Many hypotheses also seek to explain the regional extinction of mammoths in specific areas. Scientists have speculated that the mammoths of Saint Paul Island (Alaska), an isolated enclave where mammoths survived until about 8,000 years ago, died out as the island shrank by 80–90% when sea levels rose, eventually making it too small to support a viable population. Similarly, genome sequences of the Wrangel Island mammoths indicate a sharp decline in genetic diversity, though the extent to which this played a role in their extinction is still unclear. Another hypothesis, said to be the cause of mammoth extinction in Siberia, comes from the idea that many may have drowned. While traveling to the Northern River, many of these mammoths broke through the ice and drowned. This also explains bones remains in the Arctic Coast and some of the New Siberian Islands.