Proceedings of the workshop: Static Acoustic Monitoring of Cetaceans, held at the 20th Annual Meeting of the European Cetacean Society, Gdynia, Poland, 2nd April 2006 (original) (raw)
Acoustic dataloggers are used for monitoring the occurrence of cetaceans and can aid in fulfilling statutory monitoring requirements of protected species. Although useful for long-term monitoring, their spatial coverage is restricted, and for many devices the effective detection distance is not specified. A generalized additive mixed model (GAMM) was used to investigate the effects of (1) distance from datalogger, (2) animal behavior (feeding and traveling), and (3) group size on the detection probability of bottlenose dolphins (Tursiops truncatus) with autonomous dataloggers (C-PODs) validated with visual observations. The average probability of acoustic detection for minutes with a sighting was 0.59 and the maximum detection distance ranged from 1343-1779 m. Minutes with feeding activity had higher acoustic detection rates and longer average effective detection radius (EDR) than traveling ones. The detection probability for single dolphins was significantly higher than for groups, indicating that their acoustic behavior may differ from those of larger groups in the area, making them more detectable. The C-POD is effective at detecting dolphin presence but the effects of behavior and group size on detectability create challenges for estimating density from detections as higher detection rate of feeding dolphins could yield erroneously high density estimates in feeding areas.
Journal of the Marine Biological Association of the United Kingdom, 2010
Acoustic dataloggers are used for monitoring the occurrence of cetaceans and can aid in fulfilling statutory monitoring requirements of protected species. Although useful for long-term monitoring, their spatial coverage is restricted, and for many devices the effective detection distance is not specified. A generalized additive mixed model (GAMM) was used to investigate the effects of (1) distance from datalogger, (2) animal behavior (feeding and traveling), and (3) group size on the detection probability of bottlenose dolphins (Tursiops truncatus) with autonomous dataloggers (C-PODs) validated with visual observations. The average probability of acoustic detection for minutes with a sighting was 0.59 and the maximum detection distance ranged from 1343-1779 m. Minutes with feeding activity had higher acoustic detection rates and longer average effective detection radius (EDR) than traveling ones. The detection probability for single dolphins was significantly higher than for groups, indicating that their acoustic behavior may differ from those of larger groups in the area, making them more detectable. The C-POD is effective at detecting dolphin presence but the effects of behavior and group size on detectability create challenges for estimating density from detections as higher detection rate of feeding dolphins could yield erroneously high density estimates in feeding areas.
Passive acoustic monitoring of habitat use by bottlenose dolphins in Doubtful Sound
2011
In the context of testing the appropriateness of current conservation management, this study used nine moored acoustic monitoring devices (T-PODs) to monitor habitat use by bottlenose dolphins in Doubtful Sound, New Zealand, and identify current critical habitats.! Static acoustic monitoring offers several advantages over visual surveys, including detection of submerged animals, non-invasiveness, long-term 24 hour coverage, lower expense and reduced dependence on calm weather. T-PODs are relatively new devices however, and required investigation of their performance and limitations. T-POD frequency settings were found to significantly influence detection ability. The A/B filter settings of 50/30, 70/30 and 90/30 (kHz) were found most effective. The maximum range of bottlenose dolphin detection was measured at 1313m. Dolphin detection rate and probability both declined with distance from T-POD. The conservative nature of T-PODs was highlighted as only 47% of bottlenose dolphin groups were detected when within 500m of T-POD. The effective detection radius (EDR: range at which all groups can be assumed to be detected) was calculated to be 266m (95% CI; 222m-317m). Detailed inspection of T-POD data files allowed identification of foraging echolocation trains, which were used to define parameters to identify 'buzzes'; a unique echolocation signal used when capturing prey. Click trains with interclick-intervals between 18-2 ms and >20clicks were defined as foraging. These foraging parameters, when tested on a new sample of T-POD data, positively identified 92% of visually identified foraging trains. Nine separate T-POD sites within Doubtful Sound were acoustically monitored for twelve months from 1 st April 2009. Foraging behaviour was not focused in particular sites, suggesting opportunistic foraging strategies are employed by the population. Foraging and encounter rates, among all T-POD sites, were significantly higher during diel phases dusk and dawn, compared to day and night. T-POD data showed that dolphin use of the fiord varies seasonally with inner fiord sites being used most in summer and autumn, and outer fiord sites in winter and spring. Seasonal dolphin presence was positively correlated with surface water temperature. Seasonal trends from this study were consistent with previous studies, highlighting Crooked Arm (site D), Hall Arm (site B) and 'The Crossing' (site E) as most critical. Habitat use data gained in this study suggested that the current Dolphin Protection Zones, in which boat activity is voluntarily limited, do not provide adequate protection for the population. Seasonal variation in the scope of the DPZ, additional no boat zones and extensions to current DPZs are proposed for reassessed critical areas. These modifications are seen as necessary for effective conservation management, whilst being practical for Doubtful Sound stakeholders.
