1. Eurasian Otter (Lutra lutra):
- Conservation Status: Near Threatened (NT)
- Population Estimate: 100,000 to 1,000,000 individuals
2. North American River Otter (Lontra canadensis):
- Conservation Status: Least Concern (LC)
- Population Estimate: Approximately 100,000 to 1,000,000 individuals
3. Southern Sea Otter (Enhydra lutris nereis):
- Conservation Status: Threatened (T)
- Population Estimate: Approximately 3,000 individuals
4. Asian Small-clawed Otter (Aonyx cinereus):
- Conservation Status: Vulnerable (VU)
- Population Estimate: Unknown but declining due to habitat loss
5. Giant Otter (Pteronura brasiliensis):
- Conservation Status: Vulnerable (VU)
- Population Estimate: Approximately 5,000 individuals
It's important to note that these population estimates are approximate and can vary depending on various factors such as habitat quality, hunting pressures, and conservation efforts. Additionally, there are other species of otters not listed here, and their conservation statuses and population sizes can vary as well.