Biological Resources Shown on ESI Maps

Under the Environmental Sensitivity Index (ESI) method, species that are especially vulnerable to the effects of oil spills have been classified into seven general categories, such as Bird, Fish, and Marine Mammal. The categories are then further divided by grouping species together by similar taxonomy, morphology, life history, and/or sensitivity to spilled oil.

The table below lists all of the categories and subcategories for biological resources, and it also includes some information about how they are displayed on ESI maps. When a biological resource exists in a small area (such as a bird nesting site), it is indicated on an ESI map by a symbol. When a biological resource encompasses a larger area, it is represented on ESI maps by a polygon with a specific pattern and color.

Category/Sub-Category Symbol Locations Shown on Maps
Marine Mammal Horizontally-hatched region in brown, representing marine mammals.
Dolphin ESI symbol for dolphin. Concentration areas
Manatee ESI symbol for manatee. Concentration areas, cold weather refuge areas
Polar Bear ESI symbol for polar bear. Concentration areas
Sea Otter ESI symbol for sea otter. Concentration areas
Seal/Sea Lion ESI symbol for seal/sea lion. Haulouts, concentration areas
Whale ESI symbol for whale. Migratory or other concentration areas
Terrestrial Mammal Vertically-hatched region in brown, representing terrestrial mammals.
Bat ESI symbol for bat. Locations of threatened, endangered, or species of significance
Bear ESI symbol for bear. Intertidal feeding or aquatic/wetland concentration areas, areas hazardous to spill responders
Deer ESI symbol for deer. Intertidal feeding or aquatic/wetland concentration areas
Small Mammal ESI symbol for small mammal. Aquatic fur-bearer concentration areas, locations of threatened, endangered, or rare species
Bird Diagonally-hatched region in green, representing birds.
Alcid/Pelagic Bird ESI symbol for alcid/pelagic bird. Rookeries, roosting, and other concentration areas
Diving Bird ESI symbol for diving bird. Rookeries; forage/wintering areas; roosting concentration areas
Gull/Tern ESI symbol for gull/tern. Nesting sites; other concentration areas
Passerine Bird ESI symbol for passerine bird. Locations of threatened, endangered, or rare species, especially nesting areas
Raptor ESI symbol for raptor. Nesting sites; migratory/feeding concentration areas
Shorebird ESI symbol for shorebird. Nesting sites; migratory, wintering, and roosting concentration areas
Wading Bird ESI symbol for wading bird. Rookeries; feeding and roosting concentration areas
Waterfowl ESI symbol for waterfowl. Wintering and migration concentration areas; nesting sites
Reptile/Amphibian Diagonally-hatched region in red, representing reptiles and/or amphibians.
Alligator/Crocodile ESI symbol for alligator/crocodile. Concentration areas, especially nesting locations
Other Reptiles/Amphibians ESI symbol for other reptiles/amphibians. Locations of threatened, endangered, or rare species, especially aquatic/wetland concentration areas
Turtle ESI symbol for turtle. Nesting beaches; concentration areas
Fish Diagonally-hatched region in blue, representing fish.
Anadromous Fish ESI symbol for anadromous fish, diadromous fish, estuarine resident fish, freshwater fish, marine benthic fish, and marine pelagic fish. Spawning and nursery areas; locations of threatened, endangered, or rare species
Diadromous Fish ESI symbol for anadromous fish, diadromous fish, estuarine resident fish, freshwater fish, marine benthic fish, and marine pelagic fish. Spawning and nursery areas; locations of threatened, endangered, or rare species
Estuarine Nursery Fish ESI symbol for nursery fish. Spawning, nursery, and other concentration areas
Estuarine Resident Fish ESI symbol for anadromous fish, diadromous fish, estuarine resident fish, freshwater fish, marine benthic fish, and marine pelagic fish. Spawning or other concentration areas; locations of threatened, endangered, or rare species
Freshwater Fish ESI symbol for anadromous fish, diadromous fish, estuarine resident fish, freshwater fish, marine benthic fish, and marine pelagic fish. Spawning and nursery areas; locations of threatened, endangered, or rare species
Marine Benthic Fish ESI symbol for anadromous fish, diadromous fish, estuarine resident fish, freshwater fish, marine benthic fish, and marine pelagic fish. Spawning and nursery areas; reefs, kelp beds, or other concentration areas
Marine Pelagic Fish ESI symbol for anadromous fish, diadromous fish, estuarine resident fish, freshwater fish, marine benthic fish, and marine pelagic fish. Spawning or other concentration areas
Shellfish/Insect Diagonally-hatched region in orange, representing invertebrates.
Bivalve ESI symbol for bivalve. Harvest areas; abundant beds; locations of threatened, endangered, or rare species
Crab ESI symbol for crab. Nursery areas; areas of high concentrations
Echinoderm ESI symbol for echinoderm. Harvest areas
Gastropod ESI symbol for gastropod. Harvest areas; high concentrations, locations of threatened, endangered, or rare species
Insect ESI symbol for insect. Locations of threatened, endangered, or rare species
Lobster/Crayfish ESI symbol for lobster/crayfish. Nursery, spawning, and harvest areas; locations of threatened, endangered, or rare species
Shrimp ESI symbol for shrimp. Nursery areas; locations of high concentrations
Squid/Octopus ESI symbol for squid/octopus. Harvest areas; areas of high concentrations
Habitat/Rare Plant Horizontally-hatched region in purple, representing plants.
Coral/ Hardbottom Reef ESI symbol for coral/hardbottom reef. Generally restricted to water and tidal flats
Floating Aquatic Vegetation/Intermittent Coastal Wetlands ESI symbol for floating aquatic vegetation/intermittent coastal wetlands. Areas of floating aquatic vegetation
Rare Plant/Terrestrial Plant/Native Plant ESI symbol for rare plant/terrestrial plant/native plant. Locations of threatened, endangered, or rare species or communities
Submerged Aquatic Vegetation ESI symbol for submerged aquatic vegetation, seagrass beds, kelp, and algae. Areas of submerged aquatic vegetation; seagrass beds, kelp, algae

More Information about ESI Maps

ESI Species List: Download a complete list of species (in several different formats) that may be shown on ESI maps. (Not all species are shown on every ESI map.)

Anatomy of ESI Maps
: Learn about the basic elements of ESI maps.

Shoreline Sensitivity Rankings
: Refer to this complete list of ESI shoreline classifications, from 1A (exposed rocky shores) through 10E (inundated low-lying tundra).

Human-Use Resources
: Learn how ESI maps categorize and display the location of human-use resources (such as public beaches) that are vulnerable to oil spills or that could be used as access points for oil spill cleanup.