The Alphabet of Light and Dark by Danielle Wood

A tiny coin found inside a Cloudy Bay oyster, a postcard of a white-haired child leaning against a beached dinghy and a coconut peeled and carved once upon a time on the Batavian coast. These trinkets, found in a sea chest, and the fragmented memories of her grandfather's tall tales are all Essie Lewis has left of her family history.
After her grandfather's death, Essie returns to Bruny Island, Tasmania and to the lighthouse where her great-great-grandfather kept watch for nearly 40 years. Beneath the lighthouse, she begins to write the stories of her ancestors. But the island is also home to Pete Shelverton, a sculptor who hunts feral cats to make his own peace with the past. And as Essie writes, she finds that Pete is a part of the history she can never escape.