14.7: Practical Applications of Tide Knowledge

Knowledge of tides has enormous practical use. Tide predictions are as important to ship’s captains as weather reports. You best know the tides before you set sail! Knowing the height of a tide beforehand is critical for safe navigation of watercraft. During times of extreme minus tides, rocks that may be submerged during normal times can appear above the surface. Many shipwrecks, ferryboat groundings, and other boating accidents happen during extreme low tides.

Tides also affect those of us who spend time near the shore. If you ever do any hiking along the Northern California–Oregon–Washington coasts, tide charts tell you when a particular stretch of beach is passable. For example, along the Lost Coast in Humboldt County, hikers have to wait for a low tide to pass around some of the headlands. Timing your hike with the tides is critical, otherwise you may have to wait several hours, or worse, be tempted to try something stupid like swimming around a point in pounding surf. Some have tried. I don’t have to tell you what happened to them.

Fishermen religiously follow the tides. Low tides along sandy coasts mean good clamming. On the Washington coast, people “dig” for razor clams using a clam gun, a hollow metal pipe with a handle at one end. By shoving the pipe into the sand at the location of a clam siphon, and pulling it out of the sand, you capture the clam inside a column of sand. All you have to do next is spill the sand onto the beach and grab the clam before it digs back into the sand.

Tide predictions let you know the best times to observe marine organisms in the rocky intertidal zone, the region of a rocky shore alternately exposed and submerged due to the tides. You’ll also find tidepools, the shallow water-filled depressions in rocks that appear when the tide is low. During minus tides, a dazzling variety of organisms may be observed, including sea anemones, hermit crabs, and sea stars.

Of course, the best reason to own a tide chart is so you know when to see the most fabulous nighttime beach event of all, the California grunion run. From March through August, on beaches from Morro Bay, California, to Baja California, these anchovy-sized fish swarm the beach to perform their mating dance. Grunion runs typically occur two to four days after the new Moon or full Moon (i.e., at the time of the spring tide) and one to three hours after the high high tide, which occurs at night in Southern California. Though the entire event may unfold over hours on a given night, the actual mating of a pair (or trio) of grunion takes less than 30 seconds. Because the height of the high high tide following the new or full Moon is lower each night (from spring to neap), the eggs remain covered in sand on the beach for 10-14 days until the next spring tide. When the incoming waves wash up on the beach and soak the eggs, out pops a little larval grunion, not even an inch long. The larval fish swims into the surf, never to be seen until it reaches adult size and is ready for mating.