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Factors that affect cetacean perpendicular sighting distances are investigated using a Generalised Additive Modelling (GAM) framework to analyse 8,203 sightings of 34 cetacean species seen on 200,000km of shipboard line-transect surveys in the eastern Pacific in 1986-96. Perpendicular sighting distance is modelled as a non-linear function of the following predictor variables: species; an a priori species grouping; the logarithm of group size; Beaufort sea state; presence of rain or fog; sighting cue; sun glare; geographic stratum; observer; ship; year; cruise; and, in 1991-96, visibility and swell height. Based on Akaike Information Criteria (AIC), the best model for 1986-96 included all variables except rain/fog code. For the 1991-96 data, swell height anomaly was also important and replaced ship and year in the best-fit model. For independent subsets of the data, GAM coefficients were highly correlated, indicating that many of the same factors were acting in different areas and at different times. Species and sighting methods (25x binoculars vs unaided eye) had the largest effects on perpendicular sighting distances. The a priori species groups captured much, but not all of the among-species differences. Two other species-related factors (group size and sighting cue) were also important in all models. Factors related to search conditions (Beaufort sea state and swell height anomaly) and to the searchers themselves (individual observer) were also important. We anticipate that this information on the relative magnitudes of factors affecting perpendicular sighting distance can be used to improve both design and analysis of line-transect data.

The Gulf of Maine is one of the principal summer feeding grounds for humpback whales (Megaptera novaeangliae) in the North Atlantic, and was one focus of effort in an ocean-basin-wide study known as the Years of the North Atlantic Humpback (YoNAH) project. Data from that project and from subsequent surveys were used to assess stock boundaries, abundance and demographic parameters for Gulf of Maine humpbacks. Surveys on the Scotian Shelf in the summers of 1998 and 1999 produced the first substantial dataset of identified individual humpbacks observed in this region, which lies between the well-studied areas of the Gulf of Maine and Newfoundland. The results gave a match rate of approximately 27% (14 of 52 individuals) between the Scotian Shelf and the Gulf of Maine, with evidence that many of the matched whales were transient in the Gulf of Maine; there were no matches to any other location in the North Atlantic. These data suggest that the range of most whales from the Gulf of Maine usually does not extend as far east as the Scotian Shelf or Newfoundland. Only one whale was observed on the Scotian Shelf in both the 1998 and 1999 surveys, and another seen in 1998 had also been sighted there in 1994. This low inter-annual match rate suggests that the abundance of humpback whales on the Scotian Shelf is larger than previously recognised. Three different but overlapping estimates of abundance for the Gulf of Maine population were calculated. Mark-recapture data from 1992/93 gave an estimate of abundance of 652 (CV = 0.29); however, this estimate is likely biased because of heterogeneity in sampling and in animal distribution. Photo-id data also provided a minimum population estimate of 497 humpbacks known to be alive in 1997; this estimate is also likely to be negatively biased because of heterogeneity. Finally, line-transect surveys conducted in 1999 yielded estimates of 816 (CV = 0.45) or 902 humpback whales (CV = 0.41, including a portion of the eastern Scotian Shelf stratum); these transect-based estimates are more consistent with the number of humpbacks (1,273, including dead animals) in the current photo-id catalogue for the Gulf of Maine. Overall, the size of the Gulf of Maine population is likely to be in the high hundreds, but no more precise estimate can be calculated at this time. The growth rate for the Gulf of Maine population was estimated using an interbirth interval method using data from 1992-2000. The estimate was either 1.00 (for a calf survival rate of 0.51) or 1.04 (for a calf survival rate of 0.875). Although confidence limits are not available (because maturation parameters could not be estimated), both estimates of population growth rate are outside the 95% confidence intervals of the previous estimate of 1.065 for the period 1979-1991 (Barlow and Clapham, 1997). It is unclear whether this apparent decline is an artefact resulting from a shift in distribution or is a real phenomenon; if the latter, it may be related to known high mortality among young-of-the-year whales in the waters of the US mid-Atlantic states. However, calf survival appears to have increased since 1996, presumably accompanied by an increase in population growth.

