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Sperm whales

A sperm whale raises its tail flukes as it begins a dive. Colin Munro Photography

I turned around and saw him about one hundred rods directly ahead of us, coming down with twice his ordinary speed of around 24 knots, and it appeared with tenfold fury and vengeance in his aspect. The surf flew in all directions about him with the continual violent thrashing of his tail. His head about half out of the water, and in that way he came upon us, and again struck the ship.” So wrote Owen Chase, First Mate, in his 1821 account of the sinking of the whaling ship the Essex.

A sperm whale raises its tail flukes as it begins a dive. Colin Munro Photography

A sperm whale raises its tail flukes as it begins a dive.

The whale in question was a cachalot, or sperm whale.  Probably the best known whale; the whale in Herman Melville’s Moby Dick (which was actually based on the sinking of the Essex). The sperm whale, Physeter macrocephalus, is the largest toothed whale, and indeed the largest toothed predator that has ever lived.  Males average 16 metres in length and over 40 tonnes in weight (females are significantly smaller); some may exceed 20 metres and 50 tonnes.  They are the sole extant (living) species in the family Physeteridae, though fossils of several extinct species have been found.  Sperm whales look like no other whale; their massive head and relatively tiny lower jaw coupled with their huge size renders them unmistakable when seen underwater.  However that is not how they are commonly seen.  The best view most of us get of a sperm whale is of them resting almost motionless on the surface, between dives, with only the top of their back and their blowhole visible, followed by the rise of the tail flukes as it descends beneath the surface.

The blow hole and wrinkled skin of a sperm whale resting on the surface. Colin Munro Photography

The blow hole and wrinkled skin of a sperm whale resting on the surface

As sperm whales are air breathing mammals it is tempting to think of them as animals that live at the surface, diving occasionally to hunt.  Not so.  When feeding they will spend 8-10 minutes on the surface breathing, replenishing their oxygen supplies.  In contrast they will spend 35-50 minutes underwater searching for prey.

The low, bushy, forward-directed, blow of a sperm whale is almost unmistakable. Colin Munro Photography

The low, bushy, forward-directed, blow of a sperm whale is almost unmistakable

Studies indicate that sperm whales will spend 70-95% of their time in these foraging cycles so, in terms of where they spend most of their time, these are creatures that inhabit the ocean depths and surface only briefly to breathe.

Unlike most other great whales, the sperm whale does not venture into polar waters to feed, preferring tropical and temperate seas (adult males will venture in to high latitudes).  But even in the tropics it inhabits a cold world.  At a thousand metres depth, well within the normal foraging range of sperm whales, the temperature is only 4-8 degrees centigrade.  It is also a world of almost total darkness.  At 200 metres depth, even in the open ocean the light levels are less than 1/1000th of those at the surface.  At a thousand metres one enters the aphotic zone (the midnight zone) where no sunlight penetrates.  But that does not mean it is a world devoid of light.  It is a world full of bioluminescence. Light produced by chemical reactions within living organisms.  It has been estimated that that 90% of the animals that live below 1000 metres are capable of bioluminecence; glowing, flashing or pulsing green, red, but or white.  This includes many of the prey species of sperm whales. Although they do also consume fish, cephalopods (octopus, cuttlefish and squid) are by far the greatest portion of their diet.  Famously they predate on giant squid and the even larger colossal squid (which may be longer than a full grown sperm whale and is the largest known invertebrate) but they also consume a wide variety of other cephalopod species.  This includes the wonderfully named vampire squid (Vampyroteuthis infernalis is its scientific name, which translates as ‘vampire squid from hell).  Neither a vampire nor a squid it occupies a cephalopod Order all of its own, the Vampyromorphida.

There are a few spots in the oceans renowned for sperm whale sightings.  These are mostly along the edges of underwater canyons and steep drop-offs, where shallow coastal seabeds plunge sharply to hundreds or thousands of metres.  Off the Kaikoura peninsula of New Zealand is possibly the best known area, followed by the Azores islands (where volcanic seamounts rise up from deep water).  The images of mine in this blog were all take off Vesteralen, northern Norway, where a complex of deep canyons direct the seabed offshore from the Lofoten Islands and Vesteralen archipelago. It appears sperm whales hunt along these canyons, thus time spent cruising along the margins of the canyons is often rewarded by sightings of sperm whales as these surface between foraging dives to expel carbon dioxide and replenish their oxygen supplies.

 

 

 

Shortfin makos, the fastest shark of all.

A Mako shark make a half-hearted attempt to grab a cape petrel. Copyright Colin Munro Photography

When one thinks of sharks one thinks of sleek, powerful predators that appear to cruise effortlessly but are capable of dazzling bursts of speed when they attack prey.  This image of the shark is exemplified by the shortfin mako.

A Mako shark make a half-hearted attempt to grab a cape petrel. Copyright Colin Munro Photography

A Mako shark make a half-hearted attempt to grab a cape petrel.

