What is Shark Diving?
Shark diving, or cage diving, allows divers, researchers and film crews to view the extraordinary world of Great White Sharks in comfort and safety. Specially designed shark viewing cages provide adequate protection for the sharks from sport divers, while allowing divers total freedom of movement and panoramic views. Our shark diving crews are industry professionals who care about your safety and enjoyment. Equally important, they care about making our dives safe for the sharks.
Is Shark Diving Dangerous?
To date, our most serious injury has been a sunburn. White sharks have many myths surrounding them. One is that they are killing machines attacking anything in sight. We have found that even at the height of a feeding event with multiple animals around a carcass, white sharks prove to be shy, slow moving animals. Our divers are amazed to learn first hand that these animals are almost gentle. That said, divers should always maintain a healthy respect for these awesome predators, in and out of the water!
Showing posts with label Whale Watching. Show all posts
Showing posts with label Whale Watching. Show all posts
Tuesday, August 12, 2008
Monday, February 25, 2008
DIVING WITH SHARKS
DIVING WITH SHARKS AND RAYS
Source of post: http://elasmodiver.com/Shark%20diving%20101.htm
First and foremost, I can't stress enough the need to gain as much knowledge as possible about the animals and their environment. To go into the water without at least a basic idea of how the sharks are likely to react is foolhardy to say the least. If you are participating in an organized "shark diving experience" you may feel that the operator's knowledge is sufficient and that you can sit back and watch the show. It's important to remember that every shark interaction is different. Just because countless people have watched the parade of sharks at a particular site passively swim by does not mean that you will have the same experience. Following are some guidelines for minimising the dangers associated with interacting in the wild with sharks and rays. Whilst the advice hopefully is useful it should be regarded as a vague guideline only. Your experiences will differ greatly from mine and the sharks and rays you encounter may react in a completely different way. As such, I take no responsibility for the outcome of any encounters that you may have or for the validity of any information stated below.
1. Get educated!
Ask local divers and fishers what species of sharks you are likely to see. Knowing if an area is frequented by nurse sharks or tigers may make a big difference to how alert you feel you need to be on the dive. Learn the stats on different sharks. The shark attack file is a good place to start to find out which sharks have been responsible for attacks in the past.
Find out how the sharks in the area normally respond to divers. Most free swimming sharks will disappear the minute they see a noisy, bubble blowing diver heading their way but some sharks are more curious. Occasionally sharks like to wander up to divers and give them a closer look. Being buzzed or even brushed by a shark does not necessarily mean that you are about to become lunch.
First and foremost, I can't stress enough the need to gain as much knowledge as possible about the animals and their environment. To go into the water without at least a basic idea of how the sharks are likely to react is foolhardy to say the least. If you are participating in an organized "shark diving experience" you may feel that the operator's knowledge is sufficient and that you can sit back and watch the show. It's important to remember that every shark interaction is different. Just because countless people have watched the parade of sharks at a particular site passively swim by does not mean that you will have the same experience. Following are some guidelines for minimising the dangers associated with interacting in the wild with sharks and rays. Whilst the advice hopefully is useful it should be regarded as a vague guideline only. Your experiences will differ greatly from mine and the sharks and rays you encounter may react in a completely different way. As such, I take no responsibility for the outcome of any encounters that you may have or for the validity of any information stated below.
1. Get educated!
Ask local divers and fishers what species of sharks you are likely to see. Knowing if an area is frequented by nurse sharks or tigers may make a big difference to how alert you feel you need to be on the dive. Learn the stats on different sharks. The shark attack file is a good place to start to find out which sharks have been responsible for attacks in the past.
Find out how the sharks in the area normally respond to divers. Most free swimming sharks will disappear the minute they see a noisy, bubble blowing diver heading their way but some sharks are more curious. Occasionally sharks like to wander up to divers and give them a closer look. Being buzzed or even brushed by a shark does not necessarily mean that you are about to become lunch.
Are the sharks in the area regularly fed by divers? It can be disconcerting to drop down onto an area of reef where shark feeds normally take place and immediately find yourself surrounded by expectant sharks.
Ask if bait will be used or if any member of the dive group is planning to spear fish. Aggressive behaviour is significantly increased in the presence of struggling fish or when blood and other juices are in the water.
Find out if the sharks in the area are territorial. Sharks may respond to divers as threats to territory and defensively attack.
2. Dress appropriately.
There are differing points of view on the subject of what colors are most likely to attract a shark's attention. Every conceivable color combination has been tried at one time or another in an effort to deter sharks from attacking. Even broad black and white stripes have been tried in an effort to replicate the appearance of a banded sea snake which is an animal avoided by the majority of shark species.
As a rule of thumb, tropical sharks are mainly fish eaters and as such are attracted to bright and shiny objects. Therefore it would seem logical that a neon yellow wetsuit would attract the attention of sharks looking for a meal. In shark diving circles neon yellow has actually been given the nickname of "yum yum yellow". Other bright colours may also have the same effect so if you're planning on regularly putting yourself in the presence of tropical fish eating sharks it may be a good idea to tone down your fashion statement and choose a more muted color or black. Bear in mind that thousands of divers swim with tropical sharks every day wearing all manner of clothing from bikinis to camouflaged full body dive skins and the incidence of attack is extremely low.
