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Guazzo, RA, Schulman-Janiger A, Smith MH, Barlow J, D’Spain GL, Rimington DB, Hildebrand JA.  2019.  Gray whale migration patterns through the Southern California Bight from multi-year visual and acoustic monitoring. Marine Ecology Progress Series. 625:181-203.   10.3354/meps12989   Abstract

Sightings and acoustic recordings from eastern North Pacific gray whales in the Southern California Bight were analyzed for interannual changes and compared with concurrent environmental measurements during 7 migration seasons (2008-2009 to 2014-2015). Acoustic call counts recorded on an offshore hydrophone were highly variable from year to year. Assuming an average calling rate of 7.5 calls whale-1 d-1, the estimated number of whales migrating by this hydrophone would be <10% of the population within 20 km of the offshore hydrophone in most years. In contrast, the estimated number of gray whales migrating off Santa Barbara and Los Angeles based on visual surveys grew at a greater rate (11% yr-1 and 26% yr-1, respectively) than the population size growth rate (5% yr-1). Over the studied migration seasons it seems an increasing proportion of the population was using the nearshore migration corridor in the Southern California Bight, especially near Los Angeles. This trend could increase the negative anthropogenic impact on this species. Although several large-scale climatic events occurred between 2008 and 2015, neither water temperature in the Southern California Bight nor sea ice timing in the gray whale Arctic feeding area improved generalized additive models of gray whale nearshore sightings or offshore acoustic presence. Over these times, the gray whale migration timing appears to be driven more by their biological clock and instinct than by the extrinsic factors accounted for in the present analysis. Future work should test if other factors influence the gray whale migration over longer timescales.

Van Cise, AM, Mahaffy SD, Baird RW, Mooney TA, Barlow J.  2018.  Song of my people: dialect differences among sympatric social groups of short-finned pilot whales in Hawai'i. Behavioral Ecology and Sociobiology. 72   10.1007/s00265-018-2596-1   AbstractWebsite

In many social species, acoustic dialects are used to differentiate among social groups within a local population. These acoustic dialects and their corresponding social groups are often related to distinct foraging behaviors or spatial movement patterns, and it is possible that vocal repertoire variability is one of the proximate mechanisms driving or maintaining genetic and ecological diversity at a subspecies level in social species. Short-finned pilot whales (Globicephala macrorynchus) inhabiting Hawaiian waters have a stable hierarchical social structure, with familial social units associating in larger social clusters within island-associated communities. In this study, we test the hypothesis that sympatric social groups of short-finned pilot whales have acoustically differentiated dialects, which may be used to maintain the social structure. We first examined call composition of social calls collected from photographically identified social clusters of short-finned pilot whales around the Main Hawaiian Islands, using a catalog of manually classified calls, and found that call composition differed among clusters. We then conducted ANOVA and support vector machine (SVM) learning analyses of the acoustic features of social calls. Social clusters were significantly differentiated in their acoustic features, and the SVM classification accuracy was 60%. These results indicate that vocal repertoire reflects social segregation in short-finned pilot whales and may be a driving mechanism of differentiation, potentially contributing to genetic diversity within populations. This suggests divergent acoustic population structure; however, the small sample size in this study decreases the ability to detect acoustic differences among groups. Additional sampling will improve our power to detect acoustic differences among social clusters of Hawaiian pilot whales and improve classification accuracy. The pattern described here highlights the importance of increasing the spatial and temporal resolution of conservation and management plans for this species, in order to conserve subpopulation genetic and social structure.Significance statementIn some species, vocal repertoires differ among social groups or populations of a species that use the same habitat. These differences, called dialects, are thought to be important to maintaining segregation among groups of animals with overlapping distributions, and in some cases may increase intra-specific ecological or genetic variability. This study is the first to provide evidence that sympatric social clusters of short-finned pilot whales have different vocal repertoires, and that vocal repertoire within groups may change with behavioral context. In terrestrial (e.g., elephants) and marine (e.g., killer whales, sperm whales) species with similarly stable social hierarchies, where acoustic dialects, genetic diversity, and/or ecological variability are linked with social structure, anthropogenic stressors have precipitated rapid declines in abundance with slow or nonexistent recovery. Given the myriad threats faced by short-finned pilot whales in the Hawaiian Islands, including fisheries bycatch, military and commercial anthropogenic noise, and vessel strikes, understanding intra-population social structure and its links with genetic structure and ecological variability is imperative to the proper conservation and management of this species.

