Shark Tagging in Galápagos
This article appeared in the April edition of Subsea Ireland, a diving magazine in Ireland. It documents a trip I made with scientists from The Charles Darwin Research Station, University California Davis and The Galápagos National Park Service to Darwin and Wolf Islands to tag and track Hammerhead and Galápagos sharks as part of long term efforts to determine movements and ranges of these species.

Image credit: JasminePeering into the water, teetering over the edge of the zodiac, the orca  appeared not to notice me as he swam, smiling as they do and accompanied  by a smaller female a mere 2 feet away from my disbelieving head. We had  had the audacity to be unimpressed with a dive; the visibility was only ten  metres and we didn’t see any hammerhead sharks.  The surrealism and  rarity of the situation was not lost on me as I drew back from the water. So  close I was to this powerful mammal that the orca’s incredibly high dorsal  fin seemed to soar in my perspective above the cliffs of Wolf Island,  hundreds of metres high in the background. I was dramatically reminded of  the closeness to the wildlife which is found here and almost unparalleled on  the earth and also that hardly a day goes by in Galápagos without witnessing at least one spectacular sight.

No more than two rocks rising from thousands of metres depth, Darwin and Wolf islands, lying in splendid loneliness some 200km northwest of The Galápagos Archipelago in the Pacific Ocean, are possibly the last islands on earth to find great schools of hammerhead sharks. According to James Ketchum of the University of California, Davis and Migramar, this phenomenon came to an end in many other parts of the eastern Pacific some 30 years ago due to overfishing. It is regular and expected to witness the stunning and surreal vista of hundreds of these dramatically shaped animals swimming overhead on a dive in these parts. If this were not enough to see in one dive, these islands also host the magnificent whale shark, the largest fish on earth, during the months between July and December.  As we were well out of the season we knew we would not see any of these giants; I was content to settle for schooling hammerheads.

It is for this very reason I came to be located in this extraordinary part of the planet for 10 days or so last March. As a researcher with the Charles Darwin Research Station in the Galápagos Islands, I joined an international team of researchers and Galápagos National Park personnel to conduct part of a long term operation to track and understand the movements of several shark species in the eastern tropical Pacific. Our principal task on this voyage, which was undertaken on The Galápagos National Park research Vessel, MV Sierra Negra, was to tag and track several Galápagos and Hammerhead sharks among other activities complementary to the study.

Image credit; Eduardo Espinoza

On day one of the trip a fish census at ´The Cleaning Station´ which is  located underneath Darwin’s Arch, an incredibly photogenic piece of  natural architecture, was the purpose of my first immersion. Conducting a  fish census at a location such as this leads to an impressively annotated  dive slate at the end of a dive. As the islands rise abruptly from thousands  of metres depth, pelagic species such as bonito, jacks, rainbow runners,  and tuna were logged in numbers. Reef fish found throughout the  archipelago such as king angelfish, Moorish idols, triggerfish and the most  abundant reef fish in Galápagos, the Pacific Creole fish were busy fulfilling  their various roles on and above the reef. Curious and beautiful parrot fish, carrying dopey expressions will often spend an entire dive lazily inspecting you. That’s not to forget the sharks.  On only our first dive some thirty hammerheads passed, on this occasion much closer than normal. Sheltering from the powerful current in the lee of a great boulder, each diver would subconsciously retract slightly every time one of the hammerheads innocuously passed that little bit closer within our comfort zone. The unusually low visibility (8 metres) and low temperature (17 degrees) for this area lent to the drama of the situation as the sharks only came into view when already quite close.  Visibility is more normally around the 20 to 30 metre mark with 24+ temperatures in these waters. The oceanographic phenomenon of internal waves was the most likely culprit for the localised upwelling enhancing the exhiliration of our dive.

This was not my first foray with large numbers of sharks. A year previously, I passed many dives laying on the bottom gazing upward in the channel at Leon Dormido, frantically scribbling on an arm slate the hundreds of Galápagos and hammerhead sharks overhead as part of a shark census project. Leon Dormido is a spectacular monolith rising from the waters off San Cristóbal Island in the south of the Archipelago. This part of the archipelago is often overlooked for the excellent land based diving it offers. One particular close encounter with a group of 40 hammerhead females along the north wall of this rock, which plunges into hundreds of feet of water below, may be the most memorable diving experience I have had to date.

