Insights into the population structure of blue whales in the Eastern North Pacific from recent sightings and photographic identification

Blue whales were widely distributed in the North Pacific prior to the primary period of modern commercial whaling in the early 1900s. Despite concentrations of blue whale catches off British Columbia and in the Gulf of Alaska, there had been few documented sightings in these areas since whaling for blue whales ended in 1965. In contrast, large concentrations of blue whales have been documented off California and Baja California and in the eastern tropical Pacific since the 1970s, but it was not known if these animals were part of the same population that previously ranged into Alaskan waters. We document 15 blue whale sightings off British Columbia and in the Gulf of Alaska made since 1997, and use identification photographs to show that whales in these areas are currently part of the California feeding population. We speculate that this may represent a return to a migration pattern that has existed for earlier periods for eastern North Pacific blue whale population. One possible explanation for a shift in blue whale use is changes in prey driven by changes in oceanographic conditions, including the Pacific Decadal Oscillation (PDO), which coincides with some of the observed shifts in blue whale occurrence.     

BLUE WHALE, BALAENOPTERA MUSCULUS, VOCALIZATIONS FROM THE WATERS OFF CENTRAL CALIFORNIA

Low-frequency calls produced by blue whales, Balaenoptera musculus , were recorded in the northeastern Pacific Ocean off central California. Two blue whales were sighted during a vessel-based marine mammal survey, and when sonobuoys were subsequently deployed, blue whale calls were recorded. A third recording was obtained during the survey from a blue whale that was not seen. Recordings with 15, 25, and 55 min of calls were obtained from these individuals. The three recordings all contain two-part, low-frequency calls with slight interindividual variation. The calls consist of an amplitude modulated (AM) signal with a mean center frequency of 16.5 Hz, followed by a downsweep whose mean center frequency sweeps from 18.2 Hz to 16.6 Hz. The recordings are compared with blue whale recordings from the Pacific and Atlantic Oceans. The geographic variability suggests that blue whale calls may be used as an acoustic indicator of stock identity.     

Seasonal acoustic behavior of blue whales (Balaenoptera musculus) in the Gulf of California,Mexico

Six years of passive acoustic monitoring data from the Gulf of California reveal seasonality and movements for the northeastern Pacific blue whales. Three sites were studied, one from the southern (Punta Pescadero) and two from the northern (Isla Tiburon and Canal de Ballenas) regions. A total of 4,953 h were analyzed, and 15,539 blue whale calls were detected, of which 2,723 (18%) were A calls, 11,249 were B calls (72%), and 1,567 were D calls (10%). A and B calls were produced both as song units (2,524) or AB singular calls (2,026). The high rate of songs and their seasonality suggest that the GC is a winter‐breeding ground. A shift from AB call predominance in winter, to D calls in spring and early summer, especially at the entrance of the GC, suggests the importance of this area for reproduction and foraging. Analysis of calling frequency suggests a clear movement of blue whales from the southern region (Punta Pescadero) to the northern regions (Canal de Ballenas and Isla Tiburon), with subsequent southern movement in March. The seasonality and mobility of blue whales in the Gulf of California, inferred from their calling, contributes to the ecological understanding of this population.     

Seasonal detection of three types of “pygmy” blue whale calls in the Indian Ocean

The Indian Ocean is an area in which a rich suite of cetacean fauna, including at least two subspecies of blue whale, is found; yet little information beyond stranding data and short‐term surveys for this species is available. Pygmy blue whale (Balaenoptera musculus spp.) call data are presented that provide novel information on the seasonal and geographic distribution of these animals. Acoustic data were recorded from January 2002 to December 2003 by hydrophones at three stations of the International Monitoring System, including two near the subequatorial Diego Garcia Atoll and a third southwest of Cape Leeuwin, Australia. Automated spectrogram correlation methods were used to scan for call types attributed to pygmy blue whales. Sri Lanka calls were the most common and were detected year‐round off Diego Garcia. Madagascar calls were only recorded on the northern Diego Garcia hydrophone during May and July, whereas Australia calls were only recorded at Cape Leeuwin, between December and June. Differences in geographic and seasonal patterns of these three distinct call types suggest that they may represent separate acoustic populations of pygmy blue whales and that these “acoustic populations” should be considered when assessing conservation needs of blue whales in the Indian Ocean.     

