Creating a baseline understanding of communicative signals and perceptual abilities is imperative for gaining insight into a species' life history. This is especially relevant for at-risk species, as ...it can aid in monitoring and conservation efforts. Marine mammals communicate predominately through acoustic modalities for a variety of functions, including foraging and reproduction. The acoustic signals produced by marine mammals, and their ability to perceive signals produced by conspecifics, are directly impacted by the level of ambient noise in the underwater environment in which they inhabit. Modern ocean noise levels are considerably louder than historical levels, and noise is therefore considered to be a threat to acoustically communicating marine mammal species. This review summarizes the documented acoustic signals, hearing abilities, and responses to sound of a critically endangered baleen whale, the North Atlantic right whale (Eubalaena glacialis), highlights gaps in the current body of literature, and identifies priorities for future research.
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•North Atlantic right whales produce a variety of sounds, including tonal and impulsive signals•Tonal sounds generally range from 50-600 Hz and are less than 5 s, though impulsive signals are much shorter and broadband•Hearing ranges from 20 Hz-22 kHz, based on vocalization frequency, anatomical modeling, and behavioral responses•Given the overlap of right whale habitat and human activities, understanding the impacts of anthropogenic noise is critical
Acoustically adept species in the marine environment have to contend with complex and highly variable soundscapes. In the ocean today, sounds from human sources contribute substantially to the ...underwater acoustic environment. We used a 4-element hydrophone array in Glacier Bay National Park to (1) identify primary drivers of ambient sound in this region, (2) investigate whether humpback whales Megaptera novaeangliae exhibit a Lombard response in response to ambient noise, and (3) investigate whether humpback whales adjust their calling activity in response to naturally occurring and vessel-generated sounds. We found that cruise ships and tour boats, roaring harbor seals Phoca vitulina, and weather events were primary drivers of ambient sound levels, and that they varied both seasonally and diurnally. As ambient sound levels increased, humpback whales responded by increasing the source levels of their calls (non-song vocalizations) by 0.81 dB (95% CI = 0.79–0.90) for every 1 dB increase in ambient sound. There was no evidence that the magnitude of the observed response differed between natural and man-made sounds. We also found that the probability of a humpback whale calling in the survey area decreased by 9% for every 1 dB increase in ambient sound. Controlling for ambient sound levels, the probability of a humpback whale calling in the survey area was 31–45% lower when vessel noise contributed to the soundscape than when only natural sounds were present.
Remote acoustic monitoring is a non-invasive tool that can be used to study the distribution, behavior, and habitat use of sound-producing species. The North Atlantic right whale (Eubalaena ...glacialis) is an endangered baleen whale species that produces a variety of stereotyped acoustic signals. One of these signals, the "gunshot" sound, has only been recorded from adult male North Atlantic right whales and is thought to function for reproduction, either as reproductive advertisement for females or as an agonistic signal toward other males. This study uses remote acoustic monitoring to analyze the presence of gunshots over a two-year period at two sites on the Scotian Shelf to determine if there is evidence that North Atlantic right whales may use these locations for breeding activities. Seasonal analyses at both locations indicate that gunshot sound production is highly seasonal, with an increase in the autumn. One site, Roseway West, had significantly more gunshot sounds overall and exhibited a clear diel trend in production of these signals at night. The other site, Emerald South, also showed a seasonal increase in gunshot production during the autumn, but did not show any significant diel trend. This difference in gunshot signal production at the two sites indicates variation either in the number or the behavior of whales at each location. The timing of the observed seasonal increase in gunshot sound production is consistent with the current understanding of the right whale breeding season, and our results demonstrate that detection of gunshots with remote acoustic monitoring can be a reliable way to track shifts in distribution and changes in acoustic behavior including possible mating activities.
Aquatically breeding harbour seal (
) males use underwater vocalizations during the breeding season to establish underwater territories, defend territories against intruder males, and possibly to ...attract females. Vessel noise overlaps in frequency with these vocalizations and could negatively impact breeding success by limiting communication space. In this study, we investigated whether harbour seals employed anti-masking strategies to maintain communication in the presence of vessel noise in Glacier Bay National Park and Preserve, Alaska. Harbour seals in this location did not sufficiently adjust source levels or acoustic parameters of vocalizations to compensate for acoustic masking. Instead, for every 1 dB increase in ambient noise, signal excess decreased by 0.84 dB, indicating a reduction in communication space when vessels passed. We suggest that harbour seals may already be acoustically advertising at or near a biologically maximal sound level and therefore lack the ability to increase call amplitude to adjust to changes in their acoustic environment. This may have significant implications for this aquatically breeding pinniped, particularly for populations in high noise regions.
Anthropogenic underwater noise has been identified as a potentially serious stressor for the critically endangered North Atlantic right whale (NARW). The Government of Canada is undertaking steps to ...better characterize the noise sources of most concern and their associated impacts, but there is currently an insufficient understanding of which noise sources are most impacting NARW in their Canadian habitat. This knowledge gap together with the myriad possible methods and metrics for quantifying underwater noise presents a confounding and challenging problem that risks delaying timely mitigation. This study presents the results from a 2020 workshop aimed at developing a series of metrics recommended specifically for better characterizing the types of noise deemed of greatest concern for NARW in Canadian waters. The recommendations provide a basis for more targeted research on noise impacts and set the stage for more effective management and protection of NARW, with potential conservation applications to similar species.
