The Fur Seal Islands, which act as a breeding ground for the many northern fur seals that visit them each year from April to November, have been the subject of significant controversy over the years. With the purchase of Alaska in 1867, official possession of the islands transferred from Russia to the United States. However, many nations continued sealing operations in the surrounding waters of the North Pacific, greatly affecting the fur seal populations of the islands. At one point, the United States began seizing vessels that were caught sealing near the islands, but eventually halted this practice when a tribunal ruled against such actions. Since that time, various conservation treaties have been established, though they have been broken at times. Nevertheless, in the second half of the 1900s, the international agreements seemed to have garnered a certain amount of success as the numbers of fur seals inhabiting the area rose significantly. Some evidence suggests, however, that in recent years they have again begun to decline.