Fleming, AH, Yack T, Redfern JV, Becker EA, Moore TJ, Barlow J.  2018.  Combining acoustic and visual detections in habitat models of Dall's porpoise. Ecological Modelling. 384:198-208.   10.1016/j.ecolmodel.2018.06.014   AbstractWebsite

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 linetransect survey in the Califomia 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.

Haver, SM, Gedamke J, Hatch LT, Dziak RP, Van Parijs S, McKenna MF, Barlow J, Berchok C, DiDonato E, Hanson B, Haxel J, Holt M, Lipski D, Matsumoto H, Meinig C, Mellinger DK, Moore SE, Oleson EM, Soldevilla MS, Klinck H.  2018.  Monitoring long-term soundscape trends in US Waters: The NOAA/NPS Ocean Noise Reference Station Network. Marine Policy. 90:6-13.   10.1016/j.marpol.2018.01.023   AbstractWebsite

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.

Boyd, C, Barlow J, Becker EA, Forney KA, Gerrodette T, Moore JE, Punt AE.  2018.  Estimation of population size and trends for highly mobile species with dynamic spatial distributions. Diversity and Distributions. 24:1-12.   10.1111/ddi.12663   AbstractWebsite

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.

Simonis, AE, Roch MA, Bailey B, Barlow J, Clemesha RES, Iacobellis S, Hildebrand JA, Baumann-Pickering S.  2017.  Lunar cycles affect common dolphin Delphinus delphis foraging in the Southern California Bight. Marine Ecology Progress Series. 577:221-235.   10.3354/meps12247   Abstract

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 to monitor 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 warm months, 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 warm months, 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.

Barlow, J, Griffiths ET.  2017.  Precision and bias in estimating detection distances for beaked whale echolocation clicks using a two-element vertical hydrophone array. Journal of the Acoustical Society of America. 141:4388-4397.   10.1121/1.4985109   AbstractWebsite

Detection distances are critical for cetacean density and abundance estimation using distance sampling methods. Data from a drifting buoy system consisting of an autonomous recorder and a two-element vertical hydrophone array at similar to 100-m depth are used to evaluate three methods for estimating the horizontal distance (range) to beaked whales making echolocation clicks. The precision in estimating time-differences-of-arrival (TDOA) for direct-and surface-reflected-path clicks is estimated empirically using repeated measures over short time periods. A Teager-Kaiser energy detector is used to improve estimates of TDOA for surface-reflected signals. Simulations show that array tilt in the direction of the source cannot be reliably estimated given this array geometry and these measurements of TDOA error, which means that range cannot be reliably estimated. If array tilt can be reduced to less than 0.5 degrees, range can be reliably estimated up to similar to 3000 m. If array depth is increased to 200m and array tilt is less than 1 degrees, range can be reliably estimated up to similar to 5000 m. Prior information on the depth of vocalizing beaked whales and estimates of declination angle can be used to precisely estimate range, but different analytical methods are required to avoid bias and to treat distributions of depth probabilistically.