SEASONAL OCCURRENCE OF SPERM WHALE (PHYSETER MACROCEPHALUS) SOUNDS IN THE GULF OF ALASKA, 1999–2001

An acoustic survey for sperm whales was conducted in the Gulf of Alaska. Six autonomous hydrophones continuously recorded sound signals below 500 Hz from October 1999 to May 2001. After recovery, recordings were processed using an automatic process to detect usual clicks of sperm whales. The detection algorithm equalized background noise, summed the data in a frequency band, and then used autocorrelation to detect the whales' highly regular clicks. Detections were checked manually, revealing that 98% of detections did contain clicks. Results indicate that sperm whales are present in the Gulf of Alaska year-round; this result extends what is known from whaling data, which were gathered principally in summer. Sperm whales were more common in summer than winter by a factor of roughly two, and occurred less often at the westernmost site surveyed (52°N, 157°W) than elsewhere in the Gulf. This is the first study of sperm whales based exclusively on remote acoustic sensing. This methodology is feasible because sperm whale clicks extend to frequencies (∼100 Hz) low enough to be recorded by low-sample-rate instruments that operate continuously, and because the detection algorithm has a low false-detection rate. The methodology may be replicated to facilitate comparisons between different time periods and geographic regions.     

Quantifying spatial and temporal variation of North Pacific fin whale (Balaenoptera physalus) acoustic behavior

In order to help develop hypotheses of connectivity among North Pacific fin whales, we examine recordings from 10 regions collected in the spring and fall. We develop a Random Forest model to classify fin whale note types that avoids manual note classification errors. We also present a method that objectively quantifies the note and pattern composition of recordings. We find that fin whale recordings near Hawaii have distinctive patterns, similar to those found in other regions in the central North Pacific, suggesting potential migration pathways. Our results are consistent with previous studies that suggest there may be two different populations utilizing the Chukchi Sea and central Aleutians in the fall and mix to some degree in the southern Bering Sea. Conversely, we found little difference between spring and fall recordings in the eastern Gulf of Alaska, suggesting some residency of whales in this region. This is likely due to fine scale similarities of calls among the inshore regions of British Columbia, while offshore areas are being utilized by whales traveling from various distant areas. This study shows how our novel approach to characterize recordings is an objective and informative way to standardize spatial and temporal comparisons of fin whale recordings.     

AN ACOUSTIC LINK BETWEEN BLUE WHALES IN THE EASTERN TROPICAL PACIFIC AND THE NORTHEAST PACIFIC1

Blue whale calls in the eastern North Pacific Ocean consist of a two-part call often termed the A-B call. This call has been described for regions offshore of Oregon, Washington, and California, USA and the Sea of Cortez, Mexico (reviewed in Rivers 1997). Data collected from moored hydrophones in the eastern tropical Pacific (ETP) indicate that the A-B pattern is common in this region as well. There is consistency in this call type throughout the eastern North Pacific and throughout the year. This acoustic evidence indicates continuity between blue whales in the ETP and those found west of North America. The acoustic data suggest that the population of blue whales generally referred to as the “Californi/Mexico” stock might better be termed the “northeast Pacific” stock of blue whales.     

Call types of Bigg’s killer whales (Orcinus orca) in western Alaska: using vocal dialects to assess population structure

Bigg’s killer whales (Orcinus orca; i.e. ‘transient’ ecotype), as apex predators, are important to the dynamics of marine ecosystems, but little is known about their population structure in western Alaska. Currently, all Bigg’s killer whales in western Alaska are ascribed to a single broad stock for management under the US Marine Mammal Protection Act. However, recent nuclear microsatellite and mitochondrial DNA analyses indicate that this stock is likely comprised of genetically distinct sub-populations. In accordance with what is known about killer whale vocal dialects in other locations, we used the spatial distribution of group-specific call types to investigate the population structure of Bigg’s killer whales in this part of Alaska. Digital audio recordings were collected from 33 Bigg’s killer whale encounters throughout the Aleutian and Pribilof Islands in the summers of 2001–2007 and 2009–2010. Recorded calls were qualitatively classified into discrete types and then quantitatively described using 12 structural and time-frequency measures. Resulting call categories were validated using a random forest approach. A total of 36 call types and subtypes were identified across the entire study area, and regional patterns of call type use revealed three distinct dialects which correspond to proposed genetic delineations. Our results suggest that there are at least three acoustically and genetically distinct sub-populations in western Alaska, and we present an initial catalogue for this area describing the regional vocal repertoires of Bigg’s killer whale call types.     

