http://dsc.discovery.com/sharks/shark-types/thresher-shark.jpg thresher shark

http://dsc.discovery.com/sharks/shark-types/thresher-shark.jpg

Thresher Shark

Class ChondrichthyesClass Chondrichthyes

About 1000 living species divided into two About 1000 living species divided into two distinct groupsdistinct groups

Neoselachii [also known as Neoselachii [also known as elasmobranchs] (sharks, skates and rays) elasmobranchs] (sharks, skates and rays) about 950 species.about 950 species.

Holocephalii (ratfishes). About 33 species.Holocephalii (ratfishes). About 33 species.

NeoselachiiNeoselachii

NeoselachiiNeoselachii Galeomorpha: about 279 species of sharks with an Galeomorpha: about 279 species of sharks with an

anal fin. 1m to perhaps 18m in length. Sand tigers, anal fin. 1m to perhaps 18m in length. Sand tigers, mackerel sharks, threshers, basking sharks, mackerel sharks, threshers, basking sharks, hornsharks, whale sharks, nurse sharks, mako, great hornsharks, whale sharks, nurse sharks, mako, great white.white.

““Squalomorpha”: Not a monphyletic group. About 124 Squalomorpha”: Not a monphyletic group. About 124 species of deep sea sharks, dogfish, angel sharks. species of deep sea sharks, dogfish, angel sharks. 15cm to 7m.15cm to 7m.

Batoidea: skates and rays. At least 534 species. Batoidea: skates and rays. At least 534 species. Electric rays, Manta rays, stingrays, skates. 1-6m and Electric rays, Manta rays, stingrays, skates. 1-6m and up to 6 m wide.up to 6 m wide.

Figure 24.07

Diversity of sharks

Figure 24.co

Hammerhead Shark

Great White Shark

Two skates

Hammerhead sharks

Whale shark

Figure 24.12

Two species of ray

Spotted Ratfishhttp://www.elasmodiver.com/BCMarinelife/images/Spotted-ratfish.jpg

SharksSharks

Sharks represent a little less than half of the Sharks represent a little less than half of the elasmobranchs and most are specialized elasmobranchs and most are specialized predators.predators.

The largest species is the whale shark, which is The largest species is the whale shark, which is a plankton feeder, as is the basking shark, but a plankton feeder, as is the basking shark, but most of the others are predators of fish, marine most of the others are predators of fish, marine mammals, crustaceans and whatever else they mammals, crustaceans and whatever else they can catch.can catch.

Basking Sharkhttp://oursurprisingworld.com/wp-content/uploads/2008/02/disgusting_fishes_7-basking-shark.jpg

http://animals.nationalgeographic.com/staticfiles/NGS/Shared/StaticFiles/animals/images/primary/whale-shark-with-fish.jpg

Whale shark

SharksSharks

The extant sharks include at least two The extant sharks include at least two lineages and molecular studies suggest lineages and molecular studies suggest there may be several others included there may be several others included within these two.within these two.

The squaloid sharks are smaller brained, The squaloid sharks are smaller brained, mostly live in cold, deep water and include mostly live in cold, deep water and include the dogfish, megamouth, and cookie-cutter the dogfish, megamouth, and cookie-cutter sharks.sharks.

http://www.flmnh.ufl.edu/fish/Gallery/descript/Megamouth/cookie.JPG

Cookie-cutter shark

http://vivaldi.zool.gu.se/Fiskfysiologi_2001/Course_material/Introduction_fish_evolution/Images/Cookie_cutters.GIF

SharksSharks

The galeoid sharks are the dominant The galeoid sharks are the dominant carnivores of shallow, warm species rich carnivores of shallow, warm species rich parts of the ocean.parts of the ocean.

They include hammerheads, tiger sharks, They include hammerheads, tiger sharks, threshers, mackeral sharks, and the whale threshers, mackeral sharks, and the whale shark. shark.

SharksSharks

Sharks are very well streamlined, but are Sharks are very well streamlined, but are heavier than water (because they lack a heavier than water (because they lack a swim bladder) and sink if not swimming swim bladder) and sink if not swimming forward.forward.

Sharks increase their buoyancy by having Sharks increase their buoyancy by having a large oil-filled liver that reduces their a large oil-filled liver that reduces their density, but not enough to prevent them density, but not enough to prevent them from sinking.from sinking.

SharksSharks

Sharks have an asymmetrical heterocercal Sharks have an asymmetrical heterocercal tail and the vertebral column extends into tail and the vertebral column extends into the dorsal lobe. the dorsal lobe.

