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)
Related papers
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).