If you have bright metal objects such as reels or dive knifes attached to the outside of your BC try to stash them out of sight in a pocket or replace them with darker coloured alternatives. Even a diver's first stage can look good to a hungry reef shark as I found out in the Bahamas.
Wear dark gloves. From a shark's point of view there's nothing more tempting than seeing two small lily white "fish" flapping around in front of them. If you don't have any gloves try to keep your arms folded across your chest. Using your hands to swim with is asking for trouble.
Full suits are better than shorty wetsuits. This is the same principle as exposing your hands. try not to expose distinct areas of skin that a shark can focus on or mistake for a fish. Even if you have dark skin it's a good idea to cover up. A lot of injury can occur from the brush of a shark's sandpaper like skin.
Some sharks in temperate seas feed on seals and sea lions. The chances are that you will never see a white shark under water. I have a friend that lives on Catalina Island who has seen a couple but he considers himself very lucky indeed to have done so. Many divers prefer the tough guy black commando look and this is reflected by the choices of suits that manufacturers offer. Personally I think that mimicking a seal doesn't seem like such a good idea. Keep in mind again that there are plenty of fish eaters in temperate seas as well, including smaller white sharks, so flashing bright colours and shiny objects may also be unwise. I own a nice neutral blue dry suit that hopefully differentiates me from both pinnipeds and schools of fish.
Lastly, fins tend to be prime targets for bites. This is more likely to do with their movements and exposed position rather than colour but white, silver, or bright fins should probably be avoided.
3. Avoid erratic movements.
Sharks are able to pick up on disturbances in their environment. They are looking for the tell tale signature of a wounded fish or other animal. Once they find one they carry out their civic duty and remove the wounded creature from the gene pool. Thrashing around in the water may mimic the vibrations sent out by a wounded fish and/or may replicate the movements of a feeding shark. Either way, slow, rhythmic fin strokes are more likely to be ignored. Good buoyancy is also important. crashing into the reef or struggling to stay down could generate interest or may work in reverse and drive away sharks that you were hoping would stay around.
4. Look but don't touch.
The best way to get bitten by a shark is to grab it by the tail or any other part of its anatomy. You wouldn't think this needs putting into print but a surprising amount of shark bites are the direct result of divers trying to man handle otherwise docile creatures. Joe diver sees a nurse shark's tail protruding from under the reef and thinks that if he gives it a little poke or tug the nurse shark will shift into a position where Joe can get a better look at its head. He grabs the shark's tail and before he has time to register exactly what has happened he looks down to find a nurse shark jaw wrapped around his wrist. Contrary to popular belief, nurse sharks do have rows of sharp little teeth and once Joe is finally released (which sometimes doesn't happen until he is literally dragged out of the water) Joe gets to spend the rest of his holiday at the very least with a bandaged arm. Don't be Joe Diver. Sharks are extremely flexible and explosively fast.
Rays usually remain very docile if you approach them slowly until their personal space is encroached upon and then they finally either bolt or slowly lift off the bottom and relocate a few meters away. The best way to get near them is to move in close to the sea bed. Rays feel more threatened when approached from above.
In rays the two defence mechanisms that a diver needs to be aware of are: the stingrays tail barb, and the electric rays ability to shock.
Waders (often fishing) have been wounded and even killed where medical attention was not available as the result of stingray barbs entering the abdomen or other vital organs. The barbs often carry toxins which compound the medical problem and create immense pain. Luckily divers are rarely faced with stingrays using this defence mechanism as it is only employed as a last resort when the animal is pinned down. Stingrays are more than happy to move away if they are too closely approached by a diver. I am not aware of a single diver that has been stabbed whilst on a dive. This is not to say that you won't step on one with painful results whilst attempting a shore entry. If this occurs wash the wound in fresh water and apply as much heat to the area as possible. This will help to break down the toxins and relieve some of the pain. Seek medical attention as soon as possible. Stingray barbs often break up upon entry and the wound may need to be cut open and cleaned to avoid infection.
The electric organs of some rays are potentially dangerous but again in the majority of cases the ray is far more likely to move away than shock. However, torpedo rays are known to have a bad temper and there have been a few cases of these animals chasing divers and repeatedly shocking them. Some torpedo rays have been shown to be able to emit in excess of 200 volts! Usually if the animal is not harassed it will leave divers alone.
5. Stay away from the chum.
Sharks that come to a shark feed are not there to socialise. They want food and if you're between them and dinner you're in the wrong place at the wrong time. Keep your distance from any hanging bait that has been placed in the water and if the current is moving a chum slick away from the area make sure that you are positioned off to the side or up stream.
Having watched the shark's behaviour for some time you may feel confident about moving in for better pictures or a better look. Remember that if the current is running and you are down stream any sharks that are swimming up to the bait may think that those delicious odours are emanating from you. Now you're stuck in a position where a shark is coming toward you and you are drifting into it. As it's very hard to swim against even a mild current you probably now have to turn around to make headway against it to get back up stream which puts you with your back to the approaching shark. A better course of action is to swim sideways until clear of the chum slick at which point you can kick up current without looking like a fleeing wounded animal.
6. Get underwater.
Floating at the surface in the presence of sharks sends the wrong message. You want to descend as soon as you can for a few reasons:
Firstly, a body floating at the surface is high on the list of desirable objects for a shark to explore. In the ocean dead things float. Oily chum tends to create a slick on the surface that you may be covering yourself in while you remain there.