Blue and fin whale acoustic presence around Antarctica during 2003 and 2004

Seasonal and spatial variations of blue ( Balaenoptera musculus ) and fin whale ( B. physalus ) calls were analyzed from recordings collected with Acoustic Recording Packages (ARPs) deployed between January 2003 and July 2004 at four circumpolar locations: the Western Antarctic Peninsula (WAP), the Scotia Sea (SS), Eastern Antarctica (EA), and the Ross Sea (RS). Call characteristics were compared among sites using the average pressure spectrum levels from 1 month of data at each location. Presence of calls was analyzed using automatic call detection and acoustic power analysis methods. Blue whale calls were recorded year-round, with the highest detections in February–May and November. This suggests that the blue whale population may not migrate synchronously, and may indicate long duration calls are more common during migrations. Fin whale calls were detected only during February–July. Two distinct fin whale call types were recorded, suggesting a possible separation into two populations. The calls at the EA site had a secondary frequency peak in the pressure spectrum at 99 Hz and the calls at the WAP and the SS sites had a peak at 89 Hz. No fin whale calls were detected at the RS site. Acoustics are a good tool to monitor large whales in the Southern Ocean.     

North Pacific right whale (Eubalaena japonica) seasonal and diel calling patterns from long‐term acoustic recordings in the southeastern Bering Sea, 2000–2006

We assessed North Pacific right whale (Eubalaena japonica) seasonal and daily calling patterns in the southeastern Bering Sea (SEBS) using long‐term hydrophone recordings from October 2000 through January 2006. We detected right whale calls on the SEBS middle shelf (<100 m depth) as early as May, intermittently throughout summer and fall, and as late as December. Calls also were detected on one day in June 2005 on the SEBS slope (>1,000 m), but were not detected near Kodiak Island from April to August 2003. In months with calls, detections occurred on more days in July–October (≥6 d/mo), than from May to June or November to December (≤3 d/mo). Calls were clustered in time and were usually detected on 1–3 consecutive days with a median interval of 6.5 d for calls >1 d apart. Hourly calling rates were significantly higher at night than during the day. These data indicate that right whales occur in the SEBS later in the year than previously known, intermittently pass through the middle‐shelf study region, and usually remain there no longer than a few days. Right whale habitat use in the SEBS may intensify in mid‐summer through early fall based on higher monthly and daily call detection rates.     

Horizontal transmission of vocal traditions in killer whale (<Emphasis Type="Italic">Orcinus orca</Emphasis>) dialects

Unlike most other mammals, killer whales are capable of vocal learning and learn the dialect of their natal pod from their mothers. The classical model of killer whale dialect development suggests that the repertoire of calls is learned only “vertically” from mother to offspring, and calls evolve gradually with time by random drift caused by the accumulation of copying errors. However, some observations suggest that not only “vertical” (from mother to offspring) vocal learning can occur in killer whales, but also “horizontal” (between adult animals). In this study we analyzed the distribution of different call types and similarity of calls from the same type in different pods of killer whales from Kamchatka waters to estimate the probability of existence of interpod horizontal transmission of vocal traditions in killer whales. We found that the degree of similarity of K1 calls and K5 calls in different pods can differ. This situation contradicts the classical hypothesis and is possible in two cases: if different call types change with various speed in different pods, or if horizontal transmission of call features takes place. The distribution of K4 and K10 call types across pods also suggests the existence of horizontal transmission: K4 calls occur in the dialects of five of ten pods, and K10 calls, in six of ten pods, but only one pod has both K4 and K10 calls. Our results suggest that the real picture of the distribution of call features and call types in killer whale dialects contradicts the classical hypothesis of killer whale dialect evolution through the accumulation of copying errors.     

Comparing marine mammal acoustic habitats in Atlantic and Pacific sectors of the High Arctic: year-long records from Fram Strait and the Chukchi Plateau

During the International Polar Year (IPY), acoustic recorders were deployed on oceanographic moorings in Fram Strait and on the Chukchi Plateau, representing the first coordinated year-round sampling of underwater acoustic habitats at two sites in the High Arctic. Examination of species-specific marine mammal calls recorded from autumn 2008–2009 revealed distinctly different acoustic habitats at each site. Overall, the Fram Strait site was acoustically complex compared with the Chukchi Plateau site. In Fram Strait, calls from bowhead whales (Balaena mysticetus) and a variety of toothed whales (odontocetes) were recorded year-round, as were airgun pulses from seismic surveys. In addition, calls from blue whales (Balaenoptera musculus) and fin whales (B. physalus) were recorded from June to October and August to March, respectively. Conversely, at the Chukchi Plateau site, beluga (Delphinapterus leucas) and bowhead whale calls were recorded primarily from May to August, with airgun signals detected only in September–October. Ribbon seal (Phoca fasciata) calls were detected in October–November, with no marine mammals calls at all recorded from December to February. Of note, ice-adapted bearded seals (Erignathus barbatus) were recorded at both sites, primarily in spring and summer, corresponding with the mating season for that species. Differences in acoustic habitats between the two sites were related to contrasts in sea ice cover, temperature, patterns of ocean circulation and contributions from anthropogenic noise sources. These data provide a provisional baseline for the comparison of underwater acoustic habitats between Pacific and Atlantic sectors of the High Arctic.     