It is believed to be capable of bursts of speed up to 50 km per hour, some references give even greater speeds, and is generally accepted as being the fastest of all sharks.  Makos are built for speed.  I have yet to get in the water with a mako – it is one of my goals for this year.  In the meantime I have an unexpected surface encounter off Kaikoura to savour. Kaikoura, as many of you will know, is a small town on the north east coast of New Zealand’s South Island.  It is famous as one of the best places in the World for whale watching, especially sperm whales.  It also came the wider world’s attention in November 2016, when the region was struck by a 7.8 magnitude earthquake, cutting off road and rail links to the town, uplifting areas of seabed and causing a localised tsunami up to 7 metres in height. When we visited in February 2017, road connections were still disrupted and whale watching boats had difficulty operating due to sea level changes affecting there berthing alongside.  The town, highly dependent on tourism, was suffering markedly.  We were not there to look for whales though, we were looking for dolphin and albatross. Kaikoura may be most famous for whales, but it is also a fantastic place to see many species of albatross up close, and it was albatross and dolphin we were there to see.

Albatross squabble over food. Kaikoura, New Zealand. Copyright Colin Munro Photography

Albatross squabble over food. Kaikoura, New Zealand.

Whilst the big whales grab most of the international headlines, the sheer drama of seeing several species of albatross up close – really close – soaring, wheeling and plunging down to feed, is pretty hard to beat.  Nor was it just the albatrosses and giant petrels that noticed the food  in the water.  The scent of chum in the water attracted in predators from below also.  A dark triangular fin broke the surface and began weaving through the wary seabirds.  The shark was a juvenile mako, approximately 5-6ft (1.5-1.8m) long. Whilst clearly drawn towards us by the fish scraps in the water, it then became interested in the birds splashing around.

An albatross warily eyes the mako shark, whilst a westland petrel flaps away from the sharks path. Copyright Colin Munro Photography

An albatross warily eyes the mako shark, whilst a westland petrel flaps away from the sharks path.

The great albatrosses eyed the shark with a mixture of wariness and belligerence; with a wingspan probably exceeding the length of the shark they may have seemed a little large to tackle.  The smaller petrels were more anxious.  It made a grab for one cape petrel that did not move out of its path fast enough, but the attack seemed have hearted and the petrel skittered away easily enough.  There was probably enough fish remains floating in the water to keep the shark happy. Makos will occasionally take seabirds, but mostly feed on pelagic fish species such as mackerel, herring and anchovies.  Larger individuals have been found to have young seals and even common dolphins in their stomachs, as well as billfish such as marlin.  Common dolphins and marlin are both renowned for their speed, so whilst it is possible that these were injured individuals snapped up by the mako, it is also these fell prey to the makos lightening speed.

 

 

The basking shark

Large basking shark feeding
Large basking shark feeding

Large basking shark feeding

I clearly remember my first in-water encounter with a basking shark.  Quite a few years ago now, I had gone out specifically to try and video a basker underwater.  After a couple of hours we spotted a pair slowly circling a ball of plankton.  I slipped mask, fins and snorkel on and slid in to the water.  Basking sharks can be sometimes be wary and dive when one gets close, but these two seemed quite unconcerned by my presence.  I floated on the edge of the plankton ball and watched them circling.  As one approached out of the gloom I started to swim towards it.  Even through you know it’s quite harmless it is still a strange feeling watching a six metre long shark swimming straight towards you with its mouth wide open.  A mouth I could easily fit inside.  At the last moment the shark would alter course slightly and cruise past me.  The experience was similar to standing too close to the edge of the platform watching a train go past.  Again and again the sharks would circle and cruise past, sweeping by less than a metre from me.  Just me and two large sharks.  It was a mesmerising experience, but I could not help thinking ‘this is so easy!’ Little did I realise at the time quite how lucky my encounter was.  Several years and quite a few attempts would pass before I was able to repeat the experience.

The basking shark, Cetorhinus maximus, is the second largest fish in the World. Mature adults commonly reach between six and and seven metres in length, occasionally reaching around nine metres. Despite their massive size basking sharks are quite harmless. They are gentle filter feeders. During summer in the north-east Atlantic they can often be seen swimming close to the surface with their mouths gaping wide. A baskers’ gape can be over a metre top to bottom, so that’s pretty wide. As they swim forwards water is forced in to their mouths, passing across their gills where oxygen is extracted, and out through their large gill slits. This water flow serves a dual purpose. The arches between the gill slits are covered in long stiff bristles called gill rakers. These gill rakers sieve the water flow, retaining planktonic organisms. This is the food of basking sharks. In northern Atlantic waters they feed especially on copepods (planktonic crustaceans) particularly those of the genus Calanus, which occur in enormous numbers in the North Atlantic. Large numbers of such tiny creatures are required to sustain something as large as a basking shark.  Therefore baskers need to filter very large volumes of water.  It has been estimated that around 1.3 million litres of water will pass through the mouth and over the gill rakers of a large basking shark every hour.

