Acoustic differentiation of Shiho- and Naisa-type short-finned pilot whales in the Pacific Ocean

Abstract

Divergence in acoustic signals used by different populations of marine mammals can be caused by a variety of environmental, hereditary, or social factors, and can indicate isolation between those populations. Two types of genetically and morphologically distinct short-finned pilot whales, called the Naisa-and Shiho-types when first described off Japan, have been identified in the Pacific Ocean. Acoustic differentiation between these types would support their designation as sub-species or species, and improve the understanding of their distribution in areas where genetic samples are difficult to obtain. Calls from two regions representing the two types were analyzed using 24 recordings from Hawai'i (Naisa-type) and 12 recordings from the eastern Pacific Ocean (Shiho-type). Calls from the two types were significantly differentiated in median start frequency, frequency range, and duration, and were significantly differentiated in the cumulative distribution of start frequency, frequency range, and duration. Gaussian mixture models were used to classify calls from the two different regions with 74% accuracy, which was significantly greater than chance. The results of these analyses indicate that the two types are acoustically distinct, which supports the hypothesis that the two types may be separate sub-species.

Whistle Classification of Sympatric False Killer Whale Populations in Hawaiian Waters Yields Low Accuracy Rates

“…However, these whistle characteristics may make it difficult to discern the subtle differences between populations using the time-frequency measurements commonly implemented in whistle classification analyses. Frequency-modulated calls, e.g., whistles, have been categorized into call types to identify geographically isolated populations of some odontocetes based on contour shape and time-frequency characteristics (Saulitis et al, 2005;Van Cise et al, 2017). No attempt was made to categorize whistle types for false killer whales since this study was interested in the overall classification of all whistles.…”

A Collection of Best Practices for the Collection and Analysis of Bioacoustic Data

“…For each of these cases, alternate methods are needed for population sampling. With advances in acoustic methods, researchers have turned to passive acoustic surveys to assess population structures for soniferous species when traditional observational methods or genetic analyses are unavailable or inconclusive (Figure 2) [36,[96][97][98]. Many potential pitfalls in acoustic analyses of population structure parallel those that apply to acoustic species classification.…”

“…If the populations being tested are geographically segregated, the location of the recorders can provide this validation if it can be shown that there is enough distance between recorders that sounds from the adjacent population will not be recorded. However, if the populations being tested are sympatric, it is important to use independent means (e.g., visual scans) to identify the focal population or group being recorded and to ensure that individuals from other populations are not present or nearby during the recording (see, for example, [31,98]). In addition to these considerations, the parameters used in the recording and analysis of acoustic data should be consistent across the populations being tested to avoid introducing variability as an artifact of the experimental design.…”

Communication in Cook Inlet beluga whales: Describing the vocal repertoire and masking of calls by commercial ship noise

“…The vocal repertoire of a wide variety of species has been documented, including birds (Saunders, 1983;Trejos-Araya and Barrantes, 2014), primates (Hammerschmidt and Fischer, 2019;Macedonia, 1993), mustelids (Lemasson et al, 2014;Leuchtenberger et al, 2014;McShane et al, 1995), and marine mammals (Brady et al, 2020;Ford, 1989;Martin et al, 2021;Phillips and Stirling, 2001;Sayigh et al, 2013;Weilgart and Whitehead, 1997). Among marine mammals, studies have shown that vocal repertoire may be integral to the maintenance of population structure (Sharpe et al, 2019;Van Cise et al, 2017;Whitehead et al, 1998;Yurk et al, 2002) and is an important tool for mate attraction (Tyack, 1981). Communication via acoustic signaling is especially important in the marine environment, in which visibility is often limited and animals must rely primarily on sound to navigate their surroundings and communicate with conspecifics (Dudzinski et al, 2009).…”