Note: I wrote this story in 1990 only few months after Bob Cranston and I began diving with closed-circuit rebreathers that we had leased from Biomarine. Much has changed during the past sixteen years. Rebreathers have become mainstream and hammerhead sharks are seldom seen on the Marisula Seamount (El Bajo) in the Sea of Cortez. To my knowledge, no one has seen hammerhead sharks mating before or since.

The Sound of Silence

Howard Hall

Bob Cranston and I stopped at the anchor chain and waited as Marty Snyderman dropped to the Marisula Seamount and found a position to film our descent. His exhalation bubbles collided with us producing a roaring cacophony of sound like a dozen pop bottles being shaken in a burlap bag.

Marty gave us a “roll” sign and Bob and I dropped sixty feet to the Seamount and began swimming north. At the edge of the Seamount where the wall falls away into deep water, I paused to look over my shoulder at Marty. He had finished his shot and gave us a parting wave before returning to the Ambar III. For a few moments I continued to hear the receding rumble of Marty’s bubbles, but soon he was gone. Bob and I were left in silence on the Marisula Seamount. I had been dreaming of hearing this sound ever since seeing an ad in Skin Diver Magazine for an Electrolung closed circuit rebreather in 1969.

The dark water north of the Seamount beckoned. I checked the gas mixture display on my left wrist then I checked Oxygen partial pressure readings on the three Oxygen sensors inside my Mark 15.5 rebreather. Next, I checked the two battery voltage readings on my secondary display then I checked my Oxygen tank pressure and my diluent gas pressure. All the readings were within normal ranges. I looked over at Bob as he finished dialing through his Oxygen sensor readings for the second time. He gave me the okay sign and we cast ourselves off the edge of the Seamount into deep water. No bubbles rose to mark our passing. The Mark 15.5 produces no bubbles and is almost totally silent.

At one hundred feet my breathing became restricted. A valve in the diluent injection system was malfunctioning and not adding diluent gas as my depth increased. I reached around next to my left hip and injected the gas manually. I didn’t break stride. I was almost as familiar with this system as I am with my standard SCUBA gear. Bob and I expected problems with the gear and we had trained long and well in preparation for dealing with systems failures.

At 110 feet we followed a sand channel on the top of a ridge that ran north of the Seamount. Garden eels withdrew into the shell rubble as we passed. I could hear pistol shrimp snapping their claws as they hid in the rocks. And I could hear the occasional rumble as a large game fish rushed through fleeing schools of small jacks. These ambient sounds almost overwhelmed the nearly imperceptible hiss as my rebreather injected Oxygen into my breathing mixture.

Beyond the end of the sand channel I could see a dark cloud filling the sky. Suddenly something loomed over my head overtaking me from behind and I instinctively ducked. A hammerhead shark had followed us up the sand channel and passed only two feet over our heads. Just as I regained my composure, another shark passed over our heads. I turned to look down the channel and saw a dozen more sharks coming our way. I turned my 16mm movie camera in their direction and began rolling as shark after shark traveled up the sand channel and passed within inches of Bob and me. They seemed unaware of our presence. Our dark suits, black backpacks and black cameras blended with the rocks. We were ignored.We were part of the reef. The sharks continued up the sand channel then rose, angling upwards before disappearing into the dark cloud in the distance.

We crawled slowly to the end of the sand channel where a small rock ledge marked the end of the ridge. I hid behind a large gorgonian coral and Bob took shelter between two large boulders. We melted into the reef, silent and unseen. The cloud darkened as it approached. I tried to calm myself as I prepared for an experience I had dreamed about for more than a decade. I became aware of the sound of my own heartbeat. On standard SCUBA I would be trying to breathe deeply, trying to calm myself, to conserve my air. But with the Mark 15.5 I could breathe as much as I wanted and still stay down for over six hours.

The cloud became sharks. Hundreds upon hundreds of hammerhead sharks. They began passing overhead and soon the sky filled with them. In all directions, as far as I could see, from the ocean floor to the surface, there were hammerhead sharks. I raised the camera and silhouetted a hundred sharks against the sun. No bubbles escaped to spoil the shot. I let the camera roll for two minutes then turned it off. What now? After dreaming of taking this shot for years, what now? I looked over the wall and saw that small Mexican hogfish were cleaning the passing hammerheads, something I had never seen before. I adjusted the exposure and began rolling. Twenty seconds later I shut off the camera realizing that I would have to get much closer to get a usable shot. I’d have to get within four or five feet.

I slipped over the wall and dropped ten feet to the sand at 130 feet, moving very slowly. I looked up at the sun and saw that there were still hundreds of sharks passing overhead. I turned the camera toward the sun and shot another silhouette before remembering that I had already shot a two-minute silhouette only moments ago. I brought the camera down to look for more cleaning behavior.

An “alarm” light ignited on the display on my left wrist. Bad news. I immediately dropped the camera on its lanyard and checked the oxygen sensors and battery readings. The oxygen levels were high and out of normal range. I could hear the solenoid pumping more oxygen into my breathing mixture. I reached around behind my back and pulled down the switch that shuts the rebreather electronics off. The lights on my display went out and the solenoid stopped firing. For the rest of the dive I would mix my gases manually. For a brief moment I silently applauded the self-training Bob and I had endured.

I looked up at Bob and showed him my unlit wrist display then I gave him a familiar hand signal to indicate that it’s not working. Bob asked if I was okay and I motioned that I was fine and entirely in control. Bob knew the drill.

A dark shape suddenly began falling out of the sky towards Bob. I raised the camera and began swimming directly at Bob as fast as I could. He became flustered knowing something dramatic was happening, but not knowing what or where to look. Twenty feet above him two hammerheads were locked together in mating. The smaller male had his jaw clamped tightly to the larger female’s pectoral fin. His clasper was deep inside her. Locked together in this fashion the two sharks could not swim and because sharks are negatively buoyant, they were plummeting head first straight down toward the bottom! Actually, straight towards Bob’s head!

Four seconds later the sharks crashed into the reef so close to Bob that he could hear the sound of the tubastraea coral being crushed. The ten foot female and six foot male landed less than two yards away. They immediately separated and swam away. Had they hit Bob, his injuries might have been serious. It was the first time actual mating had been observed in the hammerhead schools. In fact, to my knowledge it was the first time hammerheads had ever been observed mating. And I got it on film! I was so excited my knees started to shake. I dropped the camera and checked my oxygen readings. All three readings showed 1.1 atmospheres of oxygen. I reached down by my right hip and injected a burst of oxygen into the system. Then I checked our bottom time. Bob and I were already looking at thirty minutes of decompression and we still had yet to navigate nearly a quarter mile back to the Seamount and the anchor chain of the Ambar III.

Out of film, Bob and I began following the sand channel south, back toward the Marisula Seamount. During the entire swim, we continued to be surrounded by the enormous school of sharks. How many were there? One hundred sharks in a frame at one time. How many different directions could I point the camera and get a frame like that? How many sharks? Six hundred? Eight hundred? And how many did we swim through during our navigation back to the Seamount?

We crossed the short sand plain separating the ridge from the Seamount. Only then did I see the school recede and disappear. Rising to the top of the Seamount at sixty feet I saw a column of bubbles. Mark Conlin was waiting to guide us back to the safety of the anchor chain. He was waiting and wondering if we had seen any sharks.

Mark took my camera and left Bob and me alone on the anchor chain as we began forty minutes of decompression. I looked over at Bob and he shook his head. I knew what he was thinking. I shook my head back. “Yeah, I can’t believe it either. That wasn’t included in our training. When diving with rebreathers we must also remember to check for sharks falling out of the sky.”