Keen, EM, Wray J, Meuter H, Thompson KL, Barlow JP, Picard CR.  2017.  'Whale wave': shifting strategies structure the complex use of critical fjord habitat by humpbacks. Marine Ecology Progress Series. 567:211-233.   10.3354/meps12012   AbstractWebsite

A decade of visual surveys (2005-2014) revealed that humpbacks Megaptera novaeangliae occupy a temperate fjord system in British Columbia, Canada, in a wave pattern that propagates from outer channels in the summer to deep inland channels in late fall. Monte Carlo randomization confirmed this apparent pattern statistically. 'Before' and 'after' shift phases were most evident in July and October, respectively. We hypothesized that the 'whale wave' was being driven by (1) prey following, (2) the tracking of environmental proxies, (3) fine-scale philopatry, or some combination of these three factors. To evaluate these hypotheses, we collected new data in 2015, including visual and hydroacoustic surveys and oceanographic sampling. To both full-season and monthly datasets, we fit generalized additive models (GAMs) in a stepwise procedure, using variable sets that represent our hypotheses. Prey models were generally the worst predictors of humpback distribution, while the most complex habitat models were the best. The Prey model performed best in June but increasingly poorly in remaining months. The performance of all models declined throughout the season, suggesting not only that this whale wave is being driven by needs other than food, but also that untested variable(s) inform late-season distribution. Alternative explanations of the wave include physiological maintenance and social habitat partitioning. Our findings demonstrate that marine predators can use complex spatial strategies not only to navigate vast areas of ocean but also to exploit specific habitats thoroughly. Though annually persistent and specific in structure, the whale wave would go (and has gone) unnoticed in typical marine mammal surveys.

Bradford, AL, Forney KA, Oleson EM, Barlow J.  2017.  Abundance estimates of cetaceans from a line-transect survey within the US Hawaiian Islands Exclusive Economic Zone. Fishery Bulletin. 115:129-142.   10.7755/fb.115.2.1   AbstractWebsite

A ship-based line-transect survey was conducted during the summer and fall of 2010 to obtain abundance estimates of cetaceans in the U.S. Hawaiian Islands Exclusive Economic Zone (EEZ). Given the low sighting rates for cetaceans in the study area, sightings from 2010 were pooled with sightings made during previous line-transect surveys within the central Pacific for calculating detection functions, which were estimated by using a multiple-covariate approach. The trackline detection probabilities used in this study are the first to reflect the effect of sighting conditions in the central Pacific and are markedly lower than estimates used in previous studies. During the survey, 23 cetacean species (17 odontocetes and 6 mysticetes) were seen, and abundance was estimated for 19 of them (15 odontocetes and 4 mysticetes). Group size and Beaufort sea state were the most important factors affecting the detectability of cetacean groups. Across all species, abundance estimates and coefficients of variation range from 133 to 72,528 and from 0.29 to 1.13, respectively. Estimated abundance is highest for delphinid species and lowest for the killer whale (Orcinus orca) and rorqual species. Overall, cetacean density in the Hawaiian Islands EEZ is low in comparison with highly productive oceanic regions.

Van Cise, AM, Roch MA, Baird RW, Mooney TA, Barlow J.  2017.  Acoustic differentiation of Shiho- and Naisa-type short-finned pilot whales in the Pacific Ocean. Journal of the Acoustical Society of America. 141:737-748.   10.1121/1.4974858   AbstractWebsite

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.

Jacobson, EK, Forney KA, Barlow J.  2017.  Using paired visual and passive acoustic surveys to estimate passive acoustic detection parameters for harbor porpoise abundance estimates. Journal of the Acoustical Society of America. 141:219-230.   10.1121/1.4973415   AbstractWebsite

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 km(2) 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.

Kendall-Bar, JM, Weller DW, Fearnbach H, Shane S, Schorr GS, Falcone EA, Calambokidis J, Schulman-Janiger A, Barlow J.  2016.  Movement and occurrence patterns of short-finned pilot whales (Globicephala macrorhynchus) in the Eastern North Pacific. Aquatic Mammals. 42:300-305.   10.1578/am.42.3.2016.300   AbstractWebsite
Griffiths, ET, Barlow J.  2016.  Cetacean acoustic detections from free-floating vertical hydrophone arrays in the southern California Current. The Journal of the Acoustical Society of America. 140:EL399-EL404.   10.1121/1.4967012   AbstractWebsite
Keating, JL, Barlow J, Rankin S.  2016.  Shifts in frequency-modulated pulses recorded during an encounter with Blainville's beaked whales (Mesoplodon densirostris). Journal of the Acoustical Society of America. 140:EL166-EL171.   10.1121/1.4959598   AbstractWebsite

