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Gray whales Eschrichtius robustus, while engaged in underwater signaling, circumvented noise in their environment by altering the structure and timing of their calls. Acoustic responses of whales to both naturally occurring and artificially increased levels of noise were documented during sound playback experimentation in San Ignacio Lagoon, Baja California Sur, Mexico. Nine acoustic parameters were examined and compared between experimental conditions: calling rates, call types, frequency range of calls (Hz), call peak frequencies (Hz), call received levels (dB re 1 µPa), call duration (s), percentage of calls showing frequency modulation, number of pulses per call, and call repetition rates (number of pulses s-1). Multiple acoustic strategies were employed by whales which enabled them to minimize the detrimental effect that noise had on their underwater signaling. When different sources of noise were added to their habitat, a corresponding increase was observed in calling rates, call received levels, frequency-modulated signals, number of pulses per call, and call repetition rates. Our results show that gray whales vary their calling behavior dependent upon the noise source, duration, and presentation. Acoustic responses to noise may also differ based on the behavioral activity of the whale (e.g. breeding, migrating, feeding) and on the habitat the whale is occupying (shallow lagoons, coastal or pelagic waters). Background noise (both natural and man-made) has a profound effect on the acoustic behavior of this coastal species and calling is modified to optimize signal transmission and reception. Whether these modifications ensure that effective communication takes place in higher noise situations, without causing detrimental effects to individuals in the long term, remains to be tested.

Organochlorine (OC) profiles have been used as chemical “fingerprints” to infer an animal's foraging area. North Pacific killer whale (Orcinus orca) populations are exposed to different levels and patterns of OCs based on their prey, distribution, and amount of time spent in a particular area. To characterize concentrations and profiles of OCs found in various populations of North Pacific killer whales, polychlorinated biphenyls (PCBs), including dioxin-like congeners, DDTs, and hexachlorobenzene (HCB), were measured in biopsy blubber samples of photo-identified resident (fish-eating) and transient (mammal-eating) killer whales collected from 1994 through 2002 from Russian Far East waters to the waters of the west coast of the United States, representing 10 populations. We compared blubber OC concentrations based on ecotype (resident vs. transient), sex and reproductive maturity, and geographic area. We also examined OC mixtures to determine if we could detect segregated geographical areas (foraging areas) among the six populations with sufficient sample sizes. Transients had significantly higher OC concentrations than residents and adult male whales had consistently higher OC levels compared to adult females, regardless of ecotype. Our OC profile findings indicate segregated foraging areas for the North Pacific killer whales, consistent with observations of their geographic distributions. Several potential health risks have also been associated with exposure to high levels of contaminants in top-level predators including reproductive impairment, immune suppression, skeletal deformities, and carcinoma. The results of this baseline study provide information on the geographic distribution of OCs found in North Pacific killer whales, results which are crucial for assessing the potential health risks associated with OC exposure in this species.

In this study we present empirical data on predator numbers, movements and area usage, and predation obtained from tracking transient killer whales Orcinus orca throughout the inland waters of southeastern Alaska, USA. During 1991-2007, we documented 155 transient killer whales via photo-identification methodology within the large study area (27,808 km2). Transient killer whales were distributed throughout southeastern Alaska and were present during all seasons, although not all individuals were seen every year. Resighting data suggested that within southeastern Alaska, maternal groups may partition area usage of their environment. By following whales for 1,467 km, we calculated a mean travel speed of 7.2 km/hour with mean daily movements of 134 km ± 88 km/24 hours and ranging within 59-240 km/24 hours. Photographic matches demonstrated that most of the transient killer whales (86%) identified in southeastern Alaska also utilized British Columbia and Washington State waters. In contrast, photogra...

