Divers love seeing the big stuff; from dolphins to turtles to sharks, we adore the big charismatic wild animals that we have a chance of encountering.  For some divers, the pursuit of 'big things' resembles the ghosts of the I-Spy guides from years ago. Tick each one off, add a date and a location, and then move on to try and fill the rest of the book.  I'm not sure that the Chief I-Spy still exists to countersign your completed book, but maybe the National Diving Officer would step in?
 
Of course there are significant challenges to be overcome in order to tackle a safari trip for some of the big stuff.  Planning a trip to coincide with the seasonal arrival of whale sharks off Christmas Island presents considerable logistical hurdles, but at least their arrival is linked to the predictable phases of the moon which triggers the crab spawning and the release of the whale sharks favourite high protein snack.  Other animals can be much harder to predict. 
 
Basking sharks arrive around the Isle of Man in around April/May each year, and the data suggest they are here for around 4 to 5 months.  Our old crusty divers, who have been observing these patterns for years, will repeat the mantra that the sea temperature needed to reach 11.5 degrees before the sharks appeared.  The precision of this prediction has always bemused me. Not 11 degrees but 11.5, the sharks obviously need the extra half a degree. Of course, the factors relating to basking shark sightings are more complex than that.  There is reasonable evidence to suggest that basking sharks come to Manx waters to give birth to their young and to mate.  Similar to some other sharks, basking shark young are born live, having been carried in the mother being fed on eggs that she releases while they grow to around 1.5m.  We regularly see very small basking sharks round these waters.
 
The arrival of the basking sharks each year is timed with the spring explosion of plankton, but that isn't purely driven by water temperature.  Hours of sunshine plays a huge role in the plankton bloom, driving a rapid explosion.  So an overcast spring can delay the sharks by a few days or even weeks.  This year's extensive snow fall took weeks to defrost, and the cold melt water helped to hold temperatures down.  All of which makes predicting the basking sharks' return even more difficult.  
 
One of the other aspects we need to consider is that there just simply isn’t enough information about these creatures.  A huge volunteer effort which encourages the public to report basking shark sightings reveals some interesting data, but using that information to find sharks can lead you on a wild goose chase.  Let me explain.  80% of reported sightings are in the SW of the Isle of Man, so you might think there is something special about these waters.  Yes, there is some deep upwelling of water carrying nutrients that feed the plankton, but we know that high tidal flows mix the water around anyway, so this isn’t the full picture.  The high level of sightings is directly correlated to the height of the cliffs and proximity of the coastal path.  Get up high and look down on to the sea and you have a good chance of spotting sharks.  Lower cliff heights and remote areas are less likely to have shark sightings reported nearby.

Then there’s the matter of timing.  Sightings start in April and end around September…or do they?  We have met sharks under water in October and early November.  We couldn’t see the dorsal fins on the surface, but they were still here, lurking.  You need calm surface conditions to spot shark fins, and traditionally the winds increase in September so calm days are hard to find.  The weather deteriorates so that less people are out looking anyway…leading to a statistic that indicates the sharks have left.  Experience tells us this is wrong.

So for some animals it’s not enough just to know the phases of the moon to be able to tick them off your wish list.  You’re going to need a whole lot of information and a bit of fuzzy logic to interpret it all.  Humans are generally good at fuzzy logic, although many of us would recognise it more as an ‘instinctive feeling’ which we can’t fully justify. And so we come to the last crucial factor in spotting the big stuff, a large helping of luck.  Hope you've been lucky this summer! 

Divers are a privileged section of society.  We have been places and seen things that even the most avid watcher of TV nature documentaries will not have noticed.  I’m guessing that not many film crews have hung out in Wraysbury trying to film pike, but anyone who has dived there has usually spotted at least one, especially if you go for the ‘circumnavigation around the lake’ dive.  The cost of underwater filming and the limited number of minutes or seconds of screen time mean that what the non-diving public see of diving is massively limited. In some respects it’s the equivalent of trying to infer the whole picture in a 1000 piece jigsaw puzzle by looking at just one piece of it.  Try watching the documentaries made about the filming of wildlife programmes and you’ll end up feeling massively sympathetic to the cameraman who spent 3 months sat up a tree to get 30 seconds of edited footage. 

