No otter way

How come we don't have otters in Australia?   If they are in waters as diverse as those off California, and Singapore, how come up