We used photographic mark-recapture methods to estimate the number of mammal-eating ''transient'' killer whales using the coastal waters from the central Gulf of Alaska to the central Aleutian Islands, around breeding rookeries of endangered Steller sea lions. We identified 154 individual killer whales from 6,489 photographs collected between July 2001 and August 2003. A Bayesian mixture model estimated seven distinct clusters (95% probability interval = 7-10) of individuals that were differentially covered by 14 boat-based surveys exhibiting varying degrees of association in space and time. Markov Chain Monte Carlo methods were used to sample identification probabilities across the distribution of clusters to estimate a total of 345 identified and undetected whales (95% prob- ability interval = 255-487). Estimates of covariance between surveys, in terms of their coverage of these clus- ters, indicated spatial population structure and seasonal movements from these near-shore waters, suggesting spa- tial and temporal variation in the predation pressure on coastal marine mammals.

In social species, breeding system and gregarious behavior are key factors influencing the evolution of large-scale population genetic structure. The killer whale is a highly social apex predator showing genetic differentiation in sympatry between populations of foraging specialists (ecotypes), and low levels of genetic diversity overall. Our comparative assessments of kinship, parentage and dispersal reveal high levels of kinship within local populations and ongoing male-mediated gene flow among them, including among ecotypes that are maximally divergent within the mtDNA phylogeny. Dispersal from natal populations was rare, implying that gene flow occurs without dispersal, as a result of reproduction during temporary interactions. Discordance between nuclear and mitochondrial phylogenies was consistent with earlier studies suggesting a stochastic basis for the magnitude of mtDNA differentiation between matrilines. Taken together our results show how the killer whale breeding system, coupled with social, dispersal and foraging behaviour, contributes to the evolution of population genetic structure.

Aim To assess the distribution, group size, seasonal occurrence and annual trends of cetaceans. Location The study area included all major inland waters of Southeast Alaska. Methods Between 1991 and 2007, cetacean surveys were conducted by observers who kept a constant watch when the vessel was underway and recorded all cetaceans encountered. For each species, we examined distributional patterns, group size, seasonal occurrence and annual trends. Analysis of variance (anovaF) was used to test for differences in group sizes between multiple means, and Student’s t-test was used to detect differences between pairwise means. Cetacean seasonal occurrence and annual trends were investigated using a generalized linear model framework. Results Humpback whales (Megaptera novaeangliae) were seen throughout the region, with numbers lowest in spring and highest in the fall. Fin whale (Balaenoptera physalus) and minke whale (Balaenoptera acutorostrata) distributions were more restricted than that reported for humpback whales, and the low number of sightings precluded evaluating seasonal trends. Three killer whale (Orcinus orca) eco-types were documented with distributions occurring throughout inland waters. Seasonal patterns were not detected or could not be evaluated for resident and offshore killer whales, respectively; however, the transient eco-type was more abundant in the summer. Dall’s porpoise (Phocoenoides dalli) were distributed throughout the region, with more sightings in spring and summer than in fall. Harbour porpoise (Phocoena phocoena) distribution was clumped, with concentrations occurring in the Icy Strait/Glacier Bay and Wrangell areas and with no evidence of seasonality. Pacific white-sided dolphins (Lagenorhynchus obliquidens) were observed only occasionally, with more sightings in the spring. For most species, group size varied on both an annual and seasonal basis. Main conclusions Seven cetacean species occupy the inland waters of Southeast Alaska, with distribution, group size, seasonal occurrence and annual trends varying by species. Future studies that compare spatial and temporal patterns with other features (e.g. oceanography, prey resources) may help in identifying the key factors that support the high density and biodiversity of cetaceans found in this region. An increased understanding of the region’s marine ecology is an essential step towards ensuring the long-term conservation of cetaceans in Southeast Alaska.

The diversity of exon-2 (peptide-binding region) of the DQB1 locus (Class II, major histocompatibility complex, MHC) was investigated on an extended sample of populations of three focal cetacean species (two sibling delphinid species and another in the same family). We tested the hypothesis that dolphin populations with a worldwide distribution across different habitats and geographic regions will be under differential selective pressure by comparing DQB 1 variation with variation at neutral markers and by investigating putative functional residues within the exon-2 sequence at the population level. Variation at the DQB1 locus was not correlated to neutral differentiation (assessed by comparison with microsatellite DNA markers), and overall F ST values were significantly lower for the MHC locus, consistent with expectations for balancing selection. Measures of heterozygosity and d n /d s ratios were also consistent with balancing selection. However, outliers in the F ST comparisons and the analysis of putative functional residues suggested incidences of directional selection in local populations.