The tail provides both lift and thrust, while The tail provides both lift and thrust, while the large flat pectoral fins also provide lift the large flat pectoral fins also provide lift to keep the head up.to keep the head up.

16.6

Figure 24.08

SharksSharks

A typical shark is about 2m long, but they A typical shark is about 2m long, but they range in size from a few miniature forms range in size from a few miniature forms that are 25 cm long up to perhaps 18m in that are 25 cm long up to perhaps 18m in length.length.

Despite their range of sizes all modern Despite their range of sizes all modern sharks share a suite of characteristics.sharks share a suite of characteristics.

Characteristics of sharksCharacteristics of sharks The cartilaginous vertebral centra of sharks are The cartilaginous vertebral centra of sharks are

distinctive.distinctive.

Adjacent vertebrae have depressions in their Adjacent vertebrae have depressions in their faces into which fit spherical remnants of the faces into which fit spherical remnants of the notochord.notochord.

This arrangement of a rigid vertebral column of This arrangement of a rigid vertebral column of calcified cartilage swivelling on bearings of calcified cartilage swivelling on bearings of notochord allows the axial skeleton to swing notochord allows the axial skeleton to swing from side to side.from side to side.

Dorsal intercalary plate

Characteristics of sharksCharacteristics of sharks

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

Dorsal intercalary plate

SharksSharks

Unlike earlier sharks, living species have their Unlike earlier sharks, living species have their skin entirely covered in dermal placoid scales, skin entirely covered in dermal placoid scales, which are small tooth-like structures (with which are small tooth-like structures (with enamel, dentine and pulp just like real teeth). enamel, dentine and pulp just like real teeth).

These scales give sharkskin a tough, leathery These scales give sharkskin a tough, leathery and abrasive feel. The skin is also very and abrasive feel. The skin is also very streamlined.streamlined.

16.15

Figure 24.18

Mako shark skinMako shark skin

The shortfin mako shark is capable of The shortfin mako shark is capable of swimming in brief bursts at speeds swimming in brief bursts at speeds approahing 50mph (kph).approahing 50mph (kph).

Recent research has shown that its skin is Recent research has shown that its skin is able to reduce drag by bristling, which able to reduce drag by bristling, which creates tiny depressions across the creates tiny depressions across the surface of the skin (like those on a golf surface of the skin (like those on a golf ball).ball).

Shortfin mako Sharkhttp://elasmodiver.com/images/Shortfin-Mako-022.jpg

Mako shark skinMako shark skin

The 200 micrometer long scales when held at 90 The 200 micrometer long scales when held at 90 degrees to the shark’s body cause tiny vortices degrees to the shark’s body cause tiny vortices to form in between the scales.to form in between the scales.

These vortices prevent a turbulent wake from These vortices prevent a turbulent wake from forming, which would exert a backwards pull.forming, which would exert a backwards pull.

(Lang et al. 2008. Bioinspiration and Biomimetrics; New Scientist 15 Nov (Lang et al. 2008. Bioinspiration and Biomimetrics; New Scientist 15 Nov 2008, p.16)2008, p.16)

TeethTeeth The placoid scales are modified in the mouth to produce The placoid scales are modified in the mouth to produce

the rows of replaceable teeth characteristic of sharks.the rows of replaceable teeth characteristic of sharks.

Each tooth in a shark can be rapidly replaced as it Each tooth in a shark can be rapidly replaced as it becomes worn or damaged. Teeth are arranged on a becomes worn or damaged. Teeth are arranged on a spiral or whorl shaped cartilaginous band in which spiral or whorl shaped cartilaginous band in which replacement teeth are always developing behind the replacement teeth are always developing behind the functional tooth.functional tooth.

Teeth in young sharks may be replaced as often as once Teeth in young sharks may be replaced as often as once every 8 days.every 8 days.

16.6

Figure 24.08

http://www.sharkattackphotos.com/Shark_Miscellaneous.htm

Figure 24.09

Sand tiger shark (note multiple rows of teeth)

Shark JawsShark Jaws

A shark’s jaws can open in a variety of different A shark’s jaws can open in a variety of different positions depending on the prey.positions depending on the prey.

This is because the upper jaw is attached This is because the upper jaw is attached flexibly to the chondocranium in two locations flexibly to the chondocranium in two locations (front and back) both of which can move. This is (front and back) both of which can move. This is called a called a hyostylichyostylic jaw suspension. jaw suspension.

(Movement of parts of the head skeleton is (Movement of parts of the head skeleton is called called cranial kinesiscranial kinesis.).)


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


The increase in volume is possible The increase in volume is possible because the upper jaw attachment to the because the upper jaw attachment to the chondocramnium at the front is by elastic chondocramnium at the front is by elastic ligaments and so the upper jaw can move.ligaments and so the upper jaw can move.

