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Title: Class Chondrichthyes: cartilaginous fishes


1
Class Chondrichthyes cartilaginous fishes
  • The class Chondrichthyes has two subclasses
  • Elasmobranchii, which includes the sharks and
    rays.
  • Holocephali the chimaeras ratfish and
    ghostfish.

2
16.1
3
16.2
4
Class Chondrichthyes
  • Modern Chondricthyes include the sharks, rays and
    Chimeras.
  • The Chondrichthyes well-developed jaws, highly
    developed sense organs, powerful swimming ability
    and streamlined shape have enabled them to thrive
    as marine predators for more than 350 million
    years, as other groups have come and gone.
  • There are just under 1000 living species, all of
    which have cartilaginous skeletons, even though
    they are descended from ancestors that had bone.

5
Class Chondrichthyes
  • The Chondrichthyes are an ancient group that
    although not as diverse as the bony fishes have
    persisted largely unchanged for hundreds of
    millions of years.
  • The oldest unambiguous Chondrichthyans are found
    in the Early Devonian although there are older
    fossils of scales.

6
Fossil history of Chondrichtyes
  • One of the best known extinct genera is
    Cladoselache a pelagic marine predator from the
    Devonian.
  • It was shark-like in appearance. About 2 meters
    long with a large gape and three-pronged teeth.
    As in modern sharks the teeth were arranged on a
    ligamentous band in a whorl-shaped arrangement.

7
Fossil history of Chondrichtyes
  • Cladoselache had two dorsal fins, each preceded
    by a large spine.
  • It also possessed paired pelvic and pectoral fins
    as in modern sharks, but the fins were much more
    broad based than in later sharks.
  • The tail was symmetrical externally, but
    internally asymmetrical with the notochord
    extending into the upper lobe of the tail.

8
Cladoselache picture
Cladoselache
http//www.dinosoria.com/poissons/cladoselache_03.
jpg
9
Fossil history of Chondrichtyes
  • Cladoselaches skin had few scales found on the
    fins and around the eyes.
  • In addition, Cladoselache lacked the rostrum of
    modern sharks.

10
Fossil history of Chondrichtyes
  • A contemporary genus of Cladoselache was
    Xenacanthus a freshwater shark.
  • A bottom dweller with robust fins and a heavily
    calcified skeleton.
  • Xenacanths appeared in the Devonian and died out
    in the Triassic.

11
www.toyen.uio.no/ .../montre/english/x508.htm
Xenacanthus
http//dinosaurcollector.files.wordpress.com/2008/
11/kaiyodo-xenacanthus.jpg
12
Fossil history of Chondrichtyes
  • In the Carboniferous sharks with modifications to
    feeding and locomotor structures arose.
  • An example is Hybodus of the late Triassic. It
    had heterodont dentition. Anterior teeth had
    sharp cusps for piercing and slashing softer
    foods. Posterior teeth were flattened presumably
    for crushing crustaceans and mollusks.

13
Fossil history of Chondrichtyes
  • Hybodus also had pelvic and pelagic fins
    supported by a narrow base made up of lengths of
    cartilage.
  • The narrow base (as in modern sharks) allowed the
    fin to be rotated.
  • Hybodus also had an anal fin and a true
    heterocercal tail.

14
Fossil history of Chondrichtyes
  • The elasmbranch heterocercal tail contains
    numerous radial skeletal elements which make it
    flexible.
  • Its shape can be controlled by intrinsic muscles.
  • When undulated from side to side the tail because
    of its shape generates both forward and upward
    thrust, which counteracts a sharks natural
    tendency to sink.

15
Fossil history of Chondrichtyes
  • Hybodus resembled its Cladoselache-like ancestors
    by retaining dorsal fin spines and its terminal
    mouth.

16
Hybodus
http//www.resourcemodels.org/hybodus1.jpg
17
Extant radiation of Chondrichthyes
  • By the Jurassic sharks of modern appearance had
    evolved. Several genera from that era are still
    extant.
  • The most distinctive feature of modern sharks is
    the rostrum or snout that overhangs the mouth.
  • Less prominent, but also of major importance was
    the evolution of solid calcified vertebrae.
  • Finally, the teeth are covered with thicker more
    complex enamel than in earlier sharks.