Listening for a needle in a haystack: passive acoustic detection of dolphins at very low densities
Endangered Species Research, 2011
Passive acoustic surveys have potential for detecting trends in abundance and habitat use by rare cetaceans. We deployed commercially available acoustic data loggers (T-PODs) in 4 harbours on the west coast of New Zealand's North Island between 2005 and 2008 to investigate the distribution of Maui's dolphin Cephalorhynchus hectori maui and assess whether current protection measures are sufficient. A set of decision rules was developed to minimise the potential for false positive detections. Over 3211 'T-POD days' of acoustic monitoring, 39 click trains which satisfied all of our decision rules were detected, indicating the presence of Maui's dolphins in Manukau and Kaipara Harbours. Data from the site with the most detections were fitted to 3 models, showing that the number of detections varied temporally (p < 0.001). The models were also used to show to what degree dolphins could have been present at monitored locations yet remain undetected. The study highlighted the challenges of passive acoustic monitoring of rare species, particularly of small delphinids in an environment which is both physically and acoustically challenging. Nonetheless, we demonstrated that T-PODs are effective in studies of Maui's dolphin distribution, that Maui's dolphins are found in North Island harbours and remain at risk from gillnet bycatch. We make a number of recommendations concerning acoustic monitoring studies of rare cetaceans, principally that a thorough understanding of the target signals and the acoustic environment being monitored is essential for maximising acoustic detection rates.
Journal of the Marine Biological Association of the United Kingdom, 2009
Acoustic surveys can have several advantages over visual methods in surveys of cetaceans, although verification is required that novel techniques are effective. The T-POD is an autonomous acoustic data logger with inbuilt filters that can be set to match the click characteristics of the target species. We tested the performance of the T-POD for detecting Hector's dolphins at Flea Bay, Banks Peninsula, New Zealand. Simultaneous visual surveys were conducted from a hillside overlooking the bay, with distances between the T-POD and dolphins measured using a theodolite. Wideband sound recordings confirmed that T-POD detections were echolocation clicks made by Hector's dolphins. Detection probability and click train detection rate decreased with increasing distance, with no detections made beyond 500 m. By fitting detection functions to the probability of detection versus distance we showed that the T-POD effectively detected all dolphin groups within a radius of 198 -239 m, depending on the click train categories utilized. The T-POD shows considerable promise as a tool for passive acoustic surveys of Hector's dolphins, with possible applications in studies of distribution, habitat use and echolocation behaviour.
The Journal of the Acoustical Society of America, 2010
Spectral parameters were used to discriminate between echolocation clicks produced by three dolphin species at Palmyra Atoll: melon-headed whales ͑Peponocephala electra͒, bottlenose dolphins ͑Tursiops truncatus͒ and Gray's spinner dolphins ͑Stenella longirostris longirostris͒. Single species acoustic behavior during daytime observations was recorded with a towed hydrophone array sampling at 192 and 480 kHz. Additionally, an autonomous, bottom moored High-frequency Acoustic Recording Package ͑HARP͒ collected acoustic data with a sampling rate of 200 kHz. Melon-headed whale echolocation clicks had the lowest peak and center frequencies, spinner dolphins had the highest frequencies and bottlenose dolphins were nested in between these two species. Frequency differences were significant. Temporal parameters were not well suited for classification. Feature differences were enhanced by reducing variability within a set of single clicks by calculating mean spectra for groups of clicks. Median peak frequencies of averaged clicks ͑group size 50͒ of melon-headed whales ranged between 24.4 and 29.7 kHz, of bottlenose dolphins between 26.7 and 36.7 kHz, and of spinner dolphins between 33.8 and 36.0 kHz. Discriminant function analysis showed the ability to correctly discriminate between 93% of melon-headed whales, 75% of spinner dolphins and 54% of bottlenose dolphins.