Basking shark feeding, showing large gill slits the almost encircle its head

Basking shark feeding, showing large gill slits the almost encircle its head

In the North East Atlantic basking sharks start to appear off the tip of Cornwall (SW England) in early May.  This co-incides with what local fishermen call ‘May-water’, where the coastal seas turn green and turbid due to the seasonal population explosion of plankton.  Throughout the summer months sharks will move northwards through the Irish Sea and around the west coast of Ireland.  In the years immediately following WWII the author Gavin Maxwell ran a basking shark fishery from the island of Soay in the Inner Hebrides, exploiting this northward seasonal migration. The operation was beset with problems and drove him to the edge of bankruptcy.  Basking sharks were hunted by Norwegian and Irish boats also. Due to concern over dwindling numbers, the basking shark received full legal protection in  U.K. waters in 1998.  The last British shark fisherman, a larger than life character called Howard McCrindle, ceased operations a year earlier.  The basking shark is now protected throughout E.U. waters. In 2006 hunting also ended in Norwegian waters.

A basking shark swimming through plankton rich waters off Southwest England

A basking shark swimming through plankton rich waters off Southwest England

Despite their large size, relatively slow movement and surface feeding habits there is much that remains unknown about the life history of basking sharks. Each year the they appear in late spring, then disappear again at the end of September.  Where they go and how they live for the rest of the year has been a mystery, and remains so today, though we are starting to get tantalising clues as to the the answer.  Occasionally, basking sharks would be caught in trawl nets during the winter months.  Some of these were found to have shed their gill rakers, suggesting they were not feeding.  This lead to the theory that they became dormant in winter, hibernating on the seabed.  This theory had a certain plausibility to it.  Basking sharks have enormous oil-filled livers.  The liver can be 25% of the sharks body mass (the low density oil gives the shark buoyancy, allowing it to swim efficiently at the surface; it was also this high quality oil for which they were hunted). It was suggested that this enormous store of liver oil could sustain the shark for months without feeding. Recent research using data logging tags has begun to shed light on shark behaviour during the winter months.  The tags used detach after a predetermined time and float to the surface, where they transmit the data data to satellites. The data at the time of writing indicates that basking sharks are active all year round, but spent much of their time at considerable depth, 200 and 1,000 metres.  It also seems they are highly migratory.  One 5 metre female nicknamed ‘Banba’, was tagged off Malin Head, the most northerly point of Ireland, in the summer of 2012.  On the 13th December 2012 the tag popped off and was located by satellite – just west of the Cape Verde islands 5000km to the south.  The still sparse, but growing, body of evidence now suggests that – in the North East Atlantic move in to coastal waters from deep water in April or May.  As the water warms and daylight lengthens (and so plankton blooms) there is an erratic movement northwards.  At the end of the summer they return to deeper water, heading west away from the British isles and mail and Europe, and some probably heading south also.  So in reality we should maybe consider the basking shark as a deep water species that happens to congregate in shallow water during the summer months in pursuit of rich feeding.

As a final aside it is often written that basking sharks are toothless filter feeders. Basking sharks are filter feeders utilising gill rakers in a similar fashion to the baleen plates of great whales to trap small planktonic creatures but surprisingly they also teeth.  In fact they have hundreds of tiny, backward-pointing teeth.  What, if any, purpose these teeth serve is not known.  They may be a vestige from a more predatory ancestry; equally there may be more still to learn of the basking sharks feeding habits.

You can see more of my shark images here

The extraordinary life cycle of the lion’s mane jellyfish

Lion's mane jellyfish, Cyanea capillata, underwater clearly showing tentacles trailing in many directions. Colin Munro Photography

Jellyfish, or sea jellies as they are now often called (clearly they are not fish) are amongst the most ancient of multi-organ animals.  Fossils of jellyfish (or scyphozoans, to give them their scientific name) are found only rarely as they contain no hard structures within their bodies, which are 95% water.  However, under the right conditions fossils of soft bodied creatures will form; current fossil evidence suggests they first evolved at least 500 million years ago.

Lion's mane jellyfish, Cyanea capillata, underwater clearly showing tentacles trailing in many directions. Colin Munro Photography

The lion’s mane jellyfish, Cyanea capillata, is the largest known species. The bell of individuals in colder northern waters can reach two metres across.