Beginning in the late 1980s, large groups of previously unidentified killer whales (Orcinus orca) were sighted off the west coast of Vancouver Island and in the Queen Charlotte Islands, British Columbia. Scientists working in this region produced two killer whale photo-identification catalogues that included both transient (mammaleating) whales and 65 individual whales that investigators believed represented a distinct killer whale community (Ford et al. 1992, Heise et al. 1993). It was thought that these killer whales maintained a generally offshore distribution and were provisionally termed “offshores”; a term that has since been used as a population identifier for the eastern temperate North Pacific offshore killer whale population. Then in September 1992, 75 unidentified whales entered the Strait of Juan de Fuca just south and east of Victoria, British Columbia (Walters et al. 1992). Although most of these whales had not been seen before, two were matched to killer whales in the Queen Charlotte photo-identification catalogue (Ford et al. 1992, Heise et al. 1993) and were thus listed as “offshore” killer whales. During a similar time period, other large groups of killer whales, previously unidentified, were also being sighted off Alaska and California (Dahlheim et al. 1997; Nancy Black and Alisa SchulmanJaniger, unpublished data, respectively). As the number of encounters increased, certain characteristics were consistently observed among “offshore” killer whales (Ford et al. 2000; this study, Fig. 1).

We examined the incidence of rake mark scars from killer whales Orcinus orca on the flukes of humpback whales Megaptera novaeangliae throughout the North Pacific to assess geo- graphic variation in predation pressure. We used 3650 identification photographs from 16 wintering or feeding areas collected during 1990 to 1993 to determine conservative estimates in the percentage of whales with rake mark scarring. Dramatic differences were seen in the incidence of rake marks among regions, with highest rates on wintering grounds off Mexico (26 vs. 14% at others) and feed- ing areas off California (20 vs. 6% at others), 2 areas between which humpback whales migrate. Although attacks are rarely witnessed, the prevalence of scars demonstrates that a substantial por- tion of animals are attacked, particularly those that migrate between California and Mexico. Our data also suggest that most attacks occur at or near the wintering grounds in the eastern North Pacific. The prevalence of attacks indicates that killer whale predation has the potential to be a major cause of mortality and a driving force in migratory behavior; however, the location of the attacks is inconsis- tent with the hypothesis that animals migrate to tropical waters to avoid predation. Our conclusion is that, at least in recent decades, attacks are made primarily on calves at the wintering grounds; this contradicts the hypothesis that killer whales historically preyed heavily on large whales in high- latitude feeding areas in the North Pacific.

Reproductively and geographically isolated populations of predators may be synchronized by a phenomenon known as the Moran effect—specifically if they exhibit common responses to external processes, such as climate, density dependence (parasites, disease), or prey. Prey has the ability to synchronize predators if geographically isolated predator populations target the same prey species, or if the migration and range of the prey species occurs over a large enough scale to be available to multiple predator populations. The objective of our study was to investigate evidence for correlations of demographic rates between geographically isolated populations of piscivorous killer whales in the Northeast Pacific; using long-term mark-recapture datasets collected over the last 30+ yrs, we constructed a hierarchical occupancy model, linking models of survival and fecundity in a single framework. We found strong support for synchronized demographic rates in Southeast Alaska and Southern Resident killer whales, which are geographically and reproductively isolated. Despite their isolation, they experience extremely correlated dynamics—the correlation in fecundity rates between populations exceeds 0.9. The correlation in demographic rates across these populations of killer whales in different regions of the Northeast Pacific Ocean suggests a common environmental driver. Both killer whale populations are known to prey on Chinook salmon, which have a long-distance coastal migration larger than the habitat range of killer whales. Many of these Chinook salmon are also of the same origin (southern stocks), suggesting that these populations not only consume the same prey species but the same prey populations.

