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OUR OCEAN PLANET
OUR OCEAN PLANET
SECTION 8 – OPEN OCEAN
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REVISION HISTORY
Date
Version
Revised By
Description
Aug 25, 2010
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Original
8. OPEN OCEAN
8. OPEN OCEAN
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8. OPEN OCEAN
The open ocean is vast. It covers an area of 361 million sq. km (139
million sq. miles) and more than 70% of the world’s surface. Much
of the ocean lies in the world’s tropical and sub-tropical areas, which
contains comparatively few nutrients and plankton. This massive
three-dimensional space is home to some of the most extraordinary
creatures on the planet, some of which must travel long distances up
and down the water column or across the open ocean to find food
and mates.
VERTICAL LAYERS
The open ocean is known as the pelagic realm. It contains several
vertical layers or zones with different characteristics. The layers
form a physical and chemical barrier to different organisms and few
organisms can move easily between them. The main vertical zones
are:
1. Neuston Layer
The topmost meter of the ocean is completely different from the rest
of the water mass. It is called the “neuston layer” and is
comparatively rich in nutrients because many of the waste chemicals
excreted by plankton in deeper water float to the surface and
concentrate there. This chemically enriched environment provides
and ideal habitat for bacteria, unicellular protozoans and microscopic
algae.
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8. OPEN OCEAN
2. Photic Zone (Surface)
The top 200 m (656 ft) of water is warm, highly mixed, and
effectively floats upon the colder, denser water below. It is the sunlit
zone of the ocean and is limited to the maximum depth sunlight can
penetrate. The photic zone is where phytoplankton is found since
they need sunlight for photosynthesis. It is also where most animals
are found at night.
Under water, the colours of the visible spectrum are absorbed by
water with increasing depth. Red will disappear at a depth of around
6 m (20 ft), orange at 9 m (30 ft), yellow at 18 m (60 ft) and green at
21 m (70 ft). By 30 m (100 ft), everything appears blue or greyish
green. At greater depths, all visible light is absorbed and everything
appears dark blue or black.
3. Twilight Zone (Intermediate)
Below the photic zone lies the colder and denser intermediate layer
called the twilight zone which lies between 200 m and 1000 m (656
ft and 3,300 ft). The twilight zone is where most animals are found
during the day.
4. Dark Zone (Deep)
Below 1,000 m (3,300 ft), the water is extremely heavy, dense, and
cold. It is also completely dark. In spite of these difficult conditions,
however, deep sea life can be found here.
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8. OPEN OCEAN
TEMPERATURE & OXYGEN BARRIERS
The different layers of the ocean are physically and chemically
different. The water temperature and the amount of dissolved
oxygen play important role in partitioning life vertically in the ocean.
For example;
1. Temperature
The layers have different temperatures and thermoclines (lines of
temperature differences) form. In the tropics, the surface zone water
may be as warm as 25°C (77°F) while the intermediate zone water
temperature may be just 11°C (50°F). In the dark zone, the water
becomes much colder, 5°C (41°F).
The main ocean thermocline lies within the intermediate zone. This
is a permanent feature that is rarely broken down and it proves an
impenetrable barrier to most marine life because it cannot cope with
the sudden change in temperature. By and large, this thermocline
separates the ocean’s upper-water organisms from those in the
deep.
2. Oxygen Minimum Layer
Another boundary exists within the intermediate zone. This is the
oxygen minimum zone and marks the level below which dissolved
oxygen in the water is at its minimum. Few organisms from the
warm oxygen-rich surface waters above can survive in these
oxygen-depleted conditions.
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8. OPEN OCEAN
OVERTURN
Anything that is heavier than water sinks under gravity so many
dying organisms and nutrients fall through the thermocline into the
deep zone below.
If the ocean was static, these sources of food
would be lost to the life in the surface layer.
Fortunately, in polar and temperate oceans, in a process called
“overturn”, winter chilling causes the surface water to become so
dense that it sinks into the deep ocean forcing nutrient-rich water up
from the bottom.
Winter storms further mix the water layers, ensuring that oceans in
the far north and south of the world have high nutrient levels and can
support the massive plankton populations in the summer months.
Tropical and sub-tropical oceans, however, do not experience
sufficient cooling to allow overturn to occur so here the stable
surface zone contains vastly fewer nutrients than the deep zone.
REFERENCES & FURTHER READING
Byatt, Andrew, Fothergill, Alastair and Holmes, Martha, The Blue
Planet: Seas of Life, Chapter 6, DK Publishing Inc., (2001), ISBN 07894-8265-7
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8.1.1 Vertical Migrations
In the open ocean during the day, there are very few places animals
can hide from predators. In order to avoid predators, therefore, most
animals hide in the twilight zone (200-1,000 m / 656-3,300 ft) where
they are less easily seen by predators that hunt mainly by sight.
Thus, during the day, the photic zone only contains about 10% of the
total marine life, while 75% is found in the twilight zone.
At night, however, the amount of life at the surface quadruples to
40% as a result of mass vertical migrations. Every night, millions of
tonnes of animals undertake the largest mass migration on Earth
journeying up from the ocean’s twilight zone to the photic zone in
search of food. In the middle of the night, the top 30 m (98 ft) of the
ocean teems with feeding plankton. At dawn, the same animals will
return to the twilight zone.
The extent of the vertical migration up and down the water column
varies between species. The smallest plankton probably travel just
10-20 m (33-66 ft) while larger animals may travel as much as 1000
m (3,300 ft).
As the zooplankton travel up and down the water column, so follow
their predators, including fish such as anchovies, mackerel and
herring, and jellyfish. In turn, predators of these fish and jellyfish,
such as sharks, dolphins and turtles, follow.
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8.1 LIFE IN THE OPEN
8.1.2 Migrations Across Oceans
Some animals undertake immense journeys across the oceans in
search of food and breeding grounds. The following are some of the
extraordinary travelers that undertake these great migrations across
the oceans:
1. Arctic Terns
Arctic terns fly between the Arctic and Antarctic regions to enjoy two
summers a year. They travel further than any other bird. Some
Arctic terns fly more than 35,000 km (21,000 miles) in a year from
the Arctic to the Antarctic and back!
2. Grey Whales
Grey whales swim more than 22,000 km (13,600 miles) a year
between their Arctic feeding grounds and their breeding grounds off
California. No other mammal migrates as far.
3. Wandering Albatrosses
The wandering albatross spends most of its life circling the globe
north of Antarctica. This seabird travels up to 12,000 km (7,500
miles) before returning briefly to land to breed.
4. Green Turtles
Every 2-3 years, female green turtles leave their feeding grounds off
Brazil and travel to Ascension Island in the middle of the Atlantic
Ocean where they were born. Here, they lay their eggs before
returning across the sea again. How they navigate this 2,000 km
(1,250 mile) journey is not known but some possible mechanisms
include their using currents, seamounts or the Earth’s magnetic field.
