LONG-RANGE MOVEMENTS OF SOUTH ATLANTIC RIGHT WHALES EUBALAENA AUSTRALIS

Abstract: Movements of southern right whales between Gough Island and South Africa, and between Argentina and Tristan da Cunha, southern Brazil, and South Georgia are documented through matching of six photoidentified individuals. These include the resighting of a male in a mid-oceanic locality some 4,424 km away from (and 11 yr after) its last sighting in a coastal area where it had been seen in six of the preceding eight years, a female photographed in mid-Atlantic resighted with a calf in a coastal nursery area 2,769 km away, resightings of females with calves in different nursery areas 2,051 km apart in different years, and the first example of a link between a coastal nursery area and a feeding ground in high latitudes. The possible implications of these movements for estimates of calving interval and survival rate based on resightings in coastal waters are discussed. The potential for intermingling between populations on either side of the South Atlantic seems greater than was previously considered likely from a comparison of animals photographed in coastal waters.     

ESTIMATING NATURAL MORTALITY RATE IN REPRODUCTIVELY ACTIVE FEMALE SOUTHERN RIGHT WHALES, EUBALAENA AUSTRALIS

Cow-calf pairs of southern right whales on the South African coast have been photographed in aerial surveys in October each year since 1979. In this paper 469 resightings of 177 individually identified cows photographed in the first six years of surveys have been analyzed in two ways to produce estimates of natural mortality rate. Both methods assume that all females calve either two, three, or four years after their previous calf. In Method A there is assumed to be no systematic trend with time in the probability of a female being photographed on each calving occasion. Natural logarithms of the numbers photographed 2-4, 5-7, 8-10, etc. yr after being first seen are regressed against time, the slope of which provides an estimate of natural mortality rate of 0.0255 ± 0.0071. The intercept value for this regression provides an estimate of the detection probability, or 0.769 ± 0.011. In Method B it is assumed that if a female has not been photographed for at least nine years then it is dead. Annual mortality estimates are obtained from the proportional reduction in the numbers of females known to be alive at each three-year interval after being first photographed, up to at least 6-8 yr from the present. Method B produces an estimate of natural mortality of 0.0260 ± 0.0190 (corrected to 0.0227 ± 0.0192 using the average detection probability). Both methods may be subject to various biases that tend to inflate estimates of natural mortality.     

CLUSTER ANALYSIS OF GROUP TYPES IN SOUTHERN RIGHT WHALE (EUBALAENA AUSTRALIS)

Groups of Eubalaena australis in the Gulf of San Jose, Argentina were characterized and classified. A one-zero sampling method was used for collecting data. A distance matrix was calculated with the 124 groups recorded and 10 characters including composition, size, activities, belly-up and tail-up positions, flipper and tail slaps, and breaching. Cluster analysis separated groups into 12 types. Six low-interaction group types were differentiated primarily by their composition, and extent of swimming and resting behaviors. Six interaction group types were characterized by the presence of whales in the belly-up position, by group size, by the absence of females with calves, and by sexual activity. Some interpretations of the possible functional meaning of the observed group types are discussed.     

ENVIRONMENTAL FACTORS INFLUENCING THE DISTRIBUTION OF SOUTHERN RIGHT WHALES (EUBALAENA AUSTRALIS) ON THE SOUTH COAST OF SOUTH AFRICA II: WITHIN BAY DISTRIBUTION

Environmental factors are thought to strongly influence the distribution and predictability of the coastal distribution of southern right whales ( Eubalaena australis ) off South Africa. Preferred habitat had generally shallow sloping sedimentary floors and was characteristically protected from open ocean swell and prevalent seasonal winds. This study investigated whether habitat choices at smaller scales (within bays) were similar. Fine scale distribution patterns (GPS) from three years' surveys (1997, 1999, 2000) were analyzed separately within the three main concentration areas St Sebastian Bay, De Hoop, and Walker Bay (containing ∼73% of cow-calf pairs and ∼49% of unaccompanied adults in the whole survey region). Whale density at this scale of within particular bays did not correlate well with predicted variables, but Chi-squared analysis strongly supported results at broader scales, in all bays. Post-hoc "choice" tests between similar areas differing in only one variable revealed that cow-calves preferred (presumed) sandy substrates and especially protection from swell. The strength and predictability of preferences shown at fine scale (where individual movement and weather variability could have great influence) provide strong support for findings at larger scales and emphasize the importance of environmental factors in the habitat choice of wintering right whales.     