Estimating the abundance and density of beaked whales is more difficult than for most other cetacean species. Consequently few estimates appear in the published literature. Field identification is problematic, especially for the smaller species, and visual detection rates decrease dramatically with Beaufort sea state; prior experience is very important to an observer’s ability to detect beaked whales. Passive acoustics may hold future promise for detecting beaked whales from their vocalisations, especially for the larger species. Most published estimates of abundance or density are based on visual line-transect studies that found narrower effective strip widths and lower trackline detection probabilities for beaked whales than for most other cetaceans. Published density estimates range from 0.4-44 whales per 1,000km2 for small beaked whales and up to 68 whales per 1,000km2 for large beaked whales. Mark-recapture methods based on photo-identification have been used to estimate abundance in a few cases in limited geographical areas. Focused research is needed to improve beaked whale abundance and density estimates worldwide.

Temporally dynamic environmental variables and fixed geographic variables were used to construct generalised additive models to predict Cuvier’s (Ziphius cavirostris) and Mesoplodon beaked whale encounter rates (number of groups per unit survey effort) and group sizes in the eastern tropical Pacific Ocean. The beaked whale sightings and environmental data were collected simultaneously during the Southwest Fisheries Science Center’s cetacean line-transect surveys conducted during the summers and autumns of 1986-90 and 1993. Predictions from the encounter rate and group size models were combined with previously published estimates of line-transect sighting parameters to describe patterns in beaked whale population density (number of individuals per unit area) throughout the study area. Results provide evidence that the previously proposed definition of beaked whale habitat may be too narrow and that beaked whales may be found from the continental slope to the abyssal plain, in waters ranging from well-mixed to highly stratified. Areas with the highest predicted population densities were the Gulf of California, the equatorial cold tongue and coastal waters, including the west coast of the Baja Peninsula and the Costa Rica Dome. Offshore waters in the northern and southern subtropical gyres had the lowest predicted Mesoplodon densities, but density predictions were high for Cuvier’s beaked whales in the waters southeast of the Hawaiian Islands. For both encounter rate and group size models, there was no geographic pattern evident in the residuals as measured by the ratio of pooled predicted to pooled observed values within geographic strata.

Certain anthropogenic sounds are widely believed to cause strandings of beaked whales, but their impacts on beaked whale populations are not known and methods for mitigating their effects are largely untested. The sound sources that have been coincident with beaked whale strandings are military, mid-frequency sonar (2-10kHz) and airgun arrays, both of which are used widely throughout the world for defence and geophysical exploration, respectively and for which alternative technologies are not readily available. Avoidance of beaked whale habitats is superficially a straightforward means of reducing the potential effects, but beaked whales are widely distributed and can be found in virtually all deep-water marine habitats that are free of ice. Some areas of high beaked whale abundance have been identified, but the geographic distribution is poorly known for most species. Beaked whales are both visually and acoustically difficult to detect. Commonly used mitigation measures (e.g. ‘ramp-up’ and ‘detection-modification-avoidance’) have not been assessed for their effectiveness. Surveys to detect population-level impacts would likely require many years of regular monitoring and for most areas where beaked whale strandings have occurred, there are no pre-exposure estimates of population sizes. Risk assessment models can be used to estimate the sound levels to which beaked whales might be exposed under a variety of scenarios, however, the lack of information on the causal mechanism for soundrelated beaked whale strandings makes it difficult to identify exposure levels that would warrant mitigative actions. Controlled exposure experiments, which measure the behavioural responses of animals to fully characterised sound sources, may hold the greatest potential for understanding the behavioural responses of beaked whales to sound and for designing mitigation methods to avoid future impacts.

Information regarding beaked whales is so sparse that even the most basic aspects of their biology, such as their distribution, remain poorly defined for some species. We have reviewed the known distribution of each beaked whale species and where possible, used this information to infer its global distribution. While for some species, such as the relatively commonly recorded Cuvier’s beaked whale, the inferred distribution is likely to be an accurate reflection of the species’ actual distribution, for other lesser known species, such as the spade-toothed whale, the inferred distribution is more tentative. However, even such limited distribution information is essential when assessing and mitigating potential anthropogenic impacts on beaked whales and serves to highlight gaps in our knowledge that need to be filled if assessment and mitigation are to be successfully conducted.