Red Shift,Blue Shift: Investigating Doppler Shifts,Blubber Thickness,and Migration as Explanations of Seasonal Variation in the Tonality of Antarctic Blue Whale Song

The song of Antarctic blue whales (Balaenoptera musculus intermedia) comprises repeated, stereotyped, low-frequency calls. Measurements of these calls from recordings spanning many years have revealed a long-term linear decline as well as an intra-annual pattern in tonal frequency. While a number of hypotheses for this long-term decline have been investigated, including changes in population structure, changes in the physical environment, and changes in the behaviour of the whales, there have been relatively few attempts to explain the intra-annual pattern. An additional hypothesis that has not yet been investigated is that differences in the observed frequency from each call are due to the Doppler effect. The assumptions and implications of the Doppler effect on whale song are investigated using 1) vessel-based acoustic recordings of Antarctic blue whales with simultaneous observation of whale movement and 2) long-term acoustic recordings from both the subtropics and Antarctic. Results from vessel-based recordings of Antarctic blue whales indicate that variation in peak-frequency between calls produced by an individual whale was greater than would be expected by the movement of the whale alone. Furthermore, analysis of intra-annual frequency shift at Antarctic recording stations indicates that the Doppler effect is unlikely to fully explain the observations of intra-annual pattern in the frequency of Antarctic blue whale song. However, data do show cyclical changes in frequency in conjunction with season, thus suggesting that there might be a relationship among tonal frequency, body condition, and migration to and from Antarctic feeding grounds.     

FRIENDS OF WILDLIFE SOUND AT NSA

ABSTRACT

The problem of categorization arises in any classification system because classes should be discrete while the characteristics of most natural objects and aspects of nature are more or less gradual. In systematics, this problem usually is solved by creating several levels of categories, such as class, order, family, genus and species. In the existing killer whale discrete call classification, only two levels occur—call type and call subtype. In this paper we describe structural categories at a broader level than call type in the discrete sounds of killer whales and compare these categories between and within vocal clans in a community of resident killer whales from Southeast Kamchatka, Russian Far East, and also with killer whales outside this community. We found four main classes of discrete calls in the repertoire of resident killer whales from Southeast Kamchatka. The calls of Southeast Kamchatka transient killer whales and Sakhalin killer whales do not fall into these classes. This suggests that the resident killer whale community from Southeast Kamchatka has some rules defining the structure of calls which are typical for this community. Consequently, all resident killer whales from Southeast Kamchatka can be said to share the same vocal tradition.     

THE EFFECT OF VESSEL NOISE ON THE VOCAL BEHAVIOR OF BELUGAS IN THE ST. LAWRENCE RIVER ESTUARY,CANADA

During June-July 1991, we monitored the vocal behavior of belugas before, during, and after exposure to noise from a small motorboat and a ferry to determine if there were any consistent patterns in their vocal behavior when exposed to these two familiar, but different sources of potential disturbance. Vocal responses were observed in all trials and were more persistent when whales were exposed to the ferry than to the small boat. These included (1) a progressive reduction in calling rate from 3.4–10.5 calls/whale/min to 0.0 or <1.0 calls/whale/min while vessels were approaching; (2) brief increases in the emission of falling tonal calls and the theree pulsed-tone call types; (3) at distances <1 km, an increase in the repetition of specific calls, and (4) a shift in frequency bands used by vocalizing animals from a mean frequency of 3.6 kHz prior to exposure to noise to frequencies of 5.2-8.8 kHz when vessels were close to the whales.     

Usage of monophonic and biphonic calls by free-ranging resident killer whales (Orcinus orca) in Kamchatka, Russian Far East

Killer whale discrete calls include types containing an overlapping high-frequency component (biphonic calls) and types without an overlapping high-frequency component (monophonic calls). In the resident killer whales of the Northeast Pacific, biphonic discrete calls exhibit higher source levels than monophonic calls, which suggests different active space and consequently different functions for monophonic and biphonic call types. In this study we investigate the potential communicative functions of monophonic and biphonic discrete calls produced by killer whales from Kamchatka (Northwest Pacific). We analyze how the usage of these calls depends on the number of pods present in the area and type of activity. Our results show that the usage of monophonic and biphonic calls in Kamchatkan killer whales depends on the number of pods in the area and is less dependent on the type of activity. Biphonic calls are more common when more than one pod is present in the area and could therefore function as markers of pod and matriline affiliation, serving mainly as cohesion signals. Monophonic calls dominated the vocalizations when a single pod was present, while in the presence of more than one pod both categories were used in equal proportions.     

