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.     

A new species of baleen whale (Balaenoptera) from the Gulf of Mexico,with a review of its geographic distribution

Bryde's-like whales are a complex of medium-sized baleen whales that occur in tropical waters of all three major ocean basins. Currently, a single species of Bryde's whale, Balaenoptera edeni Anderson, 1879, is recognized, with two subspecies, Eden's whale, B. edeni edeni and Bryde's whale, B. edeni brydei (Olsen, 1913), although some authors have recognized these as separate species. Recently, a new, evolutionarily divergent lineage of Bryde's-like whale was identified based on genetic data and was found to be restricted primarily to the northern Gulf of Mexico (GOMx). Here, we provide the first morphological examination of a complete skull from these whales and identify diagnostic characters that distinguish it from the other medium-sized baleen whale taxa. In addition, we have increased the number of genetic samples of these Bryde's-like whales in the GOMx from 23 to 36 individuals, all of which matched the GOMx lineage. A review of Bryde's-like whale records in the Caribbean and greater Atlantic supports an isolated distribution for this unique lineage, augmenting the genetic and morphological body of evidence supporting the existence of an undescribed species of Balaenoptera from the Gulf of Mexico.     

DIVE CHARACTERISTICS OF SATELLITE-MONITORED BLUE WHALES (BALAENOPTERA MUSCULUS) OFF THE CENTRAL CALIFORNIA COAST

Dive habits of four Northeast Pacific blue whales ( Balaenoptera musculus ) were studied using satellite-monitored radio tags. Tags summarized dive-duration data into eight 3-h periods daily. One tag additionally summarized dive depth and time-at-depth information for these same periods. Tracking periods ranged from 0.6 to 12.7 d and provided data for 17 three-hour summary periods, representing 2,007 dives (788 of which provided depth information). Total number of dives during a 3-h summary period ranged from 83 to 128. Seventy-two percent of dives were ≤ 1 min long. All whales spent >94% of their time submerged. Average duration of true dives (dives >1 min) ranged from 4.2 to 7.2 min. Seventy-five percent of depth-monitored dives were to ≤16 m, accounting for 78% of that animal's time. Average depth of dives to >16 m was 105 ± 13 m.     

VENTILATORY RATE DIFFERENCES BETWEEN SURFACE-FEEDING AND NON-SURFACE-FEEDING FIN WHALES (BALAENOPTERA PHYSALUS) IN THE WATERS OFF EASTERN LONG ISLAND, NEW YORK, U.S.A., 1981–1987

Observations of feeding and ventilatory behavior of individual fin whales ( Balaenoptera physalus )were made from various vessels during the months of May–September, 1981–1987, in the waters off eastern Long Island, N.Y., U.S.A. Intervals between blows were measured and recorded to the nearest second. Information about behavior was recorded, as were location, depth, and surface temperature at sounding dives. Animals observed feeding at the surface were noted as such, ail others were considered non-surface-feeding animals. Data were compiled by individual, month, year, and analyzed for mean interblow interval during surface activity bouts; mean dive duration; and overall mean blow interval.
Overall mean blow intervals (±SE) of 47.89 ± 0.81 set for surface-feeding ( n = 10,411), and 57.92 ±0.97 sec for non-surface-feeding animals ( n = 11,024), differed significantly (Mann-Whitney U, P < 0.001). Interblow intervals for surface activity bouts (±SE) of 12.29 ± 0.05 set for surface-feeding ( n = 7,894), and 13.58 ± 0.06 set, for non-surface-feeding animals (n = 8,187), also differed significantly (Mann-Whitney U, P < 0.001), as did mean dive duration (159.53 ± 2.16 sec, n = 2,517, for surface-feeding animals; 185.86 ± 2.53 set, n = 2,837, for non-surface-feeding animals). Yearly comparisons of blow intervals between surface-feeding and non-surface-feeding animals during surface activity bouts yielded significant differences for each year except 1981, while comparisons of dive durations yielded significant differences for all years except 1981, 1982, and 1985.     

Developing protocols for in-water morphometric measurements of cetaceans using stereo-videogrammetry

Morphometry underpins the basic knowledge of any organism's population demographics and dynamics. Such understanding enables the investigation of trends with important conservation implications including monitoring the health of individuals and changes in population dynamics over time. By detecting declines in health prior to the onset of significant mortality, monitoring of body condition can potentially allow time for a management response to avert population decline. We trialed the use of a diver-operated stereo-video (SDOV) system for making morphometric measurements of dwarf minke whales (Balaenoptera acutorostrata subsp.), a small oceanic rorqual, in the Great Barrier Reef, Australia. The SDOV system produced 68% more precise replicate total body length measurements than a single-camera system, while both systems achieved a mean error below 0.5%. The increased precision offered by a SDOV system is desirable for longitudinal monitoring of growth rates and body condition. Optimal application of this method relied on adherence to protocols for both data collection and analysis beyond those dictated by the equipment user manuals. We provide recommendations for these field and analytical protocols, which may be suitable for use with other cetaceans when in-water access is available.     

