Elasmobranch Diversity And Adaptions Flashcards
Basic characteristics of Chondrichthyes
Jawed Paired fins Scales (denticles) Cartilage skeleton Gills No gas bladder Fertilisation is internal
What are elasmobranchs?
Skates rays (batoids) and sharks
What is the body form of batoids?
Flat bodied, with pectoral fins developed into broad flat wing-like appendages
What is the major difference between skates and rays?
Rays are viviparous (live baring)
Skates are oviparous (egg laying)
What are dorsal fins like in skates and rays?
Skates have prominent dorsal fins
Rays have absent or reduced dorsal fins
What are the pelagic zones
- epipelagic: surface to 200m
- mesopelagic: 200-1000m
- bathypelagic: 1000-4000m
- abyssopelagic: 4000-sea floor
- hadopelagic: ocean trenches
How do skates reproduce?
Male use claspers to direct flow of semen into females cloaca
What shape ratio do sharks have?
3-8, ideal is 4.5 fusiform
What are shark fins used for?
Stabilising, steering, lift, propulsion
What are the possible uses of dorsal fins
They have 1 or 2, antiroll stabilising fins, or possibly spiny for defence like dogfish
What are pelvic fins used for
Stabilisation
What are pectoral fins used for
Steering and lift
What is a heterocercal tail
Where the vertebrae extend into a large lobe, so tail is asymmetrical
What is a homocercal tail
Where the vertebrae do not extend into a lobe, so tail is more or less symmetrical
What are the small rough scales on sharks called and what are they
Dermal denticles, bony plate buried in the skin
What are dermal denticles homologous in structure to
Teeth
What is their function?
Form protective barrier and aid swimming by reducing drag
Are teeth lodged permanently in the jaw?
No
What is the membrane called that shark teeth are attached to
Tooth bed
How is the tooth bed similar to a conveyor belt?
Moves rows of teeth forward as the shark grows and replace older teeth in front that have become damaged, lost or worn
How is she determined in sharks, and what is the oldest shark found?
Counting growth rings on vertebra, Greenland shark 272y
What are many species of elasmobranchs threatened by?
- fisheries (mainly for fins), protected in uk since 1999
- shark nets
- accidental catch (by catch)
Why do sharks need dynamic lift?
Because they don’t have gas bladders, more dense than the water so sink
How do they create dynamic lift?
By using their pectoral fins as lifting foils or inclining their bodies at an angle of attack
What are the problems for elasmobranchs having to create dynamic lift?
Energy expenditure
Always have to be moving to create lift
How do most bony fish create static lift
Swimbladder
How do elasmobranchs generate static lift?
- low density building materials (cartilage)
- lipids/oils
- store oil in liver and muscles
How many pair of gills do sharks have?
5-7
How does water pass over the gills
Enters through the mouth (or spiracle) into the pharynx, over the gills and exits through the gill slits, water must always be passing over the gills to oxygenate the blood
What is the spiracle
Basically a first gill slit behind the eye
What is the purpose of the spiracle
Provide oxygenated blood directly to the eye and brain
Which types of sharks are spiracles more common in?
Large, bottom dwelling sharks
What is the spiracle used for in rays
Rays it is larger and is used to actively pump water over gills while it is buried in sand
What are the ampullae of Lorenzini?
Small vesicles and pores,
A subcutaneous sensory network
Around the head as dark spots
What is each ampullae like?
Multiple nerve fibres enclosed in glycoprotein gel with electrical properties
What do the ampullae of lorenzini detect?
Weak magnetic fields produced by other fishes when muscles contract, allowing them to locate prey
AND
Use them to navigate earths magnetic fields
What is the second part of the electrosensory component
Lateral line
What did the lateral line do?
Allows sharks to orientate to particle movement or sound
What are the structures called that allow the detection in the lateral line
Neuromasts
How do sharks hear?
Very sharp sense of hearing, hear prey many miles away
Small openings with thin canal to inner ear
What is the lateral line and hearing system grouped called?
Acoustico-lateralis system
Where is the olfactory sense located
In short duct between the anterior and posterior nasal openings
What small amount of blood can some species detect?
1 part per million
What smells are sharks attracted to?
Chemicals found in guts of many species, and so found near sewage pitfalls
What do nurse sharks have to increase their ability to sense prey?
Barbels
What is the first thought for ‘why the hammer’
Hydrodynamic lift
What is the second thought for ‘why the hammer’
Sensory enhancement
- have specialised grooves which channel scent bearing water into nostrils
- ampullae of lorenzini distributed under whole hammer, act as metal prey detector
In terms of salt, what is the blood in relation to the sea
Isotonic
How are they isotonic?
High concentration of urea and TMAO, in osmotic balance with seawater
What does the fact they are isotonic mean for most sharks?
Cannot survive in freshwater
What is the exception to not being able to live in freshwater and how does it do it
Bull shark
Change kidney function to excrete large amounts of urea
What does the Nicaragua Bull shark do to counteract the fact it’s body fluids are twice as salty as freshwater fish
Pees a lot of dilute urine
Are most sharks ectotherms or endotherms?
Ectothermic
Give an example of a shark that is an endotherm
Shortfin mako shark and great white shark
How do endothermic sharks maintain body temperature higher than water?
A strip of aerobic muscle located in centre of body generates heat, which is transferred to blood by countercurrent exchange in rete mirabile
Are sharks sexually dimorphic?
Yes, females have cloaca and males have claspers
What is a clasper
Rolls of cartilage, with paired testes, right bigger than left
What is the cloaca?
Opening between the pelvic fins,
Paired ovaries, right bigger, left sometimes don’t produce any eggs
How do porbeagle sharks mate?
- sharks meet face to face
- make inserts one of his claspers into cloaca
- sperm (within spermatophore) ejected by contracting organs called siphon sacs
How can data be gotten from elasmobranchs?
- dead - fossils/bycatch
- tagging, observations etc.
Give an example of shark with limited distribution and one with wide range (across oceans)
Northern river shark - tidal rivers in N Australia
Great white/basking/salmon
What methods can be used to investigate distribution ?
ID tags, photo-id, radio satellite tags
How can population structure be investigated?
Morphometrics - (small differences in skeleton structure between non-interbreeding populations)
Genetics and DNA forensics
Ecological
How do sharks life spans vary?
Most live 20-30
But some much older such as Greenland shark 272
Sharks are k-selected reproducers, what does this mean?
Produce a small number of well developed young
How does fecundity vary in sharks?
From 2 to over 100 per cycle (1-3 years), sharks mature very slowly
What percentage of chondrichtyan are considered ‘safe’
23%
How many sharks are killed per year from commercial and recreational fishing?
40-100million
What happens to the ecosystem when you remove large scale apex predators?
- lack of prey regulation
- ecosystem shift
- possible cascading effects