18
Thresher Shark
http//dsc.discovery.com/sharks/shark-types/thresh
er-shark.jpg
19
Class Chondrichthyes
  • About 1000 living species divided into two
    distinct groups
  • Neoselachii also known as elasmobranchs
    (sharks, skates and rays) about 950 species.
  • Holocephalii (ratfishes). About 33 species.

20
Neoselachii
  • Neoselachii
  • Galeomorpha about 279 species of sharks with an
    anal fin. 1m to perhaps 18m in length. Sand
    tigers, mackerel sharks, threshers, basking
    sharks, hornsharks, whale sharks, nurse sharks,
    mako, great white.
  • Squalomorpha Not a monphyletic group. About
    124 species of deep sea sharks, dogfish, angel
    sharks. 15cm to 7m.
  • Batoidea skates and rays. At least 534 species.
    Electric rays, Manta rays, stingrays, skates.
    1-6m and up to 6 m wide.

21
Diversity of sharks
22
Hammerhead Shark
23
Great White Shark
Hammerhead sharks
Whale shark
Two skates
24
Two species of ray
25
Spotted Ratfish http//www.elasmodiver.com/BCMarin
elife/images/Spotted-ratfish.jpg
26
Sharks
  • Sharks represent a little less than half of the
    elasmobranchs and most are specialized predators.
  • The largest species is the whale shark, which is
    a plankton feeder, as is the basking shark, but
    most of the others are predators of fish, marine
    mammals, crustaceans and whatever else they can
    catch.

27
Basking Shark http//oursurprisingworld.com/wp-con
tent/uploads/ 2008/02/disgusting_fishes_7-basking-
shark.jpg
Whale shark
http//animals.nationalgeographic.com/ staticfiles
/NGS/ Shared/StaticFiles/animals/images/ primary/w
hale-shark-with-fish.jpg
28
Sharks
  • The extant sharks include at least two lineages
    and molecular studies suggest there may be
    several others included within these two.
  • The squaloid sharks are smaller brained, mostly
    live in cold, deep water and include the dogfish,
    megamouth, and cookie-cutter sharks.

29
http//www.flmnh.ufl.edu/fish/Gallery/descript /Me
gamouth/cookie.JPG Cookie-cutter shark
http//vivaldi.zool.gu.se/Fiskfysiologi_2001/Cours
e_material/ Introduction_fish_evolution/Images/Coo
kie_cutters.GIF
30
Sharks
  • The galeoid sharks are the dominant carnivores of
    shallow, warm species rich parts of the ocean.
  • They include hammerheads, tiger sharks,
    threshers, mackeral sharks, and the whale shark.

31
Sharks
  • Sharks are very well streamlined, but are heavier
    than water (because they lack a swim bladder) and
    sink if not swimming forward.
  • Sharks increase their buoyancy by having a large
    oil-filled liver that reduces their density, but
    not enough to prevent them from sinking.

32
Sharks
  • Sharks have an asymmetrical heterocercal tail and
    the vertebral column extends into the dorsal
    lobe.
  • The tail provides both lift and thrust, while the
    large flat pectoral fins also provide lift to
    keep the head up.

33
16.6
34
Sharks
  • A typical shark is about 2m long, but they range
    in size from a few miniature forms that are 25 cm
    long up to perhaps 18m in length.
  • Despite their range of sizes all modern sharks
    share a suite of characteristics.

35
Characteristics of sharks
  • The cartilaginous vertebral centra of sharks are
    distinctive.
  • Adjacent vertebrae have depressions in their
    faces into which fit spherical remnants of the
    notochord.
  • This arrangement of a rigid vertebral column of
    calcified cartilage swivelling on bearings of
    notochord allows the axial skeleton to swing from
    side to side.

36
Dorsal intercalary plate
37
Characteristics of sharks
  • In addition to the neural and hemal arches in the
    vertebral column, which protect the spinal cord
    and blood vessels all sharks possess additional
    intercalary plates that provide extra protection
    to the nerve cord and blood vessels.