Springer et al. (2003) contend that sequential declines occurred in North Pacific populations of harbor and fur seals, Steller sea lions, and sea otters. They hypothesize that these were due to increased predation by killer whales, when industrial whaling's removal of large whales as a supposed primary food source precipitated a prey switch. Using a regional approach, we reexamined whale catch data, killer whale predation observations, and the current biomass and trends of potential prey, and found little support for the prey-switching hypothesis. Large whale biomass in the Bering Sea did not decline as much as suggested by Springer et al., and much of the reduction occurred 50–100 yr ago, well before the declines of pinnipeds and sea otters began; thus, the need to switch prey starting in the 1970s is doubtful. With the sole exception that the sea otter decline followed the decline of pinnipeds, the reported declines were not in fact sequential. Given this, it is unlikely that a sequential megafaunal collapse from whales to sea otters occurred. The spatial and temporal patterns of pinniped and sea otter population trends are more complex than Springer et al. suggest, and are often inconsistent with their hypothesis. Populations remained stable or increased in many areas, despite extensive historical whaling and high killer whale abundance. Furthermore, observed killer whale predation has largely involved pinnipeds and small cetaceans; there is little evidence that large whales were ever a major prey item in high latitudes. Small cetaceans (ignored by Springer et al.) were likely abundant throughout the period. Overall, we suggest that the Springer et al. hypothesis represents a misleading and simplistic view of events and trophic relationships within this complex marine ecosystem.

Killer whale (Orcinus orca Linnaeus, 1758) abundance in the North PaciWc is known only for a few populations for which extensive longitudinal data are available, with little quantitative data from more remote regions. Line-transect ship surveys were con- ducted in July and August of 2001-2003 in coastal waters of the western Gulf of Alaska and the Aleutian Islands. Conventional and Multiple Covariate Distance Sampling methods were used to estimate the abun- dance of diVerent killer whale ecotypes, which were distinguished based upon morphological and genetic data. Abundance was calculated separately for two data sets that diVered in the method by which killer whale group size data were obtained. Initial group size (IGS) data corresponded to estimates of group size at the time of Wrst sighting, and post-encounter group size (PEGS) corresponded to estimates made after closely approach- ing sighted groups. 'Resident'-type (Wsh-eating) killer whales were more abundant than the 'transient'-type (mammal-eating). Abundance estimates of resident killer whales (991 (95% CI = 379-2,585) (IGS) and 1,587 (95% CI = 608-4,140) (PEGS)), were at least four times greater than those of the transient killer whales (200 (95% CI = 81-488) (IGS) and 251 (95% CI = 97-644) whales (PEGS)). The IGS estimate of abundance is preferred for resident killer whales because the estimate based on PEGS data may show an upward bias. The PEGS estimate of abundance is likely more accurate for transients. Residents were most abundant near Kodiak Island in the northern Gulf of Alaska, around Umnak and Unalaska Islands in the eastern Aleutians, and in Seguam Pass in the central Aleutians. This ecotype was not observed between 156 and 164°W, south of the Alaska Peninsula. In contrast, transient killer whale sightings were found at higher densities south of the Alaska Peninsula between the Shumagin Islands and the eastern Aleutians. Only two sightings of 'oVshore'-type killer whales were recorded during the surveys, one northeast of Unalaska Island and the other south of Kodiak Island. These are the Wrst estimates of abundance of killer whale ecotypes in the Aleutian Islands and Alaska Peninsula area and provide a baseline for quantifying the role of these top predators in their ecosystem.

Killer whale predation on belugas in Cook Inlet, Alaska, has become a concern since the decline of these belugas was documented during the 1990s. Accordingly, killer whale sightings were compiled from systematic surveys, observer databases, and anecdotal accounts. Killer whales have been relatively common in lower Cook Inlet (at least 100 sightings from 1975 to 2002), but in the upper Inlet, north of Kalgin Island, sightings were infrequent (18 in 27 yr), especially prior to the 1990s. Beach cast beluga carcasses with teeth marks and missing flesh also provided evidence of killer whale predation. Most observed killer whale/beluga interactions were in the upper Inlet. During 11 of 15 observed interactions, belugas were obviously injured or killed, either through direct attacks or indirectly as a result of stranding. Assuming at least one beluga mortality occurred during the other four encounters, we can account for 21 belugas killed between 1985 and 2002. This would suggest a minimum estimate of roughly 1/yr and does not include at least three instances where beluga calves accompanied an adult that was attacked.