The increase in volume powerfully sucks The increase in volume powerfully sucks water and food into the mouth.water and food into the mouth.

Great White Sharkhttp://img.dailymail.co.uk/i/pix/2007/07_03/19sharkDM_468x591.jpg


Protrusion of the upper jaw moves the Protrusion of the upper jaw moves the mouth away from the head and allows a mouth away from the head and allows a bigger bite to be taken than would be bigger bite to be taken than would be possible if the upper jaw was immobile.possible if the upper jaw was immobile.

BitingBiting

The teeth on the upper jaw The teeth on the upper jaw (palatoquadrate) have evolved to bite (palatoquadrate) have evolved to bite chunks from large prey items.chunks from large prey items.

They are bigger than the teeth on the They are bigger than the teeth on the mandible and often curved and serrated, mandible and often curved and serrated, which enables the shark to saw off a big which enables the shark to saw off a big chunk of flesh.chunk of flesh.

Tiger Shark Teeth

BitingBiting

When biting a large prey animal a shark When biting a large prey animal a shark seizes the animal sinking its upper and seizes the animal sinking its upper and lower teeth into it. lower teeth into it.

The shark then protrudes its upper jaw The shark then protrudes its upper jaw which pushes its teeth deeper into the which pushes its teeth deeper into the wound and violently shakes its head from wound and violently shakes its head from side to side.side to side.

BitingBiting

The head movements from side to side The head movements from side to side saw off a large chunk of flesh, which saw off a large chunk of flesh, which results in massive bleeding. results in massive bleeding.

Great Whites kill big prey such as sea Great Whites kill big prey such as sea lions by taking a big bite and then waiting lions by taking a big bite and then waiting for the victim to bleed to death.for the victim to bleed to death.

Prey detectionPrey detection

Sharks use a series of methods to detect Sharks use a series of methods to detect prey related to distance.prey related to distance.

Chemoreception is used to detect prey Chemoreception is used to detect prey from a distance and sharks appear to be from a distance and sharks appear to be able to detect odors as dilute a 1 part in 10 able to detect odors as dilute a 1 part in 10 billion. billion.

Prey detectionPrey detection Vibrations can also be detected from a distance Vibrations can also be detected from a distance

using the lateral line system.using the lateral line system.

Once a shark gets relatively close, vision takes Once a shark gets relatively close, vision takes over.over.

Sharks have very good vision at low light Sharks have very good vision at low light intensities. There is a high density of rods in the intensities. There is a high density of rods in the retina and a tapetum lucidum just behind the retina and a tapetum lucidum just behind the retina, which reflects light back through the retina, which reflects light back through the retina.retina.


In low light conditions the tapetum lucidum In low light conditions the tapetum lucidum is beneficial, but in bright light is not.is beneficial, but in bright light is not.

In bright light melanin containing cells In bright light melanin containing cells expand to cover the tapetum lucidum.expand to cover the tapetum lucidum.


If a familiar prey item is located an attack may If a familiar prey item is located an attack may occur quickly.occur quickly.

If the prey is unfamiliar (e.g. a person) the shark If the prey is unfamiliar (e.g. a person) the shark may circle to gather more information. may circle to gather more information.

Such a shark may bump the potential prey with Such a shark may bump the potential prey with its rostrum presumably to gather extra sensory its rostrum presumably to gather extra sensory information.information.

Shark attacks on humansShark attacks on humans 1990’s 514 documented unprovoked shark 1990’s 514 documented unprovoked shark

attacks on humans. About 13% fatal.attacks on humans. About 13% fatal.

In a typical year there are 3-4 fatalities In a typical year there are 3-4 fatalities worldwide.worldwide.

In U.S. most shark attacks are in Florida.In U.S. most shark attacks are in Florida.

http://www.flmnh.ufl.edu/fish/sharks/statistics/http://www.flmnh.ufl.edu/fish/sharks/statistics/2003attacksummary.htm2003attacksummary.htm

Shark attacks on humansShark attacks on humans

Great White, Tiger and Bull sharks are the Great White, Tiger and Bull sharks are the big three for shark attacks.big three for shark attacks.

International shark attack file statistics International shark attack file statistics (documented attacks1580-2007)(documented attacks1580-2007) White 237 attacks 64 fatalitiesWhite 237 attacks 64 fatalities Tiger 88 attacks 28 fatalitiesTiger 88 attacks 28 fatalities Bull 77 attacks 23 fatalitiesBull 77 attacks 23 fatalities

Bull sharkhttp://www.sharkdiving.us/images/bull/07.jpg

Foraging strategies of sharksForaging strategies of sharks

Various sharks employ different strategies Various sharks employ different strategies to obtain prey.to obtain prey.

