Stenella attenuata
A small dolphin with a relatively short, black beak, blackish
back, grayish sides, and white underparts; eyes usually encircled
with black rings joined by a black stripe across base of rostrum;
dorsal fin, flipper, and flukes black; the pale sides and
abdomen often covered with small blackish spots; posterior
to the dorsal fin the blackish upperparts and the flippers
often covered with grayish white dots. Teeth small (diameter
at alveolus 2.5-3.0 mm) and 38-42 in each toothrow. Total
length, 1.5-2.0 m. Similar to S. frontalis but upperparts
blackish, general size smaller, beak narrower, and the teeth
smaller and more numerous.
Occurs in the tropical and subtropical oceans of the world.
Known in Texas from three individuals that were beached near
Yarborough Pass on Padre Island during Hurricane Fern in September,
1971, and two separate individual strandings near Port Aransas
in 1989 and 1990.
These dolphins are usually seen in groups of five to 30, although
large herds of 1,000 or more are occasionally observed. Unlike
many other dolphins, groups of pantropical spotted dolphins
do not appear to be segregated by sex and age. These dolphins
feed at or near the surface on fish, including mackerel and
flying fish, squid, and shrimp.
In the eastern tropical Pacific, the following reproductive
data are known. The gestation period lasts 11.5 months and
lactation lasts about 11 months. At birth the calves average
80 cm in length and at 1 year are 1.4 m long. Males attain
sexual maturity at about 6 years of age while females reach
maturity at 5 years. The calving interval is 26 months. No
data on reproductive habits are available for the Gulf of
Mexico.
In the Pacific, these dolphins are killed incidentally in
the course of seining for tuna. In 1970, about 400,000 were
killed by U.S. vessels alone but that figure was reduced to
15,000-20,000 by 1978. Currently, incidental catch is limited
by U.S. law to 20,500 per year but is usually lower than that
due to declining tuna seining efforts and the recent adoption
of a porpoise mortality reduction program; this international
agreement by all major tuna seining countries has a goal of
reducing total incidental catch to less than 5,000 dolphins
per year by 1999. In the Atlantic and Gulf of Mexico, the
problem of incidental catch is limited and was never as great
as in the Pacific.
Remarks. This dolphin was previously known as Stenella frontalis
(Cuvier).
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