The lion’s mane jellyfish (Cyanea capillata) common throughout the North Atlantic, epitomises this image of a large, slowly pulsing, gelatinous bell (or medusa) and long trailing tentacles that pack a powerful sting, but this is in fact only one stage of a complex life cycle.  Lion’s mane medusae begin to appear in April or May in the Northern Atlantic, but are quite tiny at that stage.  These jellies are voracious predators and grow rapidly through the summer.  By August the medusae are commonly one third to half a metre across, with trailing tentacles many metres long.  However there is considerable variability;  large specimens have been reported at over two metres across with tentacles up to 37 metres long, though these generally occur within the more northern parts  of their range.  As they grow large in late summer they will often drift, under the influence of wind and tides, in to sheltered bays where they may aggregate in large numbers. This is when sperm is release and egg fertilisation takes place.  In common with most scyphozoans (the taxonomic group to which jellyfish belong) the sexes are separate; lion’s mane jellies are either male or female.  Sperm is released from the mouth of male jellies and drifts in the current, some reaching female jellies, where the eggs are fertilised. Fertilised eggs are stored in the oral tentacles of the female, where thy develop in to tiny planulae larvae. Once fully developed the planulae larvae detach and, after drifting for a short time, settle on the seabed.  Here they metamorphose into a polyp, not dissimilar to tiny sea anemones or coral polyps (both of which are relatives of jellyfish).  These polyps then grow, taking on a layered appearance until they resemble a stack of wavy-edged pancakes.  Each one of these ‘pancake layers’ will then separate from the parent polyp, once again becoming free living and drifting with the currents.  The ‘pancakes’, more properly ephyra larvae, will grow throughout the summer into the giant lion’s mane jellies and the cycle is complete.  With a lifespan on only one year, during which they can grow to be as long (possibly even longer) than blue whale, lion’s mane jellies need to catch and consume considerable amount of prey.  Each trailing tentacle is packed full of vast numbers of stinging cells, known as nematocysts.  When touched these cells fire out a harpoon-like structure which pumps toxins in to the hapless victim (this is what causes the painful sting from jellyfish).  These toxins incapacitate the prey, which is then drawn up towards the mouth of the jellyfish.  A large lion’s mane may have over 1,000 tentacles trailing far behind them.  Many SCUBA divers in Scotland and Scandinavia have experienced the situation where, having completed their dive on a sunken wreck and returned to the buoy line they planned to ascent to the surface, only to look up and see numerous lion’s mane jellies strung out along the line.  As the current sweeps the jellies along so their tentacles catch on the buoy line, leaving the divers with the unpleasant prospect of ascending through thousands of jellyfish tentacles.

A diver warily watches a large lion's mane jellyfish (Cyanea capillata) drift past. Isle of Arran, West Scotland.

A diver warily watches a large lion’s mane jellyfish (Cyanea capillata) drift past. Isle of Arran, West Scotland.

Not every creature lives in fear of lion’s mane jellies however.  Leatherback turtles, the only species of marine turtle that can tolerate the cold waters these jellies inhabit, consume them with relish, apparently oblivious to the stinging tentacles.  Lion’s mane jellies can make up 80-100% of a leatherback’s diet.  When you consider that a full grown leatherback weighs up to 800kg and may consume up to its own weight in jellyfish daily (bear in mind jellyfish are 95% water) then that equates to pretty large numbers of jellyfish being eaten.

As summer wanes and autumn approaches the lion’s mane jellies begin to die.  This provides a feeding bonanza for many scavengers.  On the surface seabirds will peck away at the gelatinous bell, whilst those that sink are often torn to shreds by shore crabs (Carcinus meanus) and velvet swimming crabs (Necora puber).

Dying lion's mane jellyfish (Cyanea capillata) that has sunk to the seabed being eaten by a velvet swimming crab (Necora puber).

Dying lion’s mane jellyfish (Cyanea capillata) that has sunk to the seabed being eaten by a velvet swimming crab (Necora puber).

At the other end of the scale these deadly tentacles can provide refuge to some unlikely creatures.  Juvenile whiting (Gadus melangus) have long been known to swim underneath the bell of lion’s mane jellies, apparently unconcerned by the curtain of tentacles they weave between. In fact they have been observed to rush into the mane of tentacles when startled by predators.  A series of fascinating experiments by the Swedish zoologist Erik Dahl in the late 1950s showed that, compared to other fish species, juvenile whiting were able to adapt their movements such that even when surrounded by tentacles they rarely came in to contact with them.  Also, unlike other fish species, when they did brush against them it seemed to cause them little concern. Biopsies of the tissue of whiting where they had contacted tentacles showed that very few if any stinging nematocysts had fired into the fish’s body; this compared to hundreds per square millimetre for other fish species.  We still don’t understand the mechanism behind this protection. So does the lion’s mane get anything in return for the refuge afforded the young whiting?  Well another creature found on lion’s mane jellies is the tiny planktonic amphipod (a type of crustacean) Hyperia galba. Hyperia is, for the jellies, a rather irritating ectoparasite. It lives on the outside of the jellies’ bell, nibbling away at it.  Now whiting don’t appear to like the taste of lion’s mane jellies, instead they are rather partial to planktonic crustaceans; in particular (you’ve guessed this already) Hyperia galba.   It is these elegant little symbiotic collaborations that make nature so beautiful.

