Sea otters are small marine mammals that prey on fish, clams, crabs, and sea urchins. Sea otters’ natural predators include bears, sharks, and killer whales, but humans have also threatened sea otter populations. Hunting of sea otters for their fur severely reduced sea otter populations in the 18th and 19th centuries. After laws and programs were put into place to protect sea otters, their populations started increasing. Some sea otter populations in Alaska are now decreasing again. Which of the following is the most likely cause of these decreases?