On a good day in the channel at this rock, and there are many good days, the amount of life present is humbling. 20 metres deep and about the same wide, to move through this channel is to move through a veritable amphitheatre of large marine life. An overwhelming assembly of turtles, schools of eagle rays, tuna, jack, barracuda, various reef fish, Galápagos, hammerhead and white tip sharks and the occasional sea lion occupy the water column at times all at once in an extraordinarily diverse display of the closest thing to a chock full marine thoroughfare.

On our third day of the trip, we changed our location to Wolf Island, Darwin’s neighbouring isle. A fish census at twenty metres revealed many interesting species in numbers but no sharks. Halfway through, an almighty upwelling reminded us of our proximity to deep water.  Instead of cursing the deep chill such an event brings to your dive, it was better to be thankful for finding ones self in the rare position of being the first human contact with water straight from the depths, fuelling the high energy ecosystem found here. If you are coming to Galápagos, bring 7mm; despite sitting plum on the equator, The Humboldt current, moving north from Antarctica, converges with the equatorial counter current to stroke the islands with cold deep water. This is not the placid diving of so many tropical locations; safety sausages and whistles are a must. Currents that pull the regulator from your mouth, which for so often seemed like a heavily over exaggerated expression to me, are quite a reality.

IMage credit; Eduardo Espinoza However the lack of sharks on our dives was slightly worrying. Aside from  the obvious pluses of viewing and counting them, we were going to need to  tag quite a few, both in and out of the water; it’s the reason we were there.  In the meanwhile, we busied ourselves with the other mechanics of the  operations. My next dive the following day was with James, installing a  radio receptor at 90 feet. These radio receptors are placed at strategic  locations around the islands, where they will record any shark carrying  one of our radio tags which pass within 500 metres of the receptor.    Conditions on this dive showed signs of improvement, visibility was up to  15/18 metres and temperatures were up a couple of degrees A long ascent meant lots of time to inspect the sea fans and other soft corals inhabiting the steep boulder drop off along with various bright anemones and the occasional strikingly blue nudibranch. Hieroglyphic hawkfish with a body pattern as their name suggest move in and out of reef spaces and numerous voided barnacle shells host the endemic Galápagos barnacle blenny, peering guardedly with its oversized goggle eyes at the world outside its protective casing.  The conundrum in dives such as this is always whether to spend your dive inspecting the array of fascinating resident organisms along the wall or face the blue in the hope of glimpsing a larger animal. 5 white tip sharks passed toward the end of the dive indicating increased large animal life; things were certainly looking better.  As we were now approaching the midway point of our ten day trip, our focus was turned to tagging sharks.

Our two types of tags required two separate and equally dramatic methods of placement. Satellite tags, which are useful for monitoring the long range movements of sharks, require careful placing toward the top of the shark’s dorsal fin, so that it may be received by satellites every time the shark comes close enough to the surface. Thus, the animal must be removed from the water, in a carefully executed operation, employing the expertise of local fishermen to catch the animal and a crew of biologists who maintain the shark’s condition by running water through its mouth and gills, the shark being out of the water for no more than 4 minutes. Every time we carefully attach a tag to this fin, we are reminded of one of the motivations for this research; the fin, so prized for its mythical and entirely unfounded qualities in shark fin soup in Asia, is driving these animals toward extinction. The information evolving from the studies will be used to learn how to better protect them as the establishment of marine protected areas needs comprehensive information regarding the movements and habitats of the animals they seek to protect.

The second type of tag is a radio tag which is designed to be detected by the array of radio receptors which are placed in strategic areas around the islands and by our own acoustic mobile tracking devices to gain an idea of shark movements and site fidelity.  That most athletic and demanding aspect of diving; freediving, is utilised to accomplish this task. Sharks display an aversion to divers bubbles and regular diving is simply too cumbersome to achieve this task which involves using a long spear to thrust the tag into the sharks dorsal flesh. It is wonderful to shed the bulkiness and restrictive apparatus of modern SCUBA diving and indulge in what feels like an altogether more primal and unadorned underwater pursuit.

