As a former lifeguard and current triathlete, I've logged hundreds of hours swimming in the Pacific Ocean, and during all that time, the thought of a shark attack has never been far from my mind.

I immediately think "Shark!" when a piece of kelp unexpectedly brushes up against my arm, when I spy through my swim goggles a shadowy figure of a large fish below or when I see a dolphin's dorsal fin pop up near me. There are times when I've unexpectedly bumped into something -- such as a buoy -- and screamed and jumped halfway out of the water.

Those of us who swim in the open ocean -- we number in the thousands in Southern California -- know the odds of a shark attack are extremely low, especially in the waters off our coast. We have a better chance of getting killed driving to the beach. But fear and rational thought are poor companions. As Mitch Thrower, co-owner of Triathlete magazine, says, we've been 100,000 years getting to the top of the food chain. Once we enter the ocean, we give that up. And unlike surfers or bodyboarders, we have nothing between us and the ocean.

Open-water swimmers overcome their constant, if mild, fear of a shark attack because of the allure of the ocean. Unlike a swimming pool, the ocean has no black line along the bottom. In the Pacific, you are freed from boredom. It's the difference between jogging in circles on a track and running on a trail through a forest.

The views -- the sea life below and the boats, pelicans and coastline above -- are often breathtaking. The smells of salt water, kelp and sunscreen all fuel the thrill of being in the aquatic wilderness. And the rhythmic sounds of bubbles passing by my ears serve as my iPod during workouts.

The triathlete and the open-water swimming communities are tight. And the death of triathlete Dave Martin, 66, stunned us all -- especially because he was swimming in a group, not far from shore. Each of us is thinking: It could have been me.

Dave Martin will weigh heavily on our minds as we swim over the coming weeks. By all accounts, he was a wonderful guy who still competed in triathlons at an age when he would qualify for Social Security. This isn't unusual for our sport; it's what makes it special.

We swimmers will be back in the ocean this weekend, working out for our next triathlon or open-water event. But with each stroke, we'll remember Dave Martin, our brother triathlete. And we'll think about sharks.

william.lobdell@latimes.com