Introduction
The study of cetaceans’ intraspecific structure and population variability is interesting in several respects. It is in this group that sympatric and parapatric populations are widespread. Due to their high plasticity, representatives of the same species can explore different ecological niches and occupy different habitats, sometimes leading to reproductive isolation without spatial barriers.
The study of such populations plays an essential role in understanding the processes of microevolution. Differences in the use of resources lead not only to a variety of hunting strategies and the use of territory but also to high variability in the social relations of cetaceans. Identifying and analyzing inter-population differences is one of the approaches in studying the adaptive evolution of morphological and behavioral traits, particularly the evolution of social organization. Many cetacean species are thus fascinating objects for studying and analyzing inter-population differences. The study of literature on this topic is the basis for forming further scientific discourse in the field under study.
The Main Features of Behavior and Social Activity
While the transit killer whales of the west coast and the transit killer whales of the Gulf of Alaska represent two parapatric populations, the latter and the AT1 community are two sympatric populations. Therefore, three distinct populations of killer whales inhabit the waters of the Gulf of Alaska: resident Alaskan killer whales, transient killer whales passing through the Gulf of Alaska, and transient killer whales from the AT1 group (Newman, 2021). Even though all these killer whales use the same territory, they do not mate, do not form mixed groups, and have different behavior (Jourdain et al., 2019). Communities of transit and resident killer whales were initially identified based on social behavior data, acoustic repertoire differences, and geographical separation (Jourdain et al., 2019). Later, reproductive isolation between the isolated communities was confirmed by molecular data.
In addition, it turned out that the territories of all three parapatric resident communities overlap. Still, on each community’s territory, there are “key” areas, which killer whales use most often. There are some differences in territory use between groups of transit orcas that make up one community (Newman, 2021). These differences are primarily related to different hunting objects (Cosentino & Oria, 2021).
In the resident community, minor differences were also found in using the water area between the pods, which had two different haplotypes of mitochondrial DNA (Jourdain et al., 2019). Pods visited the studied areas of the water with different frequencies. In general, thousands of killer whales return to traditional places of hunting, recreation, and social interaction yearly (Newman, 2021). Researchers suggest that knowledge about such places, traditional for each group, is passed from generation to generation through education (Jourdain et al., 2019). Orcas probably adopt acoustic dialects and hunting skills from older generations.
The successful transfer of traditional knowledge is facilitated by the matrilineal social structure of the population, in which powerful social ties are maintained between relatives of different generations. In addition, female killer whales continue to live after losing reproductive functions (Robeck et al., 2019). A similar property has been described for females of a small number of species, including humans (Homo sapiens) and grinds (Globicephala macrorhynchus) (Jourdain et al., 2019). These species are characterized by long-term relationships between maternal relatives (Newman, 2021). The researchers suggest that the grandmothers in the killer whale and grinds groups are carriers of knowledge about the “cultural traditions” of the family group and contribute to their transmission to new generations.
Hunting Features
Transit Orca whales are the notorious “killer whales” that hunt dolphins, whales, pinnipeds, sea otters, and sea lions. Even their attacks on deer and moose that swam across narrow coastal channels have been reported (Newman, 2021). Tooth prints of killer whales were found on the bodies of 53% of the examined fin whales, 24% of sei whales, 6% of minke whales, and 65% of sperm whales (Jourdain et al., 2019). These killer whales often concentrate in search of prey near seal and seal rookeries and in areas of whaling.
Due to the peculiarities of hunting tactics, the flocks of transit killer whales are noticeably smaller than those of resident ones, 1-5 individuals. The most intriguing method of hunting is releasing killer whales onto beaches, to sea lion rookeries that regularly occur off the coast of Patagonia (Newman, 2021). Killer whales attack seals utilizing the bottom relief adjacent to the rookeries, but only one male kills while the others watch from a distance (Jourdain et al., 2020). Small dolphins are propelled by killer whales either individually or by surrounding a group of dolphins with the combined forces of several groups (Cosentino & Oria, 2021).
Killer whales dive through ice floes to strike seals or penguins swimming there, attempting to push the prey into the ocean (Myers et al., 2021). The attack on large whales involves mainly males (Lefort et al., 2020). They attack the victim at the same time, biting her throat and fins to keep her from rising to the surface.
Male sperm whales are avoided by killer whales due to their power, whereas when attempting to attack female sperm whales, they try to stop the victim from diving deep (Jourdain et al., 2019). The killer whale might get a lethal wound from its jaws. Usually, they try to drive a whale away from the group or to remove a cub from its mother, but it is not always possible because whales can efficiently defend themselves and their offspring.