We present an ocean-basin-scale dataset that includes tail fluke photographic identification (photo-ID) and encounter data for the majority of living individual humpback whales (Megaptera novaeangliae) in the North Pacific Ocean. The dataset was built through a broad collaboration combining 39 separate curated photo-ID catalogs supplemented with community science data. All available images were compared using a recently developed machine learning artificial intelligence image recognition algorithm able to rapidly and accurately detect matches between individuals. For the study period of 2001 to 2021, a total of 27,956 unique individuals were documented in 157,379 encounters, with each individual encountered, on average, in 5.6 sampling periods (i.e., breeding and feeding seasons), and with an annual average of 87.1% of whales encountered in more than one season. The combined dataset and image recognition tool represents a living and accessible resource for collaborative, basin-wide studies of a keystone marine mammal in a time of rapid ecological change.

An acoustic survey of Cuvier's beaked whales (Ziphius cavirostris) was conducted off the U.S. West Coast in August and September 2016 using drifting recorder systems with a vertical array of two hydrophones at a depth of ~110 m. Recorders were deployed 22 times to representatively cover a 1,058,000 km2 study area from the shelf break to ~556 km offshore. Vertical angles to echolocation pulses were measured using the signal time-difference-of-arrival on the two hydrophones. Echolocation pulses of Cuvier's beaked whales were identified from their arrival angles (always from below the array) and unique acoustic characteristics. The density and abundance of Cuvier's beaked whales were estimated using a group-based point-transect analysis with 2 min time snapshots. The area effectively surveyed was estimated using a maximum simulated likelihood approach to fit the observed distribution of signal arrival angles. The acoustic availability of whales during their dive cycle was estimated from the duration of acoustic encounters using a mark-recapture approach. Overall, Cuvier's beaked whales were present during 0.60% of snapshots, and their estimated average density is 5.12 animals per 1,000 km2 (CV = 0.27). Their estimated abundance in the study area is 5,454 individuals (95% credibility intervals: 3,151 to 8,907).

Funding: Funding for this work was provided by Living Marine Resources Program Grant No. N39430-14-C-1435 and Office of Naval Research Grant No. N00014-15-1‐2142. S.F. was supported by the Department of Defense National Science and Engineering Graduate Fellowship. This is Pacific Marine Environmental Laboratory (PMEL) Contribution No. 5101. A single-hydrophone ocean glider was deployed within a cabled hydrophone array to demonstrate a framework for estimating population density of fin whales ( Balaenoptera physalus) from a passive acoustic glider. The array was used to estimate tracks of acoustically active whales. These tracks became detection trials to model the detection function for glider-recorded 360-s windows containing fin whale 20-Hz pulses using a generalized additive model. Detection probability was dependent on both horizontal distance and low-frequency glider flow noise. At the median 40-Hz spectral level of 97 dB re 1 μPa2/Hz, detection probability was near one at horizontal distance zero with an effective detection radius of 17.1 km [coefficient of variation (CV) = 0.13]. Using estimates of acoustic availability and acoustically active group size from tagged and tracked fin whales, respectively, density of fin whales was estimated as 1.8 whales per 1000 km2 (CV = 0.55). A plot sampling density estimate for the same area and time, estimated from array data alone, was 1.3 whales per 1000 km2 (CV = 0.51). While the presented density estimates are from a small demonstration experiment and should be used with caution, the framework presented here advances our understanding of the potential use of gliders for cetacean density estimation. Publisher PDF

Acoustic point-transect distance-sampling surveys have recently been used to estimate the density of beaked whales. Typically, the fraction of short time "snapshots" with detected beaked whales is used in this calculation. Beaked whale echolocation pulses are only intermittently available, which may affect the best choice of snapshot length. The effect of snapshot length on density estimation for Cuvier's beaked whale (Ziphius cavirostris) is investigated by sub-setting continuous recordings from drifting hydrophones deployed off southern and central California. Snapshot lengths from 20 s to 20 min are superimposed on the time series of detected beaked whale echolocation pulses, and the components of the density estimation equation are estimated for each snapshot length. The fraction of snapshots with detections, the effective area surveyed, and the snapshot detection probability all increase with snapshot length. Due to compensatory changes in these three components, density estimates show very little dependence on snapshot length. Within the range we examined, 1-2 min snapshots are recommended to avoid the potential bias caused by animal movement during the snapshot period and to maximize the sample size for estimating the effective area surveyed.

