Discovering sounds in Patagonia: characterizing sei whale (<i>Balaenoptera borealis</i>) downsweeps in the south-eastern Pacific Ocean

Abstract

Abstract. The sei whale (Balaenoptera borealis) is one of the least known whale species. Information on sei whale distributions and its regional variability in the south-eastern Pacific Ocean are even more scarce than that from other areas. Vocalizations of sei whales from this region are not described yet. This research presents the first characterization of sei whale sounds recorded in Chile during the austral autumn of 2016 and 2017. Recordings were done opportunistically. A total of 41 calls were identified to be sei whale downsweeps. In 2016, calls ranged from an average maximum frequency of 105.3 Hz down to an average minimum of 35.6 Hz over 1.6 s with a peak frequency of 65.4 Hz. During 2017, calls ranged from an average maximum frequency of 93.3 down to 42.2 Hz (over 1.6 s) with a peak frequency of 68.3 Hz. The absolute minimum frequency recorded was 30 Hz and the absolute maximum frequency was 129.4 Hz. Calls generally occurred in pairs, but triplets or singles were also registered. These low-frequency sounds share characteristics with recordings of sei whales near the Hawai'ian Islands but with differences in the maximum frequencies and duration. These calls distinctly differ from sounds previously described for sei whales in the Southern Ocean and are the first documented sei whale calls in the south-eastern Pacific.

Reencounter with the past: occurrence of sei whale (Balaenoptera borealis) in an old hunting area in the south-eastern Pacific Ocean

“…The sei whale is described as predominantly found in deep waters, occupying mainly pelagic habitats at distances greater than 110 km from the coast (Best & Lockyer 2002, Prieto et al 2012; however, many of our sightings occurred near the coast at distances no greater than 6 km (see Table 1) consistent with what was observed for populations of sei whales in the South Atlantic (Weir et al 2020). This greater abundance of sei whale near the coast and the feeding activity during the day, agree with the results obtained by Español-Jiménez et al (2019) on the coast of the Gulf of Penas and Tres Montes. Another data to highlight are the sightings of the same individual on more than one occasion, this suggests a stay of at least 7-10 days.…”

“…Although the sei whale was not a target species for hunting until the early 1960s (Acevedo et al 2017, Español-Jiménez et al 2019 the decrease in the most profitable whales (B. musculus, B. physalus, Megaptera novaeangliae and Eubalaena australis) led to an increase in the hunting effort of this species. In South America, this species was heavily exploited throughout its range (Zerbini et al 1997, Aguayo-Lobo et al 1998a where about 110.000 individuals were hunted by pelagic fleets in Antarctic waters between 1960and 1970(Horwood 2018.…”

Seasonal Trends and Diel Patterns of Downsweep and SEP Calls in Chilean Blue Whales

“…While SEP calls have a clearly distinctive acoustic structure [27,35], downsweep calls can be more difficult to identify with certainty, especially in the presence of vocalizations from other whale species. Several mysticete species can produce calls similar to blue whale D calls in terms of frequency range and down-sweeping pattern, including fin whales (Balaenoptera physalus; 30-100 Hz) [51], sei whales (Balaenoptera borealis; 35-100 Hz, occurring in singles, doublets, or triplets) [52], and minke whales (Balaenoptera acutorostrata; 50-130 Hz) [53]. In an effort to include in our analyses only downsweep (D) calls from blue whales, we performed a preliminary analysis of acoustic parameters of all detected calls (low, medium, and high-quality) and excluded detections that had a minimum frequency lower than 30 Hz, maximum frequency higher than 121 Hz, and a duration shorter than 0.90 s or longer than 3.71 s. These cut-offs were chosen to exclude detections that exceeded the values for 75% of the calls.…”

Phylogeography and demographic inference of the endangered sei whale, with implications for conservation

“…This event provided the largest source of information for this species in the Southern Hemisphere (Häussermann et al, 2017). In addition to highlighting the Chilean southern Patagonia as an important area for sei whales (Häussermann et al, 2017;Español-Jiménez et al, 2019;Fretwell et al, 2019;Reiss, Häussermann & Mayr, 2020), this event represents a unique opportunity to address questions regarding the phylogeographic structure of the species, with an improved coverage of the species' distribution and insight into the population demography dynamics considering a temporal framework. Here, a global phylogeographic study of the sei whale is presented, including a large number of Southern Hemisphere (SH) sei whale samples (particularly from this MME), as well as new sequences from the North Pacific (NP), substantially increasing geographic coverage of the species.…”