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5. Spiny Lobsters
Migrating spiny lobsters form “lobster trains” and match head to tail
along the seabed to protect themselves from enemies.
6. European Eels
The European eel has an amazing life cycle. From 4 to 18 years of
age, it lives in freshwater rivers and lakes. When it reaches
adulthood, it heads downstream towards the ocean. On reaching
the sea, it changes to saltwater life and heads into the open ocean.
Heading south and west, it swims 6,000 km (3,700 miles) to the
Sargasso Sea. Here, at a depth of 700 m (2,300 ft), it meets up with
thousands of other eels and spawns in the deep cold water. The
effort is terminal and all adult eels die. Their microscopic larvae
spend 3 years growing up in the plankton and following the Gulf
Stream past the Caribbean and back across the Atlantic. In their 4th
year, the young eels wriggle and slip their way up the rocky slopes
of European rivers to spend their next 14 years in freshwater.
7. Salmon
Salmon hatch in freshwater streams but mature at sea. They will
return just once to the streams of their birth to spawn and die. Some
adults will travel thousands of miles to reach the river where they
hatched.
Interesting!
The longest recorded migration
of any marine vertebrate goes to
a leatherback turtle. Scientists
from NOAA initially tagged an
animal in Papua, Indonesia and
tracked its movements for 647
days to the coast of Oregon in
the USA – a one-way swim of
20,558 km (12,774 miles) across
the Pacific Ocean.
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REFERENCES & FURTHER READING
http://www.bbc.co.uk/radio4/worldonthemove/ - Migrations
http://www.seaturtlestatus.org – Sea Turtle migrations
Byatt, Andrew, Fothergill, Alastair and Holmes, Martha, The Blue Planet: Seas of Life, Chapter 6, DK
Publishing Inc., (2001), ISBN 0-7894-8265-7
8.1 LIFE IN THE OPEN
8.1.3 Open Ocean Life
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8.1 LIFE IN THE OPEN
ALBATROSS
An albatross (Diomedeidae spp.) aloft is a magnificent sight. These
birds weigh up to 10 kg (22 lb) and have the longest wingspan of
any bird – up to 3.4 m (11 ft). The wandering albatross is the
biggest of some two dozen different species.
Albatrosses use their huge wings to ride the ocean winds and can
glide for hours without rest or even a flap of their wings. They also
float on the sea's surface though this makes them vulnerable to
aquatic predators. Albatrosses drink salt water, as do some other
sea birds. Albatrosses feed on squid or schooling fish but are
familiar to mariners because they sometimes follow ships in the
hope of dining on handouts.
These long-lived birds reach 50 years of age. They are rarely seen
on land and gather only to breed at which time they form large
colonies on remote islands. Some species mate for life. Mating
pairs produce a single egg and take turns caring for it. Young
albatrosses may fly within 3-10 months and then leave land behind
for some 5-10 years until they themselves reach sexual maturity.
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8.1 LIFE IN THE OPEN
PORTUGUESE MAN-OF-WAR
The Portuguese man-of-war (Physalia physalis) is a siphonophore – an
animal (cnidarian) made up of a colony of organisms working together.
A man-of-war comprises four separate polyps. It gets its name from the
uppermost polyp, a gas-filled bladder called a float or pneumatophore, which
sits above the water and resembles an old warship at full sail. Man-of-wars
are also known as bluebottles for the purple-blue colour of their
pneumatophores. The float may be 30 cm (12 in) long and 12.7 cm (5 in)
wide. The tentacles are the man-of-war's second organism. These long, thin
tendrils can extend 50 m (165 ft) in length below the surface, although 10 m
(30 ft) is more average. They are covered in venom-filled nematocysts used
to paralyze and kill fish and other small creatures. For humans, a man-ofwar sting is excruciatingly painful but rarely deadly. Muscles in the tentacles
draw prey up to a polyp containing the digestive organisms (gastrozooids)
while the fourth polyp contains the reproductive organisms.
Man-of-wars are found, sometimes in groups of 1,000 or more, in warm
waters of throughout the world's oceans. They have no independent means
of propulsion and either drift with the currents or catch the wind with their
pneumatophores. To avoid surface threats, they can deflate their air bags
and submerge.
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8.1 LIFE IN THE OPEN
LEATHERBACK TURTLE
Leatherback sea turtles (Dermochelys coriacea) are the world’s largest
turtles growing up to 2.6 m (8.5 ft) in length and 907 kg (2,000 lb) in weight.
While all other sea turtles have hard, bony shells, the smooth, black
carapace of the leatherback is soft and almost rubbery to the touch.
They may live over 45 years but human threats, such as fishing lines and
nets, mean most leatherbacks meet an early end. Other threats include
illegal egg harvesting and loss of nesting habitat. Hatchlings often die when
beachfront lighting draws them away from the ocean and hundreds die at
sea when they swallow plastic which they mistake for jellyfish – their main
food. They can dive to 1,230 m (4,035 ft) and remain submerged for 35
minutes.
In all, only about 1 in 1,000 leatherbacks survives to adulthood. The
worldwide population is estimated at about 26,000-43,000 nesting females
annually, but they are suffering exponential declines and are critically
endangered throughout their range and now teeter on the brink of extinction.
Their enormous range comprises the tropical and temperate waters of the
Atlantic, Pacific, and Indian oceans. Unlike other reptiles, their body
temperature stays well above the surrounding water and they have been
found in the icy seas as far north as British Columbia, Canada, and as far
south as the Cape of Good Hope, South Africa.
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8.1 LIFE IN THE OPEN
OCEAN SUNFISH
The ocean sunfish (Mola mola) is the heaviest bony fish in the world.
It has an average length of 1.8 m (5.9 ft) and an average weight of
1,000 kg (2,200 lb) although individuals up to 3.3 m (10.8 ft) in
length and weighing up to 2,300 kg (5,100 lb) have been observed.
The species is native to tropical and temperate waters around the
globe. It resembles a fish head without a tail and its main body is
flattened laterally. Sunfish can be as tall as they are long when their
dorsal and anal fins are extended.
Sunfish mainly eat jellyfish. As this diet is nutritionally poor, they
consume large amounts in order to develop and maintain their great
bulk. Females of the species can produce more eggs than any other
known vertebrate. Sunfish fry resemble miniature pufferfish with
large pectoral fins, a tail fin and body spines uncharacteristic of adult
sunfish.
Adult sunfish are vulnerable to few natural predators but sea lions,
orcas and sharks will consume them. Among humans, sunfish are
considered a delicacy in some parts of the world, including Japan
and Taiwan but sale of their flesh is banned in the European Union.
