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HAWAIIAN SPINNER DOLPHINS - NAI'A
The spinner dolphin gets its name from the spectacular leaps it
makes through the air, spinning rap-idly, sometimes rotating as
many as seven times in one leap. All dolphins are called nai'a
in Hawaiian. The spinner dolphin belongs to a large group of animals
known as whales. Like all whales, the spinner dolphin is a mammal
who bears live young, nurses its young, breathes air at the surface
through a blowhole, and is warm-blooded. Humans are also mammals.
Scientists have placed whales into two groups, baleen whales and
toothed whales. Baleen whales, such as the humpback whale, have
strips of baleen plates in their mouth which they use to filter
tiny fish and shrimp from the water. Toothed whales use their
teeth to catch and eat fish and squid. The spinner dolphin is
a toothed whale, like an orca or a sperm whale.
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DESCRIPTION
Spinner dolphins has a body shaped like a torpedo, with a dark
grey dorsal (top), a white ventral (belly), and a light grey stripe
down their side. Spinner dolphins have very strong muscles, espe-cially
along the tail. They use their tail to push themselves through
the water. Spinner dolphins can weigh up to 200 pounds and grow
up to 6 and a half feet long.
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BIRTH OF A DOLPHIN
Most spinner dolphins in Hawaiian waters breed in the summer and
fall. It takes 10 and a half months for a young dolphin to develop
within its mother. This is called gestation. At birth, spinner
dolphins weigh about 33 pounds and are called calves. They are
born fluke-first and must be taken to the sur-face of the ocean
for their first breath. They are fed milk from their mother for
a year, until the calves are old enough to catch and eat food.
After about five years, they are ready to have their own young.
FEEDING
Spinner dolphins are at the top of their food chain. The food
chain begins with sunlight and nutrients in the ocean. Microscopic
plants (phytoplankton) use the sunlight and nutrients to grow.
Microscopic animals (zooplankton) eat the phytoplankton. Fish,
squid, and many other creatures, eat the plankton. Dolphins, along
with other toothed whales and large fish, eat the fish and squid.
Spinner dolphins eat mainly mackerel, small tuna, mullet, and
squid. Normally, spinner dolphins are not eaten by any larg-er
animals, but orca have been known to catch and eat dolphins. Spinner
dolphins can dive up to 300 feet for their food. They feed at
night and spend their days resting near shore.
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| ECHOLOCATION Spinner dolphins, like most toothed whales, find
the fish and squid they eat with echolocation. Echolocation is similar
to sonar on ships and submarines. Spinner dolphins can send out
clicking sounds which bounce off of objects in the ocean and return
to their inner ear. These echoes allow dol-phins to "see" the world
around them in high detail. Dolphins can tell the shape, size, location,
texture, speed, and travel direction of objects with echolocation. |
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INTELLIGENCE
Intelligence is difficult to define in animals, but dolphins have
been compared to dogs and chim-panzees and even to humans. Dolphins
have been trained to perform in marine parks, like Sea Life Park,
and have been used by the Navy to carry out underwater jobs, such
as retrieving objects that cannot be reached by divers. Scientists
are testing the possibility of communicating with dolphins. Intelligence
may also be linked with emotions. Dolphins exhibit a variety of
emotions, including fear, distress, sadness, playfulness, and
friendliness. Dolphins have been pushing a sick dolphin to the
sur-face for air and showing distress when a dolphin dies. Dolphins
have been known to "tease" sea tur-tles and play with objects
in the water. Dolphins have long been considered "friends" with
humans, playing with children, riding the waves in front of boats,
and helping to save people lost at sea.
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DOLPHIN PROBLEMS
Dolphins, like many marine mam-mals, face a growing number of
problems. Pollution, such as toxins and heavy metals, is eaten
by fish and enters the dolphin when they eat the fish, causing
diseases and death. Red tide algae blooms are also caused by pollution.
Fertilizers from farms run off into the ocean. Algae grows quickly
because of the fertilizer and uses up all of the
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| oxygen in an area, choking other animals, such as
fish and shellfish. This pollution decreases the food supply for
dolphins. Dolphins are accidentally killed in large fishing.nets
meant for tuna, salmon, and other fish. More than 200,000 marine
mammals die each year in fishing nets. Dolphins are also hunted
for food in some places. Dolphins in the United States are pro-tected
by the Marine Mammal Protection Act, which prohibits catching, killing,
or bothering marine mammals. A growing problem is marine debris.
Old fishing nets, six pack rings, styrofoam, and plas-tic bags that
end up in the ocean do not decompose or break down. Dolphins and
other marine ani-mals become trapped in the garbage or accidentally
eat plastic, mistaking it for food. It is important to not leave
plastics on the beach. You can also help by picking up plastics
you see on the beach, either on your own or with a beach clean-up
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WATCHING DOLPHINS
Spinner dolphins are very active and can be seen leaping out of
the water just off shore. The spinner dolphin travels in herds,
sometimes numbering in the hundreds. The family groups are called
pods, averaging about thirty dolphins. Spinner dolphins are usually
seen in these large groups. Spotted dol-phins and bottlenose dolphins
are two other frequently seen dolphins in Hawaii. Dolphins such
as the rough-toothed dolphin, melon headed whale, pygmy killer
whale, false killer whale, and short-finned pilot whale, live
in Hawaiian waters but are not commonly seen. The best places
to see spinner dol-phins are at Kealakekua Bay on the Big Island,
from Barbers Point to Waianae on Oahu, at Honolua Bay and Launiupoko
State Park on Maui, at Manele Bay on Lanai, and at Kilauea Point,
the Na Pali Coast, and the Spouting Horn area on Kauai. Have fun
dolphin-watching. With protection, dolphins will always be seen
and admired in their blue ocean home. Graphics: -Food Chain Challenge
-Echolocation Game
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Food Chain Challenge
Draw lines from the plants and animals to the food or elements
they eat. Don’t forget the sun!
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