PLOS ONE
This study investigates the bottlenose dolphin (Tursiops truncatus, Montagu 1821) habitat use in the Portofino marine protected area (NW Italy) and adjacent waters, a core area for the dolphins and a highly touristic area in the Mediterranean Sea. A permanent automated real-time passive acoustic monitoring system, able to detect and track dolphins continuously, was tested in the area within the activities of the Life+ Nature project ARION. The habits of bottlenose dolphins was investigated considering the resident rate inside the area, which quantifies the amount of time dolphins spent in these waters, by means of random forest regression. The dependency of dolphin resident rate was analyzed in relation to four explanatory variables: sea surface temperature, season, time of day, and proximity to the coast. Dolphins spent more time in the area during spring and when sea surface temperature ranged between 15-16˚C. Summer resulted the season with lower dolphin residency with significant difference between working day and weekend, in the last the lowest residency was recorded. Main findings provide important information to properly manage the area in order to protect bottlenose dolphins.
PLoS ONE, 2014
Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability. We used a combined visual-acoustic survey to estimate detectability of Ganges River dolphins (Platanista gangetica gangetica) in four waterways of southern Bangladesh. The combined visual-acoustic survey resulted in consistently higher detectability than a single observer-team visual survey, thereby improving power to detect trends. Visual detectability was particularly low for dolphins close to meanders where these habitat features temporarily block the view of the preceding river surface. This systematic bias in detectability during visual-only surveys may lead researchers to underestimate the importance of heavily meandering river reaches. Although the benefits of acoustic surveys are increasingly recognised for marine cetaceans, they have not been widely used for monitoring abundance of freshwater cetaceans due to perceived costs and technical skill requirements. We show that acoustic surveys are in fact a relatively costeffective approach for surveying freshwater cetaceans, once it is acknowledged that methods that do not account for imperfect detectability are of limited value for monitoring.
Marine Mammal Science, 2014
We evaluated the performance of dolphin echolocation detectors (C-PODs) in the New River, North Carolina, by ground-truthing echolocation detections with digital acoustic recordings. We deployed C-PODs at three sites for a total of 204 monitoring hours. We also performed detection range trials at two sites where water depths ranged from 1.0 to 4.5 m. We used Detection Positive Minutes (DPMs), minutes of C-POD recordings that contained at least one echolocation click train, to indicate the presence of at least one dolphin. The C-PODs performed well in detecting dolphin click trains, although all units performed conservatively by failing to detect some echolocation events and therefore underestimated the true occurrence of dolphins. C-PODs reported only a small number of false detections, as indicated by low false positive rates ranging between 1% and 4% for individual units. Overall, C-PODs performed with a high accuracy (72%-91%) and detected echolocation at a distance of at least 933 m. We conclude that C-PODs hold considerable promise in future monitoring studies of this species, but recommend a careful study design especially in complex, coastal environments.
Journal of the Marine Biological Association of the United Kingdom, 2011
Autonomous acoustic data loggers can provide useful data on habitat use and activity patterns of vocalizing cetaceans. One type, the T-POD, uses filters that can be set to match the click characteristics of the target species. We used wideband acoustic recordings to document typical click spectra of bottlenose dolphins in Doubtful Sound, New Zealand, in order to develop T-POD settings optimal for that population. T-PODs at these settings made between 8 and 33 times as many detections as accompanying T-PODs set as in other studies of this species, confirming the value of optimizing settings for a particular dolphin population. Maximum detection range was 1313 m, and mean range of first detection was 593 m. Of 45 groups observed within 500 m of the T-POD, 47% were detected acoustically. Effective detection radius was estimated at 266 m (95% CI 222–317 m).
