Maine's eelgrass meadows form an important marine and estuarine coastal aquatic habitat for the state. Along with other plants, eelgrass forms the base of food production in the sea. Eelgrass provides shelter for juvenile fish, and invertebrates, is a site for primary settlement of the larvae of some bivalve mollusks, and in certain locations helps to stabilize unconsolidated sediments and shorelines. Between 1992 and 2013, various regions of the coast were flown and photographed. Photography was timed near low tides with low wind velocity, good water clarity, and maximum biomass of eelgrass. These factors aid in the detection of the subtidal portion a bed. Polygons delineating stands of eelgrass were screen digitized and coded using a four category scale of percent cover. Verification was carried out by boat, on foot, and by plane. Though dense patches of eelgrass approximately 6 meters in diameter and less can be identified under good conditions and in some cases were mapped, a conservative estimate of the minimum mapping unit is 150 square meters. This represents a stand of approximately 14 meters in diameter.

Eelgrass 197 contains polygons representing Maine's eelgrass meadows, which form an important aquatic habitat for the state, suitable for mapping at 1:24,000 scale. These meadows provide shelter for juvenile fish, and invertebrates. In certain locations they also help stabilize unconsolidated sediments and shorelines. As a continuing project, sections of the coast have been flown and photographed using Kodak 2448 film at a scale of 1:12000. This photography has been supplemented in the Penobscot Bay region by 1992 flights using Kodak 2445 film. The Penobscot Bay flights were contracted by the Maine Department of Transportation and interpreted by Dr. Fred Short of University of New Hampshire. Areas in the present study were flown in the July to October period during 1993 to 1997. When possible, photography was at the time of extreme low tides, low wind velocity, good water clarity, and maximum biomass of eelgrass. These factors aid in the detection of the subtidal portion a bed. Transparencies from the 1993-1997 flights were oriented beneath and eelgrass bed locations compiled on stable-base manuscripts containing the coastline and other basemap features from the 1:24000 scale USGS topographic maps. Polygons delineating stands of eelgrass were digitized and coded using a four category scale of percent cover. Verification has been carried out by boat, on foot, and by plane. Though dense patches of eelgrass approximately 6 meters in diameter and less can be identified under good conditions, a conservative estimate of the minimum mapping unit is 150 square meters. This represents a stand of approximately 14 meters in diameter.

This dataset depicts the locations of eelgrass meadows off the northeast seaboard of the United States. Eelgrass (Zostera marina) meadows are critical wetlands components of shallow coastal ecosystems throughout the region. Eelgrass meadows provide food and cover for a great variety of commercially and recreationally important fauna and their prey. Eelgrass and other seagrasses are often referred to as "Submerged Aquatic Vegetation" or SAV. This distinguishes them from algae, which are not classified as "plants" by biologists (rather they are often placed in the kingdom protista), and distinguishes them from the "emergent" saltwater plants found in salt marshes. In addition to the term SAV, some coastal managers use the term SRV or submerged rooted vegetation. The Eelgrass Meadows layer was created from several separate datasets for the states of Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, and New York. Where possible, polygon datasets depicting the most recent eelgrass surveys were used. Attributes with common themes for each dataset were integrated in order to better represent eelgrass density and year sampled. The data user is encouraged to read this and the metadata of each individual state’s data carefully, as geometry, attribute details, and timeliness are not necessarily consistent among datasets used to develop this layer. Details of each state’s data source are described in the data processing section of the metadata. Note that the eelgrass distribution data is presence-only. Because surveys of eelgrass do not encompass all coastal waters, absence of eelgrass in a particular place on the map does not necessarily mean that eelgrass does not live at that location.View Dataset on the Gateway

Maine's eelgrass meadows form an important marine and estuarine coastal aquatic habitat for the state. Along with other plants, eelgrass forms the base of food production in the sea. Eelgrass provides shelter for juvenile fish, and invertebrates, is a site for primary settlement of the larvae of some bivalve mollusks, and in certain locations helps to stabilize unconsolidated sediments and shorelines. Between the years 2001 and 2010, sections of the coast were flown and photographed using Kodak 2448 and 2427 film at a scale of 1:12000. Areas in the present study, were flown in the months of June though September during the 2001 to 2010 time period. When possible, photography was at the time of extreme low tides, low wind velocity, good water clarity, and maximum biomass of eelgrass. These factors aid in the detection of the subtidal portion a bed. Polygons delineating stands of eelgrass were screen digitized and coded using a four category scale of percent cover. Verification was carried out by boat, on foot, and by plane. Though dense patches of eelgrass approximately 6 meters in diameter and less can be identified under good conditions and in some cases were mapped, a conservative estimate of the minimum mapping unit is 150 square meters. This represents a stand of approximately 14 meters in diameter.

The dataset shows the locations where eelgrass was observed during the 2021 field season within the following waterbodies: Great Bay, the mouth of the Squamscott River, the tidal portion of the Lamprey River, the tidal portion of the Oyster River, the tidal portion of the Bellamy River, the Piscataqua River and Portsmouth Harbor and its associated creeks, and the coastal shore of Odiorne Point. Photointerpretation was completed on orthophotography collected using a UAV within Great Bay and Little Bay. Aerial orthophotography from the State of Maine was utilized to allow for photointerpretation of the Piscataqua River region, Portsmouth Harbor, Little Harbor, Newcastle, and Oriorne Point areas. Sentinel satellite imagery was also used to further complement these datasets to help within photointerpretation. Vertical UAV imagery was collected as five spectral bands inclusive of RGB, Red-Edge, and Near Infrared bands. Imagery was collected with varying 1.7 to 3.4 cm spatial resolutions based on 100 to 400 ft flight altitudes specific to FAA maximum flight restrictions around the Pease International Tradeport. Areal Vertical aerial photography was collected as for spectral bands inclusive of RGB and Near Infrared, with a nominal 1 foot spatial resolution. The Sentinel satellite imagery was acquired for the date of June 28th, 2021 with a nominal 10 meter spatial resolution. Environmental conditions included a low-sun angle, low tides, low cloud cover, calm winds, no preceding rain events, and low turbidity in the water column were maintained throughout the course of the survey. The eelgrass habitat mapped from the aerial imagery was verified using the ground truthing data from preselected locations and ad hoc locations chosen during the course of the field work. Ground truthing was done from a small boat during the same season as the photographs were taken. Ground truth observations were made on all tides using a drop camera with video recording capabilities and at low tide when visual observations were recorded. Positions were determined using high accuracy Trimble GeoXT GPS unit.