38
Dorsal intercalary plate
39
Sharks
  • Unlike earlier sharks, living species have their
    skin entirely covered in dermal placoid scales,
    which are small tooth-like structures (with
    enamel, dentine and pulp just like real teeth).
  • These scales give sharkskin a tough, leathery and
    abrasive feel. The skin is also very
    streamlined.

40
16.15
41
Mako shark skin
  • The shortfin mako shark is capable of swimming in
    brief bursts at speeds approahing 50mph (kph).
  • Recent research has shown that its skin is able
    to reduce drag by bristling, which creates tiny
    depressions across the surface of the skin (like
    those on a golf ball).

42
Shortfin mako Shark http//elasmodiver.com/images/
Shortfin-Mako-022.jpg
43
Mako shark skin
  • The 200 micrometer long scales when held at 90
    degrees to the sharks body cause tiny vortices
    to form in between the scales.
  • These vortices prevent a turbulent wake from
    forming, which would exert a backwards pull.
  • (Lang et al. 2008. Bioinspiration and
    Biomimetrics New Scientist 15 Nov 2008, p.16)

44
Teeth
  • The placoid scales are modified in the mouth to
    produce the rows of replaceable teeth
    characteristic of sharks.
  • Each tooth in a shark can be rapidly replaced as
    it becomes worn or damaged. Teeth are arranged
    on a spiral or whorl shaped cartilaginous band in
    which replacement teeth are always developing
    behind the functional tooth.
  • Teeth in young sharks may be replaced as often as
    once every 8 days.

45
16.6
46
http//www.sharkattackphotos.com/Shark_Miscellaneo
us.htm
47
Sand tiger shark (note multiple rows of teeth)
48
Shark Jaws
  • A sharks jaws can open in a variety of different
    positions depending on the prey.
  • This is because the upper jaw is attached
    flexibly to the chondocranium in two locations
    (front and back) both of which can move. This is
    called a hyostylic jaw suspension.
  • (Movement of parts of the head skeleton is called
    cranial kinesis.)

49
Shark Jaws
  • When the upper jaw is protruded, the
    hyomandibular cartilage which braces the rear of
    the upper jaw (the palatoquadrate) swings to the
    side and anteriorly which increases the distance
    between the right and left jaw articulations and
    the volume of the mouth.

50
Shark Jaws
  • The increase in volume is possible because the
    upper jaw attachment to the chondocramnium at the
    front is by elastic ligaments and so the upper
    jaw can move.
  • The increase in volume powerfully sucks water and
    food into the mouth.

51
Great White Shark http//img.dailymail.co.uk/i/pix
/2007/07_03/19sharkDM_468x591.jpg
52
Shark Jaws
  • Protrusion of the upper jaw moves the mouth away
    from the head and allows a bigger bite to be
    taken than would be possible if the upper jaw was
    immobile.

53
Biting
  • The teeth on the upper jaw (palatoquadrate) have
    evolved to bite chunks from large prey items.
  • They are bigger than the teeth on the mandible
    and often curved and serrated, which enables the
    shark to saw off a big chunk of flesh.

54
Tiger Shark Teeth
55
Biting
  • When biting a large prey animal a shark seizes
    the animal sinking its upper and lower teeth into
    it.
  • The shark then protrudes its upper jaw which
    pushes its teeth deeper into the wound and
    violently shakes its head from side to side.

56
Biting
  • The head movements from side to side saw off a
    large chunk of flesh, which results in massive
    bleeding.
  • Great Whites kill big prey such as sea lions by
    taking a big bite and then waiting for the victim
    to bleed to death.

57
Prey detection
  • Sharks use a series of methods to detect prey
    related to distance.
  • Chemoreception is used to detect prey from a
    distance and sharks appear to be able to detect
    odors as dilute a 1 part in 10 billion.

58
Prey detection
  • Vibrations can also be detected from a distance
    using the lateral line system.
  • Once a shark gets relatively close, vision takes
    over.
  • Sharks have very good vision at low light
    intensities. There is a high density of rods in
    the retina and a tapetum lucidum just behind the
    retina, which reflects light back through the
    retina.

