Fish on the Floor
What do you see in your mind when you hear
the word “fish”? Maybe you imagine a long sleek shape with short
fins leaping out of a lake or ocean. Many fish look
like that, but certain ones look very different. They’re flat and shaped
like a kite. They have eyes on top of their heads. Their fins stretch from
the sides of their heads to the end of their bodies, giving them their diamond
shape. And, you won’t usually find them on the surface. They live way
below, on or near the ocean floor. These fish are called skates and rays.
Southern fiddler rays live on the reef, sand and even sea grass beds where
they find many kinds of invertebrates to eat such as shrimp, crabs and worms.
© K.Deacon/AUSCAPE/Minden Pictures My Cousin, the Shark
This black-spotted stingray skims across the ocean floor where it may find
its next meal or rest for a bit. Skates and rays do not sleep like we do
but they do switch between periods of rest and activity.
©Gina Sanfilippo There are more than five hundred different species of
skates and rays in our oceans. Scientists say that these fish are closely related
to sharks, sharing a common ancestor from
around 400 million years ago. Some scientists suspect that skates and rays
may actually be a type of shark.
Skates, rays, and sharks are all vertebrates,
because they have backbones. Their skeletons are made of cartilage,
like your ears and nose. Cartilage is hard, but not as hard as real bone.
Skates and rays may be related to sharks, but their bodies look like they’re
from different families. Sharks are shaped to glide like submarines through
deep water. Skates and rays are flat so they can skim the ocean floor. Sharks
use their tails to steer. Skates and rays use their large fins.
Where Do Skates and Rays Live?
Skates and rays are native to the Atlantic, Pacific, and Indian Oceans. They
can be found in tropical to cold temperate climates,
living between 8
m and more than 3000
m under the surface. Skates and rays can also live in estuaries, places
where rivers meet the ocean. At least one group of stingrays lives in freshwater
in South American rivers.
Hiding out at the Bottom
The little skate settles on the ocean floor where it blends in with the
light colored sand. It can easily surprise any prey while waiting in this
position.
©A.Martinez/Stellwagen Bank National Marine Sanctuary Skates and rays skim the ocean bottom, slowly flapping their fins to propel
them forward. Many skates and rays spend most of their time down below. They
even lay their young in the soft sand. However, there are a few exceptions.
The manta ray and devil ray spend more time swimming in the ocean than on or
near the bottom.
Scientists think that the coloring of skates and rays is a type of camouflage.
Their coloring has adapted to blend into the ocean bottom. Species in deep
water are often dark-colored. Species in shallow water are often light-colored,
with wavy lines to look like watermarks from above. Males and females often
have the same coloring.
How Big?
There are big differences in how much different
skates and rays weigh. The largest ray, the manta ray, weighs up to 1300
kilograms – about as much as a young elephant, or an average-size
car! On the small end, the clearnose skate usually weighs only 1-2
kilograms, less than half the weight of a small house cat. In between,
the Southern stingray can weigh between 13
and 80 kilograms.
Reproduction and Young
Baby rays are born in groups called “litters” and have to fend
for themselves as soon as they are born.
©Tamsyn Steadwood Skates give birth to fertilized eggs in
an egg case. The case is often called a “mermaid’s purse.” The
mother skate deposits egg cases, which have tendrils that anchor them to seaweed
or rocks. The mother does not protect the egg cases during the 6-9 months that
the skates develop in their cases. Rays give birth to live young. These young
are fully formed and can protect themselves.
Skates and rays develop slowly and can live as long as 50 years. Many species
do not breed until after they’re eight years old.
Shock of Recognition
How do you recognize your parents and friends?
You probably identify them by the way they look and the sounds of their voices.
Skates have a different way. Scientists say they may use electricity to identify
family members. All skates have organs that are weakly electric.
Scientists think that different species may have different amounts of electricity.
This may be how skates recognize one another.
Other Relationships
This manta ray has a pair of remoras or suckerfish attached to it. The suckerfish
catch a free ride on the ray, get protection and feed on material dropped
by the ray.
©Flip Nicklin/Minden Pictures How about outside the family? Scientists don’t know a lot about how
skates and rays relate to other organisms. But they have observed that one
type of manta ray will swim to shallow reefs and let bony fish pick parasites
from its skin. Maybe researchers will discover more ways that rays relate.
The Sting of Self-Defense
Usually skates and rays are peaceful, but if threatened or scared they know
how to defend themselves. Electric rays can give large electric shocks. Stingrays
have a barbed, stinging tail. Eagle rays have one poisonous bony spine that
they can use to pierce predators.
Many types of skates have rows of spines on their back that can stab and tear.
Fish Food
Check out the cownose ray's mouthful of flat teeth! Those teeth make it
easy for it to crush clam and oyster shells.
©Vincent Van Dam Skates and rays are consumers in
the food
chain. This means that they cannot produce their own food. They are carnivores,
eating other animals to survive. Their diet is mostly hard- shelled invertebrates such
as snails. They trap their prey against the ocean floor from above with their
wide, flat bodies. Then they use their flat, hard teeth to crush the shells.
Threats to Populations
A number of ray species are decreasing in population.
The white skate and common skate are considered critically endangered.
The undulate ray is endangered. The sandy ray is considered vulnerable, which
means it may become endangered. A number of other types of rays are considered
near threatened, including the thornback ray, shagreen ray, blonde ray, and
smalleyed ray.
The thornback ray has three rows of sharp spikes called “thorns” along
its back and tail that protect it from predator attacks.
©C.V. Vick Why are these species threatened? Skates and rays are overfished around
the world. In the commercial fishing industry, there is no minimum size requirement
for skates and rays. This means that young rays are not returned to the ocean
when they are captured. Because skates and rays grow fairly slowly and mature
late, they can be killed before they’re old enough to reproduce.
Also, they have relatively few babies.
Studying Skates and Rays
Skates and rays are both studied in their habitats as
well as in laboratories. Scientists have tagged skates and rays to monitor
their movements. Research suggests that these fish spend their lives staying
in a relatively small area. Disrupting their habitats may lead to their death,
because they will not necessarily move elsewhere.
Conservation Efforts Can Help
Skate for sale in the seafood section of a supermarket. People from many
different countries eat skates’ fins which are sometimes called wings.
©Joshin Yamada What can we do to help protect skates and rays? We can create special areas
where they can live safely. We can limit commercial fishing to only fish of
a certain size. Restricting commercial fishing of females can help too, particularly
during spawning season.
Efforts like these are part of conservation and
the work people do to protect species.
Skates and Rays in Culture
The Chevrolet Stingray was named after the fish because the body of the
car is low and wide. This car may be fast on the road but it wouldn’t
do so well on the bottom of the ocean!
©G.E. Long Humans have both feared and admired these
unique fish. Fishermen have feared manta rays because of their immense size.
Stingrays have inspired a sports car—the low, wide-bodied Stingray, made
by Chevrolet in 1958. More recently, Steve Irwin, known as the “Crocodile
Hunter,” was killed by a stingray off the coast of Australia. The barb
of a stingray’s tail pierced his heart. This incident may have helped
spread the idea that rays attack people. But for the most part, rays do not
harm humans unless they are provoked, or startled and scared, which can happen
if they are accidentally stepped on.
How can we change the fearsome reputation of rays? The answer lies in more
research. However, sharks are the more popular members of the scientific class
they occupy with skates and rays. They get more attention, and they receive
more money for scientific research. To give skates and rays a fair shake, they
need a fair share of research funding and attention.