Echolocation signals produced by beaked whales (family: Ziphiidae) include frequency-modulated (FM) pulses that appear to have species-specific characteristics. To date there has been no established evidence that a single species of beaked whale might produce more than one type of FM pulse. In 2014 a group of Blainville's beaked whales (Mesoplodon densirostris) were sighted off of Southern California; recordings included FM pulses with significant increases in peak frequency, center frequency, and -10 dB bandwidth relative to FM pulses previously attributed to this species. This research suggests there may be greater variation in received beaked whale FM pulses than previously understood.

Fleming, AH, Clark CT, Calambokidis J, Barlow J.  2016.  Humpback whale diets respond to variance in ocean climate and ecosystem conditions in the California Current. Global Change Biology. 22:1214-1224.   10.1111/gcb.13171   AbstractWebsite

Large, migratory predators are often cited as sentinel species for ecosystem processes and climate-related changes, but their utility as indicators is dependent upon an understanding of their response to environmental variability. Documentation of the links between climate variability, ecosystem change and predator dynamics is absent for most top predators. Identifying species that may be useful indicators and elucidating these mechanistic links provides insight into current ecological dynamics and may inform predictions of future ecosystem responses to climatic change. We examine humpback whale response to environmental variability through stable isotope analysis of diet over a dynamic 20-year period (1993-2012) in the California Current System (CCS). Humpback whale diets captured two major shifts in oceanographic and ecological conditions in the CCS. Isotopic signatures reflect a diet dominated by krill during periods characterized by positive phases of the North Pacific Gyre Oscillation (NPGO), cool sea surface temperature (SST), strong upwelling and high krill biomass. In contrast, humpback whale diets are dominated by schooling fish when the NPGO is negative, SST is warmer, seasonal upwelling is delayed and anchovy and sardine populations display increased biomass and range expansion. These findings demonstrate that humpback whales trophically respond to ecosystem shifts, and as a result, their foraging behavior is a synoptic indicator of oceanographic and ecological conditions across the CCS. Multi-decadal examination of these sentinel species thus provides insight into biological consequences of interannual climate fluctuations, fundamental to advancing ecosystem predictions related to global climate change.

Rankin, S, Oswald JN, Simonis AE, Barlow J.  2015.  Vocalizations of the rough-toothed dolphin, Steno bredanensis, in the Pacific Ocean. Marine Mammal Science. 31:1538-1548.   10.1111/mms.12226   AbstractWebsite
Barlow, J.  2015.  Inferring trackline detection probabilities, g(0), for cetaceans from apparent densities in different survey conditions. Marine Mammal Science. 31:923-943.   10.1111/mms.12205   AbstractWebsite

Visual line-transect surveys are commonly used to estimate cetacean abundance. A key parameter in such studies is g(0), the probability of detecting an animal that is directly on the transect line. This is typically considered to be constant for a species across survey conditions. A method is developed to estimate the relative values of g(0) in different survey conditions (Beaufort state) by comparing Beaufort-specific density estimates. The approach is based on fitting generalized additive models, with the presence of a sighting on a survey segment as the dependent variable, Beaufort state as the key explanatory variable, and year, latitude, and longitude as nuisance variables to control for real differences in density over time and space. Values of relative g(0) are estimated for 20 cetacean taxa using 175,000km of line-transect survey data from the eastern and central Pacific Ocean from 1986 to 2010. Results show that g(0) decreases as Beaufort state increases, even for visually conspicuous species. This effect is greatest for the least conspicuous species (rough-toothed dolphins, beaked whales, minke whales, and dwarf and pygmy sperm whales). Ignoring these large effects results in a nontrivial bias in cetacean abundance estimates.