Great White SharkGreat White Shark

Great White sharks specialize in feeding on Great White sharks specialize in feeding on colonial seals and sealions, but also take a wide colonial seals and sealions, but also take a wide variety of other prey including dolphins, other variety of other prey including dolphins, other sharks, turtles and other fish. sharks, turtles and other fish.

Around sea lion nursery areas sharks attack the Around sea lion nursery areas sharks attack the mammals as they come and go. They remain mammals as they come and go. They remain deep in the water until a victim passes within deep in the water until a victim passes within range above and then rocket to the surface like range above and then rocket to the surface like a trout after a mayfly often exploding out of the a trout after a mayfly often exploding out of the water and flinging the prey in the air.water and flinging the prey in the air.

Great Whitehttp://elasmodiver.com/images/Great-White-Shark-002.jpg

http://imagecache2.allposters.com/images/pic/NYG/78027~Great-White-Shark-Posters.jpg


Great Whites appear to be relatively Great Whites appear to be relatively intelligent and there are reports of them intelligent and there are reports of them cooperating to attack a seal. cooperating to attack a seal.

There are also reports that they are very There are also reports that they are very curious and they will often raise their head curious and they will often raise their head out of the water to look something over.out of the water to look something over.


A lot of attacks on humans by Great A lot of attacks on humans by Great Whites are likely cases of mistaken Whites are likely cases of mistaken identity as a surfer on a surfboard looks a identity as a surfer on a surfboard looks a lot like a sea lion.lot like a sea lion.

Frequently people bitten by a Great White Frequently people bitten by a Great White are released. Humans (and sea otters) are released. Humans (and sea otters) lack of blubber results in them often being lack of blubber results in them often being released after an initial bite.released after an initial bite.

Shortfin makoShortfin mako

The shortfin Mako shark specializes in The shortfin Mako shark specializes in attacking fast moving prey such as attacking fast moving prey such as bluefish, mackerel, bonito, swordfish, bluefish, mackerel, bonito, swordfish, sailfish as well as dolphins and porpoises.sailfish as well as dolphins and porpoises.

A study of mako stomach contents of A study of mako stomach contents of sharks taken off of the eastern U.S. found sharks taken off of the eastern U.S. found that bluefish made up about 77% of the that bluefish made up about 77% of the diet by volume.diet by volume.

Shortfin makoShortfin mako

Because it hunts such fast prey, makos have to Because it hunts such fast prey, makos have to be fast and athletic. Its speed has been be fast and athletic. Its speed has been recorded at 50km/h (31 mph), but in bursts it can recorded at 50km/h (31 mph), but in bursts it can accelerate to 74 km/h (46 mph).accelerate to 74 km/h (46 mph).

Makos often leap high out of the water in pursuit Makos often leap high out of the water in pursuit of prey and there have been several instances of prey and there have been several instances of hooked makos landing on the decks of fishing of hooked makos landing on the decks of fishing boats.boats.

Shortfin makohttp://elasmodiver.com/Sharkive%20images/Shortfin%20Mako%20Shark%20053.jpg

Thresher SharkThresher Shark

A Thresher shark is instantly identifiable A Thresher shark is instantly identifiable thanks to the enormously elongated upper thanks to the enormously elongated upper lobes of its tailfin.lobes of its tailfin.

The tail plays a central role in their hunting The tail plays a central role in their hunting strategy. Either working alone or in strategy. Either working alone or in groups threshers surround groups of groups threshers surround groups of pelagic fish and stun or disorient them pelagic fish and stun or disorient them using their tails.using their tails.

http://www.shark-pictures.com/viewpic/thresher-shark-134.html

Tiger sharkTiger shark

Tiger sharks are indiscriminate consumers Tiger sharks are indiscriminate consumers and will eat almost anything.and will eat almost anything.

Their powerful jaws allow them to crack Their powerful jaws allow them to crack turtles shells and clams.turtles shells and clams.

Stomach contents of captured sharks have Stomach contents of captured sharks have included seals, sea snakes, birds, fish, included seals, sea snakes, birds, fish, squid and even old tires.squid and even old tires.

