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Killer whales are identified individually from unique markings on their dorsal fin and the grey saddle patch at the base of the fin. Other features can also be used, such as the eye patch, but these are not as visible to the surface observer. The markings on the dorsal fin and saddle patch are documented by a high-quality photograph, normally of the left side of the whale. The two sides often vary slightly in appearance, but, on occasion, one side is completely different. We arbitrarily chose the left side to simplify and standardize the system.

The unique characteristics of the dorsal fin are its shape, size, and scars. The scars are the result of injuries and are seen as gouges, nicks, and indentations, most of which are located along the rear edge of the fin. These injuries are permanent markings. The saddle patch, particularly its upper half, often has a unique shape. The shape does not change and its scarring and blemishes are frequently permanent. The location of the saddle patch relative to the ridge of the back and the detail of the edge of the pigmentation is also important. We developed this recognition process over many years, and we can now distinguish individuals on sight. However, we still rely on photographs for identification, especially for whales with indistinct markings.

Male and female killer whales can be distinguished by variations in the appearance of the pigmentation in the genital area. Females have dark spots marking the two mammary slits, located on either side of the genital slit, which also usually has a dark marking. The genital area is surrounded by a roughly circular or oval white patch. Males have a more pronounced dark spot at the genital slit, lack mammary slits, and have a more elongated white patch surrounding the genital slit.

Adult males can be distinguished from felmales by their relatively large dorsal fin. At the the age of sexual maturity, around 12 years, the male's dorsal fin will begin to grow or "sprout". Females have a shorter more falcate shaped dorsal fin. Adult males will also have enlarged pectoral fins and as they grow their flukes will begin to curl downward.

The dorsal fins of resident orcas, and transient and offshore killer whales differ subtly in shape, especially in adult females. With a practised eye, it is possible to determine which form of whale you are seeing based on these differences, with the help of certain other clues. It is important to note, however, that the differences described here are not seen in every individual, but are typical of the majority for each population of killer whale.

In residents, the fin tip tends to be rounded and positioned over the rear insertion of the fin to the back. The leading edge of the fin tends to be straight or curved slightly back. Although the fin tip is generally rounded, this curve ends in a rather sharp angle at the rear corner of the tip. The grey "saddle patch" at the base of the fin may be either uniform in colouration or may contain various amounts of black - the latter known as "open saddles." Residents are usually seen in groups of 6 to 50 or more and tend to surface at intervals of no more than 3-4 minutes.

The tip of the dorsal fin in transient females is typically pointed and positioned in the centre above the front and rear insertions of the fin. Also, the midpoint along the leading edge of the fin sometimes has a slight bulge. The saddle patch is typically quite large compared to residents and offshores, and open saddles are not found. Transients usually travel in groups of 6 or less and often dive for periods of 5-7 minutes.

In most respects, the offshore form of killer whales appears more similar to resident orcas than to transient killer whales. The saddle patch is roughly the same relative size as that of residents, and open saddles are occasionally seen. The dorsal fin also tends to be rounded, although the shape of the tip often differs subtly. Rather than ending in a sharp angle at the rear corner of the tip, as in residents, the dorsal fin tends to be continuously rounded over the entire tip. Alt!lough there are no measurements available, the body size seems to be somewhat smaller than that of residents or transients. Offshores are usually seen in groups of 25 or more and have diving characteristics not unlike those of residents.

Illustrations on this page by Kelly Balcomb-Bartok