Natural History

NOAA Chart #13283

The Isles of Shoals Archipelago is composed of nine islands and numerous rocky ledges, six miles (10 km) off the New Hampshire/Maine border in the western portion of the Gulf of Maine (Click here to view maps of Appledore Island). Appledore Island is one of five islands located in Maine and is the largest (95 acres; 39 ha) and highest (65 ft.; 20 m) of all the Isles.

Dorias et al. 2014

The Isles are the remnant base of an ancient mountain formed 300-400 million years ago that subsequently was eroded and most recently, scoured by ice sheets from the northwest during the Last Glacial Maximum (23,000 to 19,000 years ago). After the ice sheet receded, the Isles were connected to the mainland when the sea level was nearly 200 ft (60 m) below present levels, but gradual emergence of the Isles after the heavy ice receded and the sea level rose due to worldwide melting of glacial ice, led to separation from the mainland about 7000 years ago.

Vegetation colonized accumulated glacial til and the initial mosses and lichens, along with seabird nesting activities, began to form shallow layers of soil for subsequent colonization by more and larger species of plants. The maritime location of the Isles insures considerable deposition of salt spray, which profoundly affects virtually all island vegetation (e.g., growth, morphology, reproductive success). Appledore currently supports nearly 200 plant species (native and introduced), but the maritime exposure and shallow soil probably never supported many, if any, sizable trees. Several introduced plant species are present with the most common being purple loosestrife (Lythrum salicaria) and Japanese knotweed (Fallopia japonica). Fourteen distinct plant communities are present, ranging from salt marsh to moist shrub thickets with maritime shrub thicket and maritime meadow the dominant. The first botanical observations in the 1600's revealed a strong similarity to current patterns of vegetation cover and composition, undoubtedly because of the low level of human impact in both periods.

Crystal Lake, Appledore Island

From the late 1600s through the hotel era in the early 1900s, however, human presence and activities drastically reduced both plant diversity and abundance.  Subsequently, the intense human use of the Isles, in conjunction with sea bird nesting activities, probably explains the higher proportion of non-native vascular plant species on the Isles (42%) than in New Hampshire (27%) and Maine (30%).


No streams or running water exist on any of the islands, but fresh water ponds and springs are present on some and the largest of these are on Appledore.  Two of the three fresh water ponds on Appledore (North, Central), occasionally dry out during a dry summer, whereas the third (Crystal Lake) rarely dries completely but can be significantly reduced.

Marine Environment


The Isles of Shoals lie within the Northern Coastal Shelf, one of several marine physioregions in the Gulf of Maine, and are characterized by a variety of habitat types and complex bathymetry, as well as high biological productivity.  Numerous subtidal ledges (e.g., Jeffreys Ledge, Caches Ledge) and deep basins (e.g., Jeffreys Basin, Scantum Basin, Wilkinson Basin) are present, with substrata ranging from extensive bedrock to sand and gravel. The predominant surface current in the Gulf of Maine is broadly counter-clockwise, with water entering from the northern Scotian Shelf via the Northeast Channel and exiting via the Great South Channel just north of Cape Cod in the south.  A smaller clock-wise circulation pattern is found around Georges Bank east of the Gulf of Maine.

Gulf of Maine Council 2010



Nearshore water temperatures at the Isles vary according to tides and protected/exposed coast (colder on exposed), but range from 35-70°F (2-21°C) during the year. However, the Gulf of Maine has warmed faster than 99.9% of the world’s oceans between 2004 and 2014.


Gillemot chick

Over 200 species of songbirds and waterfowl occur on Appledore as migrants, winter visitors, or vagrants from the mainland and since 1974, over 175,000 individual songbirds from 90 species have been banded.  Since 1990, songbird banding has continued under auspices of the Appledore Island Migration Station, which is committed to the long-term study of nesting and migratory birds during spring and fall stopovers. The gray catbird is by far the most common of 12 songbird species regularly nesting on Appledore, followed by the common yellowthroat and song sparrow. Nesting waterfowl utilize the freshwater ponds and nearshore habitats of Appledore and include mallard and American black ducks, common eiders, Canada geese, and black guillemots. Essentially no common eiders were present before 1970, but over 200 nests were recorded in 2016. Snowy owls have started to overwinter on Appledore in the last four years.

