SIZE-AND AGE-CLASS SEGREGATION OF BOWHEAD WHALES SUMMERING IN NORTHERN FOXE BASIN: A PHOTOGRAMMETRIC ANALYSIS

To determine whether Hudson Bay-Foxe Basin bowhead whales segregate on the basis of age, whales summering in northern Foxe Basin, were aerially photographed in August of 1996, 1997, and 1998. Image lengths on either the negatives or contact prints were measured and total body lengths were estimated. In all three years the majority of whales photographed were ≤13.5 m long. Calves and juveniles made up 89.3%, 96.6%, and 79.3% of the total number of measured whales in 1996 (n = 28), 1997 (n = 30) and 1998 (n = 29) respectively. The number of bowheads >13.5 m, the approximate size at which females reach sexual maturity, that were photographed was directly proportional to the number of calves photographed. Our results indicate that northern Foxe Basin bowheads are part of a more widely distributed stock. Adult males and resting adult females apparently summer in another part of the range, probably northwestern Hudson Bay. Northern Foxe Basin appears to be used as a summer feeding area by cows with young-of-the-year calves and by juveniles.     

THE DISTRIBUTION OF BOWHEAD WHALES, BALAENA MYSTICETUS, IN THE CHUKCHI SEA

Under a U.S.-U.S.S.R. cooperative Marine Mammal Project, shipboard cruises were made in 1979, 1980 and 1982, primarily to determine whether there is a substock of western Arctic bowhead whales ( Balaena mysticetus ) that summers in the western Chukchi Sea instead of migrating to the Beaufort Sea. More than 100 bowheads were sighted along the north Chukotka coast of Siberia in October 1979, and more than 200 bowheads were sighted there in September 1980. None were seen anywhere in the Chukchi Sea in late July and August 1982. We conclude that the September and October sightings were of animals returning early from the Beaufort Sea and that, other than occurrences peripheral to the main migration, there are no large concentrations in the Chukchi in the summer and there is apparently no western Chukchi substock.     

FEEDING, SOCIAL AND MIGRATION BEHAVIOR OF BOWHEAD WHALES, BALAENA MYSTICETUS, IN BAFFIN BAY VS. THE BEAUFORT SEA—REGIONS WITH DIFFERENT AMOUNTS OF HUMAN ACTIVITY

This paper compares the behavior of bowhead whales of the Davis Strait/Baffin Bay stock, as observed along the east coast of Baffin Island in 1979–1986, with behavior of the Bering/Chukchi/Beaufort Sea stock observed in the Beaufort Sea in 1980–1986. All data used here were collected during late summer and early autumn in the absence of acute human disturbance. The behavioral repertoires of the two populations were similar. However, quantitative differences were found for whales engaged in all three activities studied: (1) Bowheads feeding in deep water off Isabella Bay, Baffin Island, had longer dives and surfacings, on average, than noted for bowheads feeding in the Beaufort Sea. (2) Among whales socializing in shallow water, we saw sexual interactions more often at Isabella Bay than in the Beaufort Sea. Calls emitted by socializing whales off Baffin Island were similar to those heard in the Chukchi and Beaufort Seas. However, pulsed tonal calls were longer off Baffin Island, and previously undescribed mechanical "crunch" sounds were recorded there near socializing bowheads. (3) During autumn migration, "fluke-out" dives were less common, and dive durations were longer, in the Beaufort Sea than off Baffin Island (P<0.001). Multivariate and other analyses indicated that some but not all differences can be ascribed to regional differences in the natural environment or in whale activities, However, during 1974–1986, Bering/Chukchi/Beaufort bowheads were exposed to more industrial, hunting and other human activity than Davis Strait/Baffin Bay bowheads. The "inconspicuous" behavior during autumn migration in the Beaufort may have been attributable to human activities, but causative links cannot be isolated.     

ICE-BASED CENSUS OF BOWHEAD WHALES MIGRATING PAST POINT BARROW, ALASKA, 1978-1983

Bowhead whale ( Balaena mysticetus ) census data obtained during the northward spring migration are summarized for 1978–1983. Population size estimates are derived from counts made by observers standing on the seaward edge of shorefast ice in the vicinity of Point Barrow, Alaska, from mid-April to early June. The research design utilized two counting stations: South Perch, the primary counting station, and North Perch, used to determine the number of whales missed by South Perch observers. The percentage missed is estimated for each visibility category and used here to correct the census counts. Each season's population estimate is calculated as the sum of the number of trials of several independent multinomial distributions representing different visibility conditions. Corrections are applied for unwatched hours and hours with inferior visibility. A mean estimate of the number of whales passing within view of the census station was computed as 3,674 ± 299. This estimate was based on data collected in 1978, 1981, 1982, and 1983, years with the least apparent biases. Aerial survey data provide estimates of the proportion of whales passing at various distances seaward of the census sites as follows: 0.58 from the ice edge to 2 km, 0.76 to 3 km, and 0.80 to 4 km. Correcting for whales too far offshore to be seen by the ice-based observers results in a population estimate of over 4,200 bowheads.     

