Underwater sound of three unoccupied aerial vehicles at varying altitudes and horizontal distances.

Unoccupied aerial vehicles (UAVs), or "drones," are increasingly used as a tool for cetacean research, but knowledge about how these tools contribute to underwater sound is lacking. In this study, underwater sound levels of three commonly used UAV models (Mavic Pro Platinum, Phantom 4 Pro v2.0, Inspire 1 Pro) were recorded. For each model, three replicate flights were conducted at 36 positions at standardized horizontal (0-30 m) and vertical (2-40 m) distances from a hydrophone (1 m depth). Median broadband received levels of the Inspire were highest at 96.5 dBrms 141-17 783 Hz re 1 µPa2, followed by the Phantom (92.4 dBrms 141-17 783 Hz re 1 µPa2) and Mavic, which was quietest (85.9 dBrms 141-17 783 Hz re 1 µPa2). Median ambient sound levels in the absence of an UAV were 82.7 dBrms 141-17 783 Hz re 1 µPa2. Significant increases in ambient sound levels associated with UAV flights occurred at higher altitudes than previously reported, and received levels decreased more with increasing horizontal distance of the UAV than with altitude. To minimize potential noise impacts on sensitive marine animal subjects, we recommend increasing horizontal distance to the animal, rather than altitude, and choosing the quietest UAV feasible.

Allopatric humpback whales of differing generations share call types between foraging and wintering grounds.

Humpback whales (Megaptera novaeangliae) are a cosmopolitan baleen whale species with geographically isolated lineages. Despite last sharing an ancestor ~ 2-3 million years ago, Atlantic and Pacific foraging populations share five call types. Whether these call types are also shared between allopatric breeding and foraging populations is unclear, but would provide further evidence that some call types are ubiquitous and fixed. We investigated whether these five call types were present on a contemporary foraging ground (Newfoundland, 2015-2016) and a historic breeding ground (Hawaii, 1981-1982). Calls were classified using aural/visual (AV) characteristics; 16 relevant acoustic variables were measured and a Principal Component Analysis (PCA) was used to examine within-call and between-population variation. To assess whether between-population variation influenced classification, all 16 variables were included in classification and regression tree (CART) and random forest analyses (RF). All five call types were identified in both populations. Between-population variation in combined acoustic variables (PC1, PC2, PC3) was lower within call types than among call types, and high agreement between AV and quantitative classification (CART: 83% agreement; RF: 77% agreement) suggested that acoustic characteristics were more similar within than among call types. Findings indicate that these five call types are shared across allopatric populations, generations, and behavioural contexts.

Effects of Intertidal Position on Metabolism and Behavior in the Acorn Barnacle, Balanus glandula.

The intertidal zone is characterized by persistent, tidally-driven fluctuations in both abiotic (e.g., temperature, oxygen, and salinity) and biotic (e.g., food availability and predation) factors, which make this a physiologically challenging habitat for resident organisms. The relative magnitude and degree of variability of environmental stress differ between intertidal zones, with the most extreme physiological stress often being experienced by organisms in the high intertidal. Given that so many of the constantly shifting parameters in this habitat are primary drivers of metabolic rate (e.g., temperature, [O2], and food availability), we hypothesized that sessile conspecifics residing in different tidal zones would exhibit distinct "metabolic phenotypes," a term we use to collectively describe the organisms' baseline metabolic performance and capacity. To investigate this hypothesis, we collected acorn barnacles (Balanus glandula) from low, mid, and high intertidal positions in San Luis Obispo Bay, CA, and measured a suite of biochemical (whole-animal citrate synthase (CS) and lactate dehydrogenase (LDH) activity, and aerial [D-lactate]), physiological (O2 consumption rates), morphological (body size), and behavioral (e.g., cirri beat frequency and percentage of time operculum open) indices of metabolism. We found tidal zone-dependent differences in B. glandula metabolism that primarily related to anaerobic capacity, cirral activity patterns, and body size. Barnacles from the low intertidal tended to have a greater capacity for anaerobic metabolism (i.e., increased LDH activity and increased baseline [D-lactate]), have reduced cirral beating activity-and presumably reduced feeding-when submerged, and be smaller in size compared to conspecifics in the high intertidal. We did not, however, see any D-lactate accumulation in barnacles from any tidal height throughout 96 h of air exposure. This trend indicates that the enhanced capacity of low intertidal barnacles for anaerobic metabolism may have evolved to support metabolism during more prolonged episodes of emersion or during events other than emersion (e.g., coastal hypoxia and predation). There were also no significant differences in CS activity or baseline O2 consumption rates (in air or seawater at 14°C) across tidal heights, which imply that aerobic metabolic capacity may not be as sensitive to tidal position as anaerobic processes. Understanding how individuals occupying different shore heights differ in their metabolic capacity becomes increasingly interesting in the context of global climate change, given that the intertidal zone is predicted to experience even greater extremes in abiotic stress.