2004
This paper examines the data for common dolphins collected during a general double-platform line transect cetacean survey carried out in waters around the Faroe Islands in 1995 (from southeastern Iceland to western Ireland) in order to determine the extent to which a correction factor can be estimated to account for animals missed on the trackline and for responsive movement towards the vessel. A major assumption of conventional distance-based methods is that all objects at zero distance from the line are detected (i.e. g(0)=1). If this assumption is violated the estimated density and hence abundance will be negatively biased. It also assumes that animals do not respond to the survey vessel before they are detected by the observers. If the animals are attracted to the vessel, for example, this will result in a positively biassed estimate. The g(0) estimate was obtained using the method of Borchers et al. (1998). Visual inspection of the data suggested that the dolphins were attracted to the vessel and this was accounted for following the Buckland and Turnock (1992) approach. Coefficients of variation (CVs) and confidence intervals (CIs) were estimated using a non-parametric bootstrap procedure. During the survey, almost 1,700 n.miles were sailed on primary research effort. There were 153 common dolphin sightings including 52 duplicates. The chosen model for the detection function incorporated perpendicular distance, group size and Beaufort sea state. The resulting estimate of g(0) was 0.7961 (CV=0.14). Density estimates obtained under an assumption of no responsive movement are almost six times higher than when it is taken into account, highlighting the importance of collecting appropriate data to allow analysis of this potential problem in cetacean surveys.
Changes in whistle parameters of two common bottlenose dolphin ecotypes as a result of the physical presence of the research vessel, 2022
In the presence of vessels, dolphins have been found to change their habitat, behavior, group composition and whistle repertoire. The modification of the whistle parameters is generally considered to be a response to the engine noise. Little is known about the impact of the physical presence of vessels on dolphin acoustics. Whistle parameters of the coastal and oceanic ecotypes of common bottlenose dolphins in La Paz Bay, Mexico, were measured after the approach of the research vessel and its engine shutdown. Recordings of 10 min were made immediately after turning off the engine. For analysis, these recordings were divided from minute 0 to minute 5, and from minute 5:01 to minute 10. The whistles of the oceanic ecotype showed higher maximum, minimum and peak frequency in the second time interval compared to the first one. The whistle rate decreased in the second time interval. The whistles of the coastal ecotype showed no difference between the two time intervals. The physical presence of the research vessel could have induced a change in the whistle parameters of the oceanic dolphins until habituation to the vessel disturbance. The oceanic ecotype could increase the whistle rate and decrease the whistle frequencies to maintain acoustic contact more frequently and for longer distances. The coastal ecotype, showing no significant changes in the whistle parameters, could be more habituated to the presence of vessels and display a higher tolerance.
Using T-PODs to investigate the echolocation of coastal bottlenose dolphins
Journal of the Marine …, 2007
Using T-PODs to investigate the echolocation of coastal bottlenose dolphins We investigated the feasibility of using a T-POD, a passive acoustic dolphin detector system, to monitor bottlenose dolphins in the Shannon Estuary, Ireland, from 27 June to 18 August 2005. A v.3 T-POD, logging alternate minutes, was moored in view of an observation site. Land-based theodolite tracking was used to record the position of the closest animal, school size and activity of the closest dolphin school to the T-POD. All cetacean detections on the T-POD synchronous with shore watches in sea states ≤2 were analysed. A total of 94 schools were observed at distances up to 8000 m from the observer. Acoustic detections corresponded well with visual detections, with 82% of the dolphin schools observed within 500 m of the T-POD detected acoustically. The furthest distance dolphins were observed from the T-POD during periods of acoustic detection was 1246 m. Twelve acoustic encounters were logged without corresponding visual detections, four of which may represent false positives. School size did not affect the acoustic detectability of the dolphins, as there was no difference in the size of schools observed with or without corresponding acoustic detections (Kruskal-Wallis, P=0.64). Similarly no relationship was found between acoustic detections and school sizes at different distances to the T-POD (linear regression P=0.5, r 2 =0.01). Acoustic encounters did not vary in relation to diel patterns (Mann-Whitney, P=0.13) but were related to tidal state (χ 2 =40.2, P=0.00, df=11) with more encounters logged in the 4 h after high water, probably reflecting prey-related changes in habitat use. T-POD detections correlated well with visual observations and although detection is likely to vary according to T-POD specification, sensitivity and the conditions at the deployment site, the T-POD is a useful tool that has been shown to offer the possibility of continuous monitoring, something that is difficult to achieve with visual methods alone.