These, and many more of my images, can be found at colinmunroimages.com

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Orcas and Common Seals: Summer in Norway and Scotland

A curious common seal, Shiant Islands, Hebrides, Scotland. Copyright Colin Munro

I’ve spent most of this summer sailing along the coast off Western Scotland and Norway, with a brief swing by the Faroe Islands. I think this includes some of the most dramatic scenery in the World and some of the best marine wildlife.  From the wild remoteness of St. Kilda to the sheer majesty of Troll Fjord there is little that betters the coastline of the northeast Atlantic.  The one downside is that internet has been working only intermittently and then at a glacially slow speed.  However it has been a great trip for marine mammals, with regular sightings of grey and common seals, harbour porpoise, common and bottlenose dolphins and even the occasional orca and sperm whale.  So whilst siting in a bar in Bergen on a chilly and rainy August evening I thought I’d take the opportunity to upload a few images of orcas (Orcinus orca) and common seals (Phoca vitulina).

Male orca cruising off the Lofoten Islands, Norway. copyright Colin Munro

Male orca cruising off the Lofoten Islands, Norway

We were lucky with around the Lofoten Islands, where a small family group of orcas altered course to swim alongside us for a few minutes, rather like overgrown dolphins (which is exactly what orcas are).

 

A female orca (or killer whale) Orcinus orca, cruising along near the Lofoten Islands, Norway.

A female orca (or killer whale) Orcinus orca, cruising along near the Lofoten Islands, Norway.

The western isles are always good for seals, with common seals pupping whilst we were there.  We had particularly good sightings around the Shiant Islands and The Isle of Skye, where both common seals and grey seals (Halichoerus grypus) occur together.

A curious common seal, Shiant Islands, Hebrides, Scotland. Copyright Colin Munro

A curious common seal, Shiant Islands, Hebrides, Scotland.

Very often they would pop up behind our Zodiac, always at a safe distance, but curious as to what we were doing.

A common seal cruises with its eyes and nostrils just above the water. Dunvegan, Isle of Skye, Scotland. Copyright Colin Munro. www.colinmunroimages.com Colin Munro Photography

A common seal cruises with its eyes and nostrils just above the water. Dunvegan, Isle of Skye, Scotland.

With only the tops of their heads, eyes and nostrils visible, seals can be tricky to spot. A glance in their direction frequently results in a loud splash as they duck dive out of sight, rather like inquisitive but shy children.

Common seals playing on rocks, Shiant Isles, Hebrides, Scotland.  Harbor seals, copyright Colin Munro www.colinmunroimages.com

Common seals playing on rocks, Shiant Isles, Hebrides, Scotland.

Basking on the rocks they were often quite playful.

Female common seal or harbour seal, Phoca vitulina,  dozing on the rocks, Dunvegan, Isle of Skye. Copyright Colin Munro Colin Munro Photography www.colinmunroimages.com

Female common seal or harbour seal, Phoca vitulina, dozing on the rocks, Dunvegan, Isle of Skye

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Blue sharks, graceful sea wolves

Blue shark, Prionace glauca. A female blue shark swimming close to the surface off Southwest Cornwall, UK.

The blue shark, Prionace glauca, is possibly the most beautiful of sharks.  It is a slender, fast and graceful shark, but it is the vivid, almost electric blue colouration that is most striking.

Blue shark, Prionace glauca. A female blue shark swimming close to the surface off Southwest Cornwall, UK.

A blue shark passes close by.

Blues are oceanic sharks, uncommon in shallow coastal waters.  In the tropics they are normally found in deeper, cooler waters, but in temperate seas they are more likely to be found in surface waters (thus are described as being epipelagic).  This does not mean that in temperate waters they occur only in the warmer surface layers.  Recent data from satellite tags have shown that they blues may regularly undertake dives to more than 1000 metres.  One male blue shark, nicknamed Bodi by the researchers, was logged as having dived to 1250 metres off the Bay of Plenty (New Zealand) three weeks after being tagged in 2013.  An earlier joint British- Portuguese study recorded a female blue shark diving to 1160 metres off the coast of Portugal (Queiroz et al, 2012).   This behaviour is probably linked to hunting activity.  Blue sharks are quite catholic in their diet, eating a wide range of mid-water fish and cephalopods,  but appear to be particularly fond of squid, and of course squid will often undertake marked vertical migrations, with many species occurring at considerable depth.  That this deep diving behaviour of blues is primarily foraging for food is supported by a preponderance of deep water quid species found in the gut of contents of blue sharks caught by long-lines, in particular the wonderfully named vampire squid, Vampyroteuthis infernalis, a small deep-water squid those scientific name literally translates as the vampire squid from hell.

