When a father-and-son hunting pair from Alaska poached a black bear mother and her two newborn cubs in their den last year, they initially seemed to get away with it.

There was little chance for witnesses on a remote island off Alaska’s southern coast. The hunters traveled there by boat, strapping on backcountry skis to reach the bear den. But a motion-activated camera, being used for wildlife research, captured the hunters’ actions on the island, the authorities said.

This week, after pleading guilty to various poaching charges, the father, Andrew Renner, a 41-year-old from Wasilla, Alaska, was sentenced to three months in jail and barred from hunting for a decade, said Aaron Peterson, the state’s assistant attorney general, who prosecuted the case. His son Owen Renner, 18, received a 30-day suspended sentence and was required to perform community service.

Based on state law, killing a mother bear or bear cubs is a crime. But Mr. Peterson said that defendants in poaching cases rarely get jail time. That’s because hunters often argue that they poached an animal by mistake and typically have no criminal record, he said.