ENVIRONMENTAL FACTORS INFLUENCING THE DISTRIBUTION OF SOUTHERN RIGHT WHALES (EUBALAENA AUSTRALIS) ON THE SOUTH COAST OF SOUTH AFRICA I: BROAD SCALE PATTERNS

Aerial surveys over the last 32 yr have shown that the distribution of southern right whales Eubalaena australis along the south coast of South Africa is markedly discontinuous, but highly predictable. A GIS was used at a variety of scales to investigate whether this pattern was related to environmental characteristics. Whale distribution was analyzed as density per 20-min bin of longitude over two temporal and spatial scales, namely 15 bins for 32 yr, and a wider scale but shorter time period, 23 bins for 19 yr, as well as using three years of GPS accuracy data (15 bins) for finer scale analysis. Environmental factors tested were depth, distance from shore, sea floor slope, protection from swell, protection from wind, and shore type. The majority of whales were concentrated in areas that provided reasonable protection from open ocean swell and seasonal winds, and had sedimentary floors with gentle slopes. They generally avoided exposed rocky shorelines. Cow-calf pairs were found significantly closer to shore and in shallower water than unaccompanied whales, particularly off sandy beaches. Habitat choice at this time of year may be related both to energy conservation for calves and lactating females (calm sea conditions) and to protection of the new-born.     

INCREASED HARASSMENT OF RIGHT WHALES (EUBALAENA AUSTRALIS) BY KELP GULLS (LARUS DOMINICANUS) AT PENÍNSULA VALDÉS, ARGENTINA

Kelp gulls at Península Valdés, Argentina, have recently developed the habit of feeding on pieces of skin and blubber that they gouge from the backs of southern right whales. In response, the whales flinch violently, submerge, and swim rapidly away underwater. The level of harassment in 1995 was almost five times higher than when first studied in 1984 by Thomas (1988). In 1995, 67% of attacks were aimed at large white lesions on the whales' backs. The proportion of whales with lesions increased from 0.01 in 1974 to 0.32 in 1990. Mother-calf pairs that were attacked traveled at medium and fast speeds for 3.1 h per day, compared to 0.8 h for undisturbed pairs. Mother-calf pairs are estimated to spend approximately 24% of their daylight hours in states of gullinduced disturbance. Little food is available at Península Valdés, so mothers must rely on blubber reserves to support their calves' growth, behavioral development, and migration to the feeding grounds. Even when undisturbed by gulls, mothers often curtail their calves' play and nursing bouts, suggesting that their energy reserves are limited. Increasingly intense harassment by gulls may therefore compromise calf development and might even induce right whales to abandon Península Valdés for other calving grounds.     

RATES AND POTENTIAL CAUSES OF MORTALITY IN NORTH ATLANTIC RIGHT WHALES (EUBALAENA GLACIALIS)

North Atlantic right whale mortality rates range from 2% to 17% over the first four years of life. Sources of mortality in this population include ship collisions, entanglements, and natural causes. A combined analysis of stranding data, entanglement records, and photographic information indicates that approximately one third of all right whale mortality is caused by human activities. Anthropogenic sources of right whale mortality may be a significant factor inhibiting growth in the North Atlantic population.     

RIGHT WHALES (EUBALAENA GLACIALIS) ON JEFFREYS LEDGE: A HABITAT OF UNRECOGNIZED IMPORTANCE?

North Atlantic right whales ( Eubalaena glacialis ) are known to spend the majority of the year between the Great South Channel southeast of Cape Cod, and the Nova Scotian shelf. We examined sightings of right whales on and around Jeffreys Ledge, a 54-km-long glacial deposit off the coast of northern Massachusetts, New Hampshire, and Maine. Sightings on Jeffreys Ledge were extracted from three data sets: (1) a systematic survey of the entire northeastern continental shelf between 1979 and 1982, (2) whale-watch and research-cruise sighting data from 1984 to 1997, and (3) a collaborative database of sightings collected by organizations conducting right whale research and all other available sources. Each database supported two seasonal sighting peaks. During summer (especially July and August) sightings were primarily of mother-calf pairs. Several cow-calf pairs were seen over several days to weeks. Several females were resighted in more than one year, but only when calves were present. During October, November, and December, sightings included all age classes, surface-feeding behavior was frequently observed, and some animals were resighted over several weeks. Given the relatively reduced sighting effort during fall, this number of sightings is surprising. During the 20 yr of observations, 52 of 374 photo-identified North Atlantic right whales (13.9%) were seen at least once on Jeffreys Ledge. We suggest that Jeffreys Ledge may be a more important right whale habitat than previously believed, and that it may play an important role in annual movements and distribution of this population.     

