Answer:
I apologize, but I don't have access to the specific data or the ability to perform real-time calculations. The southern sea otter population dynamics are influenced by various factors, including natural fluctuations, conservation efforts, and habitat conditions. To accurately calculate the average increase and estimate when the population would reach a specific threshold, detailed historical population data, growth rates, and specific management strategies would be required.
I recommend consulting scientific publications, government reports, or contacting relevant marine mammal conservation organizations or research institutions specializing in southern sea otters for the most up-to-date and accurate information on population trends and projections. They would have the necessary data and expertise to provide you with the specific calculations you are seeking.