A few years ago we worked with the Fish Fight team led by TV chef Hugh Fearnley-Whittingstall.  Hugh has been incredibly successful in campaigning against discards, the massively wasteful practice of throwing back the fish that are over quota as, even though the fish are dead, they can’t be legally landed.  This campaign has been fought at EU level where the fisheries policies are set.  I suspect a large number of people were surprised to find out that this even happens, as like most fishing practices it is ‘out of sight’ and therefore ‘out of mind’ too.  That series of Fish Fight programmes moved the argument on a little and looks at sustainable fisheries management, which was why the team headed for the Isle of Man, although we are a small island in the middle of the Irish Sea, we punch above our weight when it comes to looking after our marine resources.

To understand how this situation has developed you will need a little oceanography, a little history and a little politics.  The Isle of Man is a Crown Dependency (a bit like the Falklands but without the threat of invasion) and we have our own laws and govern ourselves.  For political reasons we are not directly part of the EU, but are represented at that level by Westminster.  So within the EU rules we can do what we like with our territory which for the most part is 12 miles offshore.  Over a hundred years ago Liverpool University set up a field station in Port Erin to study all things marine.  The site was carefully chosen as the confluence of warm southern waters and cold northern waters means that the Isle of Man is probably one of the most biodiverse sections of the British Isles.  Port Erin Marine Lab operated until 2006 when research was relocated to Liverpool to save money. However, many of the scientists remained on the Island and took up government funded roles, set up consultancies or became involved in charities with a marine focus. The legacy of the Marine Lab continues in our fisheries management.

The closed area outside Port Erin Bay was the first area in which scallop dredging and trawling was banned and within 4-5 years it was already possible to show that catches outside the area were on the increase. Nearly 30 years of closure means that the seabed looks as it should look, three dimensional, with tall seaweeds, seafans and hydroids galore.  The data from Port Erin is cited all around the world and has been globally used in the arguments for closing sea areas to damaging activities.  But that’s not all, we have restricted fishing seasons, restricted engine sizes, minimum landing sizes based on the reproductive ages of the scallops, a further four closed areas and active fisheries protection officers.  Hugh Fearnley-Whittingstall wanted to see all of this in action and ask why a small island of 80,000 people could still have a sustainable scallop industry when areas in England and Scotland had been fished to extinction. 
 