59
Prey detection
  • In low light conditions the tapetum lucidum is
    beneficial, but in bright light is not.
  • In bright light melanin containing cells expand
    to cover the tapetum lucidum.

60
Prey detection
  • If a familiar prey item is located an attack may
    occur quickly.
  • If the prey is unfamiliar (e.g. a person) the
    shark may circle to gather more information.
  • Such a shark may bump the potential prey with its
    rostrum presumably to gather extra sensory
    information.

61
Shark attacks on humans
  • 1990s 514 documented unprovoked shark attacks on
    humans. About 13 fatal.
  • In a typical year there are 3-4 fatalities
    worldwide.
  • In U.S. most shark attacks are in Florida.
  • http//www.flmnh.ufl.edu/fish/sharks/statistics/20
    03attacksummary.htm

62
Shark attacks on humans
  • Great White, Tiger and Bull sharks are the big
    three for shark attacks.
  • International shark attack file statistics
    (documented attacks1580-2007)
  • White 237 attacks 64 fatalities
  • Tiger 88 attacks 28 fatalities
  • Bull 77 attacks 23 fatalities

63
Bull shark http//www.sharkdiving.us/images/bull/0
7.jpg
64
Foraging strategies of sharks
  • Various sharks employ different strategies to
    obtain prey.

65
Great White Shark
  • Great White sharks specialize in feeding on
    colonial seals and sealions, but also take a wide
    variety of other prey including dolphins, other
    sharks, turtles and other fish.
  • Around sea lion nursery areas sharks attack the
    mammals as they come and go. They remain deep in
    the water until a victim passes within range
    above and then rocket to the surface like a trout
    after a mayfly often exploding out of the water
    and flinging the prey in the air.

66
Great White http//elasmodiver.com/images/Great-Wh
ite-Shark-002.jpg
67
http//imagecache2.allposters.com/images/pic/ NYG/
78027Great-White-Shark-Posters.jpg
68
Great White Shark
  • Great Whites appear to be relatively intelligent
    and there are reports of them cooperating to
    attack a seal.
  • There are also reports that they are very curious
    and they will often raise their head out of the
    water to look something over.

69
Great White Shark
  • A lot of attacks on humans by Great Whites are
    likely cases of mistaken identity as a surfer on
    a surfboard looks a lot like a sea lion.
  • Frequently people bitten by a Great White are
    released. Humans (and sea otters) lack of
    blubber results in them often being released
    after an initial bite.

70
Shortfin mako
  • The shortfin Mako shark specializes in attacking
    fast moving prey such as bluefish, mackerel,
    bonito, swordfish, sailfish as well as dolphins
    and porpoises.
  • A study of mako stomach contents of sharks taken
    off of the eastern U.S. found that bluefish made
    up about 77 of the diet by volume.

71
Shortfin mako
  • Because it hunts such fast prey, makos have to be
    fast and athletic. Its speed has been recorded
    at 50km/h (31 mph), but in bursts it can
    accelerate to 74 km/h (46 mph).
  • Makos often leap high out of the water in pursuit
    of prey and there have been several instances of
    hooked makos landing on the decks of fishing
    boats.

72
Shortfin mako http//elasmodiver.com/Sharkive20im
ages/ Shortfin20Mako20Shark20053.jpg
73
Thresher Shark
  • A Thresher shark is instantly identifiable thanks
    to the enormously elongated upper lobes of its
    tailfin.
  • The tail plays a central role in their hunting
    strategy. Either working alone or in groups
    threshers surround groups of pelagic fish and
    stun or disorient them using their tails.

74
http//www.shark-pictures.com/viewpic/thresher-sha
rk-134.html
75
Tiger shark
  • Tiger sharks are indiscriminate consumers and
    will eat almost anything.
  • Their powerful jaws allow them to crack turtles
    shells and clams.
  • Stomach contents of captured sharks have included
    seals, sea snakes, birds, fish, squid and even
    old tires.

76
Tiger shark
  • Tiger sharks trail only great whites in numbers
    of attacks on people, but because they will eat
    almsot anything they rarely leave after biting a
    human, as great whites often do.