The Journal of the Acoustical Society of America, 2008
The spectral and temporal properties of echolocation clicks and the use of clicks for species classification are investigated for five species of free-ranging dolphins found offshore of southern California: short-beaked common !Delphinus delphis", long-beaked common !D. capensis", Risso's !Grampus griseus", Pacific white-sided !Lagenorhynchus obliquidens", and bottlenose ! Tursiops truncatus" dolphins. Spectral properties are compared among the five species and unique spectral peak and notch patterns are described for two species. The spectral peak mean values from Pacific white-sided dolphin clicks are 22.2, 26.6, 33.7, and 37.3 kHz and from Risso's dolphins are 22.4, 25.5, 30.5, and 38.8 kHz. The spectral notch mean values from Pacific whitesided dolphin clicks are 19.0, 24.5, and 29.7 kHz and from Risso's dolphins are 19.6, 27.7, and 35.9 kHz. Analysis of variance analyses indicate that spectral peaks and notches within the eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. frequency band 24-35 kHz are distinct between the two species and exhibit low variation within each species. Post hoc tests divide Pacific white-sided dolphin recordings into two distinct subsets containing different click types, which are hypothesized to represent the different populations that occur within the region. Bottlenose and common dolphin clicks do not show consistent patterns of spectral peaks or notches within the frequency band examined !1-100 kHz".
Endangered Species Research, 2009
The 4 dolphin species in the genus Cephalorhynchus have small populations, restricted distributions and are threatened by anthropogenic activities. It is therefore essential that tools be developed for assessing these threats and the effects of management actions. The T-POD is a commercially available acoustic data logger. We evaluated the efficacy of the T-POD for addressing habitat use questions relevant to management by passive acoustic monitoring of Hector's dolphins C. hectori in the Banks Peninsula Marine Mammal Sanctuary (BPMMS), New Zealand. Three T-PODs were deployed at 3 inshore locations in summer and winter over a 2 yr period (n = 431 d). Acoustic detection data were summarised by detection-positive minutes per day. A linear regression model indicated that season had the largest effect on detection rate (F = 81.95, p < 0.001), with T-POD ID (i.e. variation in sensitivity between individual instruments) also having a significant effect (F = 9.45, p < 0.001). There was no significant difference between acoustic detection rates at night and during the day (paired t-test, t = 0.55, p = 0.59). The present study provides further evidence to support the yearround ban on all gill netting within the BPMMS. We demonstrated that T-PODs can be used to investigate temporal differences in habitat use by Cephalorhynchus dolphins. However, several issues must be considered when designing such experiments; namely the mode of deployment, accounting for variation in sensitivity between individual T-PODs and the possibility of false positive detections from non-target species.
Use of Active Sonar for Cetacean Conservation and Behavioral-Ecology Studies: A Paradox?
The relationship between low frequency military sonar use and some whale stranding events has attracted negative attention towards the use of active sonar in the marine environment. As a consequence, there has been only limited use of active acoustic techniques by marine mammal researchers. Instead more attention has been given to the development and use of passive acoustic methods for the detection of cetaceans. Nevertheless there is great potential for the use of active acoustic systems in ecological studies, and studies aimed at improving conservation of whales and dolphins in their natural environment: active acoustic techniques can be used for the good of cetaceans, and should not just be considered a source of disturbance. We evaluated the capability of various acoustic systems - systems that are used commonly in fisheries research - to detect and track cetaceans underwater. We collected data initially with standard scientific echosounders (SIMRAD EK500) from moving vessels an...