The ongoing construction of natural gas combined cycle (NGCC) power plants is incompatible with a transition to global net-zero greenhouse gas emissions. This work evaluates the emission pricing and technology costs required to convert an existing NGCC power plant to a biomethane-based bioenergy with carbon capture and storage (BECCS) system. The conversion was evaluated using techno-economic analysis and time-resolved life cycle assessment. At current technology costs, carbon dioxide equivalent emission prices of $142 and $215 per metric ton are required to allow a BECCS conversion to compete with normal operation or shutdown, respectively, of an existing NGCC power plant. These results show further technological development must occur in parallel with emission pricing to make BECCS viable. If mid-range emission pricing estimates are implemented ($25-$105 per metric ton), BECCS capital cost targets range from $1434 to $2098 per kW of capacity, while operational costs range from $32 to $51 per MWh of electricity produced to enable conversion. These findings indicate that operational costs associated with fuel consumption and production must be significantly reduced to make a BECCS conversion viable, even with emission pricing. All data and methods of this work have been made publicly available in an open-source model.

Depth distributions were analyzed from a study of 19 Cuvier’s beaked whales Ziphius cavirostris that were tagged with satellite transmitting instruments off southern California, USA. Over 113000 depth measurements were made over the equivalent of ~200 sampling days. The mean foraging depth was 1182 m (SD = 305 m), and the mean of the maximum depth of all foraging dives was 1427 m (SD = 298 m). Mean foraging depths increased with seafloor depths up to a maximum of ~1300 m at a seafloor depth of 1900 m, but decreased slightly to a mean of ~1200 m at seafloor depths of 2000-4000 m. Near-bottom habitat appears to be important for foraging; whales spent ~30% of their foraging time within 200 m of the bottom at seafloor depths of 1000-2000 m. However, little foraging time was spent near the bottom at seafloor depths greater than 2000 m. The percentage of time spent at near-surface depths (

International audience; Runs of homozygosity (ROH) occur when offspring inherit haplotypes that are identical by descent from each parent. Length distributions of ROH are informative about population history; specifically, the probability of inbreeding mediated by mating system and/or population demography. Here, we investigated whether variation in killer whale (Orcinus orca) demographic history is reflected in genome-wide heterozygosity and ROH length distributions, using a global data set of 26 genomes representative of geographic and ecotypic variation in this species, and two F1 admixed individuals with Pacific-Atlantic parentage. We first reconstructed demographic history for each population as changes in effective population size through time using the pairwise sequential Markovian coalescent (PSMC) method. We found a subset of populations declined in effective population size during the Late Pleistocene, while others had more stable demography. Genomes inferred to have undergone ancestral declines in effective population size, were autozygous at hundreds of short ROH (1.5 Mb) were found in low latitude populations, and populations of known conservation concern. These include a Scottish killer whale, for which 37.8% of the autosomes were comprised of ROH >1.5 Mb in length. The fate of this population, in which only two adult males have been sighted in the past five years, and zero fecundity over the last two decades, may be inextricably linked to its demographic history and consequential inbreeding depression.

Life cycle assessment is a fundamental tool used to evaluate the environmental impact of products. Standard life cycle assessment methodology ignores the impact of greenhouse gases relative to when they are emitted. In this paper, we present a method for leveraging the social cost of greenhouse gases to account for the temporal impacts of emissions in life cycle assessment and techno-economics. To demonstrate, we use this method to analyze the present value of the monetized impacts of emissions across multiple electricity generation technologies. Results show that accounting for time increases the present value across all but one of the technologies considered. Carbon intensive technologies show the highest increase, with coal rising between 26% and 62% depending on social cost scenario. Additionally, we demonstrate a second method that combines temporally resolved greenhouse gas emissions with techno-economic analysis. Considering temporal impacts of emissions within techno-economic analysis increases the levelized cost of electricity (LCOE) across all technologies considered. Carbon intensive technologies increase significantly, with the LCOE from coal rising between 37% and 263% depending on the social cost scenario. The proposed methods show that temporal resolution in life cycle assessment is critical for comparing the monetized impacts of greenhouse gas emissions across technologies.

