Association patterns and social dynamics of killer whales (Orcinus orca) in Greater Puget Sound

Killer whales were observed in the inland marine waters of Washington and British Columbia from March to November 1982 and January to November 1983. The majority of the research occurred in Haro Strait in the San Juan Islands. All whales were individually identifiable from naturally occurring marks and scars on the dorsal fin and back. Many whales were identified visually in the field with the aid of a photographic guide to individuals (Biggs et al. 1987). Seventy-two whales comprised the study population. Data collection concentrated on group composition and spacing, identification and associations of all whales present, and the recording of the dominant behavior occurring at that time. Behaviors were categorized from combinations of quantifiable parameters of group composition, spacing of individuals, speed and direction of travel, and the occurrence of specific behaviors such as leaps, tail slaps, penile erections, etc. (Osborne 1986). Behaviors were pooled into four major groups: feeding, travel, rest and social/sexual behaviors. The results suggest the following hypothesis about the social organization of the killer whales resident to Greater Puget Sound. As a whale ages, it moves from an integrated position within the community, based on its relationship with its mother to a less integrated period during adolescence in which social ties remain primarily through the older female generation. With full adulthood, dependency upon these “allo-mothers” (N.J. Haenel 1986) declines and direct affiliation with the mothers are re-established. Adult whales remain with the maternal sub-group. Close associations between adult whales appear to be based on relationship between direct kin. Fission from the main material sub-group and the establishment of separate subgroups may be the result of several factors including the age of the older female and the number, ages, and sex of her offspring, including adult sons. When older females die out, siblings or cousins may separate more permanently, forming new lineages or pods

Social Organisation of the Short-finned Pilot Whale, Globicephala macrorhynchus, with Special Reference to the Comparative Social Ecology of Delphinids

As a contribution to the understanding of comparative social trends within the cetacean family Delphinidae, a 22-month study was conducted on the shortfinned pilot whale, Globicephala macrorhynchus, which has been suggested to have a unique social system in which males and females in the same group are related and mating occurs outside of the group. The individual identification of 495 pilot whales, analysed in daily group association patterns, allowed identification of 46 pods. They were classified as productive or non-productive based on the presence or absence of immature animals. Productive pods were a significantly larger, although 12% of them lacked adult males. Two classes of whales (residents and visitors) were defined by patterns of occurrence,suggesting differential patterns of habitat use. Resident pods occasionally travelled together (41% of all groups) and associations between age and sex classes showed that in mixed-pod groups, the highest ranked associations of the reproductive females were with males from other pods, while within pods, adult males and females associated less. During summer, the proposed peak conception period, pilot whale groups were significantly larger and contained individuals from a significantly greater number of pods. These findings support the hypothesis that males and females mate when associating with individuals from other pods. A comparative analysis of sexual dimorphism, brain size, and testes size, habitat, prey and group size within the 17 delphinid genera identified a correlation between sexual dimorphism and body size, but relative measures of brain size and testes size did not correlate with broad ecological or social classifications. However, a comparison of three delphinid societies identified two distinct male mating systems: males of the small, mono-morphic Tursiops truncatus live in age/sex segregated groups and mate with a number of discrete female communities. Males in the large sexually dimorphic Glob icephala spp. and Orcinus orca mate with associated female pods and yet remain with their female kin. This corresponds to the avunculate social system described in some human societies. It could evolve from a promiscuous mating system where there is little guarantee of paternity and where males that live with their kin increase their inclusive fitness

Dolphin morbillivirus infection in different parts of the Mediterranean Sea

Morbillivirus were isolated from Mediterranean striped dolphins (Stenella coeruleoalba) dying along the coasts of Italy and Greece in 1991. They were antigenically identical to the morbilliviruses isolated from striped dolphins in Spain in 1990

Distinguishing the Impacts of Inadequate Prey and Vessel Traffic on an Endangered Killer Whale (Orcinus orca) Population

Managing endangered species often involves evaluating the relative impacts of multiple anthropogenic and ecological pressures. This challenge is particularly formidable for cetaceans, which spend the majority of their time underwater. Noninvasive physiological approaches can be especially informative in this regard. We used a combination of fecal thyroid (T3) and glucocorticoid (GC) hormone measures to assess two threats influencing the endangered southern resident killer whales (SRKW; Orcinus orca) that frequent the inland waters of British Columbia, Canada and Washington, U.S.A. Glucocorticoids increase in response to nutritional and psychological stress, whereas thyroid hormone declines in response to nutritional stress but is unaffected by psychological stress. The inadequate prey hypothesis argues that the killer whales have become prey limited due to reductions of their dominant prey, Chinook salmon (Oncorhynchus tshawytscha). The vessel impact hypothesis argues that high numbers of vessels in close proximity to the whales cause disturbance via psychological stress and/or impaired foraging ability. The GC and T3 measures supported the inadequate prey hypothesis. In particular, GC concentrations were negatively correlated with short-term changes in prey availability. Whereas, T3 concentrations varied by date and year in a manner that corresponded with more long-term prey availability. Physiological correlations with prey overshadowed any impacts of vessels since GCs were lowest during the peak in vessel abundance, which also coincided with the peak in salmon availability. Our results suggest that identification and recovery of strategic salmon populations in the SRKW diet are important to effectively promote SRKW recovery