Secondly, if your head is above water you are effectively blind to the movements of any sharks underwater.
Thirdly, a positively buoyant diver's actions are far more limited. It takes time to become negative and descend out of trouble and swimming at the surface in dive gear looks an awful lot like a thrashing animal.
7. Read the sharks.
It's important to pay attention to the behaviour of the sharks participating in a feed. Although sharks become agitated as soon as they know food is available they will usually continue to cruise around calmly waiting for the opportunity to strike at the bait. In a well organized feed, access to the bait is often restricted to keep the sharks interested but not overexcited.
If too much bait ends up in the water, the sharks may become very aggressive. They may chase each other tearing at the food and in their single-mindedness any divers that get in the way stand a chance of getting hit. To understand the significance of being thumped by a shark underwater it's necessary to look at the medium the sharks are moving through. If an adrenalin filled dog were to hit you at 20 miles an hour it would bowl you down. Now replay this scenario in a medium 800 times denser than air and you don't get bowled over anymore because you're supported by the water. However, the object hitting you is still travelling at the same speed resulting in a tremendous impact. Even a leisurely swimming shark can hurt a diver but sharks rarely collide with anything unless they are panicked. Pay attention to the dynamics of the feed.
Beyond a critical level of excitement sharks may become too aggressive for divers to safely remain in the water, and it is difficult to judge when this point is approaching. If many sharks are in attendance and ploughing into the food, seemingly indifferent to anything else around them they may become excited enough to bite randomly at whatever is close to them. Often the surprising thing is how fast the pace can change.
Some sharks regardless of food stimulus may become aggressive towards divers. Any type of posturing is a bad sign. The threat display of Grey reef sharks has been well documented. This consists of exaggerated swimming motions, back arching, raising of the snout, lowering of the pectoral fins, and head swinging. Not all sharks will give you these visual cues but you may see some small modified behaviour. The message is a clear one: BACK OFF! Hopefully the diver will notice the posturing and move away before the shark takes its next defensive strategy which is often to attack. The most common scenario in which this situation occurs is when a shark is cornered. Try to always give sharks an escape route.
It may be tempting to want to photograph posturing behaviour but this has proven to be the downfall of numerous divers in the past. A camera flash is often the catalyst that brings on the final attack. Even bringing a camera up to eye level may be enough to push a shark over the edge and it's important to remember that no matter how ready you think you are, if a shark attacks at speed you are unlikely to be able to block the attack in time.
8. Be a responsible participant.
We have come a long way since the early days of Jacques Cousteau pitting himself against the monsters of the sea. The survival of the sharks that cruise today's oceans hangs in the balance. There is no excuse for harming any shark or even interrupting important behaviours such as mating or birthing. If you feel that a shark diving situation may require the use of a power head or other weapon for protection then the dive should not take place.
It is also important to protect the fragile environment that sharks and rays inhabit. "Getting the shot" is secondary to protecting the reef regardless of what the subject is. Always practice good buoyancy skills and if the situation calls for you to crouch inconspicuously on the sea floor find a barren spot that will not damage any corals or other marine creatures. That group of orange sponges may make for a better photo location but not at the expense of the surrounding corals.
If baiting sharks in to an area is enough to create a worthwhile experience, then actual feeding is not necessary. The consensus is that it is far more harmful and behaviour changing to actually feed sharks that to just lure them into the area.
Try to avoid creating a repetitive feeding area where resident sharks wait for a handout. Whilst this may be a convenient way to re-attract sharks it provides an easy target for unscrupulous shark fishers.
Diving with sharks can be a fun and highly rewarding activity but this becomes hollow and selfish enjoyment if you in any way harm the animals that you have come to see.
SHARK EVOLUTION
MISCONCEPTIONS AND INTERPRETATIONS
Source: http://elasmodiver.com/elasmobranch_evolution.htm
There are many misconceptions regarding the evolution of sharks and rays. Contrary to popular belief they have not remained unchanged for 300 million years. However, many of the families we have today have been in existence for perhaps the last 150 million years. Compared to our own paltry 3.5 million years this makes the elasmobranch lineage very ancient indeed. The fossil record is sketchy at best when it comes to sharks. Cartilage is preserved very poorly so the body structures of many early sharks are purely speculative. Fortunately for the paleontologists, sharks discard their teeth on a regular basis and these teeth which fossilize well are often enough to allow accurate identification of individual groups and help place them correctly in the evolutionary time line. One of the pitfalls of using fossilized teeth for identification is that the teeth of sharks sometimes vary significantly depending on which area of the jaw they have come from. In the past this has led to paleontologists inventing multiple species of extinct sharks that were actually the same animal. During a shark's lifetime it's dentition also may change which only adds to the confusion. In recent years there has been a revision of extinct species that paid more attention to the herero-dental nature of modern species, and consequently the list of extinct species has been paired down.
A WORLD BEFORE FISH...
How life first came about on earth is a burning question that many scientists and theologists have dedicated their entire careers to solving. Be it by chance or divine intervention, it is likely that super heated compounds developed a complexity at which point they were able to grow by absorbing the chemicals around them. Complex compounds are a far cry from even the most basic fishes but at some point (around 3.5 billion years ago) simple organisms started evolving. These most ancient forms of life on earth were called stromatolites and they may still be seen today. Stromatolites are simple organisms that cluster together and form mounds not unlike coral reefs but with a far less complex structure.
