Heading west from the park, pick up afternoon treats at New York iconic Zabar's food market (2245 Broadway), and later, as dusk unfolds, meander the serene firefly-flecked Riverside Park amid the Upper West Side's manifold joggers, strollers and dog owners, to the stunning outdoor 79th Street Boat Basin Cafe (W 79th St at the Hudson River) for a huckleberry vodka nightcap.

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According to Dr McMahon, a big part of the problem is that both species can survive out of the water for several days, so transporting a boat overland from one river basin to another, a common practice in North America, will not necessarily kill them.

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The Calverts lived part-time on their yacht, docked at the island's Harbor Town Yacht Basin, the same marina where they managed boat slips.

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