Identifying Marine Mammals

Identifying marine mammals at sea is extremely difficult, especially if only a small portion of an animal's body is seen fleetingly as it surfaces to breathe. High-quality photographs of an animal breaching (leaping from the water) or underwater with most or all of the body in the picture, or of stranded animals (alive or dead) are an important aid to identification and can be used by researchers to identify species and even individuals of some species. Sketches are also helpful.

Identifying stranded animals is also difficult, especially when they are decomposing and external fea

Figure 30.1 Indo-Pacific humpback dolphin, Sousa chinensis. (Photo: G. Parra.)

tures are used. However, if the skull is prepared, identification is much more certain. Stranded marine mammals in the GBR region should be reported through the stranding hotline at 1300 130 372.

An untrained observer is unlikely to be able to identify other than the most common and distinctive species of dolphins and whales. Beaked whales are particularly challenging because many species are rare and there are few reference specimens. Some species have been observed only as dead and rotting carcasses, so that the real appearance of the living animal is not known. Certain features, if observed and recorded carefully, are most helpful in species identification, when one has access to reference books or the opinion of experienced observers.

The observations that are most likely to be helpful in identifying a marine mammal at sea are:

(1) length of the animal;

(2) colour, including especially colour pattern (if any) and other markings or scars;

(3) presence or absence of a dorsal fin;

(4) if present, the size, shape and position relative to the distance between snout and tail flukes of the dorsal fin;

(5) the shape of the head (e.g. broad or narrow, square, round, bulbous or flat, beaked or snub-nosed);

(6) shape and height of the 'blow' (the cloud of vapour from the blowhole as the animal breathes out);

Figure 30.2 Australian Snubfin dolphin, Orcaella hein-sohni. (Photo: G. Parra.)

(7) observed behaviour (such as frequency of surfacing, how much of the back is seen when the animal surfaces, leaping, spinning in the air, slapping the water surface);

(8) the estimated number and composition of a group (e.g. are adults, calves or juveniles present, are all about the same size?)

Figure 30.3 is a sighting sheet that will help identify the species of marine mammals most likely to be seen in the GBR region; the species listed are not exhaustive. There are several good identification guides that provide more detail (see Additional reading).

There is still much to learn about cetacean distribution and the reported distribution maps for some species are probably inaccurate. A single report, or a small number of reports, of stranded individuals does not necessarily reflect the normal distribution and range of a species.

Some of the more well known marine mammals of the GBR region are introduced briefly below.

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