A keystone species is defined as one that has a critical role in determining and maintaining the overall relationship of plants and animals within an ecosystem. If a keystone species is removed or declines, the nature of the ecosystem will change dramatically.

Sea Otters — A Classic Keystone Species

The classic tale of a keystone species is that of the sea otter, which was once found in abundance along the West Coast of North America. The story goes something like this: 1. European and Russian trappers hunt sea otters to near extinction in the 18th and 19th centuries. 2. The decline of the sea otters, which are essential to keeping sea urchins in check, allows sea urchin populations to explode. 3. The burgeoning sea
Until the 1700s, sea otters were abundant throughout the waters of the north Pacific and for centuries native groups, such as the Aleuts, hunted them. During this time, the worldwide sea otter population numbered between 150,000 to 300,000. By the mid-1700s, Russian hunters had coerced the Aleuts to exploit sea otters for the fur trade, and the once abundant sea otter population plummeted. The otters that remained were chased down by English, French, Japanese and American traders. By the 1900s, the sea otter was nearly extinct with only 1,000 to 2,000 otters left. Only 13 remnant sea otter colonies existed from Russia to Mexico when the International Fur Seal Treaty, which banned the hunting of sea otters and fur seals, was established in 1911.

CALIFORNIA
By the 1930s, a small group of 50 to 300 sea otters, a population now known as southern or California sea otters, remained near Big Sur, California. Under the protection of the International Fur Seal Treaty, this small population began a slow and steady climb from nearly extinct to a fairly stable population. From the mid 1970s to the mid 1980s, the southern sea otter population began to decline once again. About 1,000 sea otters died over a 10 year period due to entrapment in gill nets. When gill net legislation was passed in the late 1980s requiring gill nets to move farther off shore, the sea otter population began to grow again until