A. Longevity.

1. Census data from the Sarasota, Florida population suggest that a bottlenose dolphin's average life span is probably 20 years or less (Duffield and Wells, 1990). Data from other areas are not available.

2. Bottlenose dolphins have lived as long as 48 years (Duffield and Wells, 1990).

B. Aging studies.

1. As a dolphin ages, it periodically produces growth layer groups of dental material. Age is estimated by examining a sliced section of a tooth and counting these layers.

2. Scientists have developed several methods of tooth analysis in bottlenose dolphins. Some of these methods can be accurate and reliable (Hohn, 1990).

C. Disease and parasitism.

1. As in any animal population, a variety of diseases and parasites can be responsible for dolphin deaths.

a. Dolphins may suffer from viral, bacterial, and fungal infections. In addition, they may develop stomach ulcers, skin diseases, tumors, heart disease, urogenital disorders, and respiratory disorders.

b. Parasites that typically affect dolphins include tapeworms, flukes, and roundworms.

2. In 1987 and 1988, over 700 bottlenose dolphins washed up dead on the east coast of the United States. Scientists originally believed that the dolphin deaths were triggered by a naturally occurring "red tide" toxin (originating in small marine organisms called dinoflagellates) combined with bacterial and viral infections. Recent tissue analysis indicated that morbillivirus may have been a major contributing factor in most of the mortalities (Lipscomb, et al., 1994).

D. Predators.

1. Certain large shark species are predators of bottlenose dolphins. Dolphin remains are often found in the stomachs of tiger sharks, dusky sharks, and bull sharks (Shane, et al., 1986).

2. Killer whales may also occasionally prey on bottlenose dolphins, but documented cases are rare (Klinowska, 1991).

E. Human impact.

1. In the recent past, bottlenose dolphins have been taken directly for meat, leather, oil, and meal (for fertilizer and animal feed) (Klinowska, 1991).

2. Bottlenose dolphins, particularly coastal animals, are also affected by pollution, heavy boat traffic, habitat destruction, and competition with fisheries (Klinowska, 1991).

3. Dolphins are also caught accidentally in fishing gear during commercial fishing operations. Recent conservation efforts have greatly reduced the number of dolphin mortalities. Researchers believe, however, that actual takes may be much larger than reported (Klinowska, 1991).