ZOOLOGYSHARKS /

ELASMOBRANCHS

ZOOLOGYSHARKS /

ELASMOBRANCHS

Overview

Reproductive Organs Courtship Mating Development Parturition Species Examples Human Impact

Female Reproductive Organs

Cloacal opening between pelvic fins

Internal ovaries– Paired– Two forms

Eggs travel through ostium to oviduct then through shell gland

Most eggs develop in uteri

Cloacal opening shown on a

female shark

Reproductive Organs of a Female Porbeagle Shark

Male Reproductive Organs

Claspers Internal Testes

– paired Urogenital sinus Sperm is released

into groove of claspers and then into female

Claspers of a mature Male shark

Reproductive Organs of a Male Porbeagle Shark

Maturity

Age and size at maturity differs among species

Can range from 5 to 18 years to reach breeding age

Sharks are usually about 75% of their maximum size at maturity

Males are on average about 10% smaller than females at maturity

Females reach maturity about 34% faster than males

Courtship and Mating

Little known Appears to be

violent– Females have

thicker skin than males

Mate selection shown in some species

Courtship and Mating circle of the Basking Shark

Mating

Mating wounds– bite marks on pectoral fin of female Porbeagle

Mating

Mysterious Shark Birth

January 2002 Henry Doorly Zoo

in Nebraska Female

Bonnethead gave birth after being in captivity without access to males for three years

Bonnethead Shark, Sphyrna tiburo

Development Three types of development of embryos Oviparous

– “egg laying”– No parental care

Ovoviviparity/Aplacental – Most common– Embryos in uterus with yolk sac

Viviparity/Placental– Embryos in uterus with yolk sac and

placental connection

Oviparous

Considered most primitive

Most common with bottom dwelling sharks

Yolk sac for nurishment

Egg casing to protect young

Eggs are released near ocean floor with no more parental care

Egg receives no other care or nutrition

Development continues for up to a year inside the egg

Examples:– Cat Shark– Port Jackson Shark– Horn Shark– Zebra Shark– Whale Shark

Oviparous Development

1—Shark egg case after it is laid

2—The egg develops in the shell.

3—The young is fed by the yolk sack

4—The developed young breaks away from the shell.

Examples of Egg Cases

Egg case of a oviparous shark

Egg case of a Port Jackson Shark

Development of a Swell Shark

•                                              

Swell shark develops within a tough, leathery egg case.

Ovoviviparous

Fertilized eggs kept inside mother until born

Most common form of development

Eggs get nutrition through yolk sac

Produces large embryos

Eggs hatch inside mother and then are born

Provides better shelter

Examples– Dogfish Sharks– Cow Shark– Angel Shark– Frill Shark– Tiger Shark

Ovoviviparity

Portuguese shark with developing eggs in

ovaries

Oophagy and Embryophagy

Oophagy– eating eggs within the mother’s uteri

Examples:– Lamnoid Sharks– Makos– White Sharks– Threshers– Crocodile Sharks– False Catsharks

Embryophagy—eat siblings in uteri

Example:– Sand Tiger Shark35cm Porbeagle Shark

distended stomach of this specimen is full of egg yolk

from ingested eggs

50cm Shortfin Mako Shark embryo distended stomach, full

of egg yolk

Viviparous

Develop placenta or uterine milk to feed to young

Similar to development of mammals

Considered the most advanced form

Embryo develops internally

Has an umbilical cord attached to mother

Gestation is typically 9 months

Examples:– Hammerhead

sharks– Requiem sharks

Examples of viviparous development

Illustration of viviparous embryo showing the yolk sac placenta, yolk sac, uterus and embryo

Hammerhead shark showing umbilical cord

Parturition

Number of embryos born to a mother varies

Typically born after a period of 9 to 12 months

Most born tail first

Usually give birth in shallow coastal areas

Birth of a baby shark

Great White Shark Maturity at 9 to 15

years 7 to 11 per litter Young 1 meter at

birth Gestation time

unknown Ovoviviparity and

oophagy, but canabalism as once believed

Give birth every two years

                                                                                                                     

Bull Sharks

Viviparous Sexual maturity

reached at 8 to 10 years

Breed in summer Litters up to 13

pups Breed in brackish

waters

Goblin Shark

Little is known about reproduction Male mature at 2.6 meters

Ovoviviparious

Whale Shark

Only recently began to study

Up to 300 pups Oviparous Don’t know

where or when give birth or what early life is like

Sand Tiger Shark Long gestation

period Large, well

developed young at birth

Only one or two pups

Ovoviviparity, oophagy, and Embryophagy

Silky Shark

Not very much known about reproduction

Live bearing shark Litters of 2 to 14 Pup on edges of

continental shelves

Newborns stay in nursery areas

Port Jackson Shark

Return to same area to breed Oviparous Tough egg case about 7-8 cm

wide and 15 cm long Mature at 8-14 years

Southern Lantern Shark

Females mature at 62 cm and males at 52 cm total length

No evidence of a seasonal reproductive cycle

Ovulation occurs when ova reach diameter of 40-45 cm

Average number of ova is 12.7

Sexes segregate in adults except to mate

Great Hammerhead Shark

• Viviparous• Mature at a

length of 3 meters

• Litters of 20 to 40 pups

• Young are born during summer

• 70 cm in length

Shortfin Mako• Reach maturity

at around 2 meters

• Females are usually about 2.8 meters

• Size at birth is about 70 cm

• Litter size 4 to 16• Placental

viviparity• Oophagous

Angel Shark• Gestation lasts 11

months• Synchronized by

population• Ovulation occurs

in summer and birth takes place in Spring

• Gestation has two phases

Bonnethead Shark• Placental

viviparity• Shortest

gestation period known in sharks

• Store sperm for months

• Use hormones to regulate cycle

Spiny Dogfish

• Gestation period is about two years• Pup remains in uteri and the fluid

surrounding it resembles sea water• Reasons for sea water environment not

known

Basking Shark

• Difficult to study• Observed 25

different courtship episodes

• Mature sharks were 5 to 8 meters

• Took about 1.8 hours in courtship rituals

Human Impact• Because of slow

reproductive rates and small amount of pups, shark populations can not rebuild after being over fished by humans

• Environmental degradation and development threatens the nursery areas of many species

• Shark finning slaughters hundreds of thousands of sharks each year

• Could take decades to centuries for populations to recover

                                                                                        

Shark fins on sale in Hong Kong market