Summer is a busy time for any dive centre, and it’s almost with a sigh of relief that we watch autumn unfold so that things will quieten down a bit.  However, some summers are unremittingly autumnal as a misplaced jet stream can bring repeated low pressure systems rolling across the British Isles causing havoc and mayhem.  Many of our summer dive plans changed at the last minute as gale force winds and torrential rain made sea conditions treacherous and reduced visibility even in the sheltered bays. 
When I lived in west London, all my diving trips necessitated organising towing vehicles, booking accommodation and stupidly early starts.  I just don’t want to see 5am on a Saturday morning unless I have partied through the night to get there – and I suspect those days are behind me now.  Back then my dive trips were organised with almost military precision and planned weeks in advance.  Things are a little different now. 
When I first arrived on the Isle of Man two things struck me; firstly, how everything I’d been taught about dive planning, tidal flows and tides was completely trumped by local knowledge and secondly, how dives could be organised at 5 o’clock in the afternoon with the minimum of fuss and we’d all be in the water for 6.30.  My gung-ho “It’s not too rough really. I’ve planned to go diving so we are” attitude didn’t cut it here.  If you live with such fantastic diving on the doorstep, why have a slightly rough dive?  Wait 24 hours, let the wind drop away and have a really good dive instead.
The Isle of Man is close enough to the North West coast of England to be visible on a good day.  In fact it’s a local story that you can go to the top of Snaefell (our one and only mountain) and see 7 kingdoms in one go.  I’ll leave you guessing to name them all, but the location of the Isle of Man at the geographic centre of the British Isles means that every summer we have clubs setting out in their RIBs to travel across to dive in our waters.  And we offer visitors copious amounts of help to locate sites, plan around tides, transport cylinders, locate parts for their broken boats etc.  One of the visitors this year declared himself both very grateful and surprised that we should help him out so comprehensively and mentioned that other dive centres in the UK had been less than helpful.  Although, it’s true that we are pretty nice folks who want the best for our visitors, there are darker reasons at work. 
The Isle of Man is a limited community of around 80,000 and pretty much any diving story will end up with some link to our centre, whether it’s commenting about closing areas to dredging, helping out a fishing boat towed into harbour with their own nets around their prop or getting involved with videoing the local swimming club in training.  All diving links lead in our direction…..so it’s in our own selfish interests that we help out our visitors.  A lifeboat shout for lost divers swept away on an unexpected current or the hyperbaric chamber being mobilised for a recompression all reflects on us.  Some timely advice and guidance keeps the visitors out of the incident pit for a bit longer and keeps diving out of the news until we have a good news story to impart.
Of course, managing the exposure of diving in the local press plays a role in how we manage our diving activities too.  It’s been suggested that there are only 6 degrees of separation between any two people in the world, but on the Isle of Man that’s around 2 degrees.  Word of mouth is incredibly important.  We have to be safe and be seen to be safe, or our reputation would disappear overnight.  Doing my Advanced Driving test a few years back introduced me to the idea that ‘accidents don’t just happen’.  The same applies to diving, accidents are a culmination of a series of steps.  The advice that we freely give to visitors is the first point we can intervene to stop that series of events unfolding.  If you’re planning a trip across please feel free to get in touch.  If you run a dive centre that begrudgingly hands out dive planning information please have a think about how this reflects on the industry as a whole.  I promise you that it won’t undermine your charter service….the clubs that brought their own boats this year are booked to come and dive off our boat next year…..and looking forward to a less stressful trip. 
And in case you are wondering on a clear day you can see the kingdoms of Mann, England, Scotland, Ireland, Wales, Mann, Heaven and Neptune.

Sea hares (Aplysia punctata) are a common find on dives around the south, west and northern British Isle. They are usually around 7cm long but can grow up to 20cm in length. The colour of Sea hares varies from olive, brown, red and purplish black depending on the algal diet. At the head end, two slender rhinophores stand up like the ears of a hare, hence their common name.
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At first sight, Sea hares would appear to be an easy target as a meal, there’s no shell, no spines like an urchin, no claws and they move at a fairly slow pace. Sea hares have a mucous coating containing acid and other nasty compounds which might deter some predators, but their party piece is to release a cloud of sticky, purple ink when attacked by hungry predators.

The cloud of purple ink is in fact a mixture of two secretions. On the back of the Sea hare the central structure is called the mantle with an opening called the foramen. Just under the surface there’s the last remnants of what was probably a shell in the Sea hare’s evolutionary history, a protein disc which acts as an internal shell. On the roof of the mantle is the Purple Gland above the gills. The Purple Gland is responsible for storing and secreting the ink. The building blocks for noxious chemicals are obtained from their algal food, particularly from red algae, metabolised and stored here. This strategy is quite common in marine gastropods and a number of these substances are being actively tested for pain killing, antibacterial, antiviral and anticancer activity. It’s powerful stuff.

Beneath the gill on the floor of the mantle cavity is the Opaline Gland. This gland secretes a white liquid that becomes viscous upon contact with water. If you’ve ever seen the videos of Hagfish (Myxini sp.) producing copious volumes of slime as a way of evading predators, then you will already have seen opaline in action.

The ink and the opaline are secreted into the cavity in the mantle where they mix and are expelled towards the predator. The ink has an intriguing role in that it has been shown to be a phagomimetic decoy (phago = eat, mimetic = to mimic). Some species of lobster will drop the sea hare and try to manipulate and eat the ink cloud, thinking that it is food. Whilst testing this idea scientists found another ink effect. The lobsters tried to rub the ink off their antennules. The opaline in the ink blocks the receptors and response to food odours, thereby preventing the predator from recognising that Sea hares are food. It’s the lobster equivalent of a stuffy nose. Whilst the lobster is busy removing the sticky ink, the Sea hare can make its escape. So, in this aspect the ink is rather more than just a cloud to hide the escape of the Sea hare, it is an active cloud which has the effect of blinding the predator.

