Lecture 2 Flashcards
What are fins used for in sharks?
Stabilising, steering, lift and propulsion (each of the fins has a different use)
What are the dorsal fins (1 or 2) used for in sharks?
They are anti-roll stabilising fins (they may have spines for defenders and may have skin glands that produce an irritating substance
Where are the pectoral fins located and what are they used for?
They are located behind the head and extend outwards. They are used for steering and help to provide the shark with lift
Where are the pelvic fins located? What are they used for in sharks?
Found near the cloaca and are stabilisers
Anal fins may be absent in sharks but if they are present where are they located? And what are they for?
They are located between the pelvic and caudal fins. They are stabilises
What does the tail region of a shark consist of?
The caudal peduncle and the caudal fin
What does the caudal fin in sharks provide?
Thrust and forward motion
The tail in sharks can be heterocercal, what does that mean?
The top lobe is different to the bottom live, which means that the vertebrae extend into a larger lobe of the tail or that the tail is asymmetrical
What kind of tail do most fish have?
A homocercal tail where the vertebrae do not extend into a lobe and the fin is more or less symmetrical
How do the vertebrae differ in bony fish and elasmobranchs?
In bony fish the vertebrae do not extend into the tail but in the elasmobranchs the vertebral column extends into the upper lobe
What does epicercal mean?
That he upper lobe is longer (as in sharks)
What does hypocercal mean?
That the lower lobe is longer (as in flying fish)
Which fin provides the lift and the orientation of the animal?
The pectal fin
What does it mean if an animal is negatively buoyant e.g. sharks?
Means they will sink and have to move constantly to maintain their position in the water column
Describe shark skin
Feels like sandpaper because it has small rough placoid scales (dermal denticles). Rough one way and relatively smooth the other
What do the denticles in sharks skin consist of?
A bony plate buried in the skin and a raised portion that is exposed extends out
What do the denticles in sharks skin form and aid?
They form a protective barrier and aid in swimming because as the shark moves forward it decreased the amount of drag on the body as the scales reduce turbulence around the animal
How do the denticles in shark skin aid in swimming?
The low sharp edged ridges of the denticles are parallel to the direction of movement and reduced drag by delaying turbulence
What is the tooth bed?
Shark teeth are not lodged permanently within the jaw but are attached to a membrane called the tooth bed
How does the tooth bed membrane in sharks work?
The membrane is similar to a conveyor belt, moving the rows of teeth forward as the shark grows and replace older teeth in from that have become damaged, lost or worn down (you often find shark teeth lodged in large prey (such as whales and dolphins) or loose on the ocean floor)
Describe cookie cutter sharks
2 species, order Squaliformes, small 40-50cm, attach themselves to their prey and spins to cut out a cookie/ disk of flesh. Depth range 1-3500m. Diurnal migrations
How do we estimate the age of a shark? Give example
By counting growth rings on vertebra or on spine in some species
E.g: spiny dogfish
Why can’t we use teeth to age sharks?
Because they are constantly being replaced
How old are Greenland sharks estimated to be? And how do we date them?
272y (very slow growing)
392+/-120y
Use radiocarbon dating to estimate their age
Why should we study elasmobranchs?
. Protect diversity
. Top predator- indicator species
. Little information available for many species (difficult to study, don’t know their abundance). Abundance and status unknown for most species
. Tourism- swimming with whale, basking and great white sharks
What are many species of elasmobranchs threatened by?
. Fisheries (mainly for fins). (Last UK basking shark fishery closed in 1995, protected in the UK since 1999)
. Shark nets- to protect areas for swimmers
. Incidental catch (bycatch) in fisheries
What information do we need to determine the status of elasmobranchs?
. Their ecological niches
. What age they reproduce and die etc.
. Their behaviour- where they go and what they do
(Is a slow process to get data for all these things)
How do we access data to work out the status of elasmobranchs?
. Sample from dead animals (fossils, fisheries catch and bycatch)
. Samples from living animals (field work e.g. observations (behaviour, photo id- look at the unique markings to get an idea of the number of individuals), tagging (Mark-recapture and various radio/ acoustic- data tags, tissue samples) or by capturing animals. The spot tag is the GPS that transmits the data but it is also linked to a lot of other sensors telling you where the animal is moving/ if they are moving and depth recorders to find out how deep these animals are going and how lobe they spend at these different depths)
Fish that are denser than water will sink. How do they prevent this?
They generate dynamic and/ or static lift (static lift= reduced buoyancy- sharks can do that but not to the same extent as bony fish)
How do bony fish reduced their buoyancy?
They have a gland inside and an organ called a swim bladder
Sharks and rays do not have a swim bladder like bony fish so how to they reduced their buoyancy (however not as effectively as bony fish do)? What is the issue with Their method?