Forney, KA, Becker EA, Foley DG, Barlow J, Oleson EM.  2015.  Habitat-based models of cetacean density and distribution in the central North Pacific. Endangered Species Research. 27:1-20.   10.3354/esr00632   AbstractWebsite

The central North Pacific Ocean includes diverse temperate and tropical pelagic habitats. Studies of the abundance and distribution of cetaceans within these dynamic marine ecosystems have generally been patchy or conducted at coarse spatial and temporal scales, limiting their utility for pelagic conservation planning. Habitat-based density models provide a tool for identifying pelagic areas of importance to cetaceans, because model predictions are spatially explicit. In this study, we present habitat-based models of cetacean density that were developed and validated for the central North Pacific. Spatial predictions of cetacean densities and measures of uncertainty were derived based on data collected during 15 large-scale shipboard cetacean and ecosystem assessment surveys conducted from 1997 to 2012. We developed generalized additive models using static and remotely sensed dynamic habitat variables, including distance to land, sea-surface temperature (SST), standard deviation of SST, surface chlorophyll concentration, seasurface height (SSH), and SSH root-mean-square variation. The resulting models, developed using new grid-based prediction methods, provide finer scale information on the distribution and density of cetaceans than previously available. Habitat-based abundance estimates around Hawaii are similar to those derived from standard line-transect analyses of the same data and provide enhanced spatial resolution to inform management and conservation of pelagic cetacean species.

Pardo, MA, Gerrodette T, Beier E, Gendron D, Forney KA, Chivers SJ, Barlow J, Palacios DM.  2015.  Inferring cetacean population densities from the absolute dynamic topography of the ocean in a hierarchical bayesian framework. Plos One. 10   10.1371/journal.pone.0120727   AbstractWebsite

We inferred the population densities of blue whales (Balaenoptera musculus) and short-beaked common dolphins (Delphinus delphis) in the Northeast Pacific Ocean as functions of the water-column's physical structure by implementing hierarchical models in a Bayesian framework. This approach allowed us to propagate the uncertainty of the field observations into the inference of species-habitat relationships and to generate spatially explicit population density predictions with reduced effects of sampling heterogeneity. Our hypothesis was that the large-scale spatial distributions of these two cetacean species respond primarily to ecological processes resulting from shoaling and outcropping of the pycnocline in regions of wind-forced upwelling and eddy-like circulation. Physically, these processes affect the thermodynamic balance of the water column, decreasing its volume and thus the height of the absolute dynamic topography (ADT). Biologically, they lead to elevated primary productivity and persistent aggregation of low-trophic-level prey. Unlike other remotely sensed variables, ADT provides information about the structure of the entire water column and it is also routinely measured at high spatial-temporal resolution by satellite altimeters with uniform global coverage. Our models provide spatially explicit population density predictions for both species, even in areas where the pycnocline shoals but does not outcrop (e.g. the Costa Rica Dome and the North Equatorial Countercurrent thermocline ridge). Interannual variations in distribution during El Nino anomalies suggest that the population density of both species decreases dramatically in the Equatorial Cold Tongue and the Costa Rica Dome, and that their distributions retract to particular areas that remain productive, such as the more oceanic waters in the central California Current System, the northern Gulf of California, the North Equatorial Countercurrent thermocline ridge, and the more southern portion of the Humboldt Current System. We posit that such reductions in available foraging habitats during climatic disturbances could incur high energetic costs on these populations, ultimately affecting individual fitness and survival.

Calderan, S, Miller B, Collins K, Ensor P, Double M, Leaper R, Barlow J.  2014.  Low-frequency vocalizations of sei whales (Balaenoptera borealis) in the Southern Ocean. Journal of the Acoustical Society of America. 136:EL418-EL423.   10.1121/1.4902422   AbstractWebsite

Simultaneous sightings and acoustic detections of sei whales (Balaenoptera borealis) are scarce, and there are few published data describing their vocalizations. Analysis of recordings from directional frequency analysis and recording sonobuoys in the presence of sei whales in the Southern Ocean in March 2013 identified both downsweep and upsweep calls. Sound frequencies within all calls were between 34 and 87 Hz with an average call duration of 1.1 s. These very low-frequency sounds share characteristics with sei whale calls recorded near the Hawaiian Islands and off Cape Cod in winter and summer, respectively, but are the first documented sei whale calls in the Southern Ocean that are clearly less than 100 Hz. (C) 2014 Acoustical Society of America