GENETIC BASIS AND EVOLUTIONARY SIGNIFICANCE OF VENTRAL SKIN COLOR MARKINGS IN NORTH ATLANTIC RIGHT WHALES (EUBALAENA GLACIALIS)

Approximately one third of the North Atlantic right whale population has white ventral skin patches. Most white-marked animals have both a belly and a chin patch, and the distribution of white pigment suggests that the patches represent a single ventral marking that varies in size and location. Population frequencies and cow-calf inheritance patterns indicate that the white mark is an autosomal recessive trait. There is no evidence to suggest that ventral coloration patterns are currently under selection. White-marked and black cows appear to experience similar levels of reproductive success based on calving intervals and length of sighting histories. Also, white-marked animals were equally common among cows and nulliparous adult females and among live vs. dead animals. Male reproductive success could not be tested because calf paternity is not known; white-marked and black males exhibit similar survival rates. White-marked cows were more common among females that took some or all of their calves to the Bay of Fundy summer nursery area compared to females that did not visit Fundy. This suggests that female habitat-use patterns may influence nuclear gene flow. Increased sample sizes and additional markers are needed to further investigate gene flow.     

THE GUNSHOT SOUND PRODUCED BY MALE NORTH ATLANTIC RIGHT WHALES (EUBALAENA GLACIALIS) AND ITS POTENTIAL FUNCTION IN REPRODUCTIVE ADVERTISEMENT

North Atlantic right whales ( Eubalaena glacialis ) make a short, distinctive broadband sound that is produced internally called a Gunshot sound. This sound has been recorded in the Bay of Fundy, Canada from both single whales ( n = 9) and social surface active groups ( n =49). Those single whales producing Gunshot sounds whose sex could be determined ( n = 9) were all mature males. Gunshot sounds were produced as part of a stereotyped behavioral sequence by these individuals, including frequent head-lifts and flipper slapping at the surface. In surface active groups, Gunshot sounds were commonly recorded when males were present in the group. The rate of production of Gunshot sounds was weakly correlated with the total number of males present in the group. Given the behavioral context of Gunshot sound production, and production of the sound only by male whales, Gunshots may function in a reproductive context as an advertisement signal to attract females, an agonistic signal directed toward other males, or a combination of the two functions.     

RESPONSE OF NORTH ATLANTIC RIGHT WHALES (EUBALAENA GLACIALIS) TO PLAYBACK OF CALLS RECORDED FROM SURFACE ACTIVE GROUPS IN BOTH THE NORTH AND SOUTH ATLANTIC

The surface active group (SAG) is the most obvious social interaction of the North Atlantic right whale ( Eubalaena glacialis ). SAGs are typically composed of an adult female with two or more males engaged in social behavior near the surface. Distinct calls, believed to be produced by the female, are associated with these groups. Calls recorded from three North Atlantic right whale SAGs and three South Atlantic right whale ( Eubalaena australis ) SAGs were played back to North Atlantic right whales to determine if these sounds are sufficient to attract males to the groups. Playbacks of gunshot sounds produced by North Atlantic right whales were used as a control stimulus. Thirty-six trials were carried out from 1999 to 2001 in the Bay of Fundy, Canada. Whales approached 27 of 31 SAG playbacks and 0 of 5 gunshot playbacks. Where sex was determined ( n = 28), all approaches to North Atlantic SAG recordings were by males. Individuals ( n = 22) of all age and sex classes approached South Atlantic SAG playbacks. These trials indicate that SAG calls from both populations are sufficient to attract right whales to SAGs and that males and females respond differently to stimuli from the North Atlantic. The difference in response to North and South Atlantic SAG stimuli was unexpected. Novelty, species differences in calls, and different seasonal or behavioral context for the recorded stimuli may be responsible for the differences in response.     

MOVEMENTS OF NORTH PACIFIC BLUE WHALES DURING THE FEEDING SEASON OFF SOUTHERN CALIFORNIA AND THEIR SOUTHERN FALL MIGRATION1

The satellite-acquired locations of 10 blue whales (Balaenoptera musculus) tagged off southern California with Argos radio tags were used to identify (1) their movements during the late summer feeding season; (2) the routes and rate of travel for individuals on their southern fall migration; and (3) a possible winter calving/breeding area. Whales were tracked from 5.1 to 78.1 d and from 393 to 8,668 km. While in the Southern California Bight, most of the locations for individual whales were either clumped or zigzagged in pattern, suggesting feeding or foraging (searching for prey). Average speeds ranged from 2.4 to 7.2 km/h. One whale moved north to Cape Mendocino, and four migrated south along the Baja California, Mexico coast, two passing south of Cabo San Lucas on the same day. One of the latter whales traveled an additional 2,959 km south in 30.5 d to within 450 km of the Costa Rican Dome (CRD), an upwelling feature. The timing of this migration suggests the CRD may be a calving/breeding area for North Pacific blue whales. Although blue whales have previously been sighted in the Eastern Tropical Pacific (ETP), this is the first evidence that whales from the feeding aggregation off California range that far south. The productivity of the CRD may allow blue whales to feed during their winter calving/breeding season, unlike gray whales (Eschrichtius robustus) and humpbacks (Megaptera novaeangliae) which fast during that period.