Decline in energy storage in the Antarctic minke whale (<Emphasis Type="Italic">Balaenoptera bonaerensis</Emphasis>) in the Southern Ocean

The annual trend in energy storage in the Antarctic minke whale was examined using catch data from all 18 survey years in the Japanese Whale Research Program (JARPA). Regression analyses clearly showed that blubber thickness, girth and fat weight have been decreasing for nearly 2 decades. The decrease per year is estimated at approximately 0.02 cm for mid-lateral blubber thickness and 17 kg for fat weight, corresponding to 9% for both measurements over the 18-year period. Furthermore, “date”, “extent of diatom adhesion”, “sex”, “body length”, “fetus length”, “latitude”, “age” and “longitude” were all identified as partially independent predictors of blubber thickness. The direct interpretation of this substantial decline in energy storage in terms of food availability is difficult, since no long-term krill abundance series is available. However, an increase in the abundance of krill feeders other than minke whales and a resulting decrease in the krill population must be considered as a likely explanation.     

Fin whale (Balaenoptera physalus) target strength measurements

Active acoustic techniques can be used to detect whales. The ability to detect whales from a moving vessel or stationary buoy could reduce conflicts between hazardous human activities and whales, enabling implementation of mitigation procedures. In order to identify acoustic targets correctly as whales, knowledge of whale target strength (TS) is required. Active acoustic detections of fin whales (Balaenoptera physalus) were made in the Norwegian Sea; acoustic data were collected using calibrated omnidirectional sonar, operating at a discrete frequency of 110 kHz. Three fin whales of similar size (estimated between 16 and 18 m total length) had an overall average TS for all insonified body aspects of ?11.4 dB [95% CI ?12.05, ?10.8] at 110 kHz, with a total spread of nearly 14 dB. As expected, the received signals were stronger when the fin whales were insonified at broadside (?5.6 dB). Individual fin whale TS varied by approximately 12 dB, probably due to variation in lung volume with breathing, and to dynamic swimming kinematics. Our TS values are consistent with values reported previously for other large whales. All data together pave the way for development of automated acoustic whale detection protocols that could aid whale conservation.     

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.     

Genetic variation at enzyme loci in North Atlantic minke whales,Balaenoptera acutorostrata

Electrophoretic variation within and between North Atlantic minke whale samples(Balaenoptera acutorostrata) from West Greenland, Iceland, and Norway was investigated. In the West Greenland samples, 28 enzyme systems were examined, representing 36 loci, of which 6 were found to be polymorphic. In Icelandic and Norwegian samples, 22 enzyme systems were examined, representing 29 loci, of which 6 and 5 were found to be polymorphic, respectively. The average heterozygosity was 0.058 (SE=0.024) in samples from West Greenland, 0.074 (SE=0.028) in samples from Iceland, and 0.054 (SE=0.023) in samples from Norway. No significant deviations from the expected Hardy—Weinberg genotypic frequencies, within samples taken from the same area, were found. Significant differences in allele frequencies were observed, however, between samples from the three different areas. The average Nei's genetic distance was 0.014 and the averageF _st value was 0.126. The genetic differences between the samples from the different areas indicate that those from West Greenland, Iceland, and Norway represented different breeding populations.     

WHALE REACTIONS TO HUMAN ACTIVITIES IN CAPE COD WATERS

A review of our whale observations of more than 25 years indicated that each of the species commonly observed within 35 km of Cape Cod reacted differently to stimuli from human activities, and that these responses have gradually changed with time. Over the years of exposure to ships, for example, minke whales ( Balaenoptera acutorostrata ) have changed from frequent positive interest to generally uninterested reactions, finback whales ( B. physalus ) have changed from mostly negative to uninterested reactions, right whales ( Eubalaena glacialis ) have apparently continued the same variety of responses with little change, and humpbacks ( Megaptera novaeangliae ) have dramatically changed from mixed responses that were often negative to often strongly positive reactions. These reactions appeared to result mostly from three types of stimuli: primarily underwater sound, then light reflectivity, and tactile sensation. The whale reactions were related to their assessment of the stimuli as attractive, uninteresting or disturbing, their assessment of the movements of the sources of the stimuli relative to their own positions, and their assessment of the occurrence of stimuli as expected or unexpected. Whale reactions were modified by their previous experience and current activity: habituation often occurred rapidly, attention to other stimuli or preoccupation with other activities sometimes overcame their interest or wariness of stimuli, and inactivity seemed to allow whales to notice and react to stimuli that otherwise might have been ignored. The changes over time in the reactions of whales to stimuli from human activities were gradual and constantly varying with increased exposure to these activities.