•We present the first recommended metrics for assessing noise impacts on North Atlantic right whales in Canadian waters.•The types and characteristics of noise of most concern to North Atlantic right whales in Canadian waters are identified.•Recommendations were informed by the expertise of a diverse set of researchers and professionals in various fields.•Metrics to best quantify physiological and behavioural impacts from noise are discussed and recommended.•Recommendations will support targeted research efforts to better understand noise impacts on North Atlantic right whales.
Source levels of harbor seal breeding vocalizations were estimated using a three-element planar hydrophone array near the Beardslee Islands in Glacier Bay National Park and Preserve, Alaska. The ...average source level for these calls was 144 dB
re 1 μPa at 1 m in the 40-500 Hz frequency band. Source level estimates ranged from 129 to 149 dB
re 1 μPa. Four call parameters, including minimum frequency, peak frequency, total duration, and pulse duration, were also measured. These measurements indicated that breeding vocalizations of harbor seals near the Beardslee Islands of Glacier Bay National Park are similar in duration (average total duration: 4.8 s, average pulse duration: 3.0 s) to previously reported values from other populations, but are 170-220 Hz lower in average minimum frequency (78 Hz).
During the breeding season, male harbor seals (
) make underwater acoustic displays using vocalizations known as roars. These roars have been shown to function in territory establishment in some ...breeding areas and have been hypothesized to be important for female choice, but the function of these sounds remains unresolved. This study consisted of a series of playback experiments in which captive female harbor seals were exposed to recordings of male roars to determine if females respond to recordings of male vocalizations and whether or not they respond differently to roars from categories with different acoustic characteristics. The categories included roars with characteristics of dominant males (longest duration, lowest frequency), subordinate males (shortest duration, highest frequency), combinations of call parameters from dominant and subordinate males (long duration, high frequency and short duration, low frequency), and control playbacks of water noise and water noise with tonal signals in the same frequency range as male signals. Results indicate that overall females have a significantly higher level of response to playbacks that imitate male vocalizations when compared to control playbacks of water noise. Specifically, there was a higher level of response to playbacks representing dominant male vocalization when compared to the control playbacks. For most individuals, there was a greater response to playbacks representing dominant male vocalizations compared to playbacks representing subordinate male vocalizations; however, there was no statistical difference between those two playback types. Additionally, there was no difference between the playbacks of call parameter combinations and the controls. Investigating female preference for male harbor seal vocalizations is a critical step in understanding the harbor seal mating system and further studies expanding on this captive study will help shed light on this important issue.
Glacier Bay National Park and Preserve is a marine protected area in southeastern Alaska that is home to one of the largest seasonal aggregations of harbor seals (Phoca vitulina) in the region. ...Harbor seals, like the majority of phocids, are an aquatically breeding pinniped species. During the breeding season, male harbor seals use acoustic signals to defend underwater territories from other males and possibly to attract females. We used a long-term passive acoustic dataset to examine the trends in harbor seal vocal behavior near a terrestrial haulout as a function of season, tides, and time of day. Seasonality analyses indicated a sharp increase in vocal activity during the months of June and July, which correlates with the estimated timing of the breeding at this location. Contrary to previous studies, there was no effect of tidal height on the documented calling behavior of harbor seals at this location, perhaps because the recordings were made farther from shore, within 10 km of the major haul-out area. Diel analyses showed that harbor seal males call throughout the day, but, similar to other populations, calling significantly increased at night when more seals are foraging. This analysis provides evidence that specific environmental parameters play a role in harbor seal acoustic behavior in Glacier Bay and allows for behavioral comparisons among different harbor seal populations across the globe to guide future research efforts working to protect harbor seals during the breeding season.
Acoustic communication in insects is vital for reproduction. In the family Tettigoniidae, certain features of acoustic signals are impacted by ambient temperature. The current study investigates the ...correlation between increased ambient temperature and signaling behavior in four species of katydids in two subfamilies under conditions that may be encountered as environmental temperatures continue to rise due to climate change. This is the first systematic investigation into the potential effects of temperature on song parameters in these four species. Individuals were tested at five different temperatures, ranging from 20 °C to 40 °C at 5°C intervals, and measurements were taken on six acoustic parameters: buzz duration, interbuzz interval (IBI) duration, number of ticks in the IBI, tick rate in the IBI, pulse rate within a buzz, and percent time spent calling. Results indicated a statistically significant effect of temperature on pulse rate, buzz duration, and interbuzz interval duration for all species tested. The percent time calling and buzz duration increased at higher temperatures in the single species in the subfamily Tettigoniinae, in contrast with the three species in the subfamily Conocephalinae which showed decreased percent time calling and reduced buzz duration in increased temperature. These results highlight the potential differences in the behavioral responses among different species to increasing global temperatures. Further research is necessary to assess the potential impact of variable calling parameters on female choice in these and other katydid species.
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