Aquatic Mammals, 2011
Static acoustic monitoring is a cost-effective, low-effort means of gathering large datasets on echolocation click characteristics and habitat use by odontocetes. Heaviside's dolphins (Cephalorhynchus heavisidii) were monitored using an acoustic monitoring unit, the T-POD, in July 2008 at a site of known high abundance for this species in Walvis Bay, Namibia. The T-POD successfully detected clicks from Heaviside's dolphins, and these clicks were detected in the 120 to 140 kHz frequency range. A distinct diel pattern to the hourly mean inter-click interval was observed, with higher values during daylight hours than at night, suggesting that click trains are produced at faster rates at night time. There was no apparent diel pattern in the proportion of buzz trains produced, however. A diel pattern in click activity was observed, with many more detection-positive minutes per hour recorded between dusk and dawn, and vocalization activity dropping to low levels in the middle of the day. This corresponded with visual observations made on abundance of dolphins in the study area. These results suggest that Heaviside's dolphins use this site primarily during the night. Static acoustic monitoring proved to be an effective technique for monitoring patterns of habitat use by Heaviside's dolphins.
Marine Mammal Science, 2004
Active-acoustic surveys were used to determine the distribution of dusky dolphins and potential prey in two different New Zealand locations. During seven survey days off Kaikoura Canyon, dusky dolphins were found within the Deep-Scattering Layer (DSL) at 2000 when it rose to within 125 m of the surface. As the DSL rose to 30 m at 0100, the observed depth of dolphins decreased, presumably as the dolphins followed the vertical migration of their prey. Acoustically identified subgroups of coordinated animals ranged from one to five dolphins. Time, depth of layer, and layer variance contributed significantly to predicting foraging dusky dolphin subgroup size. In the much shallower and more enclosed Admiralty Bay, dolphins noted at the surface as foraging were always detected with the sonar, but were never observed in coordinated subgroups during the brief (two-day) study there. In Admiralty Bay dolphin abundance was correlated with mean volume scattering from potential prey in the water column; and when volume scattering, an index of prey density, was low, dolphins were rarely present. Ecological differences between the deep waters of Kaikoura Canyon and the shallow nearshore waters of Admiralty Bay may result in differences in how, when, and in what social groupings dusky dolphins forage.
Marine Environmental Research, 2006
Small cetacean bycatch in gillnet fisheries may be reduced by deterring odontocetes from nets acoustically. However, different odontocete species may respond differently to acoustic signals from alarms. Therefore, in this study a striped dolphin and a harbour porpoise were subjected simultaneously to sounds produced by the XP-10 experimental acoustic alarm. The alarm produced 0.3 s tonal signals randomly selected from a set of 16 with fundamental frequencies between 9 and 15 kHz, with a constant pulse interval of 4.0 s (duty cycle 8%) and a Source Level range of 133-163 dB re 1 lPa (rms). The effect of the alarm was judged by comparing the animals' respiration rate and position relative to the alarm during test periods with those during baseline periods. As in a previous study on two porpoises with the same alarm, the porpoise in the present study reacted strongly to the alarm by swimming away from it and increasing his respiration rate. The striped dolphin, however, showed no reaction to the active alarm. Based on harbour porpoise audiograms and the specific audiogram of the striped dolphin in the present study, and the low background noise levels during the experiment, both animals must have heard the alarm signals clearly. This study indicates that cetacean species are not equally sensitive to human-made noise disturbance. Therefore, source 0141-1136/$ -see front matter Ó
Dolphin-Watching Boats Affect Whistle Frequency Modulation in Bottlenose Dolphins
Frontiers in Marine Science
Bottlenose dolphins’ whistles are key in social communication, conveying information about conspecifics and the environment. Therefore, their study can help to infer habitat use and identify areas of concern due to human activities. Here we studied the whistles of bottlenose dolphins (Tursiops truncatus) in two sites of the archipelago of Bocas del Toro, Panama, that contrast in boat traffic. Almirante Bay is a site dominated by taxi-boats and Dolphin Bay is a major location for boat-based dolphin watching. Recordings were made using bottom-mounted hydrophones and from the research boat using an over-the-side hydrophone and a broadband recording system. A total recording effort time of 1,726 h was analyzed. Our results show significant differences in boat detection between sites, and a higher number of whistles detected per minute in the site with tour-boat traffic. Furthermore, whistle modulation accounted for most of the differences between sites, boat presence, and whistle types....