They produce dynamic lift which they do using their pectoral fins however, these stick out into the water and produce drag- increasing energy expenditure and they also need to go forward to create the lift
How do sharks and rays produce dynamic lift to reduce their buoyancy?
Either by using their outspread pectorals as lifting foils (their fins are shaped as fouls) or by inclining their bodies at an angle of attack
It may be energetically cheaper to be a bottom dwelling species of elasmobranchs, such as rays. However, many of the bottom living elasmobranchs do not sit on the bottom they hover above. Why is this? What do many of these elasmobranchs have?
Sharks that do this tend to have very different sized lives compared to their caudal fin because they don’t want the lower lobe going into the sand and disturbing it. So tend to have a longer upper lobe compared to the lower lobe
What is the degree of dynamic lift largely decided by?
The size and shape of the pectoral fins
How many gills do sharks have on the side of their head?
5-7 (usually less than 7)
How does gas exchange occur in sharks?
Water enters through the mouth (or the spiracles which is more important when you are a bottom dwelling animal) of the animal, into the pharynx, over the gills and exits through the gill slits (can use the forward motion to push water over the gills).
Where does respiratory gas exchange take place in sharks?
On the surface of the gill filaments as the water passes over and out the gills
What is the spiracle in sharks?
Basically a first gill skit which appears as an opening behind the eye
What is the spiracles used for in sharks?
To provide oxygenated blood directly to the eye and brain through a separate blood vessel, and/or to pump water over the gills
What kind of sharks are spiracles missing in?
Fast swimming sharks
Which type of sharks are spiracles larger in?
Bottom dwelling sharks
Describe how the spiracle differs in a Ray compared to a shark
The spiracle is larger and more developed and is used to actively pump water over the gills to allow the Ray to breathe while buried in the sand
Why are spiracles larger in rays and bottom dwelling elasmobranchs?
Because they sit on the bottom of the sea floor and the gills are underneath and therefore water can not get in through there so then the spiracle becomes the major source of bringing water into the gills
What are the ampullae of Lorenzini in elasmobranchs? And what do they do?
Small vesicles and pores around the snout of the animal, they pick up electrical signals in the water (electroreceptors) that’s form part of an extensive subcutaneous sensory network system
Where are the ampullae of Lorenzini found?
Around the head and appear as dark spots
What do the ampullae of Lorenzini detect?
Weak magnetic fields produced by other fishes
What do the ampullae of Lorenzini contain?
Multiple nerve fibres that are enclosed in a gel-filled tubules (canal of Lorenzini) (glycoprotein with electrical properties)
What is the gel in the canal of Lorenzini (gel-filled tubule) of the ampullae of Lorenzini?
A glycoprotein (so carboprotein)
How do electrical pulses get to the centre of brain in ampullae of Lorenzini?
The electrical pulses are transmitted through the gel because it has semi-conductive properties and is then picked up by the nerve cells and the information centre of the brain
How do sharks find their prey?
. All living creatures produce an electrical field by muscle contractions, sharks may pick up weak electrical stimulus from the muscle contractions of their prey and locate them
How can some sharks navigate around the world?
By using the ampullae to navigate to the electric fields of ocean currents and the earth’s magnetic fields
What does the lateral line together with the ampullae of Lorenzini comprise?
The electrosensory component of the sharks sensory system
The lateral line because it tends to be concentrated down the side of the animal allows the shark to do what?
To orient to particular movement or sound
What does the lateral line consist of?
Structures called neuromasts which are located in canals that lie just below the surface of the skin or the scales
Where are the neuromasts (what the lateral line consists of) concentrated?
The head region
How do the neuromasts work?
There are pores that open to the outside and movement caused by prey can be detected by the neuromasts. (The tubules are not gel-filled and are open to the sea water and any water movement is transmitted down these and is picked up by these neuromasts)
What are ‘pit organs’?
Surface neuromasts. Is a mechanical line system that picks up water flow and movement
Some species (such as nurse sharks) have barbels, what are these?
Whisker like tactile organ near the mouth that increase their ability to sense prey
What are the two basic thoughts as to why the hammer in hammerhead sharks have wide chemical sense organs either side?
. Hydrodynamic advantages (head is flattened on the lower surface and rounded on the upper and may therefore increase lift- like the fins in other sharks because of the shape)
. Sensory enhancement- better when finding the direction in which the chemical is coming from. The nostrils of most species are located near the tips of the hammer and have specialised grooves which channel scent-bearing water to the nostrils. By having their nostrils mounted far apart they can sample the water column in stereo. The Lorenzini ampullae are distributed over the entire undersurface of the hammer, and the width of the head may work as a ‘metal prey detector’
