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.
Bottlenose dolphins have lived as long as 48 years
(Duffield and Wells, 1990).
B. Aging studies.
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.
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.
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.
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).
Killer whales may also occasionally prey on bottlenose dolphins,
but documented cases are rare (Klinowska, 1991).
E. Human impact.
In the recent past, bottlenose dolphins have been taken directly
for meat, leather, oil, and meal (for fertilizer and animal feed)
(Klinowska, 1991).
Bottlenose dolphins, particularly coastal animals, are also
affected by pollution, heavy boat traffic, habitat destruction,
and competition with fisheries (Klinowska, 1991).
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).