A low level of genetic variation in mammalian populations where the census population size is relatively large has been attributed to various factors, such as a naturally small effective population size, historical bottlenecks and social behaviour. The killer whale (Orcinus orca) is an abundant, highly social species with reduced genetic variation. We find no consistent geographical pattern of global diversity and no mtDNA variation within some regional populations. The regional lack of variation is likely to be due to the strict matrilineal expansion of local populations. The worldwide pattern and paucity of diversity may indicate a historical bottleneck as an additional factor.

For many highly mobile species, the marine environment presents few obvious barriers to gene flow. Even so, there is considerable diversity within and among species, referred to by some as the ‘marine speciation paradox’. The recent and diverse radiation of delphinid cetaceans (dolphins) represents a good example of this. Delphinids are capable of extensive dispersion and yet many show fine-scale genetic differentiation among populations. Proposed mechanisms include the division and isolation of populations based on habitat dependence and resource specializations, and habitat release or changing dispersal corridors during glacial cycles. Here we use a phylogenomic approach to investigate the origin of differentiated sympatric populations of killer whales (Orcinus orca). Killer whales show strong specialization on prey choice in populations of stable matrifocal social groups (ecotypes), associated with genetic and phenotypic differentiation. Our data suggest evolution in sympatry among populations of resource specialists.

Vocalizations of feeding humpback whales from southeast Alaska were analyzed to characterize quantitatively the predominant vocalization associated with feeding and assess variation among vocalizations. Whales uttered series of cries similar in acoustic structure to those described previously as stereotyped, rhythmic ‘feeding calls’. Individual cries ranged in duration from 0.4 to 8.2 sec. (median = 2.6 sec). Cries typically had a short, strongly frequency modulated (FM) introductory and ending component (labeled Section A and C, respectively). Cries had relatively little FM over the main body of the call (labeled Section B) which ranged in fundamental frequency from 360 to 988 Hz (median = 553 Hz) and sometimes exhibited a frequency oscillation over a bandwidth of approximately 16 to 65 Hz. Principle components analysis indicated that most variation in the data-set (over 35%) could be attributed to measures of absolute frequency, however a substantial amount of variation was also due to other ac...

Between 1991 and 1993, Alaska harbor porpoise (Phocoena phocoena) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line-transect methodology was used, and only those observations made during optimal conditions were analyzed. Survey data indicated densities of 4.48 groups/100 km2, or approximately 3,531 harbor porpoises (95% C. I. 2,206-5,651) in Bristol Bay and 0.54 groups/100 km2, or 136 harbor porpoises (95% C. I. 11-1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km2, or an abundance estimate of 740 (95% C. I. 259-2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km2 and an abundance estimate of 551 (95% C. I. 423-719). Surveys of offshore waters from Prince William Sound to Dixon Entrance yielded densities of 4.02 groups/100 km2 and an abundance estimate of 3,982 (95% C. I. 2,567-6,177). Combining all years and areas yielded an uncorrected density estimate of 3.82 porpoises per 100 km2, resulting in an abundance estimate of 8,940 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746-11,848. Using correction factors from other studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number.

Estimations of gray whale abundance have generally assumed that shore-based observers record all whales migrating through the viewing area during periods uncompromised by visibility. We tested the repeatability of data collected at the standard gray whale census site at Granite Canyon Marine Laboratory in central California by using pairs of observers maintaining independent sighting records. Proximal shore sites were occupied 6 d (60 h) in January 1986 where one team counted 845 whales in 427 groups while the other team counted 990 whales in 477 groups. A comparison of the records showed that the first team missed 290 whales seen by the second team, and the second team missed 204 whales seen by the first team. The total number of whales in the viewing area was calculated for each team by the Petersen estimate, using mutually sighted whale groups as “recaptures”. On average, observers recorded only 79% of the whales. More whales (68%) were missed when entire groups of whales were not seen rather than when groups were undercounted (32%). Visibility did not appear to affect observed rates of missed whales. Whales migrating at intermediate distances from the shore were less often missed than were those > 6 km or < 1 km offshore. This count discrepancy test confirms that an uncorrected calculation of population size for gray whales based on sighting records from solitary observers will be underestimated.