The population density of Cuvier's beaked whales is estimated acoustically with drifting near-surface hydrophone recorders in the Catalina Basin. Three empirical approaches (trial-based, distance-sampling, and spatially explicit capture-recapture) are used to estimate the probability of detecting the echolocation pulses as a function of range. These detection functions are used with two point-transect methods (snapshot and dive-cue) to estimate density. Measurement errors result in a small range of density estimates (3.9-5.4 whales per 1000 km2). Use of multiple approaches and methods allows comparison of the required information and assumptions of each. The distance-sampling approach with snapshot-based density estimates has the most stringent assumptions but would be the easiest to implement for large scale surveys of beaked whale density. Alternative approaches to estimating detection functions help validate this approach. The dive cue method of density estimation has promise, but additional work is needed to understand the potential bias caused by animal movement during a dive. Empirical methods are a viable alternative to the theoretical acoustic modeling approaches that have been used previously to estimate beaked whale density.

In the California Current off the United States West Coast, there are three offshore cetacean species that produce narrow-band high frequency (NBHF) echolocation pulses: Dall's porpoise (Phocoenoides dalli) and two species of Kogia. NBHF pulses exist in a highly specialized acoustic niche thought to be outside the hearing range of killer whales and other potential mammal-eating odontocetes. Very little is known about the dwarf and pygmy sperm whales (K. sima and K. breviceps), including their NBHF pulse characteristics. This paper presents a multivariate clustering method using data from unmanned drifting acoustic recorders and visually verified porpoise recordings to discriminate between probable porpoise and Kogia clicks. Using density clustering, this study finds three distinct clusters whose geographic distributions are consistent with the known habitat range for Kogia and Dall's porpoise. A Random Forest classification model correctly assigned 97% of the clicks to their cluster. Visually verified Dall's porpoise clicks from towed hydrophones were strongly associated with one of the clusters, while a second cluster tended to be outside the geographic range of Dall's porpoise and unlike the Dall's porpoise cluster. These clicks, presumed to be made by Kogia, exhibited greater spectral variance than previous Kogia echolocation studies. It is possible that the structure of Kogia NBHF pulses may not be as stereotypical as previously described.

Habitat-based distribution modelling is an established method for predicting species distributions and is necessary for many conservation and management applications. Cetacean habitat models have primarily been developed using data from visual surveys. However, numerous techniques exist for detecting animal presence and each capture a portion of the true population. Combining detection data gathered from multiple survey methods, such as visual and acoustic surveys, may lead to a more robust picture of a species distribution and ecology. We compare habitat models for Dall’s porpoise built with visual versus acoustic survey data from a line-transect survey in the California Current and develop a combined model, utilizing both acoustic detections and visual sightings. Combining acoustic and visual detections increases sample size and allows for detections under a greater range of oceanographic conditions. Consequently, the combined model shows a modest expansion of predicted distribution of Dall’s porpoise compared to either single-source model. However, this study reveals that acoustic and visual methods appear to be more complementary, rather than directly additive. Models built with acoustic data display differences from those built with visual data. Different predictor variables were selected across models and the acoustic model predicts a distribution shifted slightly south of the visual distribution. Results from the current study show promise for incorporating acoustics into habitat models but also identify discrepancies in population sampling between these two methods that should inform future population assessments and modelling efforts.

The National Oceanic and Atmospheric Administration (NOAA)/National Park Service (NPS) Ocean Noise Reference Station (NRS) Network is an array of currently twelve calibrated autonomous passive acoustic recorders. The first NRS was deployed in June 2014, and eleven additional stations were added to the network during the following two years. The twelve stations record data that can be used to quantify baseline levels and multi-year trends in ocean ambient sound across the continental United States, Alaska, Hawaii, and island territories within and near to the United States Exclusive Economic Zone (U.S. EEZ). The network provides multi-year, continuous observations of low-frequency underwater sound between 10 Hz and 2000 Hz to capture anthropogenic, biological, and geophysical contributions to the marine soundscape at each location. Comparisons over time and among recording sites will provide information on the presence of calling animals and the prevalence of abiotic and anthropogenic activities that contribute to each soundscape. Implementation of the NRS Network advances broad-scale passive acoustic sensing capabilities within NOAA and the NPS and is an important tool for monitoring protected areas and marine species and assessing potential environmental impacts of anthropogenic noise sources. This analysis focuses on the first year of recordings and captures the wide variability of low-frequency sound levels among and within individual NRS sites over time. Continued data collection will provide information on long-term, low-frequency sound level trends within or near the U.S. EEZ and will be used to explore the value of using soundscape analysis to inform management and mitigation strategies.