The level of their “talkativeness” is a key distinction between resident and transit orcas: since marine animals may hear their noises, they are less loud than residents (Cosentino & Oria, 2021). As a result, if resident killer whales use active echolocation to navigate across space and follow their prey, then transit killer whales use passive listening to ocean sounds to do so (Jourdain et al., 2019). Killer whales classified as “resident” and “transit” have not cross-bred in the past 100,000 years, according to analysis of their genomes (Pinfield et al., 2019). Killer whales are starving and need 50–150 kg of food daily (Jourdain et al., 2019). Since killer whales use large (including predatory) marine animals for food, they represent the top of the food pyramid.
Features of Appearance and Behavior
The killer whale has a white neck, a white longitudinal stripe running down the middle of its belly, and black back and sides. A grey saddle-shaped patch and a white mark above each eye may be seen on the back, beneath the dorsal fin (Myers et al., 2021). Because of the diatom-covered coating, white areas in the Arctic and Antarctic seas might take on a yellowish-green or brown color (Jourdain et al., 2019). Because each killer whale’s spots are unique, it is possible to recognize specific individuals. The North Pacific Ocean has completely black (melanistic) and white (albino) individuals (Newman, 2021).
Killer whales are the friendliest predatory animals toward humans. In the wild, killer whales do not frighten people; all their assaults on people have either been carried out by injured animals or individuals acting in self-defense (Jourdain et al., 2019). Killer whales frequently approach ships and raise their muzzles above the water’s surface to investigate them. Because they are kept in captivity, they are easily trained and quickly get used to a person (Robeck et al., 2019). Since they are in the open sea, killer whales only attack mammals to express their hunger. Only during their breeding season do killer whales exhibit extreme irritability and aggression.
Conclusion
It is worth noting that cetaceans are ecologically plastic animals. Occupying different habitats or existing in the same geographical area, representatives of the same species master a variety of ecological niches. Differences in the use of resources lead to various hunting strategies and the nature of the use of the territory, but also to a high degree of variability in social relations. Almost all information about killer whales’ lives in nature was obtained from a study of populations in the northeastern Pacific Ocean. Even in a small area of the world ocean, sharp differences were revealed at the inter- and intra-population level, various ecological types, and hunting in coastal and open waters for transit killer whales.
To get an idea of the species, it is necessary to study in more detail the populations of killer whales in other areas of the world’s oceans. Thus, the information from the literature is valuable for this work as it forms a different research framework. Using the obtained information, various populations of killer whales in poorly studied regions can be studied to compare them with the previously presented species.
More than live fishing, cultural, educational, and scientific goals correspond to the actively developing direction of ecological tourism, demonstrating animals in their natural habitat. However, even in this case, there are no rules and recommendations on the proper behavior of vessels near cetaceans. Careful development of such restrictions will not only reduce the level of animal anxiety to a minimum. The care of animals rendered in this way will pay off with the calm behavior of killer whales and the long time they spend next to the vessels of ecotourism companies.
References
Cosentino, M., & Oria, N. (2021). Insights into the foraging behaviour of an understudied orca population. Latin American Journal of Aquatic Mammals, 16(1), 51-53. Web.
Jourdain, E., Andvik, C., Karoliussen, R., Ruus, A., Vongraven, D., & Borgå, K. (2020). Isotopic niche differs between seal and fish‐eating killer whales (Orcinus orca) in northern Norway. Ecology and Evolution, 10(9), 4115–4127. Web.
Jourdain, E., Ugarte, F., Víkingsson, G. A., Samarra, F. I. P., Ferguson, S. H., Lawson, J., Vongraven, D., & Desportes, G. (2019). North Atlantic killer whale Orcinus orca populations: a review of current knowledge and threats to conservation. Mammal Review, 49(4), 384–400. Web.
Lefort, K. J., Matthews, C. J. D., Higdon, J. W., Petersen, S. D., Westdal, K. H., Garroway, C. J., & Ferguson, S. H. (2020). A review of Canadian Arctic killer whale (Orcinus orca) ecology. Canadian Journal of Zoology, 98(4), 245–253. Web.
Myers, H. J., Olsen, D. B., Matkin, C. O., Horstmann, L., & Konar, B. (2021). Passive acoustic monitoring of killer whales (Orcinus orca) reveals year-round distribution and residency patterns in the Gulf of Alaska. Scientific Reports, 11(1). Web.
Newman, K. (2021). A comparison of transient killer whale (Orcinus orca) whistles in Alaska. Journal of the Acoustical Society of America, 150(4), A121. Web.
Pinfield, R., Dillane, E., Runge, A. K. W., Evans, A., Mirimin, L., Niemann, J., Reed, T. E., Reid, D. M., Rogan, E., Samarra, F. I. P., Sigsgaard, E. E., & Foote, A. D. (2019). False‐negative detections from environmental DNA collected in the presence of large numbers of killer whales (Orcinus orca). Environmental DNA, 1(4), 316–328. Web.
Robeck, T. R., St Leger, J., Robeck, H. E., Nilson, E., & Dold, C. (2019). Evidence of variable agonistic behavior in killer whales (Orcinus orca) based on age, sex, and ecotype. Aquatic Mammals, 45(4), 430–446. Web.