77
Tiger shark http//www.fearbeneath.com/wp-content/
uploads/ 2008/09/tiger-shark-roger-horrocks.jpg
78
Cookiecutter shark
  • Cookiecutter are bizarrely specialized predators
    that bite disk-shaped pieces of tissue out of
    much larger animals.
  • Cookiecutter sharks attach to their prey with
    their lips and then quickly spin using their
    proportionally enormous teeth to carve out a
    piece of flesh.
  • Cookiecutter sharks feed on megamouth, basking
    and whale sharks as well as fish such as tuna and
    marlin as well as dolphins and whales.

79
Cookiecutter shark
  • Cookiecutters are bioluminescent and appear to
    use this ability to attract victims.
  • On the ventral surface cookiecutters glow along
    their whole length except for a dark patch of
    skin under the jaw.
  • The bioluminescent areas hide the shark against
    the light of the surface water, but the dark
    patch stands out and acts as a lure for predatory
    fish, which when they attack end up being bitten
    by the shark.

80
http//www.shark-pictures.com/viewpic/cookie-cutte
r-shark-teeth-structure-625.html
81
Whale Shark
  • Whale sharks are filter feeder that sieve
    plankton, krill and other small prey from the
    water.
  • The prey is trapped using 10-cm long gill rakers,
    which are bristle-like structures that sieve the
    water before it passes through the gill slits.
  • Whale sharks filter about 1500 gallons (6000
    liters) of water each hour. Basking sharks and
    megamouth sharks also filter feed.

82
http//elasmodiver.com/Sharkive20images/Whale-sha
rk-061.jpg
83
Reproduction
  • Reproduction in all Chondrichthyes is internal
    and the male uses modified pelvic fins called
    claspers to insert sperm.
  • The presence or absence of claspers makes it easy
    to distinguish male from females.

84
Great white shark claspers
85
Reproduction
  • During copulation a clasper is inserted into the
    females cloaca and hooked in place by spines at
    the tip.
  • Sperm is ejaculated into a groove in the clasper
    and a muscular siphon sac filled with seawater is
    squeezed which washes the sperm down the groove
    into the cloaca from where the sperm swim up the
    females reproductive tract.

86
Reproduction
  • The sharks use of internal fertilization is
    coupled with their use of a reproductive strategy
    in which a few young are invested in heavily.
  • The energy investment is provided by the female
    who retains and nourishes a small number of
    offspring within her body.

87
Reproduction
  • Energy is provided either in the form of egg yolk
    or is delivered to the developing babies via the
    mothers reproductive tract.
  • The mode of nutrition depends on whether
    reproduction is oviparous or vivaparous.

88
Reproduction
  • All skates and some sharks are oviparous and lay
    eggs soon after fertilization. The eggs hatch
    later.
  • Most oviparous sharks produce large eggs with big
    yolks and a proteinaceous case is secreted around
    the fertilized egg.

89
Reproduction
  • Protuberances on the case entangle in vegetation
    or the substrate and hold it in place.
    Development takes 6-10 months within the case.
  • Movements of the embryo bring in oxygen and flush
    out wastes.

90
Reproduction
  • Other sharks are ovoviviparous. The eggs develop
    within the mothers body and hatch either in her
    or just after being released from her.

91
Egg case of cat shark
Embryo of deep sea cat shark. There is a very
large yolk sac to support the embryos growth.
92
Reproduction
  • The remaining species of shark are viviparous and
    the offspring are nourished by a placenta,
    unfertilized eggs or smaller siblings.
  • These forms of food supply are collectively
    referred to as matrotrophy.

93
Placental feeding of young
  • Some sharks develop long stringy extensions of
    the oviduct. These secrete a milky substance
    into the mouths and gill openings of the young.
  • The commonest form of viviparity in sharks uses a
    yolk sac placenta which allows the developing
    baby to obtain nutrition from its mothers blood
    stream.

94
  • In great white sharks and sand tiger sharks the
    young feed on extra eggs ovulated by the mother
    and also on their siblings.

95
Life history strategy of sharks
  • Sharks because they invest heavily in individual
    offspring produce relatively few young.
  • This reproductive strategy is similar to that of
    humans and elephants.