Tiger sharkTiger shark

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

Tiger sharkhttp://www.fearbeneath.com/wp-content/uploads/2008/09/tiger-shark-roger-horrocks.jpg

Cookiecutter sharkCookiecutter shark Cookiecutter are bizarrely specialized predators that bite Cookiecutter are bizarrely specialized predators that bite

disk-shaped pieces of tissue out of much larger animals.disk-shaped pieces of tissue out of much larger animals. Cookiecutter sharks attach to their prey with their lips Cookiecutter sharks attach to their prey with their lips

and then quickly spin using their proportionally enormous and then quickly spin using their proportionally enormous teeth to carve out a piece of flesh.teeth to carve out a piece of flesh.

Cookiecutter sharks feed on megamouth, basking and Cookiecutter sharks feed on megamouth, basking and whale sharks as well as fish such as tuna and marlin as whale sharks as well as fish such as tuna and marlin as well as dolphins and whales.well as dolphins and whales.

Cookiecutter sharkCookiecutter shark

Cookiecutters are bioluminescent and appear to Cookiecutters are bioluminescent and appear to use this ability to attract victims. use this ability to attract victims.

On the ventral surface cookiecutter’s glow along On the ventral surface cookiecutter’s glow along their whole length except for a dark patch of skin their whole length except for a dark patch of skin under the jaw. under the jaw.

The bioluminescent areas hide the shark against The bioluminescent areas hide the shark against the light of the surface water, but the dark patch the light of the surface water, but the dark patch stands out and acts as a lure for predatory fish, stands out and acts as a lure for predatory fish, which when they attack end up being bitten by which when they attack end up being bitten by the shark.the shark.

http://www.shark-pictures.com/viewpic/cookie-cutter-shark-teeth-structure-625.html

Whale SharkWhale Shark Whale sharks are filter feeder that sieve Whale sharks are filter feeder that sieve

plankton, krill and other small prey from the plankton, krill and other small prey from the water.water.

The prey is trapped using 10-cm long gill rakers, The prey is trapped using 10-cm long gill rakers, which are bristle-like structures that sieve the which are bristle-like structures that sieve the water before it passes through the gill slits.water before it passes through the gill slits.

Whale sharks filter about 1500 gallons (6000 Whale sharks filter about 1500 gallons (6000 liters) of water each hour. Basking sharks and liters) of water each hour. Basking sharks and megamouth sharks also filter feed. megamouth sharks also filter feed.

http://elasmodiver.com/Sharkive%20images/Whale-shark-061.jpg

ReproductionReproduction

Reproduction in all Chondrichthyes is Reproduction in all Chondrichthyes is internal and the male uses modified pelvic internal and the male uses modified pelvic fins called claspers to insert sperm. fins called claspers to insert sperm.

The presence or absence of claspers The presence or absence of claspers makes it easy to distinguish male from makes it easy to distinguish male from females.females.

Great white shark claspers


During copulation a clasper is inserted into the During copulation a clasper is inserted into the female’s cloaca and hooked in place by spines female’s cloaca and hooked in place by spines at the tip.at the tip.

Sperm is ejaculated into a groove in the clasper Sperm is ejaculated into a groove in the clasper and a muscular siphon sac filled with seawater is and a muscular siphon sac filled with seawater is squeezed which washes the sperm down the squeezed which washes the sperm down the groove into the cloaca from where the sperm groove into the cloaca from where the sperm swim up the female’s reproductive tract. swim up the female’s reproductive tract.


The sharks use of internal fertilization is The sharks use of internal fertilization is coupled with their use of a reproductive coupled with their use of a reproductive strategy in which a few young are invested strategy in which a few young are invested in heavily.in heavily.

The energy investment is provided by the The energy investment is provided by the female who retains and nourishes a small female who retains and nourishes a small number of offspring within her body.number of offspring within her body.


Energy is provided either in the form of Energy is provided either in the form of egg yolk or is delivered to the developing egg yolk or is delivered to the developing babies via the mother’s reproductive tract.babies via the mother’s reproductive tract.

The mode of nutrition depends on whether The mode of nutrition depends on whether reproduction is oviparous or vivaparous.reproduction is oviparous or vivaparous.


All skates and some sharks are oviparous All skates and some sharks are oviparous and lay eggs soon after fertilization. The and lay eggs soon after fertilization. The eggs hatch later. eggs hatch later.

Most oviparous sharks produce large eggs Most oviparous sharks produce large eggs with big yolks and a proteinaceous case is with big yolks and a proteinaceous case is secreted around the fertilized egg. secreted around the fertilized egg.


Protuberances on the case entangle in Protuberances on the case entangle in vegetation or the substrate and hold it in vegetation or the substrate and hold it in place. Development takes 6-10 months place. Development takes 6-10 months within the case.within the case.

Movements of the embryo bring in oxygen Movements of the embryo bring in oxygen and flush out wastes.and flush out wastes.