Sunfish are often accidentally caught in gill nets and are also
vulnerable to injury or death from encounters with floating rubbish,
such as plastic bags.
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8.1 LIFE IN THE OPEN
BOTTLENOSE DOLPHIN
Bottlenose dolphins (Tursiops truncatus) are well known as the
intelligent and charismatic stars of many aquarium shows. In the
wild, these sleek swimmers can reach speeds of over 30 kph (18
mph). They surface often to breathe, doing so two or three times a
minute. They reach 4.2 m (14 ft) in length and weigh 500 kg (1,100
lb) and can live 50 years.
Dolphins often eat bottom-dwelling fish as well as shrimp and squid.
Bottlenose dolphins track their prey through the use of echolocation.
They can make up to 1,000 clicking sounds per second. These
sounds travel underwater until they encounter objects, then bounce
back to their dolphin senders, revealing the location, size, and shape
of their target.
Bottlenose dolphins travel in social groups and communicate with
each other by a complex system of squeaks and whistles. Schools
have been known to come to the aid of an injured dolphin and help it
to the surface.
Bottlenose dolphins are found in tropical oceans and other warm
waters around the globe. They were once widely hunted for meat
and oil (used for lamps and cooking) but today only limited dolphin
fishing occurs. However, dolphins are threatened by commercial
fishing for other species, like tuna, and can become entangled in
nets and other fishing equipment.
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Interesting!
All dolphins, including the
bottlenose, are porpoises.
Although some people use these
names interchangeably,
porpoises are actually a larger
group that also includes animals
like killer whales (Orca) and
beluga whales.
8.1 LIFE IN THE OPEN
WHALE SHARK
The whale shark (Rhincodon typus) is the largest fish in the sea with
a length of 18.3 m (60 ft) length. The whale shark's flattened head
sports a blunt snout above its mouth with short barbels protruding
from its nostrils. Its back and sides are gray to brown with white
spots among pale vertical and horizontal stripes, and its belly is
white. Its two dorsal fins are set rearward on its body, which ends in
a large dual-lobbed caudal fin (or tail).
Whale sharks eat plankton which they filter from the water. They
scoop tiny animals and plants, along with any small fish that happen
to be around, with their colossal gaping mouths while swimming
close to the water's surface. It then shuts its mouth, forcing water
out of its gills and filtering out the food.
Whale sharks are found in all tropical seas. They migrate every
spring to the continental shelf of the central west coast of Australia.
The coral spawning of the area's Ningaloo Reef provides the whale
shark with an abundant supply of plankton.
Whale sharks are currently listed as a vulnerable species. However,
they continue to be hunted in parts of Asia, such as Taiwan and the
Philippines.
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8.1 LIFE IN THE OPEN
BLUE MARLIN
The blue marlin (Makaira nigricans) is the largest of the Atlantic
marlins and one of the biggest fish in the world. Females, which are
significantly larger than males, can reach 4.3 m (14 ft) in length and
weigh more than 900 kg (1,985 lb). Females can live up to 27 years
in the wild.
Native to the tropical and temperate waters of the Atlantic, Pacific,
and Indian Oceans, blue marlins are among the most recognizable
of all fish. They are cobalt-blue on top and silvery-white below with
a pronounced dorsal fin and a long, lethal spear-shaped upper jaw.
They are so-called blue-water fish, spending most of their lives far
out at sea. They are also highly migratory and will follow warm
ocean currents for thousands of kilometers.
Blue marlins prefer the higher temperature of surface waters,
feeding on mackerel and tuna, but will also dive deep to eat squid.
They are among the fastest fish in the ocean, and use their spears
to slash through dense schools, returning to eat stunned and
wounded victims.
Their meat is considered a delicacy, particularly in Japan, where it is
served raw as sashimi.
Although not currently endangered,
conservationists worry that they are being unsustainably fished,
particularly in the Atlantic.
Interesting!
It is a blue marlin that the old
fisherman battles in Ernest
Hemingway's classic story “The
Old Man and the Sea”.
8.1 LIFE IN THE OPEN
THRESHER SHARK
The thresher shark (Alopias vulpinas) is an oceanic deep-water
shark. It has a pointed snout and 5 gills slits in front of each pectoral
fin. It also has an extremely long upper lobe in caudal fin that often
exceeds length of body. The tail used to herd and stun prey. It is
often found in large numbers and is considered a large and
dangerous shark especially during maritime disasters. The thresher
shark feeds on fishes and squids and can reach 6.1 m (20 ft) length
and weigh 454 kg (1,000 lbs).
SHORTFIN MAKO
The shortfin mako (Isurus oxyrinchus) is a member of the mackerel
shark family. It is a slender, bullet-nosed shark that is bright blue to
slate blue above and white below and can reach 3.7 m (12 ft) in
length. Its front teeth are long, narrow, curved with no cusps at
base. It is a very swift and active shark that hunts tuna and other
fish. It is possibly the fastest swimming shark.
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8.1 LIFE IN THE OPEN
ATLANTIC BLUEFIN TUNA
The Atlantic bluefin tuna (Thunnus thynnus) is one of the largest,
fastest and most beautiful of the world’s fishes. Their torpedoshaped, streamlined bodies are built for speed and endurance.
Their colouring (metallic blue on top and shimmering silver-white on
the bottom) helps camouflage them from above and below. Their
voracious appetite and varied diet pushes their average size to 2 m
(6.5 ft) in length and 250 kg (550 lb) although they can reach twice
this size.
Atlantic bluefins are warm-blooded, a rare trait among fish, and are
comfortable in the cold waters off Newfoundland and Iceland, as well
as the tropical waters of the Gulf of Mexico and the Mediterranean
Sea, where they go each year to spawn. They are among the most
ambitiously migratory of all fish, and some tagged specimens have
been tracked swimming from North American to European waters
several times a year. They can live 15 years in the wild.
They are prized among sport fishermen for their fight and speed,
shooting through the water with their powerful, crescent-shaped tails
up to 70 kph (43 mph). They can retract their dorsal and pectoral fins
into slots to reduce drag. Some scientists think the series of “finlets”
on their tails may reduce water turbulence.
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8.1 LIFE IN THE OPEN
Bluefins attain their enormous size by gorging themselves almost
constantly on smaller fish, crustaceans, squid, and eels. They will
also filter-feed on zooplankton and other small organisms and have
even been observed eating kelp. The largest tuna ever recorded
was an Atlantic bluefin caught off Nova Scotia that weighed 679 kg
(1,496 lb).
Bluefin tuna have been eaten by humans for centuries. In recent
years demand and prices for large bluefins soared worldwide,
particularly in Japan, and commercial fishing operations found new
ways to find and catch these sleek giants. As a result, bluefin
stocks, especially of large, breeding-age fish, have plummeted, and
international conservation efforts have led to curbs on commercial
takes. Nevertheless, at least one group says illegal fishing in
Europe has pushed the Atlantic bluefin populations there to the brink
of extinction.
