Identifying behavioral states and habitat use of acoustically tracked humpback whales in Hawaii

Abstract

Although humpback whales have been well-studied on their Hawaiian breeding grounds, it is difficult to track individual animals over long distances without tags, particularly when they move offshore. Here, singing humpback whales were localized in three dimensions on the Pacific Missile Range Facility off Kauai, Hawaii, located between 20 km and 80 km offshore, from January 2011 through June 2014. Detailed behavioral analyses were conducted on the resulting tracks. One hundred and eight individual tracks were identified and metrics of these tracks were examined. Using these metrics, the tracks were classified into four behavior categories, described herein as Directed Travel, Repeated Stationary Dives, Mill, and tracks with Combinations of behavioral states. Some diel and seasonal patterns were identified, with Mill tracks occurring more at night than the other behaviors, Repeated Stationary Dive tracks occurring more during the day, and Directed Travel occurring only at the start and end of the breeding season. These results provide detailed insights into the movement of singing humpback whales, particularly in offshore waters where they may be migrating into or out of breeding grounds. This also contributes valuable information on the baseline behavior of humpback whales on a US Navy training range.

Fin whale singing decreases with increased swimming speed

“…All singers were swimming and changed swimming speeds throughout their singing bouts, and there was considerable variability in both swimming speed and the amount of singing within a bout. The relationship between swimming speed and song duty-cycle was bimodal, possibly representing different singer behavioural states as has been observed in humpbacks [42]. The ability to interpret the biological significance of these fin whale observations is especially challenging, given that 75% of our observations occurred from mid-September to mid-March throughout the pelagic North Atlantic, a time period and ocean area for which there are no associated or complementary visual observation reports.…”

“…This does not mean that whales are not attending to or acoustically interacting with each other at greater distances, only that we have not been able to observe what might have appeared to us as acoustically mediated interactions at longer ranges. From a synthesis of our many years of tracking, we also estimate that about 80% of singers had fairly consistent directions of travel, while around 20% tended to meander within any particular area, a possible indication that singers were in different behavioural states [42]. We conservatively estimate that under typical ambient noise conditions in the 18–28 Hz band, a listener could hear and to some degree follow the movements of a singing male within a listening range of 10–50 km, while acknowledging there would be considerable variability in this range depending on ambient noise and sound transmission loss conditions in the 18–28 Hz frequency band, and the depths of the singing and listening whales.…”

Changes in the Movement and Calling Behavior of Minke Whales (Balaenoptera acutorostrata) in Response to Navy Training

“…The PAM methods did not provide an estimated minke whale depth, so whales were assumed to be near the surface when localized. Mean reported minke whale dive depths range from 18 to 36 m (Friedlaender et al, 2014;Henderson et al, 2018), far smaller than the depths at which hydrophones are deployed at PMRF (650-4750 m), suggesting our assumption is reasonable. The covariance data was utilized to calculate the error ellipse in the horizontal plane as well as the horizontal DOP (HDOP).…”

“…The primary objective of the current paper is to distinguish call cessation from avoidance, and thus investigate whether minke whales exhibit a horizontal movement response away from sonar-producing ships. The methodological development that allows us to do this is the generation of acoustic tracks for individual whales from the localizations (Helble et al, 2015, 2020a,b Klay et al, 2015Henderson et al, 2018;Harris et al, 2019a;Guazzo et al, 2020). In addition, we assessed whether minke whales were more likely to cease calling during sonar exposure, as changes in calling behavior have been reported in response to anthropogenic noise for a number of other baleen whale species [blue whales -Melcon et al, 2012;bowhead whales (Balaena mysticetus, Blackwell et al, 2013, 2015; humpback whales- Risch et al, 2012;Cerchio et al, 2014].…”

Cetacean occurrence in the Gulf of Alaska from long-term passive acoustic monitoring

“…Humpback whale calls were automatically detected using an algorithm based on a generalized power law (Helble et al 2012). This detector can detect the wide range of humpback whale vocalizations (including both song and non-song call types) across different regions and noise conditions, while keeping missed and false detection rates below 5% (Helble et al 2012;Rekdahl et al 2017;Henderson et al 2018;Zeh et al 2020). All automatic detections were verified by a trained analyst using spectrograms that ranged 0.35-3 s in duration and 0-2,000 Hz in frequency (these windows could be modified if necessary for call verification), and any false detections were removed.…”