In the northern Atlantic at least, they appear to undertake seasonal migrations. They are unusual amongst ocean sharks in that they will sometimes aggregate in groups, often all same sex, as they roam.  This pack-like activity has lead to them being dubbed the wolves of the sea.  Around Southwest Britain blue sharks start to appear in June each year, and hang around until late October or early November.  Although there have been attacks on humans by blue sharks, aggressive behaviour is relatively rare.  Certainly in British waters, where large blues are rarely seen, most are quite timid and easy to scare off accidentally.  The largest blue caught in UK waters was approximately 2.5 metres long and weighed 107kg. This was caught off Penzance, Cornwall, in 2012 (but was also released).  Blues can grow up to 3.5 metres or more (the largest on record was 3.83 metres long) the females being significantly larger than males.

Blue shark, Prionace glauca. A female blue shark swimming close to the surface off Southwest Cornwall, UK.

Blue shark, Prionace glauca. A female blue shark swimming close to the surface off Southwest Cornwall, UK.

An underwater encounter with a blue shark is a wonderful experience, and provided one takes sensible precautions (i.e. wearing gloves, not wearing shiny bits of equipment and NOT trying to feed them) is normally quite safe.  Blue sharks have been one the shark species hardest hit by the practice of shark fining in various parts of the World and there numbers appear to have declined markedly.  Consequently it’s worth remembering that most blue sharks have far more cause to fear us that vice versa.

The above, and more of my blue shark images, can be found on my stock image website www.colinmunroimages.com. They can be licensed for publication, or purchased as fine art prints and canvas wall art.

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References cited: Queiroz N, Humphries NE, Noble LR, Santos AM, Sims DW (2012) Spatial Dynamics and Expanded Vertical Niche of Blue Sharks in Oceanographic Fronts Reveal Habitat Targets for Conservation. PLoS ONE 7(2): e32374. doi:10.1371/journal.pone.0032374

 

Photographing Blue sharks off Cornwall

Blue shark, Prionace glauca. A female blue shark swimming close to the surface off Southwest Cornwall, UK.

A few days ago I was fortunate enough to get in to the water off Cornwall with a couple of blue sharks (Prionace glauca).  Getting some good images of blues had been high on my ‘to do’ list for several years, but for one reason or another it had not happened. In part this was a result of the dreadful summers we have had in the UK for the past few years; wet and windy and severely limiting the number of days when it was possible to spend all day offshore in a small boat (and limiting even more the number of days one would want to). This summer has so far been perfect, high temperates and light winds.

Blue shark, Prionace glauca.  A female blue shark swimming close to the surface off Southwest Cornwall, UK.

Blue sharks are highly migratory, with strong evidence for there being a single well-mixed population within the Atlantic Ocean and seasonal trans-Atlantic migration.  Some studies indicate a crosswise annual migration across the temperate zone of the Atlantic but evidence for this is inconclusive.  What we do know is that blue sharks start to appear off the tip of Cornwall in early July and remain around Southwest England until late September.

Blue shark, Prionace glauca.  A female blue shark swimming close to the surface off Southwest Cornwall, UK.

Off the tip of Cornwall is one of the best areas to see blues; it also has the advantage of exceptionally clear water.  Most are found at least five miles offshore, so with the longish drive an early start was required.  By 10a.m. we were drifting with the current, a nice fish oil slick trailing from our chum bag, cameras ready and waiting.  The sky was blue, the sun hot, the sea ruffled by a light breeze and our spirits were high.  And we waited.  Mid-afternoon a brief flurry of excitement: two sharks arrived within the space of an hour, grabbed our mackerel bait….. and disappeared.  By 4.30pm our hopes were fading and our thoughts turning to when we could schedule the next trip.  Suddenly at 4.45pm a third shark arrived.  A smallish female, probably around 5ft, but most importantly she showed none of the skittishness of the previous two. She was interested in the fishy smell from our chum bag and she was hanging around.  It took a real effort of will to stay calm, remain on the boat and allow her time to settle – what if she also suddenly disappeared?  However, after a few minutes Charles, the boat skipper, gave us the nod and Richie and I slipped gently and quietly in to the water.  As we swum towards her she showed no fear at all, appearing quite curious about us, to the extent that she temporarily lost interest in the chum bag and began cicling us as we drifted slowly from the boat.  Time and again we would swing around to make close passes, to the extent that she occasionally had to be gently pushed away as she came nose to nose.  A more obliging photographic model I could not have wished for.  Around 20 minutes passed in a flash, at which point she became bored with us and disappeared.  Yet no sooner had we climbed back in to the boat than a larger female arrived.  She definately wasn’t timid; before anyone could react she had grabbed the chum bag and was tearing it to pieces.  Within seconds the water around the boat was a murky brown from the contents of the chum bag and the bag itself shredded.