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Interesting!
We often say that reptiles or fish are
cold-blooded and mammals are
warm-blooded. However, many
scientists try not to use these terms
because they are not precise and,
in some cases, inaccurate.
More precisely, some animals, such
as mammals are able to regulate
their body temperature above that
of the environment’ – these animals
are “homeothermic” – which means
they are able to keep their body
temperature constant. In contrast,
animals, such as most reptiles and
fish, cannot regulate their body
temperature and are called
“poikilothermic”. These animals rely
on warmth from the sun and the
environment to warm them up.
While most reptiles and fish cannot
regulate their body temperature,
there are exceptions. For example,
the Leatherback turtle is a reptile
that is able to regulate its
temperature while the bluefin tuna is
a fish that is able to do so.
8.1 LIFE IN THE OPEN
ATLANTIC MANTA
The Atlantic Manta (Manta birostris) is an oceanic ray and is a
member of the devil ray family. Its body is dark brown or black
above and white below, and it has long and pointed pectoral fins
(their “wings”). Manta rays also have two large cephalic (head) fins
that look like “horns” hence their “devil” ray name. They have short
whip-like tails with no spines on them. They also have a wide,
terminal mouth wide which they use to feed on plankton and small
fishes. They can reach 6.7 m (22 ft) across their wings and weigh
1,814 kg (4,000 lbs).
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ELEPHANT SEAL
There are two species of elephant seals (Mirounga spp.) – northern
and southern. Northern elephant seals can be found in California
and Baja California though they frequent offshore islands rather than
the North American mainland. Northern elephant seals live an
average of 9 years in the wild.
Southern elephant seals live in sub-Antarctic and Antarctic waters.
These are cold waters but they are rich in the fish, squid, and other
marine foods these seals enjoy. Southern elephant seals breed on
land but spend their winters in Antarctic waters near the Antarctic
pack ice.
Southern elephant seals are the largest of all seals. Males can be
over 6 m (20 ft) long and weigh up to 4,000 kg (8,800 lb). However,
these massive pinnipeds aren't called elephant seals because of
their size but take their name from their trunk-like inflatable snouts.
Southern elephant seals can dive over 4,921 ft (1,500 m) deep and
remain submerged for up to two hours. Southern elephant seals live
20 to 22 years.
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When breeding season arrives, male elephant seals define and
defend territories. They collect a harem of 40-50 females, which are
much smaller than their enormous mates. Males battle each other
for mating dominance. Elephant seals give birth in late winter to a
single pup after an 11 month pregnancy and nurse it for
approximately a month. While suckling their young, females do not
eat. Both mother and pup live off the energy stored in the reserves
of her blubber.
Elephant seals were aggressively hunted for their oil and their
numbers were reduced to the brink of extinction. Fortunately,
populations have rebounded under legal protections.
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SAILFISH
Sailfish (Istiophorus platypterus) range throughout the warm and
temperate parts of the world’s oceans. They are blue to gray in
colour with white underbellies. They get their name from their
spectacular dorsal fin that stretches nearly the length of their body
and is much higher than their bodies are thick.
Sailfish are members of the billfish family and, as such, have an
upper jaw that juts out well beyond their lower jaw and forms a
distinctive spear. They are found near the ocean surface usually far
from land feeding on schools of smaller fish like sardines and
anchovies which they often shepherd with their sails. They also feed
on squid and octopus.
Their meat is tough and not widely eaten but they are prized as
game fish. These powerful, streamlined fish can grow to more than
3 m (10 ft) and weigh up to 100 kg (220 lb). In the wild, they live
about 4 years. Sailfish are fairly abundant throughout their range
and their population is considered stable. They are under no special
status or protections.
Interesting!
Sailfish are the fastest fish in the
ocean and have been clocked
leaping out of the water at more
than 110 kph (68 mph).
8.1 LIFE IN THE OPEN
REFERENCES & FURTHER READING
http://animals.nationalgeographic.com/animals/birds/albatross.html - Albatross
http://animals.nationalgeographic.com/animals/invertebrates/portuguese-man-of-war.html
http://animals.nationalgeographic.com/animals/reptiles/leatherback-sea-turtle.html
http://animals.nationalgeographic.com/animals/mammals/bottlenose-dolphin.html
http://animals.nationalgeographic.com/animals/mammals/elephant-seal.html - Elephant seal
http://animals.nationalgeographic.com/animals/fish/bluefin-tuna.html - Atlantic Bluefin Tuna
http://animals.nationalgeographic.com/animals/fish/blue-marlin.html - Blue Marlin
http://animals.nationalgeographic.com/animals/fish/whale-shark.html - Whale shark
http://en.wikipedia.org/wiki/Ocean_sunfish - Ocean sunfish
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8.2 OCEAN LIFE
8.2 OCEAN LIFE
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8.2 OCEAN LIFE
8.2 OCEAN LIFE
8.2.1 Sharks & Rays
SHARKS
DESCRIPTION
Sharks have 5-7 pairs of gill slits – usually 5 pairs
Gill slits on lateral side of body
Most sharks have several rows of sharp pointed teeth
Fusiform shape – cylindrical and tapered at both ends
Extremely varied in size
Heterocercal caudal fin – upper tail fin lobe longer than lower
May or may not have a spiracle behind each eye
May or may not have a nictitating membrane (“eyelid”) over eye
Predators include other sharks, killer whales, and Man
Marine but a few species (e.g. Bull Shark) can enter fresh water
Sharks swim with their caudal fin (tail) and form an “S” shape with their body and tail
SIZE
Largest – Whale shark – 18.3 m (60 ft) length
Smallest (probably) – Spined pygmy shark (Squaliolus laticaudus) – 0.2 m (6 in)
Sexual dimorphism – females grow ~25% larger than males in most shark species
Of 355 species, only 39 exceed 3.1 m (10 ft) in length while 176 species stay under 0.8 m (39 in)
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8.2 OCEAN LIFE
RAYS (BATOIDS)
DESCRIPTION
Nearly all rays have 5 pairs of gill slit openings
Gill slits and mouth on the ventral side of the body
Pectoral fins enlarged & attached to sides of head
Rhomboid or circular shape
Caudal and dorsal fins reduced, sometimes absent
No anal fin
All rays have large spiracles to take in water for respiration
All lack nictitating membrane on the eye
Predators include sharks and Man
Largest family within the rays are the skates
Electric ray family can generate powerful electrical charges
Sawfish family use their “saws” for hunting
Most rays are bottom dwellers but some are pelagic (e.g. mantas)
As a group, very successful in colonizing the deep sea
Mostly marine but some (e.g. sawfishes) can enter fresh water; a few live only in fresh water
Most rays swim by flapping their pectoral fins (“wings”) but guitarfishes & sawfishes swim like sharks
SIZE
Largest – Manta Ray – 6.7 m (22 ft) across wings and 1,814 kg (4,000 lbs)
33
8.2 OCEAN LIFE
SCALES
Sharks and batoids have placoid scales which are also often called
“dermal denticles” (“skin teeth”). Placoid scales and teeth have the
same structure, consisting of 3 layers:
• Outer layer of vitro-dentine (an enamel)
• Dentine
• Pulp cavity
Placoid scales give the skin a tough sandpapery texture. Shark and
batoid skin was formerly valued as a source or leather and as an
abrasive called “shagreen”
Placoid scales are arranged in a regular pattern in sharks and an
irregular pattern in batoids.
