Lisa Munger

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.

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.

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.

From Shrimp to Whales: Biological Applications of Passive Acoustic Monitoring on a Remote Pacific Coral Reef

Passive acoustic monitoring (PAM) can be an effective tool for studying marine fauna in coral reefs and other ecosystems. We analyzed PAM data from 2006 to 2009 at French Frigate Shoals (FFS) in the Northwestern Hawaiian Islands. We measured received sound pressure levels (SPL) over time within different frequency bands from 0 to 20 kHz, and used automated and manual techniques to detect parrotfish scrapes and cetacean vocalizations. SPLs were greatest overall in the snapping-shrimp-dominated bands above 2.5 kHz, and they increased at night and decreased during cold months. In frequency bands <1.5 kHz, containing mainly fish sounds (and seasonal whale song), SPL peaked at dawn and dusk. Humpback whale song was detected in December through April; occurrence was greater during 2008–2009 than 2006–2007, possibly reflecting an increase in whale density near FFS. Parrotfish bite sounds were detected year-round, and parrotfish foraged most actively during the afternoon. Dolphins were detected on 12–64 % of days per month, with low levels of activity during the day that increased in late afternoon and were highest at night. More frequent detections of dolphins in February/March 2007, October 2008, and February/March 2009 may correspond to pulses of food availability via the mesopelagic prey community. Minke whale “boing” sounds were detected from late October, with one or two peaks in the December–March period; during March 2009 minke whale calls were present nearly every day. The results provide the first long-term record of minke whales in the NWHI, and show the potential of PAM on remote coral reefs to monitor patterns over time of many trophic levels, from herbivores to apex predators.

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.

Tethys: A workbench for bioacoustic measurements and environmental data

A growing number of passive acoustic monitoring systems have resulted in a wealth of annotation information, or metadata, for recordings. These metadata are semi-structured. Some parameters are essentially mandatory (e.g., time of detection and what was detected) while others are highly dependent upon the question that a researcher is asking. Tethys is a metadata system for spatial-temporal acoustic data that provides structure where it is appropriate and flexibility where it is needed. Networked metadata are stored in an extended markup language (XML) database, and served to workstations over a network. The ability to export summary data to OBIS-SEAMAP is in development. The second purpose of Tethys is to serve as a scientific workbench. Interfaces are provided to networked databases, permitting the import of data from a wide variety of sources, such as lunar illumination or sea ice coverage. Interfaces currently exist for Matlab, Java, and Python. Writing data driven queries using a single interface ena...

Long-term passive acoustic monitoring of parrotfishes (Scaridae) in the Hawaiian Archipelago

Parrotfishes (family Scaridae) are an important component of coral reef ecosystems, and this key functional group plays a major role in algae removal and bioerosion of reef substrate. They are also heavily fished in many locations, which may lead to ecosystem-wide impacts such as increased algal cover. In the State of Hawaii, parrotfish management is a priority for marine resource managers, with an ongoing need for accurate population monitoring that is currently addressed by diver-based visual surveys. However, parrotfishes are highly mobile and somewhat skittish around SCUBA divers, particularly in areas where fishing pressure is high. Because parrotfishes produce frequent audible scraping and crunching sounds associated with feeding, passive acoustic monitoring (PAM) can provide information on parrotfish occurrence without requiring the invasive presence of divers. Here, we present results from analyses of parrotfish foraging sounds in long-term acoustic recordings from 10 shallow reef locations throug...

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.

Acoustic monitoring of dolphin occurrence and activity in a MINEX training range

The naval forces of many nations conduct mine detonation exercises in coastal waters as part of their regular training. These exercises have the potential to disturb, injure or even kill marine mammals occurring in the same area. To address concerns about this possibility at the U.S. Navy’s Virginia Capes (VACAPES) Range Complex, an effort was conducted to monitor odontocete activity at the mine exercise (MINEX) training range using passive acoustic methods. The objectives of the project were to document the daily and seasonal patterns of occurrence of dolphins in the VACAPES MINEX training area, to detect explosions related to MINEX activities, and to investigate potential behavioral and acoustic responses of dolphins to MINEX training events. Dolphins were detected almost daily in the training area. Acoustic activity levels approximately 1 km from the epicenter of training were examined for 22 events and were found to be on average lower during both the day of and the day following the event, suggesting...

Analysis of long-term acoustic datasets for baleen whales and beaked whales within the Mariana Islands Range Complex (MIRC) for 2010 to 2013

Cetacean distribution and abundance in the Mariana Archipelago was relatively unstudied until recently. Although there has been increasing effort to understand the occurrence of various cetacean species in both near shore and offshore waters, there is still relatively little known about their occurrence seasonally, or their prevalence relative to other regions. To better understand the seasonal distribution of cetaceans in the Marianas, the NOAA Pacific Islands Fisheries Science Center (PIFSC) deployed a longterm acoustic recorder in the region in 2010, expanded that effort to two sites in 2011, and has been monitoring both sites since that time.