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Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2021)

Arctic marine mammal habitats are changing rapidly while marine shipping is increasing in some areas of the Arctic. Passive acoustic monitoring can increase understanding of Arctic marine mammal responses to change and to stressors, like ship traffic. The strength of inference from underwater sound recordings is limited by several factors that I address in this dissertation with the aim of improving the usefulness of acoustic monitoring findings for Arctic marine resource management. I provide spatial context for acoustic detections of bowhead whale sounds, enabling direct comparisons of acoustic presence across different locations and environmental conditions. Ice cover and noise substantially reduce the predicted listening area around underwater sound recorders. Spatially normalized acoustic detections reveal that bowhead whales utilize an area at least 140 km north of Alaska during their spring migration, migrating through large areas of >90% sea ice cover. I describe acoustic characteristics of beluga and narwhal echolocation clicks, which differ substantially in frequency content and rhythmic patterns. Sound absorption by seawater and apparent changes in animal orientation strongly affect frequency spectra of recorded clicks. Finally, I measure the underwater soundscape within a narwhal summer habitat and quantify underwater noise added by commercial ship traffic. The natural soundscape, excluding periods with nearby ships, is relatively quiet in an acoustically sheltered fiord. Distant sounds from regional shipping are apparent at a less-sheltered location open to long-range sound propagation. When ships pass the recording locations, sound levels are elevated above the median levels of natural sounds for periods ranging from 30 minutes up to >4 hours with each transit. Icebreaker and tanker ships radiate more underwater noise than general cargo and bulk carrier ships. Ship sounds overlap with common social sounds produced by narwhals and ringed seals at distances of 5 to >30 km from passing ships, possibly interfering with animal communication. Improved detection distance estimates and understanding of detection probability estimation coupled with increased confidence in detection and identification of beluga, narwhal, and bowhead sounds will facilitate passive acoustic density estimation of Arctic marine mammals, investigation of their relationships with habitat, and studies of their behavioral responses to ship traffic.

    Cover page: Passive acoustic monitoring of Arctic cetaceans: Site-specific detection probability, species identification and discrimination, and underwater soundscape with increasing shipping
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2022)
    Bowhead whales (Balaena mysticetus) face threats from diminishing sea ice and increasing anthropogenic activities in the Arctic. Passive acoustic monitoring is the most effective means for monitoring their distribution and population trends, based on the detection of their calls. Passive acoustic monitoring, however, is influenced by the sound propagation environment and ambient noise levels, which impact call detection probability. Modeling and simulations were used to estimate detection probability for bowhead whale frequency-modulated calls in the 80-180 Hz frequency band with and without sea ice cover and under various noise conditions. Sound transmission loss for bowhead calls is substantially greater during ice-covered conditions than during open-water conditions, making call detection ~ 3 times more likely in open-water. Estimates of daily acoustic detection probability were used to compensate acoustic detections for sound propagation and noise effects in two recording datasets in the northeast Chukchi Sea, on the outer shelf and continental slope, collected between 2012 and 2013. The compensated acoustic density suggests a decrease in whale presence with the retreat of sea ice at these recording sites. These results highlight the importance of accounting for effects of the environment on ambient noise and acoustic propagation when interpreting results of passive acoustic monitoring.
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2023)
      Eclipse Sound, in the northeastern Canadian Arctic, has experienced a substantial increase in ship traffic due to growing tourism and industrial development in the region. This study aims to describe the natural soundscape as well as to assess the noise levels associated with shipping. Underwater sound recordings were collected at two locations: Eastern Eclipse Sound (72° 43.730 N, 76° 13.519 W, 670 m) leading to Baffin Bay, and Milne Inlet (72° 15.260 N, 80° 34.205 W, 313 m) situated near the southwest end of Eclipse Sound. To capture the dynamic nature of the soundscape, the data from these two locations were divided into three seasons: late spring, summer, and early fall. These periods were selected to account for the changing contribution of sea ice to the soundscape during the sea ice break-up, two months of open water, and the sea ice freeze-up. By analyzing ship tracks and underwater acoustic recordings, we identified patterns of ship traffic and estimated underwater noise levels due to ships. Noise emitted by ships is quantified by vessel type, including three cargo ship types, passenger ships, pleasure craft, and icebreakers. Individual ship transits through the region introduce transient noise at frequencies from <20 Hz to >20 kHz, with durations lasting from a few minutes to >6 h. The impact of ship noise on the soundscape is significant, resulting in increases in sound levels by 15 to >30 dB when ships are within 10 km and measurable ship noise below 200 Hz at distances of >50 km.
