Fin whale song characteristics and potential subpopulation identity in the New York Bight.

Fin whale (Balaenoptera physalus) song can follow a highly consistent pattern, and regional differences in song patterns can be a valuable indicator of subpopulation identity and distribution. In the Northwest Atlantic, endangered fin whales are currently managed as a single stock despite previous identification of different regional song patterns, which indicates potential subpopulation structuring and vulnerability to anthropogenic disturbance if not managed accordingly. Here we document fin whale song in the New York Bight (NYB) from 2017 to 2020 using passive acoustic data to identify monthly and yearly trends in song patterns and to explore potential subpopulation structuring. The predominant song pattern observed was highly consistent with the pattern documented almost a decade prior in the NYB, with short inter-note intervals (INI) from fall-winter and long-INIs in the spring. However, in one song year the majority of songs were composed of long-INIs. This change in song pattern could be due to a shift in fin whale behavior or possibly multiple fin whale subpopulations using the NYB. Fin whales in the NYB may be particularly vulnerable to disturbance given the increasing anthropogenic pressures in this region, and further research into subpopulation structuring is needed to ensure adequate management of these endangered whales.

Automatic detectors for low-frequency vocalizations of Omura's whales, Balaenoptera omurai: A performance comparison.

Automatically detecting animal signals in soundscape recordings is of benefit to passive acoustic monitoring programs which may be undertaken for research or conservation. Numerous algorithms exist, which are typically optimized for certain situations (i.e., certain animal sound types and ambient noise conditions). Adding to the library of algorithms, this paper developed, tested, and compared three detectors for Omura's whale vocalizations (15-62 Hz; <15 s) in marine soundscape recordings which contained noise from other animals, wind, earthquakes, ships, and seismic surveys. All three detectors were based on processing of spectrographic representations. The specific methods were spectrogram cross-correlation, entropy computation, and spectral intensity "blob" tracing. The latter two were general-purpose detectors that were adapted for detection of Omura's whale vocalizations. Detector complexity and post-processing effort varied across the three detectors. Performance was assessed qualitatively using demonstrative examples, and quantitatively using Receiver-Operating Characteristics and Precision-Recall curves. While the results of quantitative assessment were dominated by the spectrogram cross-correlation method, qualitative assessment showed that all three detectors offered promising performance.

Stereotypic and complex phrase types provide structural evidence for a multi-message display in humpback whales (Megaptera novaeangliae).

Male humpback whales produce a mating display called "song." Behavioral studies indicate song has inter- and/or intra-sexual functionality, suggesting song may be a multi-message display. Multi-message displays often include stereotypic components that convey group membership for mate attraction and/or male-male interactions, and complex components that convey individual quality for courtship. Humpback whale song contains sounds ("units") arranged into sequences ("phrases"). Repetitions of a specific phrase create a "theme." Within a theme, imperfect phrase repetitions ("phrase variants") create variability among phrases of the same type ("phrase type"). The hypothesis that song contains stereotypic and complex phrase types, structural characteristics consistent with a multi-message display, is investigated using recordings of 17 east Australian males (8:2004, 9:2011). Phrase types are categorized as stereotypic or complex using number of unit types, number of phrase variants, and the proportion of phrases that is unique to an individual versus shared amongst males. Unit types are determined using self-organizing maps. Phrase variants are determined by Levenshtein distances between phrases. Stereotypic phrase types have smaller numbers of unit types and shared phrase variants. Complex phrase types have larger numbers of unit types and unique phrase variants. This study supports the hypothesis that song could be a multi-message display.

Using self-organizing maps to classify humpback whale song units and quantify their similarity.

Classification of vocal signals can be undertaken using a wide variety of qualitative and quantitative techniques. Using east Australian humpback whale song from 2002 to 2014, a subset of vocal signals was acoustically measured and then classified using a Self-Organizing Map (SOM). The SOM created (1) an acoustic dictionary of units representing the song's repertoire, and (2) Cartesian distance measurements among all unit types (SOM nodes). Utilizing the SOM dictionary as a guide, additional song recordings from east Australia were rapidly (manually) transcribed. To assess the similarity in song sequences, the Cartesian distance output from the SOM was applied in Levenshtein distance similarity analyses as a weighting factor to better incorporate unit similarity in the calculation (previously a qualitative process). SOMs provide a more robust and repeatable means of categorizing acoustic signals along with a clear quantitative measurement of sound type similarity based on acoustic features. This method can be utilized for a wide variety of acoustic databases especially those containing very large datasets and can be applied across the vocalization research community to help address concerns surrounding inconsistency in manual classification.

Acoustically detected year-round presence of right whales in an urbanized migration corridor.

Species' conservation relies on understanding their seasonal habitats and migration routes. North Atlantic right whales (Eubalaena glacialis), listed as endangered under the U.S. Endangered Species Act, migrate from the southeastern U.S. coast to Cape Cod Bay, Massachusetts, a federally designated critical habitat, from February through May to feed. The whales then continue north across the Gulf of Maine to northern waters (e.g., Bay of Fundy). To enter Cape Cod Bay, right whales must traverse an area of dense shipping and fishing activity in Massachusetts Bay, where there are no mandatory regulations for the protection of right whales or management of their habitat. We used passive acoustic recordings of right whales collected in Massachusetts Bay from May 2007 through October 2010 to determine the annual spatial and temporal distribution of the whales and their calling activity. We detected right whales in the bay throughout the year, in contrast to results from visual surveys. Right whales were detected on at least 24% of days in each month, with the exception of June 2007, in which there were no detections. Averaged over all years, right whale calls were most abundant from February through May. During this period, calls were most frequent between 17:00 and 20:00 local time; no diel pattern was apparent in other months. The spatial distribution of the approximate locations of calling whales suggests they may use Massachusetts Bay as a conduit to Cape Cod Bay in the spring and as they move between the Gulf of Maine and waters to the south in September through December. Although it is unclear how dependent right whales are on the bay, the discovery of their widespread presence in Massachusetts Bay throughout the year suggests this region may need to be managed to reduce the probability of collisions with ships and entanglement in fishing gear.