It can take quite a bit of stimulation to persuade a Sea hare to produce ink. The threshold depends on factors such as the environment (living in a turbulent environment makes inking less likely), how full the gland is and what the stimulus is (inking occurs more rapidly near anemone tentacles that it does in response to an electric shock). If a Sea hare has full ink glands then it will release nearly half of its ink at the first stimulation. Each subsequent stimulation will release 30-50% of the contents. It will take at least 2 days to replenish the gland.

Whilst aquarium owners like the grazing tendencies of Sea hares, they panic about the effect that any inking has on the fish and other residents inside their tank. The jury is out on how much effect the Sea hare ink can have. Sea anemones retract their tentacles, but the evidence for the toxic effect of the ink inside an aquarium is limited, perhaps because the Sea hares aren’t feeding on red algae that are the source of the most potent toxins.
 
 

​It’s a popular misconception that lobsters are red in colour. That’s because most people have never seen a live lobster, and what gets served up in their lobster thermidor is distinctly red in colour. It’s one of my pet hates when media shows lobsters as red, right up their with the reporter talking about the oxygen tanks worn by the scuba divers. Grrr! As divers we are well positioned to know that lobsters are a dark shade of blue-green, but it’s not just the shell that’s blue, so is the lobster’s blood.

Technically the lobster doesn’t have blood in the way that we would understand it. They have haemolymph, a fluid equivalent to blood that circulates inside arthrpods. Haemolymph is mostly watery with some salts and nutrients dissolved in. There are some cells known as haemocytes, but in arthropods these play a role in the immune system of the organism. There aren’t any red blood cells containing haemoglobin to carry oxygen like we have. Instead invertebrates have some special proteins in their haemolymph called haemocyanins that transport oxygen for them.

Haemocyanins are metalloproteins that have two copper atoms which can reversibly bind to a single oxygen molecule. Oxygenation causes a colour change from the colourless deoxygenated form to the blue oxygenated form. Haemocyanins are only found in molluscs and arthropods but aren’t limited to marine animals and can be found in tarantulas, scorpions and centipedes too. Haemocyanins turn out to be rather more efficient than haemoglobin at binding to oxygen in cold environments and when the oxygen pressure is low. Sounds ideal for the average marine crustacean.

Lobster haemolymph has been shown to have antiviral properties, but only in the uncooked state. In research it was shown to be effective against the viruses that cause shingles and warts. In fact, there is an American based company that has developed a blood-based cream for treating cold sores and skin lesions, although it’s yet to get approval from the regulatory authorities.

So, we’ve established that copper coloured proteins give lobsters their blue blood, but that’s not the explanation for the shell changing colour when the lobster is cooked. For this we have to look at another protein called crustacyanin, and its best buddy astaxanthin. Astaxanthin is a carotenoid pigment so it absorbs blue light and gives off red/orange colour. Astaxanthins are mostly synthesised by microalgae and enters the marine food chain. In shellfish the astaxanthin becomes concentrated in the shell. Its likely that astaxanthins have a string antioxidant and anti-inflammatory effect and may protect against age-related degeneration. Astaxanthins are also found in some sponges, starfish and in species of octopush and cuttlefish. They give the muscle tissue of the salmon its characteristic colour.

Crustacyanin is a very interesting chromoprotein, that changes colour depending on whether it is in water or dehydrated. When it’s bound to the lipid like astaxanthin it has a distinctly blue colour. While a lobster is alive, crustacyanin stays bound tightly to astaxanthin, so tightly that the astanxanthin’s light-absorption properties are quashed and the complex appears to be blue-green in colour. That all stops when the lobster hits the boiling water.
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Crustacyanin is not heat stable, so the boiling temperatures cause it to unravel and lose its grip on astaxanthin. The true colours of the astaxanthin then shine through in the red lobster shell. In fact, they were there all the time, you just couldn’t see them. It’s the same mechanisms for cooking shrimp too. Flamingos rather cleverly digest the crustacyanin protein to release the astaxanthins that colour their feathers soft pink.

