30 Days of OCEANS: John Cronin
A one-time commercial fisherman and one of the first official Riverkeeper’s to patrol a major U.S. river (New York’s Hudson), John Cronin long ago committed to attempting to protect waterways from up-close. In recent years he has chosen to focus his sights on the important link between ocean and river – our estuaries – as they are increasingly at risk. An excerpt from our new book, OCEANS, The Threats to Our Seas and What You Can Do to Turn the Tide.
Estuary is not a term that trips lightly off the tongue. It has a biologically suggestive sound, but human, like a vestigial organ located somewhere between the Isles of Langerhans and the Alimentary Canal. I don’t know if Ron knew of the word. I was raised in a city on the estuary, and never knew of it.
One way to understand an estuary is by its generic definition: a partially enclosed aquatic ecosystem where fresh water from rivers mixes with salt water from the sea. But I suggest you look up examples of estuaries and extract the essence for yourself. The lower 154 miles of the Hudson River is an estuary. So are Tampa Bay in Florida, Cook Inlet in Alaska, and the Tigris-Euphrates delta system in Iraq. To the unwary observer it would be difficult to find three water bodies that less resemble each other.
Most of the world’s population lives near estuaries . Most of the world’s major cities, such as Los Angeles, London, Tokyo and Calcutta, are located on estuaries. The geopolitical names of estuarine waters are better known than the fact they are estuaries, or are home to estuaries: Columbia River, Galveston Bay, San Francisco Bay, and Puget Sound; the Thames, Seine, Yangtze, Ganges, and South Africa’s St. Lucia. There are too many estuaries on the planet to name, or count.
Though the design and functioning of each estuary is singular, and can be arcane, they have essential things in common. The bottom lies below sea level allowing the tide to roll in. The freshwater that feeds the estuary flows overland, through tributaries and down rivers, from underground springs and aquifers, and from the sky above diluting the ocean salt. An estuary’s lowest reach is salty as the sea. Move away from the ocean and the waters become brackish, and then fresh in the furthest inland reaches. Were it not for all the fresh water draining from its watershed, what we call an estuary would simply be an arm of the sea.
This dynamism is the heart and soul of an estuary. One American Indian name for the lower Hudson was Muhheakantuck, loosely translated as “waters always in motion.” This is an apt description. An estuary’s ever-changing tides and currents constantly re-suspend sediments and food, energizing its incredible biological productivity. Fresh water perch and ocean sturgeon, young and adult, thrive at once in its rich nutrient soup.
American shad tell their own estuarine story. This largest member of the herring family is my role model, spending all its life following its ideal climate. Shad favor temperatures of 55 to 61 degrees Fahrenheit. They thrive in the coastal waters off Florida in winter, and around Canada’s Bay of Fundy come summer. The remainder of the year they orbit between those poles on the warming and cooling isotherms of the Atlantic Ocean. Their physical appearance suggests a life at sea: a deep, narrow body, 24 to 30 inches in length, built for long-distance swimming, with a distinctive blue-green iridescence along the back, and a silvery white underside.
In April, adult shad that hatched in the Hudson split off from the ocean-going population. Driven by a chemical trigger that roughly translates into an acute sense of smell, they find their way home after thousands of miles at sea. They take no time to feed during their upriver journey — and who can blame them? They are on their way to spawn, 100 miles north in the river’s freshwater reaches around Kingston, NY and beyond.
When their eggs hatch, the larvae slosh their way to the lower estuary along the flooding and ebbing currents of the tidal Hudson. By the time they are juveniles, sometime from late August to September, young shad are physically ready for the nourishing, brackish waters of the lower estuary, where the river is shallow and broad, the food, sunlight and plant life bountiful. When hearty enough, they head south for the saltier regions nearer the river’s mouth and, finally, to the ocean itself. Five to six years later, they return as mature adults to their original spawning grounds to perform the same ritual of reproduction as their forebears. In all, a remarkable piece of ecological choreography, repeated for millennia, on the Hudson and virtually every available inland tidewater on the coast.