        Creative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2022)
        Sperm whales (Physeter macrocephalus) are a cosmopolitan species but are only found in ice-free regions of the ocean. It is unknown how their distribution might change in regions undergoing rapid loss of sea ice and ocean warming like Baffin Bay in the eastern Canadian Arctic. In 2014 and 2018, sperm whales were sighted near Eclipse Sound, Baffin Bay: the first recorded uses of this region by sperm whales. In this study, we investigate the spatiotemporal distribution of sperm whales near Eclipse Sound using visual and acoustic data. We combine several published open-source, data sets to create a map of historical sperm whale presence in the region. We use passive acoustic data from two recording sites between 2015 and 2019 to investigate more recent presence in the region. We also analyze regional trends in sea ice concentration (SIC) dating back to 1901 and relate acoustic presence of sperm whales to the mean SIC near the recording sites. We found no records of sperm whale sightings near Eclipse Sound outside of the 2014/2018 observations. Our acoustic data told a different story, with sperm whales recorded yearly from 2015 to 2019 with presence in the late summer and fall months. Sperm whale acoustic presence increased over the 5-year study duration and was closely related to the minimum SIC each year. Sperm whales, like other cetaceans, are ecosystem sentinels, or indicators of ecosystem change. Increasing number of days with sperm whale presence in the Eclipse Sound region could indicate range expansion of sperm whales as a result of changes in sea ice. Monitoring climate change-induced range expansion in this region is important to understand how increasing presence of a top-predator might impact the Arctic food web.
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2022)
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2014)
            The acoustic repertoires of ringed, bearded, and ribbon seals are described, along with their seasonal occurrence and relationship to sea ice concentration. Acoustic recordings were made between September and June over three years (2006 - 09) along the continental slope break in the Chukchi Sea, 120 km north-northwest of Barrow, Alaska. Vocalizations of ringed and bearded seals occurred in winter and during periods of 80% - 100% ice cover but were mostly absent during open water periods. The presence of ringed and bearded seal calls throughout winter and spring suggests that some portion of their population is overwintering. Analysis of the repertoire of ringed and bearded seal calls shows seasonal variation. Ringed seal calls are primarily barks in winter and yelps in spring, while bearded seal moans increase during spring. Ribbon seal calls were detected only in the fall of 2008 during the open water period. The repertoire of known ribbon seal vocalizations was expanded to include three additional calls, and two stereotyped call sequences were common. Retrospective analyses of ringed seal recordings from 1982 and ribbon seal recordings from 1967 showed a high degree of stability in call repertoire across large spatial and temporal scales. © The Arctic Institute of North America.
              • Article
              • Peer Reviewed
              UC Santa Cruz Previously Published Works (2024)
              2022 marked the third consecutive La Niña and extended the longest consecutive stretch of negative Oceanic Niño Index since 1998-2001. While physical and biological conditions in winter and spring largely adhered to prior La Niña conditions, summer and fall were very different. Similar to past La Niña events, in winter and spring coastal upwelling was either average or above average, temperature average or below average, salinity generally above average. In summer and fall, however, upwelling and temperature were generally average or slightly below average, salinity was close to average and chlorophyll a was close to average. Again, as during prior La Niña events, biomass of northern/southern copepods was above/below average off Oregon in winter, and body size of North Pacific krill in northern California was above average in winter. By contrast, later in the year the abundance of northern krill dropped off Oregon while southern copepods increased and body sizes of North Pacific krill fell in northern California. Off Oregon and Washington abundances of market squid and Pacific pompano (indicators of warm, non-typical La Niña conditions) were high. In the 20th century, Northern anchovy recruitment tended to be high during cold conditions, but despite mostly warm conditions from 2015-2021 anchovy populations boomed and remained high in 2022. Resident seabird reproductive success, which tended in the past to increase during productive La Niña conditions was highly variable throughout the system as common murre and pelagic cormorant, experienced complete reproductive failure at Yaquina Head, Oregon while Brandt’s cormorant reproduction was average. At three sampling locations off central California, however, common murre reproduction was close to or above average while both pelagic and Brandt’s cormorant were above average. California sealion reproduction has been above average each year since 2016, and pup weight was also above average in 2022, likely in response not to La Niña or El Niño but continuous high abundance of anchovy. The highly variable and often unpredictable physical and biological conditions in 2022 highlight a growing recognition of disconnects between basin-scale indices and local conditions in the CCE. “July-December 2022 is the biggest outlier from individual “strong” La Niña (events) ever going back to the 50s.” – Nate Mantua
                Creative Commons 'BY' version 4.0 license
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