​Stefano Lorenzini was an Italian physician born in Florence in 1652. One of his teachers at the medical school in Pisa was Francesco Redi who as well as being a physician spent time experimenting to prove that spontaneous generation (life just appears) was a myth, mostly with maggots and flies. As part of his work Redi, like all scientists of a time without cameras, made incredibly detailed anatomical drawings. Redi inspired Lorenzini, who in 1678 published the work that he is best remembered for, an in-depth study on the anatomy and physiology of sharks. This work contained the discovery of the Ampullae of Lorenzini, the special electromagnetic sense organs found in sharks and rays. But although Lorenzini described and drew the Ampullae, it would take nearly 300 years before modern science could explain how sharks had an additional sensory organ not seen in most other animals.

The Ampullae of Lorenzini form a network of jelly filled canals that open in small pores through the surface of the skin which can be seen as dark spots on the skin. At the back end of the canal is a collection of receptor cells that have a unique structure and allow the shark to sense electric and magnetic fields. The gel in the canals is keratan sulfate which has one of the highest known conductivity of any known biological material (about 1.8 milliSiemens/cm). The ampullae are clustered and each cluster connects to a different part of the skin, so the shark can get detailed directional information from this network.

The cells that actually detect the electrical field have a very special structure. There is a single layer of excitable cells closely packed together. The membrane of these cells facing into the canal is packed with voltage dependent calcium channel proteins. The rest of the canal lining has a very high resistance, which means that any voltage difference is effectively concentrated on the electroreceptor cells. A change in the electric field in the jelly allows these proteins to open and calcium floods into the cells. This causes the other side of the cell (away from the canal) to release neurotransmitter signalling to the shark.

Sharks have been shown to be more sensitive to electric fields than any other animal, possibly as low as 5 nanoVolts/cm – that’s 5/1,000,000,000 of a volt detected in a 1cm long ampulla. All living creatures produce an electric field by muscle contractions and as a result of the internal body chemistry. So being able to detect weak electrical stimuli probably allows sharks to hunt prey animals, including those buried in sand. Basking sharks have been observed swerving around jellyfish whilst feeding, after all the last thing you’d want clogging up your gill rakers would be lots of jellyfish and their stinging nematocysts.
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It’s likely that the Ampullae of Lorenzini also allow sharks to sense magnetic fields.  Any moving conductor will induce an electric field, so seawater moving on ocean currents, with the Earth’s magnetic field will produce electric fields well within the range that sharks can detect. Behavioural studies have shown that magnetic fields can change the behaviour of sharks. The ability to sense and orientate along magnetic field lines may help explain some of the large distance migrations that have been found using shark tagging experiments. Great white sharks have been shown to migrate over 2000 miles in open ocean to feeding grounds in the Pacific Ocean. Whale sharks have been tracked on journeys over 4800 miles. That is an astonishing figure considering that they don’t have sat nav guiding the way! So next time you’re up close and personal with any shark or ray, have a look for the black dots around their snout and remember that 340 years ago an Italian doctor and fish fanatic spotted the same thing.

​Comb jellies are a common sight around British waters, particularly the sea gooseberry (Pleurobrachia bachei). With a clear body and measuring only a couple of centimetres long, it’s easy to overlook these beautiful little animals apart from one thing, stunning rows of rainbow coloured hairs running along their body. With no skeleton and composed of 99% water, you’d be forgiven for thinking that these were very simple creatures, but actually they have some pretty neat stuff going on.

Firstly, let’s start with where the comb jellies fit in, they are not the same phylum as jellyfish. Jellyfish (Cnidaria) have complex lifecycles and stinging cells. Comb jellies (Ctenophora) have a simple life cycle and make glue to catch prey. The problem for scientists trying to study the evolution of the Ctenophores is that they don’t make very good fossils so the records are patchy at best.  Genetic studies indicate that Ctenophores are much older in origin than other animals, and predate the bilaterian animals (those with bilateral symmetry) by millions of years.