This was too good an opportunity to miss, all four of us hit the water.  She was a real beauty.  Between 6 and 7 ft long, the most dazzling vivid blue on her dorsal surface with deep indigo patches near her dorsal fin, pure white on her underside.  As she passed close the mating scars left by the males teeth could be clearly seen on her head neck and back.  For more than 30 minutes she hung around. circling us.  It was almost 6pm when we finally climbed out of the water.  Tired but very happy.

passing under a snorkeller

Our trip was on board the RIB of Charles Hood (charleshoodphotography.com).  Charles regularly runs basking shark and blue shark trips from Penzance, Cornwall.  I would heartily recommend him.

All my blue shark photographs are available for licence and some as fine art prints along with all my other stock images at http://colinmunro.photoshelter.com. Or you can contact me directly email me

Signed canvas prints and photographs of my work can be bought through my Etsy Store

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Sunset corals

Leptopsammia prouviti, growing on undercut limestone ledges, Lyme Bay, Southwest England. colin munro photography

Sunset corals (Leptopsammia pruvoti), a little natural history.

Leptopsammia prouviti, growing on undercut limestone ledges, Lyme Bay, Southwest England. colin munro photography

Leptopsammia prouviti, growing on undercut limestone ledges, Lyme Bay, Southwest England.

For most, the word coral conjures up images of living reefs surrounded by shoals of colourful fish, in clear, brightly lit tropical waters.  Whilst this is the type of environment where the vast majority of coral species are found, it is not the exclusive habitat.  That corals are found in the chilly and turbid seas around Britain would probably surprise most of theBritish public.  In fact there are five known species of coral found in shallow waters around the UK.  The two best known species are the Devonshire cup coral, Caryophyllia smithii, and the sunset coral, Leptopsammia pruvoti.  Like all our shallow water corals they are solitary corals (apart from the Weymouth carpet coral, Hoplangia durotrix, which forms small clusters of polyps growing from a basal plate).  They don’t form large, colonial skeletons and hence don’t form reefs.The Devonshire cup coral is familiar to many divers and may even be found intertidally in shady overhangs at the very bottom of the tide.

Leptopsammia pruvoti is rather more enigmatic.  It is known to occur in only a handful of locations around Southwest Britain (The Scilly Isles, Lundy Island, Plymouth Sound, Lyme Bay and Portland Bill) though it is more widely distributed along the Atlantic coast of southern Europe and in the Mediterranean.  Leptopsammia pruvoti belongs to the taxonmic family Dendrophylliidae, a sub-group of corals.  An interesting feature of nearly all (around 91%) Dendrophylliidae corals is that they lack symbiotic zooxanthellae (technically speaking they are azooxanthellate).  At this point you may be asking ‘so why is that a big deal … and what exactly are symbiotic zooxanthellae anyway?’.  A common feature of most reef building corals (hermatypic corals) is the presence of tiny unicellular algae, termed zooxanthellae, living  within their tissues.  This is a symbiotic relationship; Zooxanthellae gain protection and some nuitrients from the coral whilst the coral gets glucose, glycerol and amino acids from the unicellular algae.  One of the key benefits for the coral is that this facilitates the production of large amounts of calcium carbonate, the material from which coral skeletons are formed.  Thus the calcuim carbonate based, skeleton-forming process in corals containing zoozanthellae is ‘turbo-charged’; they are able to produce skeletal material at a greater rate and so can grow to form large, colonial skeletons that meld together and form reefs.  Azooxanthellate corals do not have this advantage, but their lack of dependence on photosynthesising algae frees them to expand beyond the brightly-lit surface waters. Azooxanthellate corals in the family Dendrophylliidae can be found from a few metres depth down to over two thousand metres.  This takes them deep into the aphotic zone, the parts of the ocean completely devoid of light (roughly, below 1000 metres).  It also allows them to colonies niches that are out of direct sunlight, such as caves (e.g. the recently discovered coral Leptoseris troglodyta, troglodyte= ‘cave dweller’, found around Indonesia and the Philippines) or the rock overhangs of Lyme Bay.

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Common dolphins, fastest mammal in the sea

Common dolphin (Delphinus delphis) swimming at high speed. Colin munro Photography
Common dolphin (Delphinus delphis) swimming at high speed. Colin munro Photography

Common dolphin (Delphinus delphis) swimming at high speed, just below the surface.

What is the fastest marine mammal? There are a number of pretty speedy guys in the water. It’s been calculated that when an orca, weighing up to five tonnes, breaches this requires an exit speed of around 40kph. That’s around the same as the maximum speed attained by Usain Bolt in a 100 metres race. Only he doesn’t weigh five tonnes…and he’s not doing it underwater. In 2009 french swimmer Frédérick Bousquet set a World record 50m freestyle sprint, with an avergae speed of 8.6kph. A lot faster than you or I, but never gonna outswim an orca; orcas can, in fact touch 50kph when they want to. Perhaps surprisingly, given that they weigh upwards of 150 tonnes, blue whales are also pretty zippy, also able to get the needle up to 50khp when in a hurry (why would blue whales be in a hurry?). However current data suggests that the fastest dude on the block is the common dolphin (Delphinus delphinus). These guys can reach 64kph (40mph). According to the Guiness Book of records that’s a whisker slower than the fastest racehorse (Winning Brew, 2008) over 400 metres (two furlongs). I’ve owned cars that struggle to do that on hills.

