Weddell seals produce ultrasonic vocalizations.

Seals (phocids) are generally not thought to produce vocalizations having ultrasonic fundamental frequencies (≥20 kHz), although previous studies could have been biased by sampling limitations. This study characterizes common, yet, previously undescribed, ultrasonic Weddell seal (Leptonychotes weddellii) vocalizations. The vocalizations were identified in more than one year (2017-2018) of broadband acoustic data obtained by a continuously recording underwater observatory in McMurdo Sound, Antarctica. Nine recurrent call types were identified that were composed of single or multiple vocal elements whose fundamental frequencies spanned the ultrasonic range to nearly 50 kHz. Eleven vocal elements had ultrasonic center frequencies (≥20 kHz), including chirps, whistles, and trills, with two elements at >30 kHz. Six elements had fundamental frequencies always >21 kHz. The fundamental frequency of one repetitive U-shaped whistle element reached 44.2 kHz and descending chirps (≥3.6 ms duration) commenced at ≤49.8 kHz. The source amplitude of one fully ultrasonic chirp element (29.5 kHz center frequency) was 137 dB re 1 µPa-m. Harmonics of some vocalizations exceeded 200 kHz. Ultrasonic vocalizations occurred throughout the year with the usage of repetitive ultrasonic chirp-based calls appearing to dominate in winter darkness. The functional significance of these high-frequency vocalizations is unknown.

Acoustic monitoring of coastal dolphins and their response to naval mine neutralization exercises.

To investigate the potential impacts of naval mine neutralization exercises (MINEX) on odontocete cetaceans, a long-term passive acoustic monitoring study was conducted at a US Navy training range near Virginia Beach, USA. Bottom-moored acoustic recorders were deployed in 2012-2016 near the epicentre of MINEX training activity and were refurbished every 2-4 months. Recordings were analysed for the daily presence/absence of dolphins, and dolphin acoustic activity was quantified in detail for the hours and days before and after 31 MINEX training events. Dolphins occurred in the area year-round, but there was clear seasonal variability, with lower presence during winter months. Dolphins exhibited a behavioural response to underwater detonations. Dolphin acoustic activity near the training location was lower during the hours and days following detonations, suggesting that animals left the area and/or reduced their signalling. Concurrent acoustic monitoring farther away from the training area suggested that the radius of response was between 3 and 6 km. A generalized additive model indicated that the predictors that explained the greatest amount of deviance in the data were the day relative to the training event, the hour of the day and circumstances specific to each training event.

Indo-Pacific humpback dolphin occurrence north of Lantau Island, Hong Kong, based on year-round passive acoustic monitoring.

Long-term passive acoustic monitoring (PAM) was conducted to study Indo-Pacific humpback dolphins, Sousa chinensis, as part of environmental impact assessments for several major coastal development projects in Hong Kong waters north of Lantau Island. Ecological acoustic recorders obtained 2711 days of recording at 13 sites from December 2012 to December 2014. Humpback dolphin sounds were manually detected on more than half of days with recordings at 12 sites, 8 of which were within proposed reclamation areas. Dolphin detection rates were greatest at Lung Kwu Chau, with other high-occurrence locations northeast of the Hong Kong International Airport and within the Lung Kwu Tan and Siu Ho Wan regions. Dolphin detection rates were greatest in summer and autumn (June-November) and were significantly reduced in spring (March-May) compared to other times of year. Click detection rates were significantly higher at night than during daylight hours. These findings suggest high use of many of the proposed reclamation/development areas by humpback dolphins, particularly at night, and demonstrate the value of long-term PAM for documenting spatial and temporal patterns in dolphin occurrence to help inform management decisions.

Humpback whale (Megaptera novaeangliae) song occurrence at American Samoa in long-term passive acoustic recordings, 2008-2009.

Humpback whales (Megaptera novaeangliae) wintering in American Samoan waters belong to the endangered Oceania subpopulation (IUCN Red List), but survey effort in this region has been relatively limited. Humpback whale seasonal occurrence was assessed using long-term passive acoustic recordings from March 2008 to July 2009 at Tutuila, the most populous island of American Samoa, and October 2008 to September 2009 at the remote Rose Atoll, 240 km to the east. Humpback whale song occurred from mid-July through November at both locations. For days with song, the mean number of recordings per day with song was significantly greater at Tutuila than at Rose Atoll. Song incidence at Rose Atoll peaked at 82% of recordings/day in late September 2008, and at Tutuila 70-100% of recordings contained song in late August through early September 2009, when recording ceased. Song incidence at Rose Atoll decreased at midday and increased at midnight, whereas there was no significant diurnal pattern at Tutuila. The lower overall incidence of song and its episodic nature at Rose Atoll suggest lower densities of whales traveling through the likely smaller detection area there, whereas greater song incidence and longer peak periods at Tutuila suggest greater whale densities and longer residence times.

North Pacific right whale up-call source levels and propagation distance on the southeastern Bering Sea shelf.

Call source levels, transmission loss, and ambient noise levels were estimated for North Pacific right whale (Eubalaena japonica) up-calls recorded in the southeastern Bering Sea in autumn of 2000 and 2001. Distances to calling animals, needed to estimate source levels, were based on two independent techniques: (1) arrival-time differences on three or more hydrophones and (2) shallow-water dispersion of normal modes on a single receiver. Average root-mean-square (rms) call source levels estimated by the two techniques were 178 and 176 dB re 1 µPa at 1 m, respectively, over the up-call frequency band, which was determined per call and averaged 90 to 170 Hz. Peak-to-peak source levels were 14 to 22 dB greater than rms levels. Transmission loss was approximately 15∗log(10)(range), intermediate between cylindrical and spherical spreading. Ambient ocean noise within the up-call band varied from 72 to 91 dB re 1 µPa(2)/Hz. Under average noise conditions, call spectrograms were detectable for whales at distances up to 100 km, but propagation and detection distance may vary depending on environmental parameters and anthropogenic noise. Obtaining distances to animals and acoustic detection range is a step toward using long-term passive acoustic recordings to estimate abundance for this critically endangered whale population.

Acoustic detection and satellite-tracking leads to discovery of rare concentration of endangered North Pacific right whales.

The North Pacific right whale, Eubalaena japonica, is one of the most endangered species of whale in the world. On 10 August 2004, two right whales were located in the Bering Sea using headings to right whale calls provided by directional sonobuoys. A satellite-monitored radio tag attached to one of these whales functioned for 40 days. Over the 40-day period, this whale moved throughout a large part of the southeast Bering Sea shelf, including areas of the outer-shelf where right whales have not been seen in decades. In September, multiple right whales were acoustically located and subsequently sighted by another survey vessel approaching a near-real-time position from the tag. An analysis of photographs confirmed at least 17 individual whales (not including the tagged whales). Genetic analysis of biopsy samples identified 17 individuals: 10 males and 7 females. The discovery of seven females was significant, as only one female had been identified in the past. Genetics also confirmed the presence of at least two calves. Although the future of this population is highly uncertain, the discovery of additional females and calves gives some hope that this most critically endangered of all whale populations may still possess the capacity to recover.