Spatio-temporal variation in click production rates of beaked whales: Implications for passive acoustic density estimation

Warren, Victoria E.; Marques, Tiago A.; Harris, David O.; Thomas, Len; Tyack, Peter L.; Soto, Natacha Aguilar de; Hickmott, Leigh S.; Johnson, Mark

doi:10.1121/1.4978439

Cited by 32 publications

(23 citation statements)

References 57 publications

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“…As the number of detections per bin increased, click trains tended to become interleaved, resulting in higher numbers of low ICIs. While true ICIs from a single animal’s click train may be a species-specific feature [ 26 ], the interval between clicks received from multiple individuals’ trains is not informative. Similarly, high false positive rates associated with snapping shrimp at site MP affected ICI distributions.…”

Section: Discussionmentioning

confidence: 99%

Automated classification of dolphin echolocation click types from the Gulf of Mexico

et al. 2017

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Delphinids produce large numbers of short duration, broadband echolocation clicks which may be useful for species classification in passive acoustic monitoring efforts. A challenge in echolocation click classification is to overcome the many sources of variability to recognize underlying patterns across many detections. An automated unsupervised network-based classification method was developed to simulate the approach a human analyst uses when categorizing click types: Clusters of similar clicks were identified by incorporating multiple click characteristics (spectral shape and inter-click interval distributions) to distinguish within-type from between-type variation, and identify distinct, persistent click types. Once click types were established, an algorithm for classifying novel detections using existing clusters was tested. The automated classification method was applied to a dataset of 52 million clicks detected across five monitoring sites over two years in the Gulf of Mexico (GOM). Seven distinct click types were identified, one of which is known to be associated with an acoustically identifiable delphinid (Risso’s dolphin) and six of which are not yet identified. All types occurred at multiple monitoring locations, but the relative occurrence of types varied, particularly between continental shelf and slope locations. Automatically-identified click types from autonomous seafloor recorders without verifiable species identification were compared with clicks detected on sea-surface towed hydrophone arrays in the presence of visually identified delphinid species. These comparisons suggest potential species identities for the animals producing some echolocation click types. The network-based classification method presented here is effective for rapid, unsupervised delphinid click classification across large datasets in which the click types may not be known a priori.

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Section: Discussionmentioning

confidence: 99%

Automated classification of dolphin echolocation click types from the Gulf of Mexico

et al. 2017

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“…There are four deep diving cetacean species that have sufficient acoustic tag data to estimate the percentage of their dive cycle spent echolocating. They are: Blainville's beaked whale (17%), Cuvier's beaked whale (26%), Risso's dolphin (51%) and sperm whale (67%) (Watwood et al, 2006;Arranz et al, 2016;Warren et al, 2017). It appears that beaked whales are prone to echolocation a smaller percentage of the time than either sperm whales or Risso's dolphin.…”

Section: Vocal Activitymentioning

confidence: 99%

“…Based on these options for comparison we find Blainville's beaked whale (Mesoplodon densirostris, Md) as the best analog for Kogia given the similarity of their moderate dive depths, small group sizes and stealthy behavior. The proportion of time Kogia spent clicking was estimated from Blainville's beaked whale tag data collected in the Bahamas (Warren et al, 2017) since their respective lengths (4.7 m Md and 3.8 m Kb) and weights (∼1000 kg Md and ∼450 kg Kb) are more similar than for other beaked whale species, and they are presumed to have similar diving behavior. The mean vocal (echolocating) proportion of the Md dive cycle P cyc was used as a proxy for the proportion of vocally active one-min bins used in groupbased density estimates.…”

Section: Vocal Activitymentioning

confidence: 99%

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Assessing Seasonality and Density From Passive Acoustic Monitoring of Signals Presumed to be From Pygmy and Dwarf Sperm Whales in the Gulf of Mexico

et al. 2019

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Pygmy sperm whales (Kogia breviceps) and dwarf sperm whales (Kogia sima) are deep diving cetaceans that commonly strand along the coast of the southeast US, but that are difficult to study visually at sea because of their elusive behavior. Conventional visual surveys are thought to significantly underestimate the presence of Kogia and they have proven difficult to approach for tracking and tagging. An approach is presented for density estimation of signals presumed to be from Kogia spp. based on passive acoustic monitoring data collected at sites in the Gulf of Mexico (GOM) from the period following the Deepwater Horizon oil spill (2010-2013). Both species of Kogia are known to inhabit the GOM, although it is not possible to acoustically separate the two based on available knowledge of their echolocation clicks. An increasing interannual density trend is suggested for animals near the primary zone of impact of the oil spill, and to the southeast of the spill. Densities were estimated based on both counting individual echolocation clicks and counting the presence of groups of animals during one-min time windows. Densities derived from acoustic monitoring at three sites are all substantially higher (4-16 animals/1000 km 2) than those that have been derived for Kogia from line transect visual surveys in the same region (0.5 animals/1000 km 2). The most likely explanation for the observed discrepancy is that the visual surveys are underestimating Kogia spp. density, due to the assumption of perfect detectability on the survey trackline. We present an alternative approach for density estimation, one that derives echolocation and behavioral parameters based on comparison of modeled and observed sound received levels at sites of varying depth.

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“…These models also allow us to determine if periods of silence are increased as an anti-jamming response, via a reduction in click rates per dive. Since our data contained multiple observations per individual, generalized estimation equations (GEEs) were fitted in R [34][35][36][37] with package geepack [38] using foraging dive as the sampling unit and tag deployment as the clustering factor. Click and buzz rates per foraging dive were the response variables in separate models with group size as the predictor variable.…”

Section: Methodsmentioning

confidence: 99%

Deep-diving beaked whales dive together but forage apart

et al. 2021

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Echolocating animals that forage in social groups can potentially benefit from eavesdropping on other group members, cooperative foraging or social defence, but may also face problems of acoustic interference and intra-group competition for prey. Here, we investigate these potential trade-offs of sociality for extreme deep-diving Blainville′s and Cuvier's beaked whales. These species perform highly synchronous group dives as a presumed predator-avoidance behaviour, but the benefits and costs of this on foraging have not been investigated. We show that group members could hear their companions for a median of at least 91% of the vocal foraging phase of their dives. This enables whales to coordinate their mean travel direction despite differing individual headings as they pursue prey on a minute-by-minute basis. While beaked whales coordinate their echolocation-based foraging periods tightly, individual click and buzz rates are both independent of the number of whales in the group. Thus, their foraging performance is not affected by intra-group competition or interference from group members, and they do not seem to capitalize directly on eavesdropping on the echoes produced by the echolocation clicks of their companions. We conclude that the close diving and vocal synchronization of beaked whale groups that quantitatively reduces predation risk has little impact on foraging performance.

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Spatio-temporal variation in click production rates of beaked whales: Implications for passive acoustic density estimation

Cited by 32 publications

References 57 publications

Automated classification of dolphin echolocation click types from the Gulf of Mexico

Automated classification of dolphin echolocation click types from the Gulf of Mexico

Assessing Seasonality and Density From Passive Acoustic Monitoring of Signals Presumed to be From Pygmy and Dwarf Sperm Whales in the Gulf of Mexico

Deep-diving beaked whales dive together but forage apart

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