Encased in a streamlined, flooded housing, a SoundTrap ST300HF hydrophone recording system was towed on voyages to South Georgia Island and the South Sandwich Islands and to the Antarctic Peninsula in December 2019–February 2020. Recordings were analyzed to identify acoustic detections of cetacean species. Acoustically identified species included sperm whales (Physeter macrocephalus), southern bottlenose whales (Hyperoodon planifrons), Arnoux's beaked whales (Berardius arnuxii), killer whales (Orcinus orca), and long-finned pilot whales (Globicephala melas). Acoustic detections also included several recognized types of beaked whale echolocation pulses (BW37/39 and BW58) as well as two likely beaked whale echolocation pulse types that do not match any previous descriptions. Narrow-band high-frequency echolocation signals (NBHF) (typical of porpoises and some dolphin species) were detected in many locations, and one of these coincided with a sighting of hourglass dolphins (Lagenorhynchus cruciger). This study shows the utility of an autonomous towed hydrophone system on a vessel of opportunity to study the distribution of cetaceans in rough seas that are difficult to study by visual survey methods.

Funding: the Mexican Government (through the Mexican Secretaría de Medio Ambiente y Recursos Naturales), especially Minister R. Pacchiano and A. Michel; U.S. Marine Mammal Commission, in particular T. Ragen, R. Lent, and P. Thomas; the World Wildlife Fund (WWF) Mexico, in particular O. Vidal and E. Sanjurjo; Le Equipe Cousteau; The Ocean Foundation; Fonds de Dotation pour la Biodiversité; MAAF Assurances (Save Your Logo); WWF-US; Opel Project Earth; Fideicomiso Fondo para la Biodiversidad; Instituto Nacional de Ecología y Cambio Climático; Comisión Nacional de Áreas Naturales Protegidas; and Directorate of the Reserva de la Biósfera Alto Golfo de California y Delta del Río Colorado. The vaquita is a critically endangered species of porpoise. It produces echolocation clicks, making it a good candidate for passive acoustic monitoring. A systematic grid of sensors has been deployed for 3 months annually since 2011; results from 2016 are reported here. Statistical models (to compensate for non-uniform data loss) show an overall decline in the acoustic detection rate between 2015 and 2016 of 49% (95% credible interval 82% decline to 8% increase), and total decline between 2011 and 2016 of over 90%. Assuming the acoustic detection rate is proportional to population size, approximately 30 vaquita (95% credible interval 8–96) remained in November 2016. Publisher PDF

Aim To develop a more ecologically realistic approach for estimating the population size of cetaceans and other highly mobile species with dynamic spatial distributions. Location California Current Ecosystem, USA. Methods Conventional spatial density models assume a constant relationship between densities and habitat covariates over some time period, typically a survey season. The estimated population size must change whenever total habitat availability changes. For highly mobile long-lived species, however, density–habitat relationships likely adjust more rapidly than population size. We developed an integrated population-redistribution model based on a more ecologically plausible alternative hypothesis: (1) population size is effectively constant over each survey season; (2) if habitat availability changes, then the population redistributes itself following an ideal free distribution process. Thus, the estimated relationship between densities and habitat covariates adjusts rather than population size. We constructed Bayesian hierarchical models corresponding to the conventional and alternative hypotheses and applied them to distance sampling data for Dall's porpoise (Phocoenoides dalli), a highly mobile cetacean with distribution patterns closely tied to cool sea-surface temperatures. Results The Dall's porpoise data provided strong support for the hypothesis based on an ideal free redistribution process. Our results indicate that the population size of Dall's porpoise within the survey region was relatively stable over each summer/fall survey season, but the distribution expanded and contracted with the extent of suitable habitat. Over multiple survey seasons, the model partitioned variation in observed densities among three sources: variation in population size, the density–habitat relationship and measurement error, leading to lower and more ecologically plausible estimates of interannual variation in population size. Main conclusions We conclude that the integrated population-redistribution model (IPRM) presented here represents an ecologically plausible model for use in future assessments of the population size and dynamics of cetaceans and other highly mobile long-lived species with variable spatial distributions.

