Leatherbacks are the largest sea turtles in the world and are the species most commonly seen by boaters in southern New England waters. They can reach lengths of 8 feet, weigh up to 1500 pounds, and are slate gray/black. Leatherbacks are readily identified by their large size and the fore-and-aft ridges which run along the carapace (upper shell). Fishermen and boaters often report seeing a leatherback's large head, which can resemble a seal's head from a distance, lifted above the surface. Observers have reported leatherbacks as looking like an overturned dinghy, or as the size of a Volkswagen beetle. They feed primarily on jellyfish and other gelatinous organisms. Leatherbacks have the ability to raise their internal body temperature above that of the surrounding seawater, allowing them to swim in much colder water than do other sea turtles. Entanglement in fishing/lobstering gear is a threat to leatherbacks when they become entangled in the vertical lines and cannot get to the surface to breathe. They are known to ingest plastic trash, which can be fatal. Leatherbacks and fishermen sometimes occur simultaneously in "hotspots." Such a hotspot occurred in 2010 on Lucas Shoal (Vineyard Sound), where fishermen were catching fluke, and leatherbacks were eating jellyfish.