Waking to a fogged-in harbor, I feared our plans for a seafaring excursion would be scrapped, but by the time we’d finished the hearty breakfast quiche at our B&B, the heavy cover seemed to be slowly lifting.

I’d had to do some digging online and make a few calls, but I finally tracked down a boat captain willing to take us out to Seguin Island, a remote spit of land measuring only 64 acres, about two and a half miles out to sea, and this was the morning for our adventure. (When I contacted t...