1.4 billion years later the first cells with a nucleus were ooching around looking for a way to take advantage of both the chemicals in their environment and each other. As is the nature of evolution, a radiation took place after this point that enabled these basic creatures to fill every niche that was available to them. By about 600 million years ago, multi-cellular organisms such as jellyfish, worms, sea-pens, and more obscure soft bodied invertebrates had taken over the ocean deserts.
540 million years ago near the beginning of the Phanerozoic Eon (which last to this day and is split into the Cambrian, Palaeozoic, Mesozoic, and Cenozoic Periods) Most of the modern groups of animals were developing. This era heralded the development of shelled creatures which have been preserved very well in the fossil record.
There is some conjecture regarding how primitive fishes managed to develop from these invertebrates. Most likely, fishes evolved from the larval forms of their predecessors. Most invertebrates release eggs and sperm which after combining, develop into free swimming, fish-like larvae. These larvae drift within the planktonic soup until they reach a point of metamorphosis. In many groups such as corals and tunicates this metamorphosis is highly dramatic, involving a complete restructuring of the body to adapt to a sessile lifestyle. However, if the planktonic environment were rich enough it would be prudent for some larvae to remain as free swimming organisms permanently. Which group of invertebrates are responsible for spawning the first fishes is not known but it is possible that it may have been the echinoderms (seastars and sea cucumbers) as they share an early cell developmental process with vertebrates. Some scientists believe that sea squirts are responsible. Recent fossil evidence also points to a now extinct animal called a conodont that was characteristically fish-like and may have been the true predecessor.
THE AGNATHA
Around 500 to 450 million years ago the first primitive fishes appeared in the fossil record. They were the Agnathans and they were characterized by two (dorsal and ventral) bony shields on the head with many trunk scales tapering towards a primitive caudal fin in which the notocord turned upwards rather like the sharks of today. Agnathans were very successful and diversified to dominate every niche available until well into the Devonian period towards the late Paleozoic. The various groups developed many of the characteristics associated with vertebrates today including: paired limbs, cellular bone, a complex sensory line system, dentine, and complex eyes and inner ears. Sadly these pioneers of all that represents our ancenstry, mostly vanished during the Devonian extinctions. Today the two remaining groups of agnatha are represented by the Hagfishes and Lampreys. They are jawless, limbless, and have cartilaginous skeletons.
THE RISE OF JAWED FISHES
At some point during the Ordovician Period also known as the early Paleozoic, the major groups separated themselves from eachother.
Between about 400 and 350 million years ago the seas were beginning to fill. The major groups were:
Osteichthyes - the bony fishes which eventually outnumbered all other vertebrates by species.
Crossopterygii - which split to form the Porolepiformes which evolved into salamanders and the Osteolepiformes which eventually evolved into frogs and toads, reptiles, birds, and mammals.
Dipnoans - the lungfishes
Acanthodians - also called the spiny sharks - Superficially shark like with strong broad spines strengthening all of their fins except the caudal fin which was upturned (heterocercal) as in the true sharks. Their bodies were covered with small flat bony scales. The Acanthodians survived into the early permian about 200 million years ago.
Placoderms - a large group of fishes covered with big bony plates and blade like jaws that proliferated during the Devonian and then died out at the beginning of the carboniferous period.
Chondrichthyes - the cartilaginous fishes that evolved into today's sharks, skates, rays, and chimaeras.
THE FIRST SHARK - Cladoselache
Although Chondrichthyes are rooted in the Ordovician period the first, well preserved early shark fossil to be discovered was Cladoselache dating from approximately 350 million years ago. The fossil of this shark was found miraculously intact in the Cleveland Shale of Lake Erie. It was so well preserved that its muscle fibers were visible as were its kidneys. Cladoselache Had two low dorsal fins both with prominent spines, broad based pectoral fins and eyes set far forward on the head. The mouth was at the front of the head as opposed to the under slung mouths of modern sharks, and the teeth had a large central pointed cusp with a smaller point on each side. Although cladoselache was almost certainly not the first ever true elasmobranch, armed with Cladoselache, Paleontologists were able to categorically state that elasmobranchs had arrived.
TWO VISIBLE SUBCLASSES
At the end of the Devonian another group of cartilaginous fish became evident. These fish known as Chimaeras or Ghost sharks had distinct mobility differences in their skeletal structure. The upper jaw was fused to the skull, the pectoral fins were large and able to flap unlike the rigid fins of sharks and their bodies tapered to a thin whip like tail. Due to the great distance between the chimaeras and the modern elasmobranchs, extant chimaeras are considered in the separate subclass Holocephali and presently consist of three families.
AN EXPLOSION OF FORMS
During the evolution of chrondrichthyes there have been many groups with bizarre appearances. Sometimes these families are collectively referred to as "paraselachians" . Many fossil skeletons contain unusual appendages. Most of which have as yet not been conclusively explained.
Some examples of these paraselachians include:
Stethacanthus - a Cladodont which lived through the Silurian Period between 380 and 300 million years ago. It had a modified first dorsal fin that terminated in a spine covered pad reminiscent of an inverted scrubbing brush. Its forehead also had a similar surface. These surfaces may have been used for pinning prey or for mating.