Intraspecific resource partitioning and social affiliations both have the potential to structure populations, though it is rarely possible to directly assess the impact of these mechanisms on genetic diversity and population divergence. Here, we address this for killer whales (Orcinus orca), which specialize on prey species and hunting strategy and have long-term social affiliations involving both males and females. We used genetic markers to assess the structure and demographic history of regional populations and test the hypothesis that known foraging specializations and matrifocal sociality contributed significantly to the evolution of population structure. We find genetic structure in sympatry between populations of foraging specialists (ecotypes) and evidence for isolation by distance within an ecotype. Fitting of an isolation with migration model suggested ongoing, low-level migration between regional populations (within and between ecotypes) and small effective sizes for extant local populations. The founding of local populations by matrifocal social groups was indicated by the pattern of fixed mtDNA haplotypes in regional populations. Simulations indicate that this occurred within the last 20,000 years (after the last glacial maximum). Our data indicate a key role for social and foraging behavior in the evolution of genetic structure among conspecific populations of the killer whale.

Top predators in the marine environment integrate chemical signals acquired from their prey that reflect both the species consumed and the regions from which the prey were taken. These chemical tracers—stable isotope ratios of carbon and nitrogen; persistent organic pollutant (POP) concentrations, patterns and ratios; and fatty acid profiles—were measured in blubber biopsy samples from North Pacific killer whales (Orcinus orca) (n = 84) and were used to provide further insight into their diet, particularly for the offshore group, about which little dietary information is available. The offshore killer whales were shown to consume prey species that were distinctly different from those of sympatric resident and transient killer whales. In addition, it was confirmed that the offshores forage as far south as California. Thus, these results provide evidence that the offshores belong to a third killer whale ecotype. Resident killer whale populations showed a gradient in stable isotope profiles from west (central Aleutians) to east (Gulf of Alaska) that, in part, can be attributed to a shift from off-shelf to continental shelf-based prey. Finally, stable isotope ratio results, supported by field observations, showed that the diet in spring and summer of eastern Aleutian Island transient killer whales is apparently not composed exclusively of Steller sea lions.

Hearing capabilities of several odontocetes have been investigated through behavioral response techniques (Johnson, 1967; Anderson, 1970; Hall and Johnson, 1971; Jacobs and Hall, 1972; Ljungblad et al., 1982; Thomas et al., 1988), cortical evoked potential techniques (Seeley et al., 1976), and electrophysiological methods (Bullock et al., 1968; Ridgway et al., 1981). Past studies have been limited to toothed whales and dolphins held in captivity. Because of their large size, it is unlikely that mysticete whales will be kept in captivity for long-term behavioral studies. Similarly, it also is unlikely that a baleen whale could be restrained temporarily for a physiological hearing test. Alternative, non-invasive techniques will be necessary to test hearing in baleen whales. Hearing data on baleen whales are important to judge potential impacts from underwater man-made noise on these animals.

Responses of gray whales to increased levels of noise were documented during playback experiments. Nine sound parameters were compared between control and experimental conditions: call rates, call types, frequency range (Hz), emphasized frequencies (Hz), received levels of sound (dB re: 1 μPa), call duration (s), calls exhibiting frequency modulation, pulses per series, and signal repetition rates. Whale surface behavior (i.e., dive durations, movements, and abundance) was also investigated. Analyses yielded: a description of call types; a characterization of acoustical habitats; and a determination of relationships between whale calls and habitats; and a determination of relationships between whale calls and habitats. Gray whales employed multiple behavioral strategies (e.g., modification of calling to optimize signal transmission and reception, movement out of the study area, etc.) to circumvent increased levels of noise in their environment. Responses varied with sound source and may also differ with g...