There are 2 major cell layers, the external epidermis and the internal gastrodermis. Between these layers is the mesoglea, a jelly like layer.  The Ctneophores have muscles running through them and the outer epidermis contains a basic nervous system known as the nerve net. Comb jellies are named for their unique feature, plates of giant fused cilia (small hair-like cells) which run in eight rows up and down their bodies.  These cilia are used to propel the comb jelly through the water.
Many comb jellies have a single pair of tentacles and often these tentacles are branches and give the illusion of many tentacles.  The branched tentacles are used to catch prey, but unlike the toxins from jellyfish, comb jellies use glue.  Special cells called colloblasts respond to touch by firing a spiral filament and releasing sticky glue. Once the prey is stuck the comb jelly reels in the tentacles and brings the food to its mouth. Most comb jellies are carnivorous and will eat anything. Until recently it was believed that comb jellies spat out the indigestible waste particles, but it now seems like they release them through pores in the rear end – which is probably part of the evolutionary puzzle in explaining when animals developed anuses.

What about the beautiful rainbow coloured pulses of light? Whilst some comb jellies can produce light by a special chemical reaction to give photoluminescence, our sea gooseberry can’t. The rainbow colouring is caused by refraction of light through the hair like cilia cells. Light travels at a constant speed in a vacuum, but when light encounters a material that is more dense, it slows and its pathway bends. The different wavelengths in visible light bend at slightly different angles.  This means that the cilia act like the glass prism you played with in physics classes as a schoolchild, splitting the light into separate wavelengths. The refractive index (how much the light will bend is almost the same for the comb jelly tissue as it is for the salty sea water. The hair like cilia amplify the refractive effect creating an iridescent pulse that is mesmerising to watch. The effect works across the visible and UV light wavelengths, meaning a fluorescent torch will also give a great image.
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Lastly, there’s a few things you should know about comb jelly reproduction. Comb jellies are hermaphrodites (both sexes in one individual) and can spawn eggs and sperm freely into the sea, through their mouths. They do this on a continuous basis unless they are starved of food, when they will shrink down and stop breeding. But feed them up again and they will start spawning again. Rainbow coloured hair, sticky glue fishing nets and continual reproduction – what’s not to admire?

​Normally the ferries coming to the Isle of Man run at sensible times, but there is one particular scheduled service that leaves the port of Heysham at 02.15. In the winter, when the only other crossing is 14.15, I seem to find myself on the ‘overnight’ boat far more often than I would like. The boat doesn’t load until at least 01.30, so for a couple of hours I usually try to sleep in the carpark. Cold, rainy and situated next to the nuclear power station, it’s not exactly conducive to any restful sleep. Even if I do doze off I still have that dreadful anticipation of being woken by the port staff to drive onto the car deck.
I’ve learned now to book one of the cabins on the ferry. Head to the customer services desk, collect the key and find the cabin with the beds made up ready. If I’m quick I can kick my shoes off and be asleep before the safety announcement. The journey is just under 4 hours and the arrival in the Isle of Man is accompanied by an announcement and the lights in the cabin coming on. It doesn’t feel like I’ve actually slept at all. After a short drive home, I usually try for more sleep, but it’s not always easy during the day. I usually need a good night’s sleep to recover from my acute sleep deprivation.
As divers we often travel some distance by road, ferry or plane to get to our dive destinations. Travel arrangements can involve early check-ins and sleeping in unfamiliar places. There is considerable research into the effect of sleep deprivation and its effect on behaviour, particularly for in relation to driving. Sleep deprivation has the same hazardous effect as being drunk. Research has shown that being awake for 17-19 hours impairs performance to an extent that is comparable to having a blood alcohol level over the drink driving limit for the UK. As drink-driving has now become socially unacceptable, how many of us are aware that our driving could be as impaired by lack of sleep?
I think back to my days living in London, getting up at 4am to tow the club boat to the South coast, two waves of two dives and some food followed by the drive home. The boat would be stowed away by about 10pm, so the last few hours of towing a rib would have had me well into the fatigue zone.  The evidence suggests that performance decline sets in after 16 hours awake, add this to sub-clinical decompression related post-dive tiredness and I think I was in dangerous territory.
How many times though do our trip risk assessments include fatigue? I got up at 5am this morning to collect a group coming in from the ferry. During the summer there is an 03.00 crossing from Liverpool arriving in the Isle of Man at 05.45. If I think I felt tired as I arrived at the ferry terminal – you should have seen the divers we collected! Some of them had managed a little sleep in the airline style seats, but not much. We’ve brought them back to the accommodation and sent them all to bed. We expect to be diving this afternoon, and one of the risks I’m now assessing is how much sleep they haven’t had.
I can’t find any specific research into the impact of fatigue on diving, but I am happy to accept that driving is a reasonably good surrogate activity. Drowsy drivers experience difficulty remembering the last bit of road and slower reaction times. Impaired cognitive and motor performance aren’t good for divers either. We learn about the impairment due to narcosis (with that amazing slide that has several pints of beer on!), but being awake for long periods is going to cause those effects without even stepping in the water. Maybe there are hints about this in our training, we do advise to have a good interval between flying and diving, but there’s nothing explicit regarding sleep deprivation. If you aren’t convinced that this is a problem, perhaps you should know that it’s been estimated that sleep deprivation is implicated in 1 in 5 road accidents. Sleep deprived drivers are much more likely to get angry with other road users and deal poorly with stressful situations (like navigating unfamiliar roads).
Caffeine can help, but only in the short term and not with all the aspects. It can improve alertness and reduce reaction time, but fine motor control isn’t improved even with high doses. So, I could send all the divers to the local coffee shop and insist they top up their espresso quota, but I know that won’t last. Instead, I hope they have their heads down and are napping now. Me? I’m too wide awake and writing columns instead!

