is a unique species that adapted resistance to the toxic effects of the PCBs polluting the river. Scientists identified the genetic mutation that conferred the resistance, and found that the mutated form was present in 99 percent of the tomcods in the river, compared to fewer than 10 percent of the tomcods from other waters. The hogchoker flatfish have been historically abundant in the river, where farmers would use them for inexpensive livestock feed, giving the fish its name. Other unusual fish found in the river include the northern pipefish, the lined seahorse, and the northern puffer. The Atlantic sturgeon, a species about 120 million years old, enter the estuary during their annual migrations. The fish grow to a considerable size, up to and . The fish are the symbol of the Hudson River Estuary. Their smoked flesh was commonly eaten in the river valley since 1779, and it was sometimes known as "Albany beef". The city of Albany was called "Sturgeondom" or "Sturgeontown" in the 1850s and 1860s, with its residents known as "Sturgeonites". The "Sturgeondom" name lost popularity around 1900. The fish have been off limits from fishing since 1998. The river's population of shortnose sturgeon have quadrupled since the 1970s, and are also off limits to all fishing as they are a federally endangered species. Lined seahorse or northern seahorse (Hippocampus erectus) is found in the brackish waters of the Lower New York Bay, New York Harbor and surrounding waters (including Raritan Bay and Sandy Hook Bay) and the Hudson River estuary. Marine and invasive species Marine life is known to exist in the estuary, with seals, crabs, and some whales reported. On March 29, 1647, a white whale swam up the river to the Rensselaerswyck (near Albany). Herman Melville, author of Moby-Dick, lived in and near Albany from 1830 to 1847, and was known to have ancestry from New Netherland, leading some to believe stories of the whale sighting inspired his novel. Non-native species often originate in New York Harbor, a center of long-distance commerce. Over 100 foreign species reside in the river and its banks. Many of these have had significant effects on the ecosystem and natural habitats. The water chestnut produces a vegetative mat that reduces oxygen content in the water below, enhances sedimentation, impedes small vessel navigation, and is a hazard to swimmers and walkers. The zebra mussel arrived in the Hudson in