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

Embryo of deep sea cat shark. There is a very large yolk sac to support the embryo’s growth.

Egg case of cat shark


The remaining species of shark are The remaining species of shark are viviparous and the offspring are nourished viviparous and the offspring are nourished by a placenta, unfertilized eggs or smaller by a placenta, unfertilized eggs or smaller siblings.siblings.

These forms of food supply are collectively These forms of food supply are collectively referred to as matrotrophy.referred to as matrotrophy.

Placental feeding of youngPlacental feeding of young

Some sharks develop long stringy Some sharks develop long stringy extensions of the oviduct. These secrete extensions of the oviduct. These secrete a milky substance into the mouths and gill a milky substance into the mouths and gill openings of the young.openings of the young.

The commonest form of viviparity in The commonest form of viviparity in sharks uses a yolk sac placenta which sharks uses a yolk sac placenta which allows the developing baby to obtain allows the developing baby to obtain nutrition from its mothers blood stream.nutrition from its mothers blood stream.

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

Life history strategy of sharksLife history strategy of sharks

Sharks because they invest heavily in Sharks because they invest heavily in individual offspring produce relatively few individual offspring produce relatively few young.young.

This reproductive strategy is similar to that This reproductive strategy is similar to that of humans and elephants. of humans and elephants.


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


Survivorship curves can be classified into Survivorship curves can be classified into three general typesthree general types Type I, Type II, and Type IIIType I, Type II, and Type III

Figure 52.5

I

II

III

50 10001

10

100

1,000

Percentage of maximum life span

Num

ber

of s

urvi

vors

(lo

g sc

ale)

Type I curveType I curve

Type I curve typical of animals that Type I curve typical of animals that produce few young but care for them well produce few young but care for them well (e.g. humans, elephants). (e.g. humans, elephants).

Death rate low until late in life where rate Death rate low until late in life where rate increases sharply as a result of old age increases sharply as a result of old age (wear and tear, accumulation of cellular (wear and tear, accumulation of cellular damage, cancer).damage, cancer).

Type II curveType II curve

Type II curve has fairly steady death rate Type II curve has fairly steady death rate throughout life (e.g. rodents).throughout life (e.g. rodents).

Death is usually a result of chance Death is usually a result of chance processes over which the organism has processes over which the organism has little control (e.g. predation) little control (e.g. predation)

Type III curveType III curve

Type III curve typical of species that produce Type III curve typical of species that produce large numbers of young which receive little or no large numbers of young which receive little or no care (e.g. Oyster).care (e.g. Oyster).

Survival of young is dependent on luck. Larvae Survival of young is dependent on luck. Larvae released into sea have only a small chance of released into sea have only a small chance of settling on a suitable substrate. Once settled settling on a suitable substrate. Once settled however, prospects of survival are much better however, prospects of survival are much better and a long life is possible.and a long life is possible.


Because sharks are slow breeders their Because sharks are slow breeders their populations are very vulnerable to an populations are very vulnerable to an increase in adult mortality and/or a increase in adult mortality and/or a reduction in survival of offspring.reduction in survival of offspring.

In recent years fishing has drastically In recent years fishing has drastically increased adult mortality and caused increased adult mortality and caused many shark populations to decline sharply.many shark populations to decline sharply.

Fishing and sharksFishing and sharks Historical records by early explorers, merchants and Historical records by early explorers, merchants and

others often mention the number and large size of the others often mention the number and large size of the sharks that trailed their ships.sharks that trailed their ships.

Sharks were competitors for the schools of herring, Sharks were competitors for the schools of herring, mackerel, capelin and other commercial that humans mackerel, capelin and other commercial that humans hunted, but not fished for themselves.hunted, but not fished for themselves.

In the early 20In the early 20thth century the seas of the world still teemed century the seas of the world still teemed with sharks, but that has changed dramatically.with sharks, but that has changed dramatically.

Fishing and sharksFishing and sharks

In the 1950’s longline fisheries for tuna, In the 1950’s longline fisheries for tuna, swordfish, marlin and other prized species swordfish, marlin and other prized species treated sharks as a nuisance bycatch and treated sharks as a nuisance bycatch and many were cut free.many were cut free.

Today the growing wealth of Asian Today the growing wealth of Asian countries where shark fins are a delicacy countries where shark fins are a delicacy has made them a valuable catch.has made them a valuable catch.

http://advocacy.britannica.com/blog/advocacy/wp-content/uploads/shark-fin.jpg

Shark Finshttp://www.lessfeelsbetter.net/upload/1215781554SHARKFI8crop.jpg


Dried sharkfin can cost more than $500 a kilo Dried sharkfin can cost more than $500 a kilo and sharkfin soup up to $90 a bowl.and sharkfin soup up to $90 a bowl.