Some rays are covered with denticles (small prickles) while others
are naked or have only small patches of denticles. Many have a
median (middorsal) row of enlarged denticles (spines) down the
back and tail. In stingrays and their relatives, some tail denticles are
modified into long barbed spines – these and the spines at the front
of the dorsal fins are commonly called “stings” and can cause severe
wounds.
34
8.2 OCEAN LIFE
TEETH & JAWS
Teeth are modified, enlarged placoid scales
Size and shape of teeth vary enormously
Sharks
Can be serrated wedges, smooth & pointed or blunt for crushing
Bite force exerted by some sharks up to 8,000 PSI
Often possess multiple rows of teeth
Rows of teeth roll forward replacing old, broken or missing teeth
A shark's jaws are loosely connected to the rest of the skull at two
points. As the upper jaw extends forward from the mouth, teeth of the
lower jaw first encounter prey. The lower jaw teeth puncture and hold
prey while the upper jaw teeth slice.
Rays
Stingrays and eagle rays have teeth that are fused into plates
Flattened teeth suited to grinding or crushing shellfish
Some skates have many rows of teeth – Winter Skate >72 rows
Filter-feeders have reduced non-functional teeth. Devil rays, basking
and megamouth sharks strain plankton from the water with gill rakers
(filaments composed of thousands of tiny “teeth”). Whale sharks
strain plankton through a spongy tissue supported by cartilaginous
35
8.2 OCEAN LIFE
DIET
Sharks eat almost anything: fishes, crustaceans, molluscs, marine
mammals, sea birds, and other sharks and rays. Most rays eat
clams, mussels, and oysters but rays also eat a variety of fishes,
squids, and crustaceans. For example:
Sharks
 Bull sharks eat fishes & other sharks
 Great white sharks eat sea lions & other marine mammals
 Hammerhead sharks eat fishes & stingrays
 Wobbegongs eat shrimps
 Tiger sharks eat several species of sea turtles & sea birds
 Whale and basking sharks feed on plankton
Rays
 Sawfishes – eat fishes
 Electric rays – eat bottom organisms, flounders and small sharks
 Stingrays – eat clams and oysters
 Eagle rays – eat molluscs
 Manta rays – strain plankton from the water
36
8.2 OCEAN LIFE
BREEDING & REPRODUCTION
All sharks and rays utilize internal fertilization
“Claspers” – male sex organs in cartilaginous fish; modified pelvic
fins
Clasper is turned forward and inserted into female cloaca
Sharks can be oviparous, ovoviviparous or viviparous
Skates lay eggs but other rays are ovoviviparous
Eggs are often called “Mermaid’s Purses”
Oviparous (“egg-laying”) – e.g. Horn Shark, Skates
Eggs are laid by the female and develop outside her body. The
eggs contain yolk and provide nourishment to the growing embryo.
Ovoviviparous (“egg & live-bearing”) – e.g. Sand Tiger Shark
Fertilized eggs develop within the female but the embryo gains no
nutritional substances from the female. As a result, once the egg
yolk runs out, young must eat other eggs or one another to survive
(“uterine cannibalism”).
Viviparous (“live-bearing”) – e.g. all Hammerhead and Requiem
Sharks (except the Tiger Shark which is ovoviviparous).
Shark embryo develops inside the body of the female from which it
gains nourishment through a complex yolk-sac placenta. Female
37
8.2 OCEAN LIFE
38
SENSES
Sight
 Sharks have a basic vertebrate eye but it is laterally compressed; lens is large and spherical
 Eyes are particularly sensitive to moving objects
 In clear water, a shark's vision is effective at a distance up to ~15.2 m (50 ft)
 Unlike those of other fishes, a shark's pupil can dilate and contract
 Cone cells are present indicating sharks may have some colour vision
 Eyes have numerous rods that detect light intensity changes making sharks sensitive to contrast
 Sharks see well in dim light. Eye has a layer of reflecting plates (“tapetum lucidum”) behind the retina.
These plates act as mirrors to reflect light back through the retina a second time.
Smell
 Sharks have an acute sense of smell & can detect minute quantities of substances in water (e.g. blood)
 Can detect concentrations as low as one part per billion of some chemicals (e.g. certain amino acids)
 A shark’s sense of smell functions up to hundreds of meters (yards) away from a source
 Nurse sharks have “barbels” near their nostrils which enhance tactile or chemo receptors
Taste
 Sharks and batoids have taste buds inside their mouths
 Taste may be responsible for a shark's final acceptance or rejection of prey items
 Some sharks prefer certain foods and will spit out things that have an unpleasant taste
8.2 OCEAN LIFE
39
Acoustic
 Sharks have an inner ear only; use sound to initially detect prey
 The lateral line system is a series of fluid-filled canals just below the skin of the head and along the
sides of the body. The canal is open to the surrounding water through tiny pores. The lateral line canals
contain a number of sensory cells called neuromasts. Tiny hair-like structures on the neuromasts project
out into the canal. Water movement created by turbulence or vibrations displaces these hair-like
projections, stimulates the neuromasts, and triggers a nerve impulse to the brain. Like the ear, the
lateral line senses low-frequency vibrations.
Sensory Pit
 A sensory pit is formed by the overlapping of two enlarged placoid scales guarding a slight depression
in the skin. At the bottom of the pit is a sensory papilla: a small cluster of sensory cells that are probably
stimulated by physical factors such as water currents. Sensory pits are distributed in large numbers on
the back, flank, and lower jaw.
Electrical – Ampullae Of Lorenzini
 External pores dot the surface of a shark's head. Each pore leads to a jelly-filled canal that leads to a
membranous sac called an ampulla. In the wall of the ampulla are sensory cells innervated by several
nerve fibres. These ampullae detect weak electrical fields generated by all living organisms and are
used to help detect prey in the final stages of prey capture. The ampullae may also detect temperature,
salinity, changes in water pressure, mechanical stimuli, and magnetic fields.
