Abstract
Although Bryde’s whale (Balaenoptera edeni) has worldwide distribution, it is considered one of the most difficult species of baleen whales to study. Two populations existing in the Gulf of California have been proposed, but difficulties in obtaining biopsies have complicated testing the hypothesis of discrete stock difference between north and south of the Gulf. On the other hand, bioacoustics analyses have been used to differentiate populations from other whale species. Therefore, to provide information for the previously proposed hypothesis, the most common Bryde’s call (Be4) in the region was analyzed. Acoustic data was collected using a High-frequency Acoustic Recording Package (HARP) system placed at two locations in the Gulf of California: one in the north from November 2006 to June 2007 and other one in the south from August to December 2008. Duration and frequency range were measured for calls with a signal-to-noise ratio (SNR) greater than 27 dB. The Mann–Whitney-Utest was performed to compare distributions in both geographic areas, and the results were compared with a photo-identification analysis. Of the 903 Be4 calls detected, 103 (north) and 92 (south) met the SNR requirement. Duration showed a significant difference (Mann–Whitney test,U= 11238,z-statistics = 2.91,p= 0.003) with southern calls being longer than the northern ones. The results suggest that the northern population remains resident in the north with some movement toward the south, also verified by photo-identification. A detailed inspection showed a double distribution in the south (Mann–Whitney test,U= 2211,z-statistics = −8.39,p= 4.4776e-17), suggesting the presence at the same time of resident and transient populations. The latter has been suggested to belong to the Eastern Tropical Pacific. The results suggest a geographic variation inB. edeniBe4 call type and support the existence of two populations within the Gulf of California.
Highlights
Bryde’s whale (Balaenoptera edeni) -considered one of the least known Balaenopteridae family members (Cummings, 1985; Kato and Perrin, 2009; International Whale Commission, 2020) and one of the most difficult mysticete species to study (Constantine et al, 2018)- has a worldwide distribution inhabiting mainly temperate and tropical oceans
Acoustic data was collected using a stationary High-frequency Acoustic Recording Package (HARP) (Highfrequency Acoustic Recording Package) system designed and deployed by Scripps Institution of Oceanography at the University of California, United States consisting of a hydrophone [Transducers AQ-1s and ITC-1042 (10–100 kHz response)] sensitivity −193 dB VRMS/μPa, 40 dB preamp (Wiggins, 2003), batteries, and memory disks, everything contained on polyvinyl chloride (PVC) sealed cylinders
From HARP systems, a total of 902 Be4 calls were detected in 932 h revised: 407 from Punta Pescadero and 495 from Bahía de Los Ángeles
Summary
Bryde’s whale (Balaenoptera edeni) -considered one of the least known Balaenopteridae family members (Cummings, 1985; Kato and Perrin, 2009; International Whale Commission, 2020) and one of the most difficult mysticete species to study (Constantine et al, 2018)- has a worldwide distribution inhabiting mainly temperate and tropical oceans. Bryde’s Whale Call Geographic Variation since no agreement exists whether B. edeni includes two subspecies (Balaenoptera edeni edeni and Balaenoptera edeni brydei) or they are two different species (Kato and Perrin, 2009; Committee on Taxonomy, 2020). Bryde’s whales due to similar coloration, dorsal fin and body shape could be confused at sea with sei whales (Balaenoptera borealis) or young fin whales (Balaenoptera physalus); in the western Pacific, confusion might happen with Omura’s whales (Balaenoptera omurai) (Jefferson et al, 2008; Kato and Perrin, 2009). The scarce existing information mentions that Bryde’s whales may congregate in groups of as many as 10–20 individuals when they feed (Jefferson et al, 2008)
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