A study of hearing abilities of killer whales was conducted to help assess the impact of noise produced by vessels. The study had five objectives: (1) determine the range of frequencies that killer whales can hear; (2) determine the ability to hear these frequencies in the presence of bandlimited masking noise; (3) determine whether vessel noise affects the ability to hear pure tones; (4) determine whether noise from different directions has different masking properties; and (5) determine the ability to detect simulated killer whale sounds in the presence of vessel noise. Data were collected using conditioned responses of four captive killer whales. Conclusions reached include: killer whales are sensitive to a wide range of frequencies (0.5–105 kHz); noise reduces the ability to detect signals of similar frequencies; very loud, low frequency, noise reduces the ability to detect signals even at much higher frequencies; noise has the strongest effect when it comes from in front of the whale, and the least effect when it is from the side or behind; and the ability to detect broadband signals such as killer whale calls and clicks is not substantially affected by low levels of vessel noise.

An acoustical study was conducted on captive killer whales (Orcinus orca) to determine if individuals or groups differed in their vocalizations. Twenty‐one different underwater vocalization categories produced by 13 animals were recorded within a 40 Hz to 20 kHz bandwidth. Eight acoustical variables (starting and ending frequencies of the signal, duration, harmonic interval, starting and ending frequencies of the fundamentals, and low and high concentration of energy) were measured for each vocalization. multivariatediscriminant analysis was used to determine whether individual, oceanarium, or sexual differences were detectable in their vocalizations. Results showed distinct acoustical groupings by individuals, by oceanariums, and by sex.

The development of the click sounds of sperm whales (Physeter catodon) has been investigated through comparisons of these vocalizations from calves of different sizes. The observations include sounds from four small stranded calves held for short periods in aquaria at Miami, Florida, and Seattle, Washington, and in a bay on Long Island, New York. These vocalizations were compared with those of larger calves encountered at sea. All the calves produced typical sperm whale sounds -- clicks with broadband spectra, often produced in short series. Vocalizations from the smaller calves sometimes included slightly noisy, tonal components -- similar noisy click sounds were also occasionally heard in the presence of calves at sea, and they were interpreted as the result of improperly formed clicks. The smallest calves produced few temporally repetitive click patterns, but the larger (older) ones produced sequences with stereotyped “coda”-like temporal patterns. The use of such patterned click sequences increased with the apparent age of the calves. In the larger calves, the sounds appeared more organized in sequences similar to the communicative signals of adults. None of the calves appeared to use their sounds in ways that were related to echolocation.

In order to focus on the problem of increasing nonbiological noise in the environment of the gray whale (Eschrichtius robustus) and to answer the question as to how this species uses its acoustic signaling most efficiently, a study was undertaken at Laguna San Ignacio, Baja California Sur, Mexico, in February 1983 to determine the responses of gray whales to projected sound sources. A series of underwater “playback” experiments were conducted. The playback included the projection of nonbiological as well as biological sound sources. The acoustical and behavioral responses of the whales were recorded during pretrial, trial, and post‐trial playback periods. Sounds were projected back only during the “trial” periods. With the onset of increased levels of man‐made noise, the gray whale's acoustical activities increased, as did the source levels of their calls. Observations on the behavioral activities of these whales in response to increased noise resulted in (1) prolonged dive times and (2) direct movements on the part of the whales away from the transducers. The acoustical and visual responses of the whales appear to differ depending upon the sound stimuli being presented.

Investigations on gray whales (Eschrichtius robustus) in Laguna San Ignacio have previously documented “curious” or “friendly” whale behavior towards vessels. This behavior was encountered during acoustical studies conducted in March 1981 in this lagoon. The initial response appears' triggered by the underwater sound generated from outboard engines. Whales actively seek out the sound source and physically contact slow (2–4 kts) moving small vessels (inflatable Avons, Zodiacs, wooden and aluminum skiffs). Engines kept in idle (running but out of gear) maintained these whales in close proximity for periods up to 3 hours. Some whales terminated this activity when the engine was shut off. These behaviors around vessels were video taped. Sound profiles on engine noise and ambient noise levels were collected and analyzed. This “curious” behavior is prevalent only in areas where whales are repeatedly exposed to small vessel activity. This unique behavior has occurred for the past four years in Laguna San Ignacio...