8.2 OCEAN LIFE
INTERESTING FACTS
Sharks
 Sharks can detect electrical impulses generated by the muscles of
other animals through the ampullae of Lorenzini.
 Sharks are often known as “obligate ram ventilators” – this means
sharks are obliged to keep moving to ram or force water through
their gills in order to ventilate or breathe. However, it is not true that
ALL sharks must constantly keep moving in order to breathe – some
(such as whitetip reef shark and nurse shark) can rest on the sea
floor and pump water over their gills.
 Only a comparatively small number of sharks are dangerous to
Man – of 355 species, about 25 are known to have attacked Man
and another 40 are potentially dangerous.
 Sharks may or may not have a nictitating membrane. This is an
eyelid-like structure which is drawn over the eye to give it extra
protection from injury caused by thrashing prey. When a shark,
such as the Great White, bites its prey, it does not actually see what
it is biting as each eye is covered by a nictitating membrane at the
last moment. Rays do not have nictitating membranes over their
eyes.
40
8.2 OCEAN LIFE
Rays
 Some skates have numerous rows of teeth. For example, Winter
Skates have 72 or more rows of teeth (usually > 80) in upper jaw!
Sawfish use their “saws” to scythe through schools of fish when
hunting prey.
 Sawfishes are ovoviviparous – eggs are retained in uterus and live
young are born with their saw encased in a sheath to protect the
mother.
 Some rays, such as the Atlantic Torpedo, have electric organs
capable of delivering powerful electric shocks (~200V).
41
8.2 OCEAN LIFE
42
THREATS
Sharks have been around for hundreds of millions of years but they are seriously threatened today.
Sharks reach sexual maturity slowly and have few young. In addition, as a top predator, their actual
numbers are comparatively small. The primary threat to their continued existence is probably humans.
Threats include:
 Pollution
 Sharks are often caught as a by-catch and discarded
 Sport and trophy hunting
 Use of shark cartilage and other body parts in both Eastern and Western medicine
 Fishing – people eat the pectoral fins (“wings”) of certain rays; fins also used to make Shark’s Fin Soup
 “Finning” – cutting the fins off sharks and then discarding the body
Perhaps the greatest challenge with shark conservation is convincing people of the need to protect them
.
 Sharks often eat sick and weak prey. This actually improves the gene pool for the stronger, healthier
individuals that go on to reproduce. Shark over-fishing removes this vital link in the delicate balance of
the ocean ecosystem.
 When sharks were over-fished around Australia, the octopus population increased dramatically. The
octopus then preyed heavily on spiny lobsters and decreased that population. By destroying sharks,
therefore, humans may unwittingly be removing a key that keeps ocean populations healthy.
8.2 OCEAN LIFE
43
CONSERVATION
 Fisheries management programs are necessary for a sensible shark harvest. As of 2007, only the
United States, New Zealand, and Canada have started shark management plans.
 In 1993, the National Marine Fisheries Service (NMFS) implemented a plan to manage U. S. shark
fisheries of the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. This plan included:
o Annual commercial quotas, which are divided into half- yearly quotas.
o Provisions for closing a fishery for a species group when the semi-annual quota is met.
o Catch limits for recreational anglers.
o Permit requirements for commercial vessels that catch sharks.
o A requirement that vessels land fins in proportion to carcasses (effectively prohibiting the
practice of shark finning).
o A requirement that when sharks are not kept, they are released in a manner that ensures the
probability that they will survive.
 The state of California passed a law the same year totally protecting the great white shark.
 The law set forth by NMFS placed limits on 22 species of large coastal, seven species of small coastal,
and 10 pelagic species of sharks. A yearly catch limit of 5.4 million pounds of sharks still failed to stop
declining shark populations. In the spring of 1997, NMFS cut the quota of large sharks to 1.285 metric
tons, limited the catch of small coastal sharks, and banned the commercial harvest of whale, great white,
basking, sand tiger, and bigeye sand tiger sharks.
8.2 OCEAN LIFE
CLASSIFICATION
44
45
8.2 OCEAN LIFE
SHARK ORDERS & FAMILIES
Approximately 8 orders, 30 families and 355 species
Order Hexanchiformes
Family Hexanchidae – cowsharks, 6-gill & 7-gill sharks *
Family Chlamydoselachidae – frilled sharks
Order Pristiophoriformes
Family Pristiophoridae – sawsharks
Order Squatiniformes
Family Squatinidae – angelsharks
Order Heterodontiformes
Family Heterodontidae – horn sharks *
Order Orectolobiformes
Family Orectolobidae – wobbegong sharks
Family Ginglymostomatidae – nurse sharks *
Family Rhincodontidae – whale shark *
Family Parascylliidae – collared carpet sharks
Family Brachaeluridae – blind sharks
Family Hemiscylliidae – bamboo sharks *
Family Stegostomatidae – zebra sharks
* Discussed here
Order Squaliformes
Family Squalidae – dogfishes
Family Echinorhinidae – bramble sharks
Family Oxynotidae – rough sharks
Order Lamniformes
Family Odontaspididae – sand tiger sharks *
Family Mitsukurinidae – goblin shark
Family Lamnidae – mackerel sharks *
Family Cetorhinidae – basking shark *
Family Alopiidae – thresher sharks *
Family Pseudocarchariidae – crocodile sharks
Family Megachasmidae – megamouth shark
Order Carcharhiniformes
Family Scyliorhinidae – catsharks
Family Proscylliidae – ribbontail catsharks
Family Psoudotriakidae – false catsharks
Family Leptocharildae – barbeled houndsharks
Family Triakidae – smoothhound sharks *
Family Hemigaleidae – weasel sharks
Family Carcharhinidae – requiem sharks *
Family Sphyrnidae – hammerhead sharks *
46
8.2 OCEAN LIFE
RAY ORDERS & FAMILIES
Approximately 4 orders, 11 families, and 470 species
Order Rajiformes
Family Rajidae – skates *
Family Rhinobatidae – guitarfish *
Order Torpediniformes
Family Torpedinidae – electric rays *
Order Pristiformes
Family Pristidae – sawfish *
* Discussed here
Order Myliobatiformes
Family Dasyatidae – stingrays *
Family Myliobatidae – eagle rays *
Family Mobulidae – devil rays *
Family Rhinopteridae – cownosed rays *
Family Urolophidae – round stingrays
Family Gymnuridae – butterfly rays
Family Potamotrygonidae – river rays
8.2 OCEAN LIFE
SHARK SPECIES
1. WHALE SHARK – RHINCODON TYPUS
Whale Shark Family
Grey-brown with distinctive pattern of yellow or white spots and bars
Caudal fin nearly vertical; upper lobe much longer
3 prominent ridges along each side of back
Teeth tiny and numerous
Feeds mainly on plankton but will eat fishes and squid
Each eggs is in a large, horny case
Largest fish and also largest shark
To 18.3 m (60 ft) length
2. BASKING SHARK – CETORHINUS MAXIMUS
Basking Shark Family
Dark grey or slate-coloured above; lighter below
Gill slits very long – across entire side & nearly meeting below
Each gill has long, closely set gill rakers that strain plankton from
water
Mouth large, teeth tiny
Sheds gill rakers in winter, goes to bottom and fasts while new gill
rakers grow
Generally harmless but its size can make it hazardous to small boats
Often hit by ocean-going ships
To 13.7 m (45 ft) length
47
8.2 OCEAN LIFE
3. WHITE SHARK – CARCHARODON CARCHARIAS
Mackerel Shark Family
Slate blue or leaden grey above, dirty white below
Heavy body, large head, pointed snout
Teeth large and triangular with serrated edges
Largely oceanic but will stray in coastal waters
Large & dangerous shark made infamous through “Jaws”
To 7.9 m (26 ft) length but usually less than 4.9 m (16 ft)
4. SHORTFIN MAKO – ISURUS OXYRINCHUS
Mackerel Shark Family
Bright blue to slate blue above, white below
Slender bullet-nosed shark
Front teeth long, narrow, curved with no cusps at base
Very swift and active shark
Possibly the fastest shark – hunts tuna
Important game fish
Frequently marketed as “swordfish”
To 3.7 m (12 ft) length
48
8.2 OCEAN LIFE
5. TIGER SHARK – GALEOVERDO CUVIERI
Requiem Shark Family
Brownish grey above, whitish below with conspicuous dark blotches
and bars.
