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

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 viviparous.reproduction is oviparous or viviparous.


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.

Developing skate in its egg case

http://www.youtube.com/watch?v=ZEpOmjLb2e8


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.

Sand tiger shark eats siblings in utero

http://www.youtube.com/watch?v=ZrqgPjZ07Ts&feature=related

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 sharks themselves were not fished for.hunted, but sharks themselves were not fished for.

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 long-line fisheries for tuna, In the 1950’s long-line fisheries for tuna, swordfish, marlin and other prized species swordfish, marlin and other prized species treated sharks as a nuisance by-catch and treated sharks as a nuisance by-catch 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.that contain 30,000 baited hooks.

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 and often collapsed, less desirable species including sharks have been species including sharks have been targeted by commercial fishing fleets.targeted by 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 534-631 depending on More species (about 534-631 depending on who’s classifying them) than there are sharks.who’s classifying them) than there are sharks.

As is the case for sharks, skates and rays have As is the case for sharks, skates and rays have a cartilaginous skeleton and an enlarged oil-a cartilaginous skeleton and an enlarged oil-filled liver that reduces their buoyancy. They filled liver that reduces their buoyancy. They also possess the same electro sensors sharks also possess the same electro sensors sharks do (Ampullae of Lorenzini)do (Ampullae of Lorenzini)

Skates and rays

Skates and rays have characteristically Skates and rays have characteristically dorsoventrally flattened bodies dorsoventrally flattened bodies greatly enlarged pectoral fins, which attach to greatly enlarged pectoral fins, which attach to

the side of the head.the side of the head. gill slits placed ventrally and eyes dorsally gill slits placed ventrally and eyes dorsally

placed.placed.

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

Skates and raysSkates and rays

There are also dorsoventrally flattened There are also dorsoventrally flattened sharks e.g. the wobbegong and angel sharks e.g. the wobbegong and angel sharks. sharks.

They have large wing-like pectoral fins but They have large wing-like pectoral fins but these are not attached to the head. these are not attached to the head.

Spotted wobbegonghttp://www.biolib.cz/IMG/GAL/122294.jpg


Most skates and rays depend on Most skates and rays depend on undulating their pectoral fins to swim but undulating their pectoral fins to swim but some such as the torpedo rays use their some such as the torpedo rays use their caudal (tail) fin for movement.caudal (tail) fin for movement.

Atlantic torpedo rayhttp://www.junglewalk.com/shop/Products/Atlantic-Torpedo-Ray-Magnet-4623.htm


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.

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.

Flatfish (flounder a bony fish note the asymmetrical head)http://biochemicalsoul.com/2009/02/adaptation-of-the-week-flatfish-recapitulation/


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

Stingray teethhttp://www.flmnh.ufl.edu/fish/Gallery/Descript/atlanticstingray/atlanticstingray.html

http://misc.thefullwiki.org/Ray_and_Skate

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

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.

http://img.21food.com/20110609/product/1306507703542.jpg

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

Skates are oviparous.

Differences between skates and Differences between skates and raysrays

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

Rays are viviparous and most lack a Rays are viviparous and most lack a rostrumrostrum

http://www.marinebiodiversity.ca/skatesandrays/Classification%20Overall.htm


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

http://media.photobucket.com/image/spiracles%20in%20rays/nairboarding/sp.jpg

Skates and raysSkates and rays Skates and rays are usually well camouflaged and sit on Skates and rays are usually well camouflaged and sit on

the bottom to hide from predators.the bottom to hide from predators.

A few species are dangerous because of their sharp and A few species are dangerous because of their sharp and barbed tail (stingrays) or because they can generate barbed tail (stingrays) or because they can generate severe electric shocks (electric rays).severe electric shocks (electric rays).

Most species are bottom feeders that eat invertebrates. Most species are bottom feeders that eat invertebrates. However, the largest species (e.g. manta rays), like However, the largest species (e.g. manta rays), like whale sharks and basking sharks, are planktivores. whale sharks and basking sharks, are planktivores.

Manta Ray

Blue spotted ray

Stingray

A stingray’s tail possesses a sharp pointed, barbed spine halfway along the length of the tail that it uses for defense.

Many species of stingray have a venom gland associated with the spine and the venom can be fatal to humans. Stingray spines have been used as spear points by many cultures.

http://elasmodiver.com/Sharkive%20images/Stingray-Barb-004.jpg

Stingray barb.

http://www.flmnh.ufl.edu/fish/Gallery/Descript/atlanticstingray/atlanticstingray.html

Electric rays

The up to 40 species of electric rays belong to the order Torpediniformes.

They can produce an electrical discharge that is used for hunting and protection.

The discharge can range from 8 to 220 volts and be up to 30 amperes (it’s the amperage that’s dangerous. Amperage is a measure of the amount of electricity flowing).

Marbled torpedo rayhttp://elasmodiver.com/MarbledTorpedoRay.htm

Electric rays

The electric organs are modified from striated muscle fibers and consist of stacks of flattened cells supplied with nerves on one side.

Because the cells are stacked in columnar series (called electroplaques) the small electrical charges generated by each cell sum together to produce a large charge that can stun or kill other fish.

Electric rays

The electric organs are up to one sixth of an electric rays body weight and are located on the side of the ray just ahead of the pectoral fins.

In some species the organs are wired to direct a shock upwards. In others they are pointed downwards.

Electric rays appear to hunt mostly at night and may slowly move over a fish and then stun it or lurk buried under sand until a suitable prey fish swims overhead.

Sawfishes The seven species of sawfishes inhabit tropical

and subtropical coastal bays and estuaries and prefer shallow silty water.

They are big (1.4 to 7 meters in length).

They possess a distinctive “tooth” edged rostrum or saw (the teeth are modified tooth-like structures called denticles). The rostrum is covered with motion and electro detectors that allow the sawfish to detect hidden prey.

http://www.elasmoworld.org/sawfish.html

http://www.elasmoworld.org/sawfish.html

Sawfishes

Usually sawfish forage on the bottom and eat crabs, crustaceans and small fish. They often stir up silt and mud with their saws to startle prey.

Sawfish also slash with the saw to kill or disable prey and use the saw to defend themselves also.

Subclass Holocephali: ChimaerasSubclass Holocephali: Chimaeras

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

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

Their lineage diverged from the sharks about 400 mya. Their lineage diverged from the sharks about 400 mya. Formerly they were more diverse.Formerly they were more diverse.

Male spotted ratfish

Subclass Holocephali: ChimaerasSubclass Holocephali: Chimaeras

Have a large head often with an elongated snout filled with Have a large head often with an elongated snout filled with sensory structuressensory structures

Have a cover over the gills (operculum) as in bony fishes)Have a cover over the gills (operculum) as in bony fishes) Have a venomous spine located in front of the dorsal fin.Have a venomous spine located in front of the dorsal fin. Lack both a spiracle and stomach. Lack both a spiracle and stomach.

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

Chimaeras

Like other Chondricthyes males use claspers for mating and eggs are laid in leathery cases.

Males also possess retractable sexual appendages on the head and in front of the pelvic fins that apparently are used to grasp the female during mating.

Chimaeras

They appear to mostly feed on sea They appear to mostly feed on sea urchins, shrimp, and mollusks that they urchins, shrimp, and mollusks that they grind using plate-like grinding teeth.grind using plate-like grinding teeth.

Unlike in sharks the upper jaws are fused Unlike in sharks the upper jaws are fused to the skull.to the skull.

Documents

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