Sharks

Question 1

What are 3 reasons sharks are important to coral reef ecosystems?

Answer 1

1. EAT - sharks remove weak/sick fish from the population, ensuring only healthy individuals continue to breed - increase in biodiversity and biomass.
2. PREY - smaller reef sharks are eaten by larger fish (eg sharks, groupers).
3. POOP - nutrient rich poop fertilises the reef with nitrogen.

Question 2

Name 5 threats to sharks.

Answer 2

1. FINNING (100 million sharks per year)
2. OVERFISHING
3. HABITAT DESTRUCTION
4. CLIMATE CHANGE
5. ANTHROPOGENIC PRESSURES

Question 3

What are the male shark reproductive organs and where are they found?

Answer 3

Males have two external organs called CLASPERS on the VENTRAL (underbelly) side of the body between the PELVIC FINS.

Question 4

How do male sharks fertilise female eggs?

Answer 4

A male inserts one of his CLASPERS into the CLOACA (opening) of the female to transfer SPERMATOPHORES (sperm packets) whilst biting the female.

Question 5

HINT: think of methods of embryo nutrition.

What are the 3 methods of embryo development in sharks and what are their gestation periods?

Less nutritional aid from mothers means lower gestation period.

Answer 5

1. OVIPARITY - egg is laid with yolk sac nutrition (mermaid purses). The eggs attack to rocks/coral and the embryo relies on the yolk sac for developmental nutrition. 8-12 months gestation. EG cat sharks, bamboo sharks.
2. VIVIPARITY - live birth with placental nutrition. Once the yolk sac has absorbed it elongates, attaching to the uterine wall and forms a yolk sac placenta. 11-12 months gestation. EG hammerheads. grey reef shark.
3. OVOVIVIPARTY - live birth with “egg eating” nutrition. Embryos develop relying on the yolk sac and then gain extra nutrition by consuming near undeveloped eggs (omophagy). 10-15 months gestation.

Question 6

Explain some morphological differences between coastal and benthic shark species.

HINT: differences in head shape, pectoral fins, body shape, caudal fin lobes, caudal peduncles and tail notches.

Answer 6

1. Coastal sharks have a more flattened head whilst benthic sharks have larger heads.
2. Coastal sharks have large pectoral fins whilst benthic sharks have shorter pectoral fins.
3. Coastal sharks have a less-deep body shape whilst benthic sharks have a deeper body (thorax?)
4. Coastal sharks’ tails have larger lower lobes whilst benthic sharks’ tails have smaller lower lobes.
5. Coastal sharks have broader caudal peduncles without any lateral keels (the space between the body and tail).
6. Benthic sharks have large sub-terminal notches in the tail.