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OUR OCEAN PLANET

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Title: OUR OCEAN PLANET


1
OUR OCEAN PLANET
  • OUR OCEAN PLANET
  • SECTION 8 OPEN OCEAN

2
REVISION HISTORY
Date Version Revised By Description
Aug 25, 2010 0.0 VL Original
3
8. OPEN OCEAN
8. OPEN OCEAN
4
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 worlds surface. Much of the
ocean lies in the worlds 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.
5
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.
6
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 25C
(77F) while the intermediate zone water
temperature may be just 11C (50F). In the dark
zone, the water becomes much colder, 5C (41F).
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 oceans 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.
7
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 0-7894-8265-7
8
8.1 LIFE IN THE OPEN
8.1 LIFE IN THE OPEN
9
8.1 LIFE IN THE OPEN
8.1 LIFE IN THE OPEN 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 oceans 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.
10
8.1 LIFE IN THE OPEN
11
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 Earths magnetic field.
12
8.1 LIFE IN THE OPEN
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.
13
8.1 LIFE IN THE OPEN
14
8.1 LIFE IN THE OPEN
15
8.1 LIFE IN THE OPEN
REFERENCES FURTHER READING http//www.bbc.co.uk/
radio4/worldonthemove/ - Migrations http//www.sea
turtlestatus.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
16
8.1 LIFE IN THE OPEN
8.1.3 Open Ocean Life
17
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.
18
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-of-war 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.
19
8.1 LIFE IN THE OPEN
LEATHERBACK TURTLE Leatherback sea turtles
(Dermochelys coriacea) are the worlds 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.
20
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.
21
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.
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.
22
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.
23
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.
24
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.
25
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 worlds fishes. Their
torpedo-shaped, 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.
26
8.1 LIFE IN THE OPEN
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.
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.
27
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).
28
8.1 LIFE IN THE OPEN
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.
29
8.1 LIFE IN THE OPEN
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.
30
8.1 LIFE IN THE OPEN
SAILFISH Sailfish (Istiophorus platypterus) range
throughout the warm and temperate parts of the
worlds 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).
31
8.1 LIFE IN THE OPEN
REFERENCES FURTHER READING http//animals.nation
algeographic.com/animals/birds/albatross.html -
Albatross http//animals.nationalgeographic.com/an
imals/invertebrates/portuguese-man-of-war.html htt
p//animals.nationalgeographic.com/animals/reptile
s/leatherback-sea-turtle.html http//animals.natio
nalgeographic.com/animals/mammals/bottlenose-dolph
in.html http//animals.nationalgeographic.com/anim
als/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//animal
s.nationalgeographic.com/animals/fish/whale-shark.
html - Whale shark http//en.wikipedia.org/wiki/Oc
ean_sunfish - Ocean sunfish
32
8.2 OCEAN LIFE
8.2 OCEAN LIFE
33
8.2 OCEAN LIFE
8.2 OCEAN LIFE 8.2.1 Sharks Rays SHARKS DESCR
IPTION 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)
34
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)
35
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.
36
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 gt72
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 rods
between the gill arches instead of using gill
rakers.
37
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

38
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 Mermaids 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 then gives birth to live offspring.
39
8.2 OCEAN LIFE
  • 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 sharks 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

40
8.2 OCEAN LIFE
  • 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.

41
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.

42
8.2 OCEAN LIFE
  • Rays
  • Some skates have numerous rows of teeth. For
    example, Winter Skates have 72 or more rows of
    teeth (usually gt 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).

43
8.2 OCEAN LIFE
  • 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 Sharks
    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.

44
8.2 OCEAN LIFE
  • 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
  • Annual commercial quotas, which are divided into
    half- yearly quotas.
  • Provisions for closing a fishery for a species
    group when the semi-annual quota is met.
  • Catch limits for recreational anglers.
  • Permit requirements for commercial vessels that
    catch sharks.
  • A requirement that vessels land fins in
    proportion to carcasses (effectively prohibiting
    the practice of shark finning).
  • 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.

45
8.2 OCEAN LIFE
CLASSIFICATION
46
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
47
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
48
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
49
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
50
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
51
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
52
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)
53
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 To
6.1 m (20 ft) length and 454 kg (1,000 lbs)
54
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
55
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
56
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)
57
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
58
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
59
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 gt 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)
60
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)
61
8.2 OCEAN LIFE
REFERENCES FURTHER READING http//www.elasmodive
r.com - Sharks, rays and chimaeras http//www.seaw
orld.org/animal-info/info-books/sharks--rays/inde
x.htm - Sharks and rays Robins, C.R. et al., A
Field Guide to Atlantic Coast Fishes of North
America, Houghton Mifflin Pub. (1986)
62
8.3 ACTIVITIES
8.3 ACTIVITIES
63
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
64
8.3 ACTIVITIES
(b) Name several dangerous sharks (c) What is
the worlds 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?
65
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
66
8.3 ACTIVITIES
(b) Name several dangerous sharks The great
white, tiger, and bull sharks are known to be
dangerous sharks (c) What is the worlds largest
shark? What does it eat? The worlds 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.
67
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 worlds largest ray? What does
it eat?
68
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 worlds largest ray? What does
it eat? The worlds largest ray is the manta
ray. It eats plankton and small fishes.
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