Longliners can set lines as much as 100km long Longliners can set lines as much as 100km long that contain 30,000 baited hooks and the that contain 30,000 baited hooks and the catches.catches.

In 1997 Hawaiian longliners caught more than In 1997 Hawaiian longliners caught more than 100,000 sharks and tossed almost 99% of the 100,000 sharks and tossed almost 99% of the body mass back. Why? They just kept the fins.body mass back. Why? They just kept the fins.

http://mythix.com/images/projects/ Shark_Finning_-_dead_shark_in_ocean.jpg

http://www.scubadiving.com/upload/images/Travel/20070326_sharkfinning_head.jpg


As worldwide fish stocks have declined As worldwide fish stocks have declined and often collapsed less desirable species and often collapsed less desirable species including sharks have been targeted by including sharks have been targeted by commercial fishing fleets.commercial fishing fleets.

As cod stocks collapsed, species such as As cod stocks collapsed, species such as spiny dogfish (marketed as “rock cod”) spiny dogfish (marketed as “rock cod”) began to be served as a replacement in began to be served as a replacement in fish and chips.fish and chips.


The Norwegian fishing fleet targeted sharks of The Norwegian fishing fleet targeted sharks of the genus the genus LamnaLamna (porbeagles or salmon sharks) (porbeagles or salmon sharks) for intensive fishing to sell as steaks as a for intensive fishing to sell as steaks as a substitute for swordfish.substitute for swordfish.

Initial harvests were as much as 8060 tons in a Initial harvests were as much as 8060 tons in a year from the northeast Atlantic. Within seven year from the northeast Atlantic. Within seven years the catch collapsed to 207 tons and hasn’t years the catch collapsed to 207 tons and hasn’t been over 100 tons since the 1970’s.been over 100 tons since the 1970’s.

Porbeagle http://dsc.discovery.com/sharks/shark-types/porbeagle-shark.jpg


Data from analyses of catch records Data from analyses of catch records worldwide show similar massive declines worldwide show similar massive declines worldwide (see Callum Roberts’ “The worldwide (see Callum Roberts’ “The Unnatural History of the Sea” for sources).Unnatural History of the Sea” for sources).

More than 90% of sharks have been taken More than 90% of sharks have been taken from massive areas of the world’s oceans.from massive areas of the world’s oceans.

Sharks caught on longlines.http://onfinite.com/libraries/1353690/324.jpg


Some species populations have been Some species populations have been devastated. devastated.

Once the oceanic whitetip was probably Once the oceanic whitetip was probably the commonest large animal in the world. the commonest large animal in the world. Today it’s numbers have declined 150-fold Today it’s numbers have declined 150-fold in the Gulf of Mexico and probably by the in the Gulf of Mexico and probably by the same amount elsewhere.same amount elsewhere.

Oceanic whitetip (Red Sea)http://www.flmnh.ufl.edu/fish/gallery/


Along with declines in numbers another Along with declines in numbers another pattern common to other fisheries has pattern common to other fisheries has emerged, the sizes of the animals caught emerged, the sizes of the animals caught has fallen.has fallen.

Between the 1950’s and 1990’s the size of Between the 1950’s and 1990’s the size of individuals caught fell in a variety of individuals caught fell in a variety of species. species.


Percentage decline in size of individuals Percentage decline in size of individuals caughtcaught Oceanic whitetips (-33%)Oceanic whitetips (-33%) Mako (-50%)Mako (-50%) Blue (-50%)Blue (-50%) Dusky (-60%)Dusky (-60%) Silky (-83%)Silky (-83%)


This decline is because fishing often This decline is because fishing often preferentially removes older animals and preferentially removes older animals and even if it doesn’t fishing pressure is so even if it doesn’t fishing pressure is so intense that animals don’t live long enough intense that animals don’t live long enough to grow large.to grow large.


The simple truth is that shark populations The simple truth is that shark populations cannot be intensively harvested cannot be intensively harvested sustainably.sustainably.

They are long-lived, slow maturing and They are long-lived, slow maturing and slow reproducing.slow reproducing.


For example, female spiny dogfish do not For example, female spiny dogfish do not mature until about 10-12 years of age and mature until about 10-12 years of age and produce only 2-14 pups biennially.produce only 2-14 pups biennially.

They can live 40-50 years, but not with They can live 40-50 years, but not with fishing pressure.fishing pressure.

Other sharks have similar reproductive Other sharks have similar reproductive profiles.profiles.


Even with a total ban on fishing, Even with a total ban on fishing, overfished shark populations will take overfished shark populations will take many, many years to recover.many, many years to recover.

