“How deep can you dive?” It’s a question frequently asked by Aquarium visitors attending one of our daily diver shows. And it prompted us to look into depths overall—specifically, what you might see at various depths in Puget Sound.
First, some perspective. The Space Needle, that towering icon of the Seattle skyline, is 650 feet tall. Puget Sound, at its lowest point just north of Seattle, is almost a full third deeper: 930 feet. And there’s plenty going on between the surface and the low point. For instance…
0–300 feet deep:
Sunlight limits bull kelp growth to depths of about 80 feet. Scuba divers are typically certified at depths down to 130 feet, but this can be increased with specialized equipment and gas mixtures. The shallow-dwelling cabezon (a cool-looking fish that lays poisonous eggs!) has been observed down to 250 feet. Sea otters can descend to depths of up to 300 feet. Marine mammals can induce bradycardia, slowing their heart rates from 55–120 beats per minute to 4–15 beats per minute to conserve oxygen while diving. In this state, their bodies shunt blood toward the brain and heart, preserving these essential functions during a deep dive. Marine mammals also collapse their lungs and store oxygen in their muscle tissue when diving, to prevent pressure-related injuries and help them sink rapidly (alcids do this too—see the next section for more details!).
300–600 feet deep:
At this range, we might find some of the same animals seen on the beach at low tide, such as the leather star. Down to 300 feet, this star can find its prey, such as anemones and sea pens. The average depth of Puget Sound, by the way, is 450 feet. Amazingly, the common murre has been documented at a depth of 492 feet below the surface. Alcids, or diving birds, have a variety of adaptations that allow them to dive deeply, including: special muscles for flattening their feathers and pushing out trapped air to reduce buoyancy; a clear nictitating membrane, or “inner eyelid” to enhance their vision underwater; and the ability to slow their heart rates during dives, reducing their need for oxygen.
600–900 feet deep:
Below 600 feet is considered “the twilight zone” because little light penetrates at this depth. Photosynthesis is not possible. You might be surprised to learn that surface-dwelling salmon can be seen at depths of up to 820 feet. They typically spend time near the surface to find their food, but may need to dive that deep to avoid becoming food themselves.
900–1,200 feet deep:
The deepest part of Puget Sound is off Point Jefferson, five miles northwest of Seattle, where the sea floor drops to 930 feet. Rockfish, on average, are found at depths of around 900 feet—but they’ve been documented well past 3,500 feet and are adapted for extreme high-pressure, low oxygen environments. Orcas average 1,000 feet.
Interested in learning more? Visit the Seattle Aquarium and don’t miss our daily diver shows!