Limited vocal compensation for elevated ambient noise in bearded seals: implications for an industrializing Arctic Ocean.

Vocalizing animals have several strategies to compensate for elevated ambient noise. These behaviours evolved under historical conditions, but compensation limits are quickly being reached in the Anthropocene. Acoustic communication is essential to male bearded seals that vocalize for courtship and defending territories. As Arctic sea ice declines, industrial activities and associated anthropogenic noise are likely to increase. Documenting how seals respond to noise and identifying naturally occurring behavioural thresholds would indicate either their resilience or vulnerability to changing soundscapes. We investigated whether male bearded seals modified call amplitudes in response to changing ambient noise levels. Vocalizing seals increased their call amplitudes until ambient noise levels reached an observable threshold, above which call source levels stopped increasing. The presence of a threshold indicates limited noise compensation for seals, which still renders them vulnerable to acoustic masking of vocal signals. This behavioural threshold and response to noise is critical for developing management plans for an industrializing Arctic.

Acoustically advertising male harbour seals in southeast Alaska do not make biologically relevant acoustic adjustments in the presence of vessel noise.

Aquatically breeding harbour seal (Phoca vitulina) 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.

Some things never change: multi-decadal stability in humpback whale calling repertoire on Southeast Alaskan foraging grounds.

Investigating long term trends in acoustic communication is essential for understanding the role of sound in social species. Humpback whales are an acoustically plastic species known for producing rapidly-evolving song and a suite of non-song vocalizations ("calls") containing some call types that exhibit short-term stability. By comparing the earliest known acoustic recordings of humpback whales in Southeast Alaska (from the 1970's) with recordings collected in the 1990's, 2000's, and 2010's, we investigated the long-term repertoire stability of calls on Southeast Alaskan foraging grounds. Of the sixteen previously described humpback whale call types produced in Southeast Alaska, twelve were detected in both 1976 and 2012, indicating stability over a 36-year time period; eight call types were present in all four decades and every call type was present in at least three decades. We conclude that the conservation of call types at this temporal scale is indicative of multi-generational persistence and confirms that acoustic communication in humpback whales is comprised of some highly stable call elements in strong contrast to ever-changing song.

More of the same: allopatric humpback whale populations share acoustic repertoire.

BACKGROUND: Humpback whales (Megaptera novaeangliae) are a widespread, vocal baleen whale best known for producing song, a complex, repetitive, geographically distinct acoustic signal sung by males, predominantly in a breeding context. Humpback whales worldwide also produce non-song vocalizations ("calls") throughout their migratory range, some of which are stable across generations. METHODS: We looked for evidence that temporally stable call types are shared by two allopatric humpback whale populations while on their northern hemisphere foraging grounds in order to test the hypothesis that some calls, in strong contrast to song, are innate within the humpback whale acoustic repertoire. RESULTS: Despite being geographically and genetically distinct populations, humpback whales in Southeast Alaska (North Pacific Ocean) share at least five call types with conspecifics in Massachusetts Bay (North Atlantic Ocean). DISCUSSION: This study is the first to identify call types shared by allopatric populations, and provides evidence that some call types may be innate.

Source levels of foraging humpback whale calls.

Humpback whales produce a wide range of low- to mid-frequency vocalizations throughout their migratory range. Non-song "calls" dominate this species' vocal repertoire while on high-latitude foraging grounds. The source levels of 426 humpback whale calls in four vocal classes were estimated using a four-element planar array deployed in Glacier Bay National Park and Preserve, Southeast Alaska. There was no significant difference in source levels between humpback whale vocal classes. The mean call source level was 137 dBRMS re 1 µPa @ 1 m in the bandwidth of the call (range 113-157 dBRMS re 1 µPa @ 1 m), where bandwidth is defined as the frequency range from the lowest to the highest frequency component of the call. These values represent a robust estimate of humpback whale source levels on foraging grounds and should append earlier estimates.

Source levels and call parameters of harbor seal breeding vocalizations near a terrestrial haulout site in Glacier Bay National Park and Preserve.

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 dBRMS re 1 µPa at 1 m in the 40-500 Hz frequency band. Source level estimates ranged from 129 to 149 dBRMS 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).