REACTIONS OF HUMPBACK WHALES TO SKIN BIOPSY SAMPLING ON A WEST INDIES BREEDING GROUND

Abstract: Reactions of humpback whales, Megaptera novaeangliae , to the taking of skin biopsies and to associated activities were studied on one of their principal West Indies breeding grounds on Silver Bank (Dominican Republic). Results were in some cases different from those reported from a similar study of this species in a high-latitude feeding area. Almost half (44.1%) of 565 biopsied whales showed no immediate reaction to a hit, while a further 22.5% showed only low-level reactions. A total of 375 (87.8%) of 427 misses involved no reaction. Only one strong reaction was recorded. Behavior changes were recorded following 31 (5.5%) of 569 hits, and 18 (4.5%) of 404 misses. Evasive behavior related to vessel approach was exhibited prior to 72 (12.0%) of 598 hits and 100 (24.1%) of 415 misses. Mothers showed significantly fewer reactions to hits than other whales, and a similar frequency and type of behavior changes, although they tended to be more evasive before a shot was made. Presumed males in competitive groups also showed significantly fewer reactions to shots, and very few behavior changes. Overall, this study supports the belief that the biopsy itself has little effect on a whale and that, if the associated vessel approach is conducted with care, samples can usually be taken with minimal disturbance to the target animal. However, approaches may affect the probability of obtaining fluke photographs for individual identification.     

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.     

ESTIMATES OF THE NUMBERS OF HUMPBACK WHALES OBSERVED MIGRATING PAST CAPE VIDAL, SOUTH AFRICA, 1988–1991

A recovery-monitoring program of the African east coast humpback whale population was carried out through shore-based visual surveys from Cape Vidal, northern Natal. Surveys of the northward migration were undertaken each winter from 1988 to 1991, and a survey of the southward migration was undertaken in 1990. Independent observer surveys were undertaken during June 1990 and during the entire 1991 survey. Hourly densities of groups sighted each day were adjusted for groups missed by observers with distance from the shore and under different sighting conditions. Densities were multiplied by 24 h and the mean group size of the survey year to give resulting daily densities of individuals, which were summed to provide totals of whales sighted during each year's survey. The best estimate of population size was 1,711 (made during the northward migration of 1990), although this is likely to be biased downwards by a proportion of the population passing outside of observers'view. Bootstrapping of the 1991 daily data resulted in CVs between 11.4% and 12.2%. The numbers sighted show the population to have undergone considerable recovery since protection in October 1963.     

ASSESSMENT OF HETEROGENEITY IN SIGHTING PROBABILITIES OF HUMPBACK WHALES WITHIN VIEWING RANGE OF CAPE VIDAL, SOUTH AFRICA

The migrations of humpback whales on the African east coast were monitored between 1988 and 1991 at Cape Vidal, South Africa. Shore-based surveys of the northward migration were undertaken each winter, and a survey of the southward migration was undertaken in 1990, from an approximately 60-m-high vantage point on a headland. Independent-observer surveys were carried out in both 1990 (22 d) and 1991 (51 d) to determine the proportion of the population within the survey area that were being missed by observers using a single mark-release model. Results were stratified into three distance intervals from the shore and three sighting condition intervals; there were constant sighting probabilities from the south tower under different sighting conditions, while those from the north tower increased slightly as sighting conditions improved. Sighting probabilities from both towers were highest in the intermediate distance interval and decreased in both the inshore and offshore regions.     

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.     

SEASONAL AND DIURNAL TRENDS OF CHORUSING HUMPBACK WHALES WINTERING IN WATERS OFF WESTERN MAUI

A portable data logger controlled by a Tattletale 7 microcontroller was used to record humpback whale choruses during the 1998 humpback whale winter season in Hawaii. The data logger sampled the sounds for four minutes every half hour using a digitizing rate of 2 kHz, and the data were stored on a hard disk. The results between January and April showed a peak in the sound pressure level between mid-February and mid-March. This peak of approximately 120 dB re 1 μPa coincided with the peak in the number of whales sighted by aerial survey on 7 March 1998. The choruses had spectral peaks at 315 Hz and 630 Hz. Some of the sounds at 630 Hz were second harmonics of the 315 Hz peak and others were not. The data also indicated a diurnal pattern in the sound pressure level, with levels at night significantly louder than the daytime levels. The sound levels began to increase during sunset and remained relatively high until sunrise, when they progressively decreased to a minimum. The nighttime peak occurred within an hour before and after midnight, and the daytime minimum occurred between 1100 and 1500. That more humpback whales appear to sing at night may reflect a switch to sexual advertisement as the primary male mating strategy at this time. It may also indicate that daylight and vision play key roles in the formation of competitive groups. It is suggested that the relative number of humpback whales in a given locale may be estimated by monitoring changes in sound pressure levels.     

Habitat preference reflects social organization of humpback whales (Megaptera novaeangliae) on a wintering ground

Habitat preference is driven by a complex interaction among behavioural patterns, biological requirements, and environmental conditions. These variables are difficult to determine for any species but are further complicated for migratory marine mammals, such as humpback whales Megaptera novaeangliae . Patterns of habitat use in relation to social organization potentially exist for this species on their wintering grounds. Using an integrated GIS approach, we examined the degree to which spatial patterns of habitat stratification are correlated within different humpback whale group types from 6 years of sighting data (1996–2001) collected on the Antongil Bay, Madagascar, wintering ground. Stratification of humpback whale sightings by behavioural classification showed significant variation in depth and distance from shore. Distribution by depth could not be described as a function of group size but could be described as a function of social organization, with mother–calf pairs showing a strong preference for shallower water compared to all other group types. Group size and social organization seem to be factors in distribution by distance from shore. Significant diurnal patterns in distribution by depth and distance from shore also exist, where mother–calf groups maintain a relatively stable distribution and pairs and competitive groups are the most variable. Patterns of habitat preference on this wintering ground appear to be guided by social organization, where distribution by depth and distance from shore highlight areas critical to conservation.