In the Southern California Bight, the common dolphin Delphinus delphis is the most abundant dolphin species and preys upon small pelagic fish, mesopelagic fish, and cephalopods. Mesopelagic fish and many cephalopods are available throughout the year, and they form deep scattering layers, some of which characteristically undergo strong diel vertical migrations. The extent of vertical migration depends on the degree of sea surface solar and lunar illumination. At their daytime depth, mesopelagic prey are beyond the range of shallow-diving dolphins. Autonomous acoustic recorders were used tomonitor dolphin echolocation at 2 offshore recording locations from 2009 to 2014. Manual and automated classification techniques were used to identify periods of high echolocation activity, indicative of common dolphin foraging. Clear lunar patterns existed in cool months, when echolocation activity was highest during the darkest periods of the night and lunar month, indicating times when dolphins were foraging, possibly on mesopelagic prey. Echolocation was more abundant during warmmonths, but diel and lunar patterns in echolocation were weaker. Generalized additive mixed models show that the observed patterns in echolocation activity are correlated with lunar day and position of the moon in the night sky. Seasonal patterns may represent geographic shifts in common dolphin populations, shoaling scattering layers, or prey switching behavior during the warmmonths, whereby dolphins target small pelagic fish not associated with the deep scattering layers. Overall, dolphin foraging activity declined from 2009 to 2014 during warm months, which may be related to a declining abundance of small pelagic fish.

Divergence in acoustic signals used by different populations of marine mammals can be caused by a variety of environmental, hereditary, or social factors, and can indicate isolation between those populations. Two types of genetically and morphologically distinct short-finned pilot whales, called the Naisa- and Shiho-types when first described off Japan, have been identified in the Pacific Ocean. Acoustic differentiation between these types would support their designation as sub-species or species, and improve the understanding of their distribution in areas where genetic samples are difficult to obtain. Calls from two regions representing the two types were analyzed using 24 recordings from Hawai'i (Naisa-type) and 12 recordings from the eastern Pacific Ocean (Shiho-type). Calls from the two types were significantly differentiated in median start frequency, frequency range, and duration, and were significantly differentiated in the cumulative distribution of start frequency, frequency range, and duration. Gaussian mixture models were used to classify calls from the two different regions with 74% accuracy, which was significantly greater than chance. The results of these analyses indicate that the two types are acoustically distinct, which supports the hypothesis that the two types may be separate sub-species.

Passive acoustic monitoring is a promising approach for monitoring long-term trends in harbor porpoise (Phocoena phocoena) abundance. Before passive acoustic monitoring can be implemented to estimate harbor porpoise abundance, information about the detectability of harbor porpoise is needed to convert recorded numbers of echolocation clicks to harbor porpoise densities. In the present study, paired data from a grid of nine passive acoustic click detectors (C-PODs, Chelonia Ltd., United Kingdom) and three days of simultaneous aerial line-transect visual surveys were collected over a 370 km2 study area. The focus of the study was estimating the effective detection area of the passive acoustic sensors, which was defined as the product of the sound production rate of individual animals and the area within which those sounds are detected by the passive acoustic sensors. Visually estimated porpoise densities were used as informative priors in a Bayesian model to solve for the effective detection area for individual harbor porpoises. This model-based approach resulted in a posterior distribution of the effective detection area of individual harbor porpoises consistent with previously published values. This technique is a viable alternative for estimating the effective detection area of passive acoustic sensors when other experimental approaches are not feasible.

Passive acoustic monitoring of dolphins is limited by our ability to classify calls to species. Significant overlap in call characteristics among many species, combined with a wide range of call types and acoustic behavior, makes classification of calls to species challenging. Here, we introduce BANTER, a compound acoustic classification method for dolphins that utilizes information from all call types produced by dolphins rather than a single call type, as has been typical for acoustic classifiers. Output from the passive acoustic monitoring software, PAMGuard, was used to create independent classifiers for whistles, echolocation clicks, and burst pulses, which were then merged into a final, compound classifier for each species. Classifiers for five species found in the California Current ecosystem were trained and tested using 153 single-species acoustic events recorded during a 4.5 mo combined visual and acoustic shipboard cetacean survey off the west coast of the United States. Correct classification scores for individual species ranged from 71% to 92%, with an overall correct classification score of 84% for all five species. The conceptual framework of this approach easily lends itself to other species and study areas as well as to noncetacean taxa.