behaviours in free living animals. Within a marine context such devices have been largely deployed on vertebrates with comparatively little attention paid to commercially important invertebrates such as cephalopod molluscs. Here we tested the utility of tri-axial accelerometers to tease apart six discrete behaviours in the common cuttlefish Sepia officinalis. By considering depth profiles in conjunction with body pitch and roll and overall dynamic body acceleration we were able to make distinctions between resting at the seabed, active swimming, mating, post-coital panting and active manoeuvring along the seabed.

Identifying foraging events in deep diving southern elephant seals, Mirounga leonina, using acceleration data loggers

Southern elephant seals (Mirounga leonina) range widely throughout the Southern Ocean and are associated with important habitats (e.g., ice edges, shelf) where they accumulate energy to fuel their reproductive efforts on land. Knowledge of the fine scale foraging behaviour used to garner this energy, however, is limited. For the first time, acceleration loggers were deployed on three adult southern elephant seals during a translocation study at Kerguelen Island. The aims of the study were to (1) identify prey capture attempts using 2-D accelerometer tags deployed on the head of southern elephant seals, (2) compare the number of foraging dives identified by simple dive depth profiles and accelerometer profiles and (3) compare dive characteristics between prey encounter and non-prey encounter dives. The 2-D loggers recorded depth every second, surge and heave accelerations at 8 or 16Hz and were carried for periods between 23 and 121h. Rapid head movements were interpreted to be associated with prey encounter events. Acceleration data detected possible prey encounter events in 39–52% of dives whilst 67–80% of dives were classified as foraging dives when using dive depth profiles alone. Prey encounters occurred in successive dives during days and nights and lasted between tenths of a second and 7.6min. Binomial linear mixed effect models showed that seals were diving significantly deeper and increased both descent rate and bottom duration when encountering prey. Dive duration, however, did not significantly increase during dives with prey encounters. These results are in accordance with optimal foraging theory, which predicts that deep divers should increase both their transit rates and the time spent at depth when a profitable prey patch is encountered. These findings indicate that this technique is promising as it more accurately detects possible prey encounter events compared with dive depth profiles alone and thus provides a better understanding of seal foraging strategies.

Detection of feeding behaviour in common carp Cyprinus carpio by using an acceleration data logger to identify mandibular movement

Miniaturized acceleration data loggers were attached to the lower mandible of common carp Cyprinus carpio to remotely identify feeding behaviour. Whether the acceleration signal could distinguish the quantity and quality of food was also investigated. The frequency and amplitude of the lower mandible stroke, calculated from surging acceleration determined by continuous wavelet transformation, significantly increased during the feeding period compared to that during the non-feeding period. These characteristic movement patterns were maintained for mean ±s.e. 187·3 ± 38·2 s when the fish were fed a single item of food and for mean ±s.e. 419·3 ± 28·6 s when they consumed multiple items. The dominant cycle and amplitude calculated according to feeding event duration, however, did not differ significantly between the two types of diets the fish consumed. Surging acceleration could detect mean ±s.e. 89·8 ± 13·5% of feeding events, although the false detection rate was mean ±s.e. 25·9 ± 10·9%. The results indicate that the mandible acceleration measurement method could be utilized to detect and record the feeding events in fishes that use a suction feeding mode similar to C. carpio.

Vertical movement of dolphinfish Coryphaena hippurus as recorded by acceleration data-loggers in the northern East China Sea

Environmental changes influence foraging behavior for most animals. Dolphinfish, Coryphaena hippurus, are epipelagic predators and have a cosmopolitan tropical to warm-temperate (>20°C) distribution. We simultaneously obtained the ambient temperature and the foraging behavior (i.e., swimming speed, depth and tailbeat acceleration) of dolphinfish, using an acceleration data-logger in May, September, October, November 2007, June 2008, May and July 2010 for 8 individuals. Although the dolphinfish spent a mean ± standard deviation of 43.4 ± 27.7% of their time at the surface (0–5 m), dive excursions from the surface (DES) were observed in all individuals and maximum DES depths ranged from 50.1 to 95.4 m. DES events resulted dives below the thermocline for these dolphinfish, and there was a significantly positive relationship between the isothermal layer depth (ILD) and DES depth. Our results demonstrate that dolphinfish avoided the rapid thermal change beyond the thermocline, and their prey is most likely found in the upper layers of the thermocline. Gliding behavior during the DES phase was also observed and dolphinfish gradually descended to deeper waters with gliding. The gliding time was longer when the ILD was deeper, and fish tended to dive deeper. We suggest that dolphinfish adopt gliding behavior to search a broader range of depths for prey, while minimizing energy use.

Assessing the Validity of the Accelerometry Technique for Estimating the Energy Expenditure of Diving Double-Crested CormorantsPhalacrocorax auritus

Over the past few years, acceleration-data loggers have been used to provide calibrated proxies of energy expenditure: the accelerometry technique. Relationships between rate of oxygen consumption and a derivation of acceleration data termed "overall dynamic body acceleration" (ODBA) have now been generated for a range of species, including birds, mammals, and amphibians. In this study, we examine the utility of the accelerometry technique for estimating the energy expended by double-crested cormorants Phalacrocorax auritus to undertake a dive cycle (i.e., a dive and the subsequent pause at the surface before another dive). The results show that ODBA does not calibrate with energy expenditure in diving cormorants, where energy expenditure is calculated from measures of oxygen uptake during surface periods between dives. The possible explanations include reasons why energy expenditure may not relate to ODBA but also reasons why oxygen uptake between dives may not accurately represent energy expenditure during a dive cycle.

Underwater and surface behavior of homing juvenile northern elephant seals

Northern elephant seals, Mirounga angustirostris, travel between colonies along the west coast of North America and foraging areas in the North Pacific. They also have the ability to return to their home colony after being experimentally translocated. However, the mechanisms of this navigation are not known. Visual information could serve an important role in navigation, either primary or supplementary. We examined the role of visual cues in elephant seal navigation by translocating three seals and recording their heading direction continuously using GPS, and acceleration and geomagnetic data loggers while they returned to the colony. The seals first reached the coast and then proceeded to the colony by swimming along the coast. While underwater the animals exhibited a horizontally straight course (mean net-to-gross displacement ratio=0.94±0.02). In contrast, while at the surface they changed their headings up to 360 deg. These results are consistent with the use of visual cues for navigation to the colony. The seals may visually orient by using landmarks as they swim along the coast. We further assessed whether the seals could maintain a consistent heading while underwater during drift dives where one might expect that passive spiraling during drift dives could cause disorientation. However, seals were able to maintain the initial course heading even while underwater during drift dives where there was spiral motion (to within 20 deg). This behavior may imply the use of non-visual cues such as acoustic signals or magnetic fields for underwater orientation.