Deep learning algorithm outperforms experienced human observer at detection of blue whale D‐calls: a double‐observer analysis

Abstract An automated algorithm for passive acoustic detection of blue whale D‐calls was developed based on established deep learning methods for image recognition via the DenseNet architecture. The detector was trained on annotated acoustic recordings from the Antarctic, and performance of the detector was assessed by calculating precision and recall using a separate independent dataset also from the Antarctic. Detections from both the human analyst and automated detector were then inspected by an independent judge to identify any calls missed by either approach and to adjudicate whether the apparent false‐positive detections from the automated approach were actually true positives. A final performance assessment was conducted using double‐observer methods (via a closed‐population Huggins mark–recapture model) to assess the probability of detection of calls by both the human analyst and automated detector, based on the assumption of false‐positive‐free adjudicated detections. According to our double‐observer analysis, the automated detector showed superior performance with higher recall and fewer false positives than the original human analyst, and with performance similar to existing top automated detectors. To understand the performance of both detectors we inspected the time‐series and signal‐to‐noise ratio (SNR) of detections for the test dataset, and found that most of the advantages from the automated detector occurred at low and medium SNR

Diel patterns of fin whale 20 Hz acoustic presence in Eastern Antarctic waters

This study presents evidence of diel patterns in fin whale (Balaenoptera physalus) 20 Hz acoustic presence in Eastern Antarctic waters. Passive acoustic recordings were collected at four sites in Eastern Antarctica from 2013 to 2019. A generalized linear model fitted by a generalized estimating equation was used to test the hypothesis that fin whale 20 Hz acoustic presence shows significant variation between light regimes dawn, day, dusk and night. In the Indian sector of Antarctica, at the Prydz and Southern Kerguelen Plateau sites, fin whale acoustic presence was significantly more common during the night and dawn before declining during the day and dusk periods. A different diel pattern was observed in the Pacific sector, at the Dumont d'Urville site: fin whale acoustic presence was significantly more common during the day than dusk and night periods. No diel pattern was identified at the Casey site. The identified diel patterns in the Indian sector of Eastern Antarctica correlate with previously identified diel patterns of the fin whales' prey. We suggest an indirect association between fin whale acoustic presence and foraging, with the animals more likely to produce the 20 Hz pulse during the night when not foraging and less likely to vocalize when foraging during the day

Seasonal Distribution of the Fin Whale (Balaenoptera physalus) in Antarctic and Australian Waters Based on Passive Acoustics

The fin whale is listed as globally vulnerable, with ongoing threats to their population, yet little is known about the distribution and movements of the Southern Hemisphere sub-species, Balaenoptera physalus quoyi. This study assesses fin whale distribution in the Southern Hemisphere analysing acoustic recordings from 15 locations in Antarctic and Australian waters from 2002 to 2019. A seasonal acoustic presence of fin whales in Antarctic waters from late austral summer to autumn (February to June) with long-term, consistent annual usage areas was identified at the Southern Kerguelen Plateau and Dumont d’Urville sites. In comparison, limited vocal presence of fin whales was observed at the Casey site. In Australian waters, fin whales were seasonally present from austral autumn to mid-spring (May to October) on east and west coasts, with a decadal pattern of acoustic presence observed at Cape Leeuwin, WA. Two migratory pathways are identified, from the Indian sector of Antarctica to the west coast of Australia and from the Pacific sector of Antarctica to the east coast of Australia. The identified seasonal distributions and migratory pathways provide valuable information to aid in monitoring the recovery of this vulnerable sub-species. We suggest the identified distribution and dispersal from the Southern Kerguelen Plateau and Dumont d’Urville sites to the west and east coasts of Australia respectively, as well as the spatial separation between Antarctic sites, provide preliminary evidence of separate sub-populations of the Southern Hemisphere sub-species of fin whale