Casco Bay

The 500 acres of rocky shore in Casco Bay provide habitat for a wide range of species, from seaweeds, periwinkles, mussels, barnacles, and crabs to starfish and seals. Waterfowl such as eider ducks use rocky shore habitat for feeding. The composition of the sea bottom (i.e., fine mud, sand, gravel, cobble, boulders, and rock) determines which plants and animals live in particular subtidal habitats. For example, lobsters, crabs, and sea urchins generally live on hard bottom, whereas scallops and worms dwell in soft-bottom areas. Thirty-six species of finfish reside in Casco Bay. The most abundant year-round fish in the bay are bottom feeders such as pollock, sculpin, and skate. The shallow protected coves in Casco Bay provide perfect spawning habitat for fish that deposit eggs on the bottom (e.g., sculpin, winter flounder, rock gunnel, tomcod, and skate). There are numerous marine mammals in Casco Bay including two species of seals, four species of whales, two species of dolphins, and harbor porpoises.

Casco Bay contains 758 islands, islets, and exposed ledges at mean high tide, a few of which are important habitat for colonial nesting seabirds. Uninhabited outer islands often provide prime nesting sites for seabirds, being inaccessible to predators such as fox, mink, and racoons. The bay has 50 seabird nesting islands, of which 17 support nationally significant populations of nesting birds. The 17 major nesting colonies collectively represent more than 15 percent of the states nesting seabird population. There are 41 documented seal haulouts in Casco Bay, on either small islands with no terrestrial vegetation or half-tide ledges that are under water at high tide.