Helicoprion - from the Permian Period, had a conveyor belt of teeth that spiraled out of its lower jaw and a thin corresponding line of sharp teeth in the upper jaw. The lower whorl of teeth rotated out of the jaw as the shark grew. Unlike most sharks it retained the smaller previous teeth which rotated back into the jaw forming a spiral or whorl not unlike the growth pattern of a shell. The two dermal surfaces sliced against each other giving it a formidable shearing weapon.
Falcatus - from the carboniferous period had a curving, forward facing appendage in place of its first dorsal fin. It has been suggested that only the male may have had this sword like structure.
Xenacanthus - a member of the pleurocanthids. It had a long backward facing spike extending from the back of its skull and an eel like or ribbon like fin running down the length of its back.
Iniopteryx - Iniopterygians lived from the Devonian into the Carboniferous period. More closely related to modern day chimaeras, they had flexible pectoral fins which were disproportionately long and rayed for strength. It is unclear whether these "wings" were used to glide above the water or to paddle under it. The leading edge of the wings were covered with sharp toothy denticles.
Most of these evolutionary experiments were probably adaptations to the demands of life in an ever more competitive environment. During the Carboniferous Period the ranks of the sharks swelled to their greatest diversity ever but towards the beginning of the Permian Period many ancient forms became extinct along with the majority of the more experimental forms.
ENTER THE NEOSELACHIANS
As the Permian Period was drawing to a close the seas were filling with Actinopterygians - the ray finned fishes. This was a food source that could not be ignored by the oceans predators. In response the elasmobranchs began to radiate again and during the early Triassic a shark appeared in the fossil record that was similar enough in appearance to modern day sharks to be considered one of the first of the "modern sharks". The name of this shark was Palaeospinax.
Palaeospinax was morphologically similar to the dogfish of the family squalidae. It had a calcified sectioned vertebral column instead of a continuous notochord, its two dorsal fins had supportive leading edge spines, and most notably it had the under slung mouth of a modern shark.
NEOSELACHIAN RADIATION
Amongst the first of the presently extant sharks to swim in the seas were the slow swimming Horn sharks and the Cow sharks but towards the mid cretaceous the fair to be had in the mid oceans was enough to push the development of fast moving predators that could pick off large, schooling, off shore fishes. At the time the seas were ruled by enormous icthyosaurs and plesiosaurs so this new food source did not come without risk to the sharks.
During the Cretaceous most of the present genera were firmly established and then around 60 million years ago at the end of the Cretaceous a catastrophe occurred which wiped out the dinosaurs and many other species, leaving the remaining sharks as the supreme rulers of the oceans.
CARCHARODON MEGALODON
About 50 million years ago a super predator evolved, the size of which the world had not previously seen. Megalodon was similar in shape and dentition to the White shark (Carcharodon carcharias) the most notorious shark of today's temperate oceans. Its size however was spectacular. The largest of its fossilized teeth that have been found to date have measured over six inches long from point to base. Extrapolating this information and using Carcharodon carcharias as a guide, it would not be unreasonable to assume that Megalodon reached somewhere between 50 to 100 feet in length. Sadly but perhaps just as well for us, no Megalodon have been seen for some time. Estimates on the time of its extinction vary widely. Some popular literature would like us to believe that Megalodon is still down there somewhere lurking in the shadows. More likely Megalodon faded away some time within the last 30 million years due to a combination of a waning food supply and a changing climate.
RAY RADIATION
Meanwhile, back at the end of the Triassic, at about the same time as Palaeospinax was swimming around the coastline of the super continent Pangaea, another group of sharks were adapting well to the bottom terrain of the shallow slopes. By the upper Jurassic Period the first guitarfishes were grubbing around for food and blending into the bottom sediments. These rays were a little more primitive than those of today. The main differences being a more shark like skeletal structure and the presence of fin spines. It has been suggested that all modern rays were derived from primitive guitarfishes but it is unclear exactly where the families are linked. The most recent addition to the batoid tree are the stingrays which showed up a mere 60 million years ago yet fill the shallows of most tropical and temperate continental waters.
Source: http://elasmodiver.com/elasmobranch_evolution.htm
There are many misconceptions regarding the evolution of sharks and rays. Contrary to popular belief they have not remained unchanged for 300 million years. However, many of the families we have today have been in existence for perhaps the last 150 million years. Compared to our own paltry 3.5 million years this makes the elasmobranch lineage very ancient indeed. The fossil record is sketchy at best when it comes to sharks. Cartilage is preserved very poorly so the body structures of many early sharks are purely speculative. Fortunately for the paleontologists, sharks discard their teeth on a regular basis and these teeth which fossilize well are often enough to allow accurate identification of individual groups and help place them correctly in the evolutionary time line. One of the pitfalls of using fossilized teeth for identification is that the teeth of sharks sometimes vary significantly depending on which area of the jaw they have come from. In the past this has led to paleontologists inventing multiple species of extinct sharks that were actually the same animal. During a shark's lifetime it's dentition also may change which only adds to the confusion. In recent years there has been a revision of extinct species that paid more attention to the herero-dental nature of modern species, and consequently the list of extinct species has been paired down.
A WORLD BEFORE FISH...
How life first came about on earth is a burning question that many scientists and theologists have dedicated their entire careers to solving. Be it by chance or divine intervention, it is likely that super heated compounds developed a complexity at which point they were able to grow by absorbing the chemicals around them. Complex compounds are a far cry from even the most basic fishes but at some point (around 3.5 billion years ago) simple organisms started evolving. These most ancient forms of life on earth were called stromatolites and they may still be seen today. Stromatolites are simple organisms that cluster together and form mounds not unlike coral reefs but with a far less complex structure.
