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Defenders Magazine
Gallery: Water Wonders
Whistling, jumping, teasing, wrestling and
playing with their food, dolphins embody all the energy of a school cafeteria at
lunchtime. They have been lauded for their intelligence and charisma,
immortalized on ancient frescoes and featured in movies. Perhaps our fascination
for dolphins is due to the human-like qualities we attribute to
them.
Dolphins are found in oceans worldwide as well as in some rivers.
Five river dolphin species and 34 oceanic species have been identified,
including the orca and melon-headed and pilot whales. Dolphin species can be
distinguished by their location, body features and skin patterns. They range in
color from the pink hump-backed dolphins to the stark black and white
Commerson's dolphin.
As marine mammals, dolphins breathe air
through a blowhole on top of their head, extracting enough oxygen to stay
submerged for 15 minutes. When they dive, muscles close the blowhole and their
ribcage collapses to keep air bubbles from forming in the bloodstream. Some
species such as the pilot whale can dive to depths of nearly 2,000
feet.
At 32 feet long and up to 19,000 pounds, orcas are the largest
dolphin. In comparison, the tucuxi, one of the smallest dolphins, is about 5
feet long and 100 pounds. Most dolphins hunt in groups and eat squid, fish and
occasionally turtles. Orca pods have even been known to prey on the blue whale —
a massive species more than 22 times their size!
Like bats, dolphins use
echolocation, an internal sonar system, to help them navigate, avoid predators
and find food. A dolphin emits a series of high-frequency clicking sounds that
bounce off objects and back to the dolphin, letting it know everything about the
object including size, shape and location.
Dolphins take about a year to
produce a single calf, which is born tail-first and pushed to the surface by its
mother to breathe. Nursing calves stay with their mothers for two to four years
and remain with the pod for life. River dolphins usually travel alone or in
small groups, but ocean species like the Pacific white-sided dolphin move in
pods of up to several thousand. Dolphins communicate through clicks, whistles
and body language. For example, the spinner dolphin "spins," a move that
scientists believe signals the pod to move forward and to mark the boundaries of
the traveling line.
Dolphins' bulging foreheads hint at large-brain
intelligence. Researchers have found that dolphins can complete complex tasks,
remember past events and use tools. These marine mammals also have an uncanny
ability to detect distress in others. Atlantic spotted dolphins, for example,
aid sick and dying members of their group by supporting them with their beaks.
There have even been a few documented cases of dolphins supporting drowning
swimmers to shallow water.
Despite their popularity, dolphins face
many threats. River dolphins are losing habitat to pollution, water development
projects and dangerous fishing methods like gillnets and explosives. The Chinese
River dolphin, the world's most endangered cetacean, is on the brink of
extinction. Pakistan's Indus River dolphin is also listed as endangered.
Entanglement in fishing gear threatens many ocean species. The fishing industry
alone has killed millions of dolphins over the last several decades, affecting
spinner, common and spotted dolphins. In the Eastern Tropical Pacific, fishing
vessels use dolphins to locate tuna and set huge purse-seine nets that stretch
for miles directly on top of the dolphins. These nets can drown and injure
dolphins as well as separate nursing calves from their mothers. Concerned
citizens came to the rescue with a 1990 boycott on the tuna industry that forced
them to agree to buy tuna from boats that do not intentionally harm dolphins.
However, the Department of Commerce recently announced plans to weaken the
current "dolphin-safe" label on tuna (see Defenders in Action on page
34).
The good news is we have seen that action by ordinary people can
make a huge difference for dolphins. We can fight for continuing protection and
more research that can help us learn to share their world.
See more information on dolphins.