96
Life history strategy of sharks
  • Humans, elephants and sharks all have a high
    expectation of survival and they have what is
    called a type I survivorship curve.

97
Life history strategy of sharks
  • Survivorship curves can be classified into three
    general types
  • Type I, Type II, and Type III

Figure 52.5
98
Type I curve
  • Type I curve typical of animals that produce few
    young but care for them well (e.g. humans,
    elephants).
  • Death rate low until late in life where rate
    increases sharply as a result of old age (wear
    and tear, accumulation of cellular damage,
    cancer).

99
Type II curve
  • Type II curve has fairly steady death rate
    throughout life (e.g. rodents).
  • Death is usually a result of chance processes
    over which the organism has little control (e.g.
    predation)

100
Type III curve
  • Type III curve typical of species that produce
    large numbers of young which receive little or no
    care (e.g. Oyster).
  • Survival of young is dependent on luck. Larvae
    released into sea have only a small chance of
    settling on a suitable substrate. Once settled
    however, prospects of survival are much better
    and a long life is possible.

101
Life history strategy of sharks
  • Because sharks are slow breeders their
    populations are very vulnerable to an increase in
    adult mortality and/or a reduction in survival of
    offspring.
  • In recent years fishing has drastically increased
    adult mortality and caused many shark populations
    to decline sharply.

102
Fishing and sharks
  • Historical records by early explorers, merchants
    and others often mention the number and large
    size of the sharks that trailed their ships.
  • Sharks were competitors for the schools of
    herring, mackerel, capelin and other commercial
    that humans hunted, but not fished for
    themselves.
  • In the early 20th century the seas of the world
    still teemed with sharks, but that has changed
    dramatically.

103
Fishing and sharks
  • In the 1950s longline fisheries for tuna,
    swordfish, marlin and other prized species
    treated sharks as a nuisance bycatch and many
    were cut free.
  • Today the growing wealth of Asian countries where
    shark fins are a delicacy has made them a
    valuable catch.

104
http//advocacy.britannica.com/blog/advocacy/wp-co
ntent/uploads/shark-fin.jpg
105
Shark Fins http//www.lessfeelsbetter.net/upload/1
215781554SHARKFI8crop.jpg
106
Fishing and sharks
  • Dried sharkfin can cost more than 500 a kilo and
    sharkfin soup up to 90 a bowl.
  • Longliners can set lines as much as 100km long
    that contain 30,000 baited hooks and the catches.
  • In 1997 Hawaiian longliners caught more than
    100,000 sharks and tossed almost 99 of the body
    mass back. Why? They just kept the fins.

107
http//mythix.com/images/ projects/
Shark_Finning_ -_dead_shark_in_ocean.jpg
http//www.scubadiving.com/upload/images/Travel/20
070326_sharkfinning_head.jpg
108
Fishing and sharks
  • As worldwide fish stocks have declined and often
    collapsed less desirable species including sharks
    have been targeted by commercial fishing fleets.
  • As cod stocks collapsed, species such as spiny
    dogfish (marketed as rock cod) began to be
    served as a replacement in fish and chips.

109
Fishing and sharks
  • The Norwegian fishing fleet targeted sharks of
    the genus Lamna (porbeagles or salmon sharks) for
    intensive fishing to sell as steaks as a
    substitute for swordfish.
  • Initial harvests were as much as 8060 tons in a
    year from the northeast Atlantic. Within seven
    years the catch collapsed to 207 tons and hasnt
    been over 100 tons since the 1970s.

110
Porbeagle http//dsc.discovery.com/sharks/shark-t
ypes/porbeagle-shark.jpg
111
Fishing and sharks
  • Data from analyses of catch records worldwide
    show similar massive declines worldwide (see
    Callum Roberts The Unnatural History of the
    Sea for sources).
  • More than 90 of sharks have been taken from
    massive areas of the worlds oceans.

112
Sharks caught on longlines. http//onfinite.com/li
braries/1353690/324.jpg
113
Fishing and sharks
  • Some species populations have been devastated.
  • Once the oceanic whitetip was probably the
    commonest large animal in the world. Today its
    numbers have declined 150-fold in the Gulf of
    Mexico and probably by the same amount elsewhere.