Snout short and broadly rounded from below
Spiracle present
Teeth broad and coarsely serrated with deep notch on outer edge
Mostly pelagic but commonly enters shallow bays to feed
Large and dangerous shark, known to attack Man
To 7.3 m (24 ft) length
6. BULL SHARK – CARCHARHINUS LEUCAS
Requiem Shark Family
Gray to dull brown above, white below
Heavy body
Snout short, very broad and rounded from below
Upper teeth nearly triangular, serrated
Common large shark in coastal water
Also found in rivers and lakes; survives well in fresh water.
Implicated in several attacks on humans in NJ rivers
To 3.5 m (11.5 ft) length
49
8.2 OCEAN LIFE
7. SANDBAR SHARK – CARCHARHINUS PLUMBEUS
Requiem Shark Family
Heavy body
Dark grey to brown above; becoming paler below
Infamous relatives are bull, tiger and oceanic whitetip sharks
Bears live young (like all requiem sharks)
To 3.1 m (10 ft) length
8. WHITETIP REEF SHARK – TRIAENODON OBESUS
Requiem Shark Family
Small, slender shark
Extremely short, broad snout, oval eyes
Spiracles usually present
Gray above, lighter below and sometimes with dark spots on sides
First dorsal-fin lobe and dorsal caudal-fin lobe with conspicuous
white tips
Second dorsal-fin lobe and ventral caudal-fin lobe often white-tipped
Viviparous
Sluggish inhabitant of lagoons and seaward reefs
Often found resting in caves or under coral ledges during the day
More active at night
Feeds on benthic animals such as fishes, octopi, spiny lobsters and
crabs
To 2.1 m (7 ft) length
50
8.2 OCEAN LIFE
9. BONNETHEAD SHARK – SPHYRNA TIBURO
Hammerhead Shark Family
Head spade shaped
Small harmless species
Feeds mainly on crustaceans
Bears live young (like all hammerheads)
To 1.5 m (5 ft) length
10. NURSE SHARK – GINGLYMOSTOMA CIRRATUM
Nurse Shark Family
Rusty brown with small yellowish eyes
No nictitating membrane on eye
Mouth small; teeth in a crushing series
Feeds on crustaceans and shellfish
Use their thick lips to create suction and pull prey from holes &
crevices
Has “barbels” (“whiskers”) front edge of each nostril
Barbels used to find food on the ocean bottom.
Caudal fin with no distinct lower lobe
Will bite if provoked but otherwise relatively harmless
Large eggs in horny capsules
To 4.3 m (14 ft) length but usually less than 3.1 m (10 ft)
51
8.2 OCEAN LIFE
11. SAND TIGER – ODONTASPIS TAURUS
Sand Tiger Family
Greyish brown or tan above with dark spots especially towards the
tail
Paler below
All 5 gill slits in front of pectoral fins
Teeth long and curved, pointed, non-serrated – feeds on fish
Sluggish species
Not known to attack man, in spite of ferocious appearance
1 or 2 young retained in oviducts; feed on eggs produced by mother
To 3.2 m (10.5 ft) length
12. THRESHER SHARK – ALOPIAS VULPINAS
Thresher Shark Family
Oceanic deep-water sharks
Extremely long upper lobe in caudal fin (often exceeds length of
body)
Pointed snout
5 gills slits in front of each pectoral fin
Tail used to herd and stun prey
Often occur in large numbers
Considered dangerous especially during maritime disasters
Feeds on fishes and squids
Corral schools of fish using the long upper lobe of their tails
52
8.2 OCEAN LIFE
13. SIXGILL SHARK – HEXANCHUS GRISEUS
Hexanchidae Family
Six gill slits
Long caudal fin
Six large trapezoidal teeth on each side of lower jaw
Coffee-coloured to brown or greyish on back, paler below
Mostly in deep water
Spiracle present
Live bearing
To 4.9 m (16 ft) length and 590 kg (1,300 lbs)
14. HORN SHARK – HETERODONTUS FRANCISCI
Horn Shark Family
Tan to dark brown with black spots above; pale yellowish below
Snout short and blunt
Ridge above eye
2 dorsal fins each with a spine
Sluggish, solitary, active at night
Eats crabs and small fishes
Lays large (to 5”) eggs – eggs have spiral flanges
To 0.9 m (3 ft) length
53
8.2 OCEAN LIFE
15. WHITE-SPOTTED BAMBOO SHARK – CHILOSCYLLIUM
PLAGIOSUM
Bamboo Shark Family
Nostrils sub-terminal on snout
Caudal fin with a pronounced notch but without a ventral lobe
Transverse dark bands and numerous white or bluish spots
Oviparous
A common but little-known inshore bottom shark
Utilized for human consumption and used in Chinese medicine
To 0.8 m (2.5 ft) length
16. LEOPARD SHARK – TRIAKIS SEMIFASCIATA
Smoothhound Shark Family
Broad black bars, saddles and spots
Snout short, bluntly rounded
Feed mainly on crabs, shrimps, bony fish – large variety of food in
diet
Strong-swimming, nomadic
Ovoviviparous with 4-29 in a litter
Good for human consumption
To 2.1 m (7 ft) length
54
8.2 OCEAN LIFE
RAY SPECIES
1. ATLANTIC MANTA – MANTA BIROSTRIS
Devil Ray Family
Dark brown to black above, white below
Pectoral fins long and pointed
Two large cephalic (head) fins – look like “horns” (hence “devil”
rays)
Mouth wide, terminal
Tail whip-like but short and no spine
Oceanic
Feeds on plankton and small fishes
To 6.7 m (22 ft) across wings and 1,814 kg (4,000 lbs)
2. SPOTTED EAGLE RAY – AETOBATUS NARINARI
Eagle Ray Family
Disk dark grey to brown above with a pattern of white spots and
streaks
Whitish below
Long graceful wings (pectoral fins)
Long whip-like tail with a long spine near base
Frequently seen in large schools during non-breeding season
To 2.4 m (8 ft) across wings and 227 kg (500 lbs)
55