SURFACE MORPHOLOGY OF THE FOREBRAIN OF THE BOWHEAD WHALE, BALAENA MYSTICETUS

Observations were made on 11 brains from bowhead whales subsistence-harvested by Alaskan Eskimos under International Whaling Commission guidelines. This study is part of a larger project to determine the basic morphology of this endangered species. The bowhead brain is similar to other cetacean brains, particularly that of the southern right whale. Long olfactory peduncles are reflected upon the rostrodorsal surface of the cerebral hemispheres. Olfactory bulbs have not been recovered but are presumed to exist since nerve fibers have been identified histologically in the olfactory peduncles. The induseum griseum is evident on the corpus callosum. The hippocampus proper is small but protrudes into the lateral ventricle. The cruciate sulcus runs diagonally across the rostral surface, limiting a small frontal lobe. The structure of the floor of the sylvian fissure varies from a few short gyri radiating toward the circular sulcus to a more extensive and complex two-tiered arrangement including numerous gyri perpendicular to the gyrus bordering the paleocortex. Pineal-body-like tissue was present in one specimen. There is no interthalamic adhesion. The lateral geniculate body is elevated but smaller than the large medial geniculate body. The neurohypophysis was adherent on most brain specimens received.     

RATE OF INCREASE, 1978–1988, OF BOWHEAD WHALES, BALAENA MYSTICETUS, ESTIMATED FROM ICE-BASED CENSUS DATA

The number of bowhead whales, Balaena mysticetus , passing within viewing range of the ice-based census at Point Barrow, Alaska, during spring migrations from 1978 to 1988 is estimated from the visual census data. The trend in the annual numbers yields an estimated rate of increase of 3.1% per year with a 95% confidence interval ranging from 0.1% to 6.2% for the Bering-Chukchi-Beaufort Seas bowhead stock during this period. Alternative treatments of the data suggest less precise or somewhat lower estimates, but all results indicate that the stock was increasing.     

IDENTIFICATION OF GEOGRAPHIC FORMS OF COMMON DOLPHIN (Delphinus delphis) FROM AERIAL PHOTOGRAMMETRY

Abstract: At least four morphologically distinct forms of common dolphins are found in the eastern Pacific, We compared length data for common dolphins photographed from the northern, central and southern regions as defined by Perrin et al. (1985) and found significant differences in average length for adult animals (>150 cm) and for "adult females" defined for our purposes as animals accompanied by calves. Analyses of calculated birth dates for calves demonstrated differences in timing of reproduction between the geographically adjacent forms. Length distributions from aerial photographs and samples collected from the purse seine fishery were strikingly similar. This work demonstrates a new, non-invasive method for obtaining unbiased life history and morphological data.     

AERIAL CENSUS OF PACIFIC WALRUSES IN THE CHUKCHI SEA, 1985

The U.S. Fish and Wildlife Service conducted a survey of the walruses in the pack ice of the Chukchi Sea between 16 September and 2 October 1985, as part of a joint effort with the Soviet Union to estimate the size of the Pacific walrus population. American observers conducted censuses from two aircraft along randomly selected north–south lines over the pack ice. The observers counted walruses within a constant viewing angle that corresponded to a total strip width of 1.38 km at an altitude of 152 m.
In nine days of flying, 15,312 walruses were observed, of which 10,140 were on 5,764 km² of census strips. Few walruses were observed east of 161°W longitude or west of 170°W longitude, hence the census effort was stratified. Walrus concentrations between 161° and 170° shifted slightly westward during the 2-wk duration of the censuses. The differences among days in observed walrus density were due to changes in the numbers of walruses on the ice within 37 km of the ice edge. The number of observable walruses in pack ice of the eastern Chukchi Sea was estimated to be 62,177 (SD = 19,480), based on censuses conducted on 29 and 30 September and 1 October. At that time there were also at least 15,238 in Bristol Bay, Bering Sea. The Soviets counted 39,572 on the shores of the western Chukchi and Bering seas and estimated 115,531 in pack ice of the western Chukchi Sea. Summing U.S. and Soviet estimates, the total population of Pacific walruses in 1985 was 232,518. This number was comparable with earlier estimates from censuses conducted jointly by the U.S. and the Soviets. However, information on fraction hauled out, segregation, and movements is needed for more precise estimates.     

Increasing abundance of bowhead whales in West Greenland

In April 2006, a dedicated survey of bowhead whales (Balaena mysticetus) was conducted on the former whaling ground in West Greenland to determine the current wintering population abundance. This effort included a double platform aerial survey design, satellite tracking of the movements of nine whales, and estimation of high-resolution surface time from 14 whales instrumented with time-depth recorders. Bowhead whales were estimated to spend an average of 24% (cv=0.03) of the time at or above 2m depth, the maximum depth at which they can be seen on the trackline. This resulted in a fully corrected abundance estimate of 1229 (95% CI: 495-2939) bowhead whales when the availability factor was applied and sightings missed by observers were corrected. This surprisingly large population estimate is puzzling given that the change in abundance cannot be explained by a recent or rapid growth in population size. One possible explanation is that the population, which demonstrates high age and sex segregation, has recently attained a certain threshold size elsewhere, and a higher abundance of mature females appears on the winter and spring feeding ground in West Greenland. This in combination with the latest severe reduction in sea ice facilitating access to coastal areas might explain the surprising increase in bowhead whale abundance in West Greenland.