1.4 billion years later the first cells with a nucleus were ooching around looking for a way to take advantage of both the chemicals in their environment and each other. As is the nature of evolution, a radiation took place after this point that enabled these basic creatures to fill every niche that was available to them. By about 600 million years ago, multi-cellular organisms such as jellyfish, worms, sea-pens, and more obscure soft bodied invertebrates had taken over the ocean deserts.
540 million years ago near the beginning of the Phanerozoic Eon (which last to this day and is split into the Cambrian, Palaeozoic, Mesozoic, and Cenozoic Periods) Most of the modern groups of animals were developing. This era heralded the development of shelled creatures which have been preserved very well in the fossil record.
There is some conjecture regarding how primitive fishes managed to develop from these invertebrates. Most likely, fishes evolved from the larval forms of their predecessors. Most invertebrates release eggs and sperm which after combining, develop into free swimming, fish-like larvae. These larvae drift within the planktonic soup until they reach a point of metamorphosis. In many groups such as corals and tunicates this metamorphosis is highly dramatic, involving a complete restructuring of the body to adapt to a sessile lifestyle. However, if the planktonic environment were rich enough it would be prudent for some larvae to remain as free swimming organisms permanently. Which group of invertebrates are responsible for spawning the first fishes is not known but it is possible that it may have been the echinoderms (seastars and sea cucumbers) as they share an early cell developmental process with vertebrates. Some scientists believe that sea squirts are responsible. Recent fossil evidence also points to a now extinct animal called a conodont that was characteristically fish-like and may have been the true predecessor.
THE AGNATHA
Around 500 to 450 million years ago the first primitive fishes appeared in the fossil record. They were the Agnathans and they were characterized by two (dorsal and ventral) bony shields on the head with many trunk scales tapering towards a primitive caudal fin in which the notocord turned upwards rather like the sharks of today. Agnathans were very successful and diversified to dominate every niche available until well into the Devonian period towards the late Paleozoic. The various groups developed many of the characteristics associated with vertebrates today including: paired limbs, cellular bone, a complex sensory line system, dentine, and complex eyes and inner ears. Sadly these pioneers of all that represents our ancenstry, mostly vanished during the Devonian extinctions. Today the two remaining groups of agnatha are represented by the Hagfishes and Lampreys. They are jawless, limbless, and have cartilaginous skeletons.
THE RISE OF JAWED FISHES
At some point during the Ordovician Period also known as the early Paleozoic, the major groups separated themselves from eachother.
Between about 400 and 350 million years ago the seas were beginning to fill. The major groups were:
Osteichthyes - the bony fishes which eventually outnumbered all other vertebrates by species.
Crossopterygii - which split to form the Porolepiformes which evolved into salamanders and the Osteolepiformes which eventually evolved into frogs and toads, reptiles, birds, and mammals.
Dipnoans - the lungfishes
Acanthodians - also called the spiny sharks - Superficially shark like with strong broad spines strengthening all of their fins except the caudal fin which was upturned (heterocercal) as in the true sharks. Their bodies were covered with small flat bony scales. The Acanthodians survived into the early permian about 200 million years ago.
Placoderms - a large group of fishes covered with big bony plates and blade like jaws that proliferated during the Devonian and then died out at the beginning of the carboniferous period.
Chondrichthyes - the cartilaginous fishes that evolved into today's sharks, skates, rays, and chimaeras.
THE FIRST SHARK - Cladoselache
Although Chondrichthyes are rooted in the Ordovician period the first, well preserved early shark fossil to be discovered was Cladoselache dating from approximately 350 million years ago. The fossil of this shark was found miraculously intact in the Cleveland Shale of Lake Erie. It was so well preserved that its muscle fibers were visible as were its kidneys. Cladoselache Had two low dorsal fins both with prominent spines, broad based pectoral fins and eyes set far forward on the head. The mouth was at the front of the head as opposed to the under slung mouths of modern sharks, and the teeth had a large central pointed cusp with a smaller point on each side. Although cladoselache was almost certainly not the first ever true elasmobranch, armed with Cladoselache, Paleontologists were able to categorically state that elasmobranchs had arrived.
TWO VISIBLE SUBCLASSES
At the end of the Devonian another group of cartilaginous fish became evident. These fish known as Chimaeras or Ghost sharks had distinct mobility differences in their skeletal structure. The upper jaw was fused to the skull, the pectoral fins were large and able to flap unlike the rigid fins of sharks and their bodies tapered to a thin whip like tail. Due to the great distance between the chimaeras and the modern elasmobranchs, extant chimaeras are considered in the separate subclass Holocephali and presently consist of three families.
AN EXPLOSION OF FORMS
During the evolution of chrondrichthyes there have been many groups with bizarre appearances. Sometimes these families are collectively referred to as "paraselachians" . Many fossil skeletons contain unusual appendages. Most of which have as yet not been conclusively explained.
Some examples of these paraselachians include:
Stethacanthus - a Cladodont which lived through the Silurian Period between 380 and 300 million years ago. It had a modified first dorsal fin that terminated in a spine covered pad reminiscent of an inverted scrubbing brush. Its forehead also had a similar surface. These surfaces may have been used for pinning prey or for mating.