Returning to Darwin Island, six days into our trip, we set about realising this role reversal of man chasing shark. The very real benefits to science and conservation are welcome outcomes of this pursuit normally associated with the more destructive practise of spearfishing.  Our patience for good conditions had paid off, we were greeted by 30 metres of visibility, and at times hundreds of hammerhead sharks schooling around Darwin’s Arch, a field site I will surely struggle to match in my scientific career.  Once again, the amount of life present was overwhelming. The powerful currents and abundance of sharks was complemented by schools of bottle nosed dolphins, begging the remarkable question of, which is the more captivating to freedive with, hundreds of hammerheads or dolphins? In between tagging events, we would slip quietly from the zodiac to the water, realising that the 20 or so dolphins seen on the surface is the tip of the iceberg in terms of the hundreds more occupying the water column below. Their whistles and clicks make you feel like a stranger in a foreign land, helpless amid a sea of incomprehensible tongues.

Image credit; Eduardo Espinoza

On day eight, our last dive was a final census at The Cleaning Station, with again, almost too much life to take account of. We were lucky to spot an olive ridley turtle, a relatively rare sight among the thousands of pacific green turtles one sees here. A variety of moray eel species including mosaic and jewel morays, all exhibiting intricate and complex body colouring patterns inhabit the reef spaces along the bottom. A quick check for the presence of a moray was advisable before clutching a reef crevice to steady oneself against the ever present terrific current. Solitary trumpetfish, unique in bodyshape, flit about above the reef, as do black durgon, a decorously appointed triggerfish, its black and white trim lending it a formal appearance amidst the assortment of colours  displayed by its reef companions.

A large school of brilliantly yellow Mexican goatfish was doing a good job of holding my attention until towards the end of our dive, as happens a lot in these parts, the small animals tend to be out competed for our interest by the larger spectacles when they arrive. This time we had the pleasure of viewing another school of hundreds of hammerheads from the bottom up, the perfect visibility enabling dramatic silhouettes between ourselves and the sun splashed surface 20m above.

Approaching the end of the trip one of our last tasks was the continuos tracking of a tagged shark for 48 hours using underwater acoustic equipment mounted aboard a small lancha (speedboat). Returning to Wolf Island, having successfully marked a number of sharks both in and out of the water, we set about finding our last shark to tag and be the object of our pursuit. A fruitless hour was spent looking for sharks under the south-eastern cliffs of Wolf, with the only interesting sight being two turtles copulating. A change of location found us above thirty or so hammerheads, James tagging one within seconds of entering the water from the dinghy. The pursuit was on, the information valuable in understanding movement patterns of sharks over small time scales. I was lucky enough to gain the nightshift, a most spectacular night spent under the moonlit cliffs trying to stay on top of a shark that spent 8 hours doing laps and never straying from a 300 metre zone.

Our journey back to Santa Cruz Island, where The Charles Darwin Research Station is based in the small town of Puerto Ayora was punctuated by some short dives to check on and change more radio receptors located around the archipelago. To round off our comprehensive review of marine life on our trip, dozens of manta rays presented themselves at Cousins Rock, where black coral and longnose hawkfish are found underneath the overhanging reef while at neighbouring Bartholomé Island Galápagos penguins jumped and swam proudly as the only penguins to be found north of the equator.

It is scarcely believable that the spectrum of wildlife detailed above encompassing coral, orcas and penguins is to be found on one ten day dive trip. I have been fortunate enough to view these diving wonders through the eyes of a scientific researcher, with our dives providing much more than just recreational wonder. The work we do will directly benefit our understanding of these animals as we seek to mitigate the destructive forces of over fishing, especially for the shark fin industry which based on anecdotal evidence has decimated Galápagos shark populations in the last twenty years or so. The effects permeate right down through the ecosystem, with major challenges ahead for the people responsible for managing the Galápagos Marine Reserve. This was scientific diving of the most exciting and dramatic calibre which now provokes the question as I dream of grinning Orcas, how does one follow this?

A mere three weeks after our arrival back in port a satellite image emailed from James exhibited the fruits of our endeavour and the scope of our capacity to track these powerful and ranging sharks. One of our tag recipients was already halfway to Cocos Island, some 500 miles to the northeast, halfway between Galápagos and Costa Rica. The other had followed a similar route for some time and now appeared to have changed direction, heading westward toward the open Pacific; one hopes far from the menacing longlines and an ungracious end at the hands of shark fin fishermen.

www.darwinfoundation.org

www.migramar.org

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