Killer Whale Biology, Behavior, and Population Decline

Introduction

Orcinus orca, commonly known as the killer whale, is a top predator marine mammal. Orcas are highly social animals that live in pods. During the past 30 years, extensive research has been conducted on the species regarding behavioral ecology, genetics, population monitoring, and acoustic research. Much of that research has been dedicated to the study of resident orcas. In recent years there has been a sharp decline in the numbers of resident orcas. This paper outlines the various proposed causes of that decline, including declining fish populations, vessel traffic, toxic exposure, and underwater noise pollution. It also addresses the common misconception that killer whales pose a lethal threat to humans and fishermen.

The biological classification of Orcinus orca is as follows:

Classification and Distribution

Kingdom: Animalia | Phylum: Chordata | Subphylum: Vertebrata | Class: Mammalia | Order: Cetacea (all whales, dolphins, and porpoises) | Suborder: Odontoceti (all toothed whales) | Family: Delphinidae (all ocean dolphins) | Genus: Orcinus | Species: orca ("British Columbia Killer Whale Adoption Program" 2004).

After humans, killer whales are the most widely distributed mammals on Earth. Although they are found in all oceans, they prefer colder regions — particularly polar areas — and are most abundant in Antarctica, northern Japan, Iceland, Norway, Alaska, and the Pacific Coast of North America. The largest population is estimated at 160,000 individuals in Antarctica. Much of the research on orcas has been conducted in British Columbia and southeastern Alaska. Two types of orcas are found in these regions: resident and transient. These two types differ in terms of morphology, habitat, diet, and vocal patterns. Resident orcas are further divided into northern and southern clans.

Transient and resident orcas have been located along the western coast of North America from southeastern Alaska to California. Offshore orcas have been encountered well away from the coastline, from the west coast of Vancouver Island to Los Angeles.

Physical Structure and Senses

The killer whale — sometimes called the "wolf of the sea" — is the largest member of the dolphin family Delphinidae. Orcas are distinguished by their striking black-and-white coloration and large dorsal fins. Adult males grow up to 9 meters in length and weigh approximately 10,000 kg; females reach about 7 meters and 7,500 kg; calves measure roughly 2.5 meters and 200 kg at birth. The average life expectancy of females is longer than that of males: 50 to 90 years for females compared to 30 to 60 years for males ("British Columbia Killer Whale Adoption Program" 2004).

The principal physical difference between male and female orcas is the length, weight, and shape of the dorsal fin. The male's dorsal fin is taller and more upright, whereas the female's curves slightly backward. The male dorsal fin can reach up to 2 meters in height; the female's reaches about 1 meter. Determining the sex of a juvenile orca is difficult because its dorsal fin closely resembles that of an adult female (Lacey, Hughes, and Miller 2000).

The killer whale has a stocky body with lateral tail fins, a rounded head, large pectoral fins (flippers), and a sickle-shaped triangular dorsal fin. In transient killer whales, the dorsal fin is more pointed and centrally positioned. The vertical movement of the symmetrical tail fins and the pectoral fins can propel a killer whale to a maximum speed of 45 km/hr. Average traveling speed is 6 to 8 km/hr. The ability to produce short bursts of high speed is highly effective when pursuing prey.

Killer whales have very acute senses of sight and hearing and respond well to touch. A distinctive white patch is located over each eye and ear. Their large teeth are conical, enameled, and interlocking — a maximum of 26 pairs (52 teeth) in an adult — and they are angled inward and backward to assist in capturing prey.

The blowhole is located near the top of the head. Orcas breathe air at the water's surface through this nostril and emit a low, misty spout. Although killer whales generally remain near the surface, when they dive the blowhole is sealed by nasal plugs controlled by fast-acting muscles. Killer whales can dive to depths of around 100 meters. Transient orcas can remain submerged for 5 to 15 minutes, while residents typically stay underwater for no more than 4 minutes ("The (Orca) Killer Whale" 2004).

For hunting purposes, camouflage is essential. The orca's dark upper skin blends with the water when viewed from above, while its white lower skin is indistinguishable from the light-filtered surface when viewed from below.

Conclusion

As a result of all these harmful activities, the status of northern resident orcas is classified as "threatened," southern residents as "endangered," transients as "threatened," and offshore orcas as a "special concern" ("British Columbia Killer Whale Adoption Program" 2004). Over the last five years prior to this study, the resident population had fallen by 4.9%. When all identified threats are accounted for, the estimated time to extinction for killer whales is approximately 74 years, with a 95% confidence interval of 33 to 121 years (Ylitalo et al. 2000; Taylor and Plater 2000).