SPERM WHALES IN THE GULF OF CALIFORNIA: RESIDENCY, MOVEMENTS, BEHAVIOR, AND THE POSSIBLE INFLUENCE OF VARIATION IN FOOD SUPPLY

Sperm whale movements, residency, population structure, and behavior were investigated in the Gulf of California in 1998 and 1999. Variations in sperm whale movement patterns and behavior were related to changes in prey abundance (jumbo squid, Dosidicus gigas ) determined by fishery statistics. Photo-identification data revealed that seven female sperm whales moved into the Gulf of California from the Galapagos Islands, traveling up to 3,803 km. These are among the longest documented movements for female sperm whales. There were significant differences in speed and distance traveled during a dive cycle between 1998 and 1999 (low and high squid abundance). In 1999 there were also significant differences in small-scale movements and behavior between the northern and the southern part of the study area (high and low prey abundance). These results suggest that when food resources are low, sperm whales travel in straighter lines, dive for longer periods, travel larger distances during dive cycles, and at higher speed. In 1999 there were significant differences in time spent socializing in areas of high prey abundance versus areas of low abundance. All of these changes in behavior were consistent with increased foraging effort when squid abundance was low. A high proportion of mature males and first-year calves were observed in the Gulf of California, suggesting that it is an important sperm whale breeding ground.     

Synchronous Seasonal Change in Fin Whale Song in the North Pacific

Fin whale (Balaenoptera physalus) song consists of down-swept pulses arranged into stereotypic sequences that can be characterized according to the interval between successive pulses. As in blue (B. musculus) and humpback whales (Megaptera novaeangliae), these song sequences may be geographically distinct and may correlate with population boundaries in some regions. We measured inter-pulse intervals of fin whale songs within year-round acoustic datasets collected between 2000 and 2006 in three regions of the eastern North Pacific: Southern California, the Bering Sea, and Hawaii. A distinctive song type that was recorded in all three regions is characterized by singlet and doublet inter-pulse intervals that increase seasonally, then annually reset to the same shorter intervals at the beginning of each season. This song type was recorded in the Bering Sea and off Southern California from September through May and off Hawaii from December through April, with the song interval generally synchronized across all monitoring locations. The broad geographic and seasonal occurrence of this particular fin whale song type may represent a single population broadly distributed throughout the eastern Pacific with no clear seasonal migratory pattern. Previous studies attempting to infer population structure of fin whales in the North Pacific using synchronous individual song samples have been unsuccessful, likely because they did not account for the seasonal lengthening in song intervals observed here.     

SEASONAL OCCURRENCE OF NORTH ATLANTIC RIGHT WHALE (EUBALAENA GLACIALIS) VOCALIZATIONS AT TWO SITES ON THE SCOTIAN SHELF

A year-long acoustic survey for critically endangered North Atlantic right whales was conducted at two sites on the central and western Scotian Shelf. Autonomous hydrophones recorded sound continuously from July 2004 to August 2005. Right whale contact calls (upcalls) were identified using automatic recognition software, and the resulting detections were checked manually. Substantial numbers of hours with upcalls were observed at both sites, with approximately four times as many hours with calls at the western site as the central one. Calls occurred mainly from August through October, with the earliest calls in late June and the latest at the end of December at both sites. In addition to this seasonal trend, there was a significant diel pattern in calling at the central site but not at the more westerly site. Results are analyzed in light of feeding ecology and broad-scale movements of right whales.     

Temporal and Contextual Patterns of Killer Whale (Orcinus orca) Call Type Production

Fish-eating killer whales Orcinus orca in the northeastern Pacific live in highly stable matrifocal social groups called pods. Each pod produces a repertoire of seven or more stereotyped call types. We compared the relative production of call types of free-ranging killer whale pods over time and between social contexts. The relative production of call types by each pod during directional travel was distinct over a 27-yr period; however, both temporal stability and pod distinctiveness were strongly influenced by a subset of dominant call types within the repertoire of each pod. Some call types within the repertoires contain biphonation (two overlapping independently modulated tones) and have a higher estimated active space than call types containing just one tone. In multi-pod aggregations the relative production of the dominant call types of each pod decreased and the relative production of a subset of call types that are rarely recorded from single-pod groupings increased. The majority of these contained biphonation. The data suggest a distinction between a subset of dominant call types that may function to identify the pod and a subset of less common call types including several call types containing biphonation that are more commonly produced during inter-pod affiliations.