Black-backed and herring gulls were severely depleted along the US east coast during the 1800s because of egging and shooting for feathers in the millinery trade (beginning in 1876). By 1900, black-backs were found only north of the Bay of Fundy and herring gulls only on the islands of eastern Maine (10,000 pairs).  Herring gulls began to nest on Duck Island in the early 1920s and the first record of black-backeds breeding in the US was on Duck Island in 1928. During the 1940s, both species began nesting on Appledore and gradually increased after WWII after the island was abandoned by military personnel, open landfills and dumps appeared on the mainland, the Migratory Species Act (1914) was passed (which protected gulls), and lobster fishing increased (providing lobster bait and other waste). Herring gull numbers on Appledore have dropped considerably since 2003 probably because several mainland landfills have been closed and increased predation by black-backed gulls (primarily on chicks) and 13 raccoons (introduced and removed in 2004). The black-backed population, however, has remained relatively constant.

Great Black-backed Gull

The Appledore Island Gull Banding project was initiated in 2004 with project leaders and students banding hundreds of adults and chicks of each species each year. The project monitors adult abundance, chick abundance and survivorship, and off-island resights.  Most resights occur along NH and MA beaches, but Appledore gulls have been resighted in Florida and Texas. Gull populations now seem to have stabilized, with about 700 pairs of herring gulls and 500 pairs of great black-backed gulls nesting on Appledore each year from 2009-2016.

Roseate Tern

Supported by the New Hampshire Fish and Game Department, the SML Tern Conservation Program implements research, restoration, and management of threatened and endangered terns on White and Seavey Islands in the Isles of Shoals. These islands are New Hampshire’s only successful breeding colony for Common (Sterna hirundo), Roseate (S. dougallii) and Arctic (S. paradisaea) terns, and are therefore a key conservation focus for the state.

Fluctuating populations of muskrats (commonly sighted) and Norway rats (rarely sighted) are present throughout the year.  Genetic studies have revealed that the muskrat population probably was introduced in the early 1900s from the Rye (NH) area for the fur trade; rats undoubtedly were introduced when Europeans first settled in the area in the 1600s. An indeterminable number of bats migrate over and/or briefly stop on the island. The smooth green snake and northern brown snake were introduced in the 1930's. Red-backed salamanders and painted turtles were first observed in 1987 and 2005, respectively.

Harbor Seal

Hundreds of harbor (Phoca vitulina) and grey (Halichoerus grypus) seals haul out on Duck Island and adjacent ledges during the summer (some harbor seals also pup on the island in spring) and have been monitored photographically by SML research interns since 2011.  In 2016, over 800 seals were observed at times, consisting of ca 600 and 200 harbor and grey seals, respectively. Adult seals of both species rarely, if ever, haul out on Appledore, although young harbor seals occasionally are observed in late summer.


Intertidal zone

The intertidal and shallow subtidal are inhabited by over 130 species of macroalgae and over 450 species of invertebrates; over 60 species of fish are found in nearshore waters. The overall species composition is essentially a subset of European and Icelandic marine communities, with a similarity to cold-water Canadian Maritime communities at depths greater than 60 ft (20 m). Introduced species of macroalgae and invertebrates are common on Appledore and in some cases, become a dominant component of the intertidal and/or subtidal assemblages. Dominance is highly variable and unpredictable, ranging from one year/season to decades. Tunicates (e.g. Botryloides violaceus, Didemnum vexillum, Diplosoma listerianum, Botryllus schlosseri), bryozoans (e.g., Membranipora membranacea, Tricellaria inopinata) and macroalgae (e.g., Codium fragile, Daysiphonia japonica, Colpomenia peregrina) are the main groups of introduced species. Other ecologically important introduced species include the periwinkle Littorina littorea (and two other species of Littorina), the green crab (Carcinus maenas), and Asian shore crab (Hemigrapsus sanguineus). Intertidal flora and fauna have been quantitatively monitored at five sites (exposed and sheltered) with replicated permanent vertical transects and photoplots by SML research interns since 2011. Intertidal temperature data have been collected continuously in exposed and sheltered locations since 2014.

Bathymetric view of Jeffreys Ledge in the eastern Gulf of Maine

The waters around the Isles of Shoals hold a great diversity of fish. The most common species in the shallow nearshore subtidal during summer months are the cunner (Tautogolabrus adspersus), pollock (Pollachius virens), winter flounder (Pseudopleuronectes americanus), rock gunnel (Pholis gunnellus),  sculpins (Myoxocephalus spp), haddock (Melanogrammus aeglefinus), Acadian Redfish (Sebastes fasciatus), and spiny dogfish (Squalus acanthias). Atlantic Cod (Gadus morhua) are found in the area with breeding locations located in nearby Ipswich Bay and off shore. Atlantic bluefin tuna (Thunnus thynnus) are summer visitors to surrounding waters and Jefferys Ledge, located just off shore of Appledore island are known for productive fisheries.

Full Species lists are maintained for Shoals Marine Laboratory for flora and fauna.