Forney, KA, Barlow JP, Hildebrand JA, Douglas AB, Calambokidis J, Sydeman WJ.  2014.  Effects of fluctuations in sea-surface temperature on the occurrence of small cetaceans off Southern California. Fishery Bulletin. 112:159-177.   10.7755/fb.112.2-3.5   AbstractWebsite

The link between ocean temperature and spatial and temporal distribution patterns of 8 species of small cetaceans off Southern California was examined during the period 1979-2009. Averages and anomalies of sea-surface temperatures (SSTs) were used as proxies for SST fluctuations on 3 temporal scales: seasonal, El Nino-Southern Oscillations (ENSO), and Pacific Decadal Oscillations (PDO). The hypothesis that cetacean species assemblages and habitat associations in southern California waters co-vary with these periodic changes in SST was tested by using generalized additive models. Seasonal SST averages were included as a predictor in the models for Dall's porpoise (Phocoenoides dalli), and common dolphins (Delphinus spp.), northern right whale dolphin (Lissodelphis borealis), and Risso's dolphin (Grampus griseus). The ENSO index was included as a predictor for northern right whale, long-beaked common (Delphinus capensis), and Risso's dolphins. The PDO index was selected as a predictor for Dall's porpoise and Pacific white-sided (Lagenorhynchus obliquidens), common, and bottlenose (Tursiops truncatus) dolphins. A metric of bathymetric depth was included in every model, and seafloor slope was included in 5 of the 9 models, an indication of a distinctive spatial distribution for each species that may represent niche or resource partitioning in a region where multiple species have overlapping ranges. Temporal changes in distribution are likely a response to changes in prey abundance or dispersion, and these patterns associated with SST variation may foreshadow future, more permanent shifts in distribution range that are due to global climate change.

Miller, BS, Collins K, Barlow J, Calderan S, Leaper R, McDonald M, Ensor P, Olson PA, Olavarria C, Double MC.  2014.  Blue whale vocalizations recorded around New Zealand: 1964-2013. Journal of the Acoustical Society of America. 135:1616-1623.   10.1121/1.4863647   AbstractWebsite

Previous underwater recordings made in New Zealand have identified a complex sequence of low frequency sounds that have been attributed to blue whales based on similarity to blue whale songs in other areas. Recordings of sounds with these characteristics were made opportunistically during the Southern Ocean Research Partnership's recent Antarctic Blue Whale Voyage. Detections of these sounds occurred all around the South Island of New Zealand during the voyage transits from Nelson, New Zealand to the Antarctic and return. By following acoustic bearings from directional sonobuoys, blue whales were visually detected and confirmed as the source of these sounds. These recordings, together with the historical recordings made northeast of New Zealand, indicate song types that persist over several decades and are indicative of the year-round presence of a population of blue whales that inhabits the waters around New Zealand. Measurements of the four-part vocalizations reveal that blue whale song in this region has changed slowly, but consistently over the past 50 years. The most intense units of these calls were detected as far south as 53 degrees S, which represents a considerable range extension compared to the limited prior data on the spatial distribution of this population. (C) 2014 Acoustical Society of America.

Bradford, AL, Forney KA, Oleson EM, Barlow J.  2014.  Accounting for subgroup structure in line-transect abundance estimates of false killer whales (Pseudorca crassidens) in Hawaiian waters. Plos One. 9   10.1371/journal.pone.0090464   AbstractWebsite