8.2 OCEAN LIFE
3. COWNOSE RAY – RHINOPTERA BONASUS
Eagle Ray Family
Dark brown to olive above with no spots or marks
Snout squarish with an indentation in the centre
Free-swimming ray that swims by flapping its pectoral fins
Eats molluscs
Whip-like tail with venomous spine (note: spine venomous, not the
tail itself)
Oceanic; sometimes jumps out of the water and slaps back down
Several theories as to why this occurs; e.g. parasite removal but
probably more to do with territorial display
Frequently gathers in large schools
Bears live young (like all eagle rays)
To 0.9 m (3 ft) across disk
4. SOUTHERN STINGRAY – DASYATIS AMERICANA
Stingray Family
Disk almost perfect rhombus
Most stingrays are bottom-dwellers
Often lie submerged in sand except for the eyes
Whip-like tail with venomous spine (note: spine venomous, not the
tail itself)
Generally stingrays will not bite, sting or hurt you although you may
be stung if you inadvertently step on one
Bears live young (like all stingrays)
To 1.5 m (5 ft) across disk
56
8.2 OCEAN LIFE
5. ROUGHTAIL STINGRAY – DASYATIS CENTROURA
Stingray Family
Disk with numerous scattered spines
Tail with numerous rows of small spines
One of the largest stingrays
Similar to Southern Stingray
To 2.1 m (7 ft) across disk and 4.3 m (14 ft) long
6. YELLOW STINGRAY – UROLOPHUS JAMAICENSIS
Stingray Family
Disk almost round
Tail stout with spine placed back
Disk yellowish with dark spots
Common ray from Florida to northern South America
To 0.4 m (14 in) across disk and 0.7 m (26 in) long but usually much
smaller
57
8.2 OCEAN LIFE
7. WINTER SKATE – RAJA OCELLATA
Skate Family
Disk broad, rhombic-shaped and spotted
Tail thick – not whip-like – tail never has a large spine or “sting”
Usually 1-4 ocelli on each side of disk
At least 72 rows of teeth (usually > 80) in upper jaw
Bottom-dweller
Good for human consumption
To 1.1 m (43 in)
8. ATLANTIC GUITARFISH – RHINIOBATOS LENTIGINOUS
Guitarfish Family
Pectoral fins joined in front to head
Spiracles large
Gill slits and mouth on underside
Long triangular disk; thick, tapered body
Brownish above usually with many small white spots below
To 0.8 m (30 in)
58
8.2 OCEAN LIFE
9. SMALLTOOTH SAWFISH – PRISTIS PECTINATA
Sawfish Family
Pectoral fins joined in front to head
Spiracles large
Gill slits and mouth on underside
“Saw” is about ¼ length of the fish
24 or more teeth on each side of “saw”
Caudal fin has no distinct lower lobe
Not aggressive and no threat to man unless caught and handled
Saws are dried and sold as souvenirs
Moves its head from side to side and scythes/strikes prey with its
long rostrum
May also use the front of its snout to dig for prey buried under sand
To 5.5 m (18 ft)
10. ATLANTIC TORPEDO – TORPEDO NOBILIANA
Electric Ray Family
Disk round without spines
Chocolate to dark grey above without spots, whitish below
Produce 200V but not generally aggressive
Kidney shaped electric organ found on each side of the head
Sluggish bottom-dwellers
Feeds on other bottom-dwellers including flounders and small
sharks
To 1.8 m (6 ft) and 91 kg (200 lbs)
59
8.2 OCEAN LIFE
60
REFERENCES & FURTHER READING
http://www.elasmodiver.com - Sharks, rays and chimaeras
http://www.seaworld.org/animal-info/info-books/sharks-&-rays/index.htm - Sharks and rays
Robins, C.R. et al., A Field Guide to Atlantic Coast Fishes of North America, Houghton Mifflin Pub.
(1986)
8.3 ACTIVITIES
8.3 ACTIVITIES
61
8.3 ACTIVITIES
8.3 ACTIVITIES
8.3.1 Sharks
CORE ACTIVITY
(a) Colour the great white
shark slate grey above and
white below, and add the
following labels to your picture:
• Dorsal Fin
• Caudal Fin (Tail)
• Pectoral Fin
• Gill Slits
• Jaws
• Snout
• Eye
62
8.3 ACTIVITIES
(b) Name several dangerous sharks
(c) What is the world’s largest shark? What does it eat?
(d) How many senses does a shark have and what are they? How many senses does a human have?
63
8.3 ACTIVITIES
ANSWERS
(a) Colour the great white
shark slate grey above and
white below, and add the
following labels to your picture:
• Dorsal Fin
• Caudal Fin (Tail)
• Pectoral Fin
• Gill Slits
• Jaws
• Snout
• Eye
64
8.3 ACTIVITIES
65
(b) Name several dangerous sharks
The great white, tiger, and bull sharks are known to be dangerous sharks
(c) What is the world’s largest shark? What does it eat?
The world’s largest shark (and fish) is the whale shark. It primarily eats plankton but it will also eat fishes
and squid.
(d) How many senses does a shark have and what are they? How many senses does a human have?
A shark has 6 senses
• Sight
• Smell
• Touch
• Hearing
• Taste
• Electrical
A human has 5 senses; we have all the senses a shark has except the electrical sense.
8.3 ACTIVITIES
8.3.2 Rays
CORE ACTIVITY
(a) Colour the Southern
stingray dark grey, and add
the following labels to your
picture:
• Spines
• Tail
• Sting (barb)
• Eye
• Pectoral Fin
• Rhomboid Disk
(b) What is the world’s largest ray? What does it eat?
66
8.3 ACTIVITIES
ANSWERS
(a) Colour the Southern
stingray dark grey, and add
the following labels to your
picture:
• Spines
• Tail
• Sting (barb)
• Eye
• Pectoral Fin
• Rhomboid Disk
(b) What is the world’s largest ray? What does it eat?
The world’s largest ray is the manta ray. It eats plankton and small fishes.
67