Tides dictate livelihoods from the sea
Ebb & Flow
by Amandine Surier
The earth has many rhythms, and tides are the oceans’ beat. Twice a day, the sea rises and falls, pulled by the monumental masses of the moon and sun. Back in Normandy where I grew up, ebbing tides gave me mile-long playgrounds only to claim them back a few hours later. Irked by the inevitable daily loss of the hundreds of wading pools full of crabs and minnows, I started asking questions and realized that the man on the moon was to blame. It is useful to remember that gravitational forces exerted by an object like the moon, are proportional to the distance to this object. In short, the closer we are to the moon, the stronger we are being pulled towards it. Imagine yourself on a Vineyard beach, standing in the water. When the moon is directly up above (i.e. a zenith moon), gravitational forces pull the water upwards and the tide is high.
Twelve and a half hours later, the earth has rotated and the moon is directly on the other side of our planet. Although in this configuration the moon is the farthest it can be from us, the tide is also high on our Vineyard beach. Why? It’s all about the force of the moon. The gravitational pull exerted on the earth is strong—stronger than the pull exerted on the water we are standing in. So it appears to us that the water is rising, when it’s really the earth that is being pulled in the opposite direction. In between these points, the diagonal or transverse force pulls the water down, causing the tide to fall.
Every two weeks, when the moon is new or full, the sun, moon and earth align. The gravitational pull of the sun is added to that of the moon, and the range of the tide is at its maximum (spring tide). When the moon is at first or third quarter, the sun and moon form a 90° angle with the earth and cancel each other out. That’s when the tide is at its minimum (neap tide).
The geographical shape of the nearshore bottom also affects the range of the tide. The shallower the bays, the further the sea will pull back during low tide. The Bay of Fundy in Canada experiences the largest tidal range in the world with the sea dropping 53 feet during a tidal cycle. Back home, the English Channel is quite shallow and so my childhood was filled with tales of tides ebbing farther than the eye could see and rising as fast as a galloping horse—claiming the lives of wandering sheep and incautious shell seekers.
But on the Vineyard, I rarely think of the tide. The bottom drops fast in ponds and bays, and at the Shellfish hatchery’s pier, where I work in Vineyard Haven, low tide might uncover an extra 20 feet of rocks. I tend to forget that for watermen, tides still set the rhythm to fish—and hence live—by.
Jack Blake, an oyster grower in Edgartown, needs to wait for slack tide (when the tide slows down right before turning) to tie buoys on his cages. He has only 40 minutes in the day to do it, otherwise the current is too strong. When Jack fished for hard clams, knowing the tides was even more critical. “When I was quahogging, I knew the tides exactly,” said Jack. Since he was going every day, he would just add 40 minutes to know when the tide was the next day. “I also had a tide clock at home,” said Jack. Tide clocks keep track of the moon’s apparent motion around the earth, they tell you when high and low tide are in your area. “I never had charts or looked at the newspaper, I always knew,” said Jack. He worked six hours—four before low tide and two after. When the first low tide occurred at daybreak, he could go quahogging twice a day.
“I like a low tide for striper fishing” said Tony Jackson, who fishes from the shores almost every day, “It seems to be lucky for me. In the middle of the tide when it’s really ripping hard, your lure doesn’t work the right way and fish seem harder to catch,” he explained. Tony likes to fish a few days before and after, a full moon. He also just “knows” when the tide is, but when he needs a reminder, he goes by the newspaper tide chart, “It’s not accurate at all in Edgartown (since the opening of the barrier beach). Not even a little bit,” he laughed, “but it’s pretty accurate everywhere else.”
As for those who make a living offshore on lobster or conch boats, knowing the tide can save precious time, fuel, and money. “If I’m going through Vineyard Sound for conching, I always check to leave on a fair tide,” said Wes Brighton, a lobsterman out of Menemsha harbor. “You gain so much speed and save so much time.” Wes owns an Eldridge Tide and Pilot book, a chart that has been published by the same family for the past 130 years. But he rarely checks it. It seems that once you’ve lived with the ocean’s rhythm, it never leaves you.