It is hard moving fast through water compared to air, so how do they do it? In 1936 zoologist Sir James Gray looked at this and concluded that dolphins simply shouldn’t be able to generate sufficient power to move them through the water as fast as they appeared able to do. This became known as Gray’s Paradox. It is now believed that the hydrodynamic shape of dolphins greatly reduces form drag, and thus the power required. There is also some evidence that the dolphin’s soft skin, which is continually shed, reduces friction drag. Even so, that a dolphin can travel as fast as a thoroughbred racehorse, through a medium almost 800 times more dense than air, is pretty impressive.

How many common dolphin species?
Until the 1960s all common dolphins were considered one single species. Genetic studies have indicated that there are probably at least two, possibly three distinct species. These are the short-beaked common dolphin (Delphinus delphis) which is the species most likely to be encountered in british waters; the long-beaked common dolphin (Delphnus capensis), and possibly a third species, the arabian common dolphin (Delphinus tropicalis) although many marine biologists consider this a subspecies of the long-beaked common dolphin.

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Porbeagle populations in the N.E. Atlantic critically endangered.

Porbeagle shark, Lamna nasus, caught as bycatch, on the deck of a fishing vessel, Irish Sea, UK. Colin Munro Photography

Porbeagle shark, Lamna nasus, caught as bycatch, on the deck of a fishing vessel, Irish Sea, UK. Colin Munro Photography

Porbeagle shark, Lamna nasus, caught as bycatch, on the deck of a fishing vessel, Irish Sea, UK.


Porbeagle sharks (Lamna nasus) are a temperate water species of shark belong to the mackerel shark family (Lamnidae), the same family as salmon sharks, makos and great whites. Adults are around 2.5 metres long and and weigh about 140kg. They are considered vulnerable throughout their range. The population around UK shores (NE Atlantic) is considered critically endangered (IUCN). The International Committee for Exploration of the Seas (ICES) advises that the NE Atlantic stocks may be close to collapse. A quota system for porbeagles was introduced in 2008. The Total Allowable Catch (TAC) was reduced to 436 tonnes in 2009. In UK waters a total ban on targetted fishing by commercial fishermen has been in place since 2010, with release of accidental bycatch whenever possible. ICES has called for a zero TAC since 2006; there are now proposals to bring this in to effect throughout the EU.

There is a still a problem in that porbeagles, are fast swimming predators that feed on squid and fish. Freuqently the species that fishermen are also targetting. Porbeagles may end up as accidental bycatch in trawls or in set nets. Like other mackerel sharks, porbeagles’ gills work by obligate ram ventilation. This means they need a constant flow of water past their gills in order to oxygenate their blood. Trapped in nets they quickly drown. As set nets are often deployed on the seabed then hauled 12 or 24 hours later, even if the fishermen would like to release them alive it will be too late. The Centre for Environment, Fisheries and Aquaculture Science (CEFAS) is currently conducting a DEFRA commissioned study in to the threats posed by accidental bycatch to porbeagle in UK waters. Hopefully this will result in guidance for fishermen as to the best ways to minimise the risk of accidentally catching porbeagles.

Save our Seas is working with the Marine Institute in Ireland to satellite tag porbeagles. This should help us understand portbeagle migration and possibly identify nursey areas. This has so far shown that porbeagles tagged off northern coast of Ireland have resurfaced off Lisbon, Portugal. Details of the study can be seen here.

Interesting fact: All fish are cold blooded right? Not quite. Recent studies have found that most mackerel sharks (salmon sharks, great whites, shortfin mako and porbeagles) are able to maintain their body temperature above that of the surrounding water, as marine mammals do. They acheive this by passing deoxygenated blood, heated by muscle activity and biochemical reactions, past a network of cold, oxygenated blood travelling through a network of fine arteries (the rete mirable, literally ‘wonderful net’) thus transferring heat to the arterial blood rather than simly losing it to the external environment. Salmon sharks (Lamna ditropis) sharks have been found to maintain their core temperature up to 21 degrees C above that of the surrounding water (Goldman et al, 2004)

Update
Porbeagles are endangered throughout the Atlantic. The EU has now voted to ban commercial porbeagle fishing. Currently only Canada allows a commercial fishery, although the Canadian Government are coming under considerable pressure from conservationists within and outside Canada. More more information on this read the Friends of Hector article here.

References
Goldman, K.J., Anderson, S.D., Latour, R.J. and Musick, j.A., 2004. Homeothermy in adult salmon sharks, Lamna ditropis. Environmental Biology of Fishes 71 (4): 403–411.