In 1984, I found myself on a research expedition off the coast of New Caledonia, a picturesque archipelago located 750 miles from Australia. This mission aimed to observe the daily movements of the nautilus, recognized as the longest-living marine creature known to science. Among my companions was Mike Weekley, a 26-year-old marine biologist with a wealth of experience and remarkable diving skills.

On the fifth day of our expedition, we spotted thieves attempting to raid one of our holding cages tethered to a buoy, where we had secured ten nautiluses for our studies. Nearby, a long rope led down to a deeper cage, where we were conducting an essential experiment to determine the maximum depth at which a nautilus could expel water from its chamber.

As we raced toward the thieves, our French captain readied his rifle, but they were already too far ahead in their swift boat. We noticed them lifting the buoy of the first cage from a mile away. Had they discovered the deeper cage? Mike and I quickly plunged into the water. Fortunately, both the rope and the cage remained intact. My task was to inspect the rope for any damage while Mike was to keep aggressive white-tip sharks at bay. After a few minutes, I turned to signal to Mike, who should have been close behind. To my horror, he was nowhere to be seen, only a barely audible “hoot” emanating from below.

The waters around New Caledonia are remarkably clear. As I peered down, I spotted a small figure far beneath me, eerily still. My heart raced as I descended past the 100-foot mark of a sheer reef wall, the figure becoming more distinct. I willed it to move, but as I crossed the 200-foot threshold, nitrogen narcosis hit me like a freight train. When I reached Mike, he was nestled in black coral, like a child cradled by its mother. His regulator hung uselessly, and I pushed it back into his mouth, praying he would inhale. In that moment, I realized the gravity of the situation as I looked into his eyes; they reflected a silent scream of terror.

I pulled Mike from his resting place and began our ascent, attempting to expel air from his lungs before it expanded