Helicoprion - from the Permian Period, had a conveyor belt of teeth that spiraled out of its lower jaw and a thin corresponding line of sharp teeth in the upper jaw. The lower whorl of teeth rotated out of the jaw as the shark grew. Unlike most sharks it retained the smaller previous teeth which rotated back into the jaw forming a spiral or whorl not unlike the growth pattern of a shell. The two dermal surfaces sliced against each other giving it a formidable shearing weapon.
Falcatus - from the carboniferous period had a curving, forward facing appendage in place of its first dorsal fin. It has been suggested that only the male may have had this sword like structure.
Xenacanthus - a member of the pleurocanthids. It had a long backward facing spike extending from the back of its skull and an eel like or ribbon like fin running down the length of its back.
Iniopteryx - Iniopterygians lived from the Devonian into the Carboniferous period. More closely related to modern day chimaeras, they had flexible pectoral fins which were disproportionately long and rayed for strength. It is unclear whether these "wings" were used to glide above the water or to paddle under it. The leading edge of the wings were covered with sharp toothy denticles.
Most of these evolutionary experiments were probably adaptations to the demands of life in an ever more competitive environment. During the Carboniferous Period the ranks of the sharks swelled to their greatest diversity ever but towards the beginning of the Permian Period many ancient forms became extinct along with the majority of the more experimental forms.
ENTER THE NEOSELACHIANS
As the Permian Period was drawing to a close the seas were filling with Actinopterygians - the ray finned fishes. This was a food source that could not be ignored by the oceans predators. In response the elasmobranchs began to radiate again and during the early Triassic a shark appeared in the fossil record that was similar enough in appearance to modern day sharks to be considered one of the first of the "modern sharks". The name of this shark was Palaeospinax.
Palaeospinax was morphologically similar to the dogfish of the family squalidae. It had a calcified sectioned vertebral column instead of a continuous notochord, its two dorsal fins had supportive leading edge spines, and most notably it had the under slung mouth of a modern shark.
NEOSELACHIAN RADIATION
Amongst the first of the presently extant sharks to swim in the seas were the slow swimming Horn sharks and the Cow sharks but towards the mid cretaceous the fair to be had in the mid oceans was enough to push the development of fast moving predators that could pick off large, schooling, off shore fishes. At the time the seas were ruled by enormous icthyosaurs and plesiosaurs so this new food source did not come without risk to the sharks.
During the Cretaceous most of the present genera were firmly established and then around 60 million years ago at the end of the Cretaceous a catastrophe occurred which wiped out the dinosaurs and many other species, leaving the remaining sharks as the supreme rulers of the oceans.
CARCHARODON MEGALODON
About 50 million years ago a super predator evolved, the size of which the world had not previously seen. Megalodon was similar in shape and dentition to the White shark (Carcharodon carcharias) the most notorious shark of today's temperate oceans. Its size however was spectacular. The largest of its fossilized teeth that have been found to date have measured over six inches long from point to base. Extrapolating this information and using Carcharodon carcharias as a guide, it would not be unreasonable to assume that Megalodon reached somewhere between 50 to 100 feet in length. Sadly but perhaps just as well for us, no Megalodon have been seen for some time. Estimates on the time of its extinction vary widely. Some popular literature would like us to believe that Megalodon is still down there somewhere lurking in the shadows. More likely Megalodon faded away some time within the last 30 million years due to a combination of a waning food supply and a changing climate.
RAY RADIATION
Meanwhile, back at the end of the Triassic, at about the same time as Palaeospinax was swimming around the coastline of the super continent Pangaea, another group of sharks were adapting well to the bottom terrain of the shallow slopes. By the upper Jurassic Period the first guitarfishes were grubbing around for food and blending into the bottom sediments. These rays were a little more primitive than those of today. The main differences being a more shark like skeletal structure and the presence of fin spines. It has been suggested that all modern rays were derived from primitive guitarfishes but it is unclear exactly where the families are linked. The most recent addition to the batoid tree are the stingrays which showed up a mere 60 million years ago yet fill the shallows of most tropical and temperate continental waters.
Whale Watching in Peninsula Valdés, Argentina
Whale Watching in Peninsula Valdés, Argentina - A Personal Experience
by Genevieve Johnson
Everybody remembers seeing their first whale, and most people experience their first close encounter on a whale watch trip. For me, it was a magnificent blue whale off Monterey Bay, California. But watching whales in Patagonia is a whale watching experience like no other, watching whales here, is truly a close encounter!.
Southern right whales in Peninsula Valdés are perhaps the best-known wild cetaceans on earth. I made my first acquaintance with these right whales last year, and felt compelled to return to see them again.
The whale watching industry has boomed in the last two decades, and is the best way there is to get people excited about whales, and in turn, excited about the oceans. Getting up close and personal with one of the biggest animals ever to live on the planet is a humbling experience. One is simply not prepared for anything to be that large.
I joined about 60 other whale watchers on a large catamaran. I participate in whale and dolphin watches all over the world, but nothing compares to Patagonia. You really don't even have to go on a boat to whale watch, they really are that close to shore, just look at the photo!
We are on the water for less than two minutes, and less than a kilometer from shore before we are with a mother and calf pair. Four other boats are near by, but there is no need to share our whales, there are plenty to go around. I do a quick blow count and there is at least 8 whales within the immediate vicinity. This is not an exceptional day, this happens everyday between June and December in Gulfo Nuevo, Peninsula Valdés.