​Scallops (Pecten maximus) are a national concern on the Isle of Man. We have some of the most protected scallop populations in the British Isles. Licensed boats can only fish during daylight hours in certain areas of the sea and not during the summer months when the scallops are breeding. The catch is landed into harbours around the island; creamy, pink shells in 25kg bags loaded onto pallets for the forklift truck to move them into wagons.
If you glance down into the harbour its usually possible to spot the white inside of a few discarded shells shining on the seabed below. These shells eventually wash across the bay and onto the beaches, but they don’t always arrive in the same colour as when they were discarded. Many of the shells are stained dark brown or black, colours we never see during dive surveys of scallops.
Shells are mostly made of calcium carbonate which is white in colour, mixed in with about 2% of protein. As molluscs develop they absorb minerals from their environment and secrete calcium carbonate from their mantle to create their shell. The protein makes the shell very strong, but lightweight and resistant to dissolving in water. Shells are self-repairing, and the mollusc can secrete more shell material as needed for repair or growth. Naturally occurring colour and patterns in shells is as a result of mineral ions incorporated into the shell structure. But that doesn’t explain the post-mortem colouration of the scallop shells.
Shallow burial of shells causes iron oxides to form in the tiny pits on the surface of the shell and causes brown staining. The black colour is usually due to microscopic crystals of iron sulphide. These crystals form in the absence of free oxygen which can occur if shells become buried deeper in mud or sand.
Although my local harbour is sheltered, it doesn’t provide the deep mud conditions required to blacken shells, but there is a much more common cause. Burial under just a few centimetres of seaweed rotting on the beach will provide suitable anoxic conditions for sulphide formation. Hence blackened shells on the beach is a relatively quick process occurring under mounds of kelp and wrack.
There are some mollusc species that live well buried into deeper sediment. The Ocean Quahog (Arctica islandica) is a subtidal species of clam that is renowned for it’s longevity. Some individuals have been recorded at over 500 years old. The shells of Quahogs have dark black colouration, but they have a long time to absorb the necessary pigment. Whilst the shell is buried in the sediment, a siphon to the water provides for food and oxygen to the creature below.
Naturally acquired pigment probably strengthens the shell. Colour patterns often align with spiral or axial sculpture. Instead of producing and transporting a thicker shell, it might be more energy efficient for molluscs to make pigments. Pigments impede propagation of a crack in the shell. The structural explanation also works for colour inside of shells. A good example is Mercenaria mercenaria (the quahog or cherrystone clam). The purple inside the shell, hidden when the animal is alive, lies along the edges of the shell, just where predator whelks are likely to attack. Strangely young Merceneria don’t make the purple pigment. Their shells are too thin to resist attack anyway, so they concentrate their efforts on growing a thicker shell and surviving to when their pigment strengthened shell is going to ensure a long life.
There are lots of other reasons for shells to have different colours.  A favourite project for marine science students is to send them to look for colour variation in Flat Periwinkles (Littorina obtusata). In this case pigment is used for camouflage, allowing the winkles to hide amongst the bladder wrack on the shore. Pigments may serve as a warning to possible predators, or the pigmentation pattern may provide a template for future growth of the shell. But there doesn’t have to be a reason for pigmentation in all cases. Oxygenated mammalian blood is red, not for any evolutionary reason, but because that’s the chemistry of the situation.