For biological populations that form aggregations (or clusters) of individuals, cluster size is an important parameter in line-transect abundance estimation and should be accurately measured. Cluster size in cetaceans has traditionally been represented as the total number of individuals in a group, but group size may be underestimated if group members are spatially diffuse. Groups of false killer whales (Pseudorca crassidens) can comprise numerous subgroups that are dispersed over tens of kilometers, leading to a spatial mismatch between a detected group and the theoretical framework of line-transect analysis. Three stocks of false killer whales are found within the U. S. Exclusive Economic Zone of the Hawaiian Islands (Hawaiian EEZ): an insular main Hawaiian Islands stock, a pelagic stock, and a Northwestern Hawaiian Islands (NWHI) stock. A ship-based line-transect survey of the Hawaiian EEZ was conducted in the summer and fall of 2010, resulting in six systematic-effort visual sightings of pelagic (n = 5) and NWHI (n = 1) false killer whale groups. The maximum number and spatial extent of subgroups per sighting was 18 subgroups and 35 km, respectively. These sightings were combined with data from similar previous surveys and analyzed within the conventional line-transect estimation framework. The detection function, mean cluster size, and encounter rate were estimated separately to appropriately incorporate data collected using different methods. Unlike previous line-transect analyses of cetaceans, subgroups were treated as the analytical cluster instead of groups because subgroups better conform to the specifications of line-transect theory. Bootstrap values (n = 5,000) of the line-transect parameters were randomly combined to estimate the variance of stock-specific abundance estimates. Hawai'i pelagic and NWHI false killer whales were estimated to number 1,552 (CV = 0.66; 95% CI = 479-5,030) and 552 (CV = 1.09; 95% CI = 97-3,123) individuals, respectively. Subgroup structure is an important factor to consider in line-transect analyses of false killer whales and other species with complex grouping patterns.

Fearnbach, H, Durban JW, Ellifrit DK, Waite JM, Matkin CO, Lunsford CR, Peterson MJ, Barlow J, Wade PR.  2014.  Spatial and social connectivity of fish-eating "Resident" killer whales (Orcinus orca) in the northern North Pacific. Marine Biology. 161:459-472.   10.1007/s00227-013-2351-0   AbstractWebsite

The productive North Pacific waters of the Gulf of Alaska, Aleutian Islands and Bering Sea support a high density of fish-eating "Resident" type killer whales (Orcinus orca), which overlap in distribution with commercial fisheries, producing both direct and indirect interactions. To provide a spatial context for these interactions, we analyzed a 10-year dataset of 3,058 whale photo-identifications from 331 encounters within a large (linear similar to 4,000 km) coastal study area to investigate the ranging and social patterns of 532 individually identifiable whales photographed in more than one encounter. Although capable of large-scale movements (maximum 1,443 km), we documented ranges generally < 200 km, with high site fidelity across summer sampling intervals and also re-sightings during a winter survey. Bayesian analysis of pair-wise associations identified four defined clusters, likely representing groupings of stable matrilines, with distinct ranging patterns, that combined to form a large network of associated whales that ranged across most of the study area. This provides evidence of structure within the Alaska stock of Resident killer whales, important for evaluating ecosystem and fisheries impacts. This network included whales known to depredate groundfish from longline fisheries, and we suggest that such large-scale connectivity has facilitated the spread of depredation.

Moore, JE, Barlow JP.  2013.  Declining Abundance of Beaked Whales ( Family Ziphiidae) in the California Current Large Marine Ecosystem. Plos One. 8 AbstractWebsite

Beaked whales are among the most diverse yet least understood groups of marine mammals. A diverse set of mostly anthropogenic threats necessitates improvement in our ability to assess population status for this cryptic group. The Southwest Fisheries Science Center (NOAA) conducted six ship line-transect cetacean abundance surveys in the California Current off the contiguous western United States between 1991 and 2008. We used a Bayesian hidden-process modeling approach to estimate abundance and population trends of beaked whales using sightings data from these surveys. We also compiled records of beaked whale stranding events (3 genera, at least 8 species) on adjacent beaches from 1900 to 2012, to help assess population status of beaked whales in the northern part of the California Current. Bayesian posterior summaries for trend parameters provide strong evidence of declining beaked whale abundance in the study area. The probability of negative trend for Cuvier's beaked w!