As I stand mesmerized at the hand rail, its almost unfathomable that these animals come anywhere near us after the near annihilation of their species, by our own. I take a moment, reluctantly turning from the whales, but I am almost equally intrigued by the looks on the faces of the tourists. I sit for a moment, watching people, watching whales. No spectacle on earth that I know of, can cause the same expression on every single face in a crowd, sheer awe!
The potential for power is belied by the ponderous grace of the 50-ton bulk of the right whale, which actually appears to move in slow motion. Suddenly a whale explodes through the surface off our bow, even when breaching these whales give the appearance of moving slower than they ought too. Propelling a 50-foot, 50-ton body is a feat requiring phenomenal amounts of strength and speed.
I befriend a British couple as a right whale mother rests her giant head not less than 2 feet from the starboard beam of the boat. She has maintained this position for fully 10 minutes as her calf swims boisterously around the boat, she appears as content as her baby is playful - the crowd is mesmerized, and so am I. The British couple tell me they have never seen a whale before and know nothing about them. They were traveling through Argentina and a friend told them the whales were a 'must see.' With nothing better to do today, they decided to give it a go. They have filled the two memory cards for digital camera. As I stand beside them, they cannot stop smiling, yet can't quite bring themselves to speak coherently. This is the effect whales have on people, This is the power of whales, and this is the value of whale watching! And with more countries starting whale watching tourism, and more people watching whales, the desire to protect them and their habitat is growing.
There is some criticism of whale watching, but if well regulated, which most are now, there is no problem. Simply do a little research before choosing an operator.
So if you want on help the whales and the oceans, go out on a whale watch, learn more about whales. A percentage of your money goes back into the local community, and often conservation efforts. Seeing a whale will change you forever, ask anyone who has been whale watching, and then try it for yourself. Who said you can't have the time of your life and help the environment at the same time!
Source of articles: http://www.earthocean.tv/series/whale_watching.html
http://www.earthocean.tv/ VISIT THE SPONSERS SITE FOR INFO~
by Genevieve Johnson
Everybody remembers seeing their first whale, and most people experience their first close encounter on a whale watch trip. For me, it was a magnificent blue whale off Monterey Bay, California. But watching whales in Patagonia is a whale watching experience like no other, watching whales here, is truly a close encounter!.
Southern right whales in Peninsula Valdés are perhaps the best-known wild cetaceans on earth. I made my first acquaintance with these right whales last year, and felt compelled to return to see them again.
The whale watching industry has boomed in the last two decades, and is the best way there is to get people excited about whales, and in turn, excited about the oceans. Getting up close and personal with one of the biggest animals ever to live on the planet is a humbling experience. One is simply not prepared for anything to be that large.
I joined about 60 other whale watchers on a large catamaran. I participate in whale and dolphin watches all over the world, but nothing compares to Patagonia. You really don't even have to go on a boat to whale watch, they really are that close to shore, just look at the photo!
We are on the water for less than two minutes, and less than a kilometer from shore before we are with a mother and calf pair. Four other boats are near by, but there is no need to share our whales, there are plenty to go around. I do a quick blow count and there is at least 8 whales within the immediate vicinity. This is not an exceptional day, this happens everyday between June and December in Gulfo Nuevo, Peninsula Valdés.
As I stand mesmerized at the hand rail, its almost unfathomable that these animals come anywhere near us after the near annihilation of their species, by our own. I take a moment, reluctantly turning from the whales, but I am almost equally intrigued by the looks on the faces of the tourists. I sit for a moment, watching people, watching whales. No spectacle on earth that I know of, can cause the same expression on every single face in a crowd, sheer awe!
The potential for power is belied by the ponderous grace of the 50-ton bulk of the right whale, which actually appears to move in slow motion. Suddenly a whale explodes through the surface off our bow, even when breaching these whales give the appearance of moving slower than they ought too. Propelling a 50-foot, 50-ton body is a feat requiring phenomenal amounts of strength and speed.
I befriend a British couple as a right whale mother rests her giant head not less than 2 feet from the starboard beam of the boat. She has maintained this position for fully 10 minutes as her calf swims boisterously around the boat, she appears as content as her baby is playful - the crowd is mesmerized, and so am I. The British couple tell me they have never seen a whale before and know nothing about them. They were traveling through Argentina and a friend told them the whales were a 'must see.' With nothing better to do today, they decided to give it a go. They have filled the two memory cards for digital camera. As I stand beside them, they cannot stop smiling, yet can't quite bring themselves to speak coherently. This is the effect whales have on people, This is the power of whales, and this is the value of whale watching! And with more countries starting whale watching tourism, and more people watching whales, the desire to protect them and their habitat is growing.
There is some criticism of whale watching, but if well regulated, which most are now, there is no problem. Simply do a little research before choosing an operator.
So if you want on help the whales and the oceans, go out on a whale watch, learn more about whales. A percentage of your money goes back into the local community, and often conservation efforts. Seeing a whale will change you forever, ask anyone who has been whale watching, and then try it for yourself. Who said you can't have the time of your life and help the environment at the same time!
Source of articles: http://www.earthocean.tv/series/whale_watching.html
http://www.earthocean.tv/ VISIT THE SPONSERS SITE FOR INFO~
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