​Seals are collectively known as pinnipeds, which means from the Latin pinna (fin) and pes (foot). This classification includes the walruses, eared seals and true seals. The Isle of Man and the rest of the British Isles are home to resident populations of Grey seals (Halichoerus grypus) and Common seals (Phoca vitulina). Common seals (also known as Harbour Seals) are found in both the North Atlantic and North Pacific.  About 35% of the European population of common seals lives in UK waters.  By contrast Grey seals are only found in the North Atlantic, Baltic and Barents Sea.  The entire world population of Grey seals is probably no more than 400,000 individuals, with about 40% of them living in UK waters. Although we tend to take seals for granted, we should perhaps appreciate how lucky we are to have them in the waters around us and see them so often.
There’s been a long understanding that the pinnipeds evolved from land based mammals. This concept in itself is a little strange, as the general gist of evolution is that our ancient ancestors left the watery environment for a life on land. But somewhere millions of years ago, some of the mammals returned to the sea to take advantage of the feeding opportunities that existed there. Whales and dolphins have definitely taken their return to the marine environment to the extreme and evolved to the point that they can no longer safely return to the land. When they do, the amazing guys from the British Divers Marine Life Rescue swoop in and work their hardest to throw them back into the briny again.  In the pinnipeds we have a group of species who spend their time mostly in the marine environment, returning to land only when necessary. On land seals are ungainly, slow and clumsy, which made them an easy target for hunting. In the water, they are agile hunters, capable of diving to about 200 metres for up to 15 minutes.
The clues to the pinnipeds evolutionary past are clear in a number of ways. Their forelimb has five webbed fingers, with claws that are used for grooming and fighting. This five fingered (pentadactyl) limb structure is a common evolutionary feature, linking many vertebrates including reptiles, birds, mammals and amphibians. Just let that sink in for a moment.  You can see the same bone structure in pretty much every group of animals with bones. The humerus at the top, an elbow where the radius and ulna join, a wrist connecting to fingers. It’s there in the bats wing (with elongated fine boned fingers and skin stretched over them), it’s there in frogs (although the ulna and radius have partly fused), and cats and dogs and tigers and crocodiles and in us..
In seals the flipper bones that would be the equivalent of your arm are shortened, so that what appears to be their armpit is in fact their elbow (front flipper) or ankle (hind flipper). Their metatarsals (fingers) are elongated compared to ours and the skin in between gives them something akin to swimming gloves. Close interaction with a seal will reveal that they can still bend their webbed fingers to grip and hold onto objects or, if you are lucky enough, onto you as you are diving. Their flippers are well adapted to propel them through the water. When swimming quickly, the hind flippers are used in a side to side motion, and the front flippers are held against the body.  If you have watched seals turn under water, you’ll know that they stick out a front flipper to perform sudden changes of direction. Cruising speed for seals is about 2 to 3 knots, but when hunting seals can move at an astounding 20 knots (that’s probably faster than most club ribs!).
Seals are part of the Caniformia (dog like) sub order of the Carnivora group of Mammals. In fact, most divers that have had encounters with seals will tend to describe them as being like big puppies. Despite this, there have been many studies suggesting that seals are in fact more closely related to bears than they are to dogs. Perhaps the fact that we are more likely to have encountered and interacted with dogs rather than bears gives rise to our misconception? Remember that Grey seals are the largest living carnivore in Britain, can grow up to 2.3 metres and weigh over 300kg and treat these amazing creatures with the respect they deserve.  When you get to shake hands with a seal next time, count his fingers and say hello to a very distant cousin.