Skates and raysSkates and rays

More than half of all elasmobranchs are skates More than half of all elasmobranchs are skates and rays.and rays.

More species (about 534) than there are sharks.More species (about 534) than there are sharks.

They have characteristically dorsoventrally They have characteristically dorsoventrally flattened bodies and greatly enlarged pectoral flattened bodies and greatly enlarged pectoral fins, which they swim with using a wavelike fins, which they swim with using a wavelike motion.motion.


Skates and rays should not be confused with Skates and rays should not be confused with flatfishes (e.g. sole and halibut), which are bony flatfishes (e.g. sole and halibut), which are bony fishes.fishes.

Skates and rays have gill slits placed ventrally Skates and rays have gill slits placed ventrally and eyes dorsally placed.and eyes dorsally placed.

In flatfish the body is twisted during development In flatfish the body is twisted during development to bring both eyes and gills to the dorsal surface, to bring both eyes and gills to the dorsal surface, but not symmetrically. but not symmetrically.


The group is specialized for bottom dwelling and The group is specialized for bottom dwelling and feeding on hard foods (e.g. molluscs and feeding on hard foods (e.g. molluscs and crustaceans) that have to be ground up.crustaceans) that have to be ground up.

Teeth are flat crowned plates that form an Teeth are flat crowned plates that form an arrangement like paving stones.arrangement like paving stones.

The mouth is located underneath the body and The mouth is located underneath the body and can be rapidly protruded to suck up prey.can be rapidly protruded to suck up prey.

Differences between skates and Differences between skates and raysrays

Skates have an elongated but thick tail stalk, Skates have an elongated but thick tail stalk, which has two dorsal fins and a caudal fin at the which has two dorsal fins and a caudal fin at the end.end.

Skates are oviparous.Skates are oviparous. Generally skates also have a rostrum a pointed Generally skates also have a rostrum a pointed

nose-like extension of the braincase.nose-like extension of the braincase.

Rays typically have a whip-like tail and the fins Rays typically have a whip-like tail and the fins are replaced by serrated venom-containing are replaced by serrated venom-containing barbs.barbs.

Rays are viviparous and most lack a rostrumRays are viviparous and most lack a rostrum

http://www.flmnh.ufl.edu/fish/education/questions/rayskatesawfish.jpg


The spiracles (openings behind the eye) The spiracles (openings behind the eye) are much larger in rays than in sharks are much larger in rays than in sharks because water for the gills enters because water for the gills enters exclusively through them as the mouth is exclusively through them as the mouth is usually buried in the sand.usually buried in the sand.


Skates and rays are usually well camouflaged Skates and rays are usually well camouflaged and sit on the bottom. A few species are and sit on the bottom. A few species are dangerous because of their sharp and barbed dangerous because of their sharp and barbed tail (stingrays) or because they can generate tail (stingrays) or because they can generate severe electric shocks (electric rays).severe electric shocks (electric rays).

Most species are bottom feeders that eat Most species are bottom feeders that eat invertebrates. However, the largest species invertebrates. However, the largest species (e.g. manta rays) as in sharks are planktivores. (e.g. manta rays) as in sharks are planktivores.

Manta Ray

Blue spotted ray

Skate egg casehttp://people.whitman.edu/~yancey/skateEggCase.JPG

Subclass Holocephali: ChimaerasSubclass Holocephali: Chimaeras

Chimaeras are a small group (about 33 species) Chimaeras are a small group (about 33 species) of deep sea (>80m) cartilaginous fishes known of deep sea (>80m) cartilaginous fishes known commonly as ratfish or ghostfish. commonly as ratfish or ghostfish.

Because they live mainly in deep water they are Because they live mainly in deep water they are not a well known group.not a well known group.

Male spotted ratfish

Subclass Holocephali: ChimaerasSubclass Holocephali: Chimaeras

They have a large head, plate-like grinding They have a large head, plate-like grinding teeth, a cover over the gills and lack both a teeth, a cover over the gills and lack both a spiracle and stomach. spiracle and stomach.

They appear to mostly feed on sea urchins, They appear to mostly feed on sea urchins, shrimp, and mollusks.shrimp, and mollusks.

The tail is thin and tapers to a point (hence the The tail is thin and tapers to a point (hence the name ratfish) and not much use in swimming. name ratfish) and not much use in swimming. Instead chimaeras depend on flapping their Instead chimaeras depend on flapping their pectoral fins for much of their movement.pectoral fins for much of their movement.

http://dsc.discovery.com/sharks/shark-types/thresher-shark.jpg thresher shark

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