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Two hundred and fifty miles south of the tip of Baja California lays a small archipelago consisting of three islands and a rock called the Islas Revillagigedo. More commonly known in the dive travel community as Socorro, after the largest island, because it is much easier on the gringo tongue. Socorro is known for big animal diving, primarily for the exceedingly friendly giant manta rays.  This photo diary is from a trip to this incredible place.


The Revillagigedo Islands include: San Benedicto Island, a recently active pile of volcanic ash and lava flows about 3 miles long; Socorro Island, another active volcano almost 4,000 ft. high and 10 miles across; and Roca Partida or Split Rock, a 300 foot long, 120 foot high navigational hazard, the erosional remnant of an extinct volcano.  Our trip included two days of diving at each of the three locations.  We did not visit Clarion Island far off to the west.  These are volcanic hot spot islands growing out of the deep ocean floor.  They are very isolated and attract lots of wandering pelagic life forms.

San Benedicto
San Benedicto

Socorro Island

Roca Partida
Roca Partida

Andrea Marshall, a manta researcher based in Mozambique published a paper in 2009 identifying two species of manta ray:  the giant manta (Manta birostros) and the reef manta (Manta alfredi) based on differing morphology and behavior.  The giant manta is larger, up to 20 feet across, and appears to migrate over large areas.  It also has a vestigial stinger structure at the base of its tail, a remnant of its stingray ancestors.   The reef manta averages about 12 feet across, tends to stay in one general location and has no vestigial stinger.  This two species proposal is new and may still be controversial.  In any case the mantas at Socorro are giants, we saw a few individuals well over 15 feet across.  

Giant Manta
Black Manta

The come in two color schemes, the stealth bomber black mantas and so-called chevron mantas with white markings on their top surface.

Giant Manta
Chevron Manta

Mantas are the largest rays.  Relatives of sharks they also have cartilaginous skeletons, the males have external sex organs called claspers, and, like sharks, they breed and reproduce slowly,  giving live birth to one or two offspring about every two years.  

They evolved from bottom feeding stingrays to feed on plankton. Their mouth has migrated to the front and is essentially a large jet intake, bounded by two adapted structures known as cephalic fins which help funnel water and food into their gaping maw.

Giant Manta
Giant Manta with Cephalic Fins Curled

It is from these fins, often curled up and looking like horns, that they got the name Devil Ray. No label could do more of a diservice to its namesake. Mantas have very large brains for fish and exhibit complex behaviors and intelligence levels more in line with mammals than other fish.

Giant Manta
Giant Manta with Cephalic Fins Uncurled

And that is what attacts divers from all over the world to Socorro. Nowhere else on earth are giant manta rays this friendly.  They literally seek out divers and stay with you throughout your dive. Not all of them do this but many of them do exhibit this playful behavior. They seem to enjoy the feeling of divers bubbles and will often hover over you while your bubbles tickle their belly.  I even saw then shiver in apparent pleasure as they get their bubble massage.  They also seem to be curious and will swim up and look you in the eye.  

Giant Manta & Remora
Eyeballin'  (with Remora)

They almost always sport one of two remoras. They are tag-along fish with dorsal fins adapted into a sucker mechanism on the top of their head.  Research has shown that the species of remoras found on mantas are also plankton feeders and probably do not provide much if any benefit to their host.  They just get a free ride to the food.

Giant Manta
For scale

You may have seen video of divers riding on the backs of giant mantas. We now know that they are covered with a fairly heavy coating of mucus on the top surface which probably protects them from disease so this practice is not allowed on current dive trips. You are allowed to, within reason, give them a light stoke on the belly.  I stopped taking photos long enough to give one a gentle one finger stoke and found the surface incredibly rough.

Giant Manta
Graceful Giant

It is impossible to describe the feeling of being face to face with one of the graceful, gentle giants of the sea.  This ain't no ordinary fish.

Giant Manta with Blaze and David
Say Cheese!

The Mexican government set aside the Islas Revillagigedo as a biosphere reserve in 1994 after some particularly gruesome footage of fisherman slaughtering mantas made international news. No fishing of any kind is allowed. It is one of the few places on earth that these creatures are protected (along with Hawaii, Yap and the Maldives).  Unfortunately enforcement is far from adequate and actually the dive boat operators provide the primary defense of these islands. The operators Solmar V and Nautilus Explorer have provided money and are gathering donations to fund random small plane flights over the island to spot poachers, who can work around dive boat schedules posted on the internet.

Manta wth Steve and Alex
Manta Goodness

Sadly manta gill rakers (structures for sifting plankton) are valued in, wait for it, traditional Chinese medicine. Words can't adequately describe my feelings when I was informed of that little factoid. Also manta wingtips can double as shark fins in a pinch. Humans!

Speaking of sharks....

Whitetip Reef Sharks
Pile o' Whitetip Reef Sharks

You do also see sharks, especially at Roca Partida. There are ledges where whitetip reef sharks from baby twelve inchers to fat six footers rest in piles like cordwood.

Whitetips & Panamic Moray
Sharing Space with Morays

More impressive than the whitetips are large pelagic sharks like:
Silvertip Sharks
Silvertip Sharks

Dusky Shark
Ten Foot Female Dusky Shark

In addition to silvertips and duskys we saw Galapagos sharks and there was a large school of scalloped hammerheads that stayed just at the edge of visibility and beyond.

There is still lots of life in the ocean around the islands although shark numbers have reportedly dropped significantly in the past twenty years.  When they first started diving Roca Partida over twenty years ago they would see up to hundreds of sharks.  We saw a few handfulls every dive at Roca Partida. We also saw evidence of fishing with some sharks sporting hooks in their mouths, and if you look near the tail of that silvertip shark above you can see trailing monofilament fishing line.

But there are still lots of fish.  Huge schools of creole fish, bigeye jacks and countless other species.


I am incredibly fortunate to be able to visit such a beautiful place.  I hope I have conveyed some of the magic and beauty that I found there.

Steel Pompano
Steel Pompano

What HinH diary would be complete without one of these?
What You Lookin' At?!  - Booby

If you have a problem with this diary I refer you to the Complaint Department:

Oh.. I didn't mention the dolphins did I?
Bottlenose Dolphins
Bottlenose Dolphins

Or the night snorkel off the back of the boat with silky sharks.
Silky Shark
Silky Shark
That was exciting!


Originally posted to Haole in Hawaii on Sat Jan 22, 2011 at 07:08 PM PST.



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