114
Oceanic whitetip (Red Sea) http//www.flmnh.ufl.ed
u/fish/gallery/
115
Fishing and sharks
  • Along with declines in numbers another pattern
    common to other fisheries has emerged, the sizes
    of the animals caught has fallen.
  • Between the 1950s and 1990s the size of
    individuals caught fell in a variety of species.

116
Fishing and sharks
  • Percentage decline in size of individuals caught
  • Oceanic whitetips (-33)
  • Mako (-50)
  • Blue (-50)
  • Dusky (-60)
  • Silky (-83)

117
Fishing and sharks
  • This decline is because fishing often
    preferentially removes older animals and even if
    it doesnt fishing pressure is so intense that
    animals dont live long enough to grow large.

118
Fishing and sharks
  • The simple truth is that shark populations cannot
    be intensively harvested sustainably.
  • They are long-lived, slow maturing and slow
    reproducing.

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Fishing and sharks
  • For example, female spiny dogfish do not mature
    until about 10-12 years of age and produce only
    2-14 pups biennially.
  • They can live 40-50 years, but not with fishing
    pressure.
  • Other sharks have similar reproductive profiles.

120
Fishing and sharks
  • Even with a total ban on fishing, overfished
    shark populations will take many, many years to
    recover.

121
Skates and rays
  • More than half of all elasmobranchs are skates
    and rays.
  • More species (about 534) than there are sharks.
  • They have characteristically dorsoventrally
    flattened bodies and greatly enlarged pectoral
    fins, which they swim with using a wavelike
    motion.

122
Skates and rays
  • Skates and rays should not be confused with
    flatfishes (e.g. sole and halibut), which are
    bony fishes.
  • Skates and rays have gill slits placed ventrally
    and eyes dorsally placed.
  • In flatfish the body is twisted during
    development to bring both eyes and gills to the
    dorsal surface, but not symmetrically.

123
Skates and rays
  • The group is specialized for bottom dwelling and
    feeding on hard foods (e.g. molluscs and
    crustaceans) that have to be ground up.
  • Teeth are flat crowned plates that form an
    arrangement like paving stones.
  • The mouth is located underneath the body and can
    be rapidly protruded to suck up prey.

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Differences between skates and rays
  • Skates have an elongated but thick tail stalk,
    which has two dorsal fins and a caudal fin at the
    end.
  • Skates are oviparous.
  • Generally skates also have a rostrum a pointed
    nose-like extension of the braincase.
  • Rays typically have a whip-like tail and the fins
    are replaced by serrated venom-containing barbs.
  • Rays are viviparous and most lack a rostrum

125
http//www.flmnh.ufl.edu/fish/education/questions/
rayskatesawfish.jpg
126
Skates and rays
  • The spiracles (openings behind the eye) are much
    larger in rays than in sharks because water for
    the gills enters exclusively through them as the
    mouth is usually buried in the sand.

127
Skates and rays
  • Skates and rays are usually well camouflaged and
    sit on the bottom. A few species are dangerous
    because of their sharp and barbed tail
    (stingrays) or because they can generate severe
    electric shocks (electric rays).
  • Most species are bottom feeders that eat
    invertebrates. However, the largest species
    (e.g. manta rays) as in sharks are planktivores.

128
Blue spotted ray
Manta Ray
129
Skate egg case http//people.whitman.edu/yancey/s
kateEggCase.JPG
130
Subclass Holocephali Chimaeras
  • Chimaeras are a small group (about 33 species) of
    deep sea (gt80m) cartilaginous fishes known
    commonly as ratfish or ghostfish.
  • Because they live mainly in deep water they are
    not a well known group.

131
Male spotted ratfish
132
Subclass Holocephali Chimaeras
  • They have a large head, plate-like grinding
    teeth, a cover over the gills and lack both a
    spiracle and stomach.
  • They appear to mostly feed on sea urchins,
    shrimp, and mollusks.
  • The tail is thin and tapers to a point (hence the
    name ratfish) and not much use in swimming.
    Instead chimaeras depend on flapping their
    pectoral fins for much of their movement.
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