Congress passed the Endangered Species Act under President Nixon in 1973 to protect plant species, animal species and ecosystems threatened with harm or extinction. The U.S. Fish and Wildlife Service, along with the Commerce Department's National Marine Fisheries Service (NMFS), are responsible for managing the act upon land and in sea. NMFS monitors sea-based life like whales and fish – salmon – that return to the place of their birth to breed.

To define endangered species, the ESA created two specific categories. Under the terms of the ESA, there exist two categories of animals, those "threatened" and those "endangered." The endangered animals' definition includes all animals in immediate danger of extinction. Animals defined as threatened by the act include all species of plants, animals and insects – except for 'pest' insects – that will probably become endangered in the future. Animals and plants officially added to the threatened or endangered list under the ESA cannot be hunted, killed or foraged without consequence under the law.

The ESA makes it a crime to:

• Hunt, kill, take or injure a species protected by the ESA.
  
• Import or export animals and plants into or out of the United States,
• Remove any of these species from within the "territorial" seas of the U.S.
• Transport any of these listed species upon the oceans.
• Own, sell, deliver, carry or transport

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by any means

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these listed

species. * Receive, deliver, sell, carry or ship species between states or by foreign means.

All of these crimes under ESA are subject to fines and penalties – and maybe even jail time depending on the extent of the crimes – between $100 (for violating a study permit) to $13,000 for stiffer crimes.

The purpose of enacting these laws is to help protect and aid in the recovery of plants and animals classed as threatened or endangered under the act, so they can someday come off the list. Once a specific species makes it to the threatened or endangered list, like the black-footed ferret in 2013, the government devises and implements a recovery plan. The plan details the specific actions recommended for the protection and recovery of the species. The plan includes strategies, goals, objectives and recovery criteria, which may include captive breeding programs.

The main cause of endangered species is human activity. Humans are primarily responsible for the animals that have gone extinct within recent centuries. Hunting an animal to extinction upsets the balance of nature. But hunting isn't the only cause of endangered species: Housing developments, road development, dam building and other activities all lead to endangered and threatened species. For example, hunters that use lead shot can also kill animals they aren't hunting. Animals shot with lead, but not recovered by the hunter, often die in the wild where other creatures eat them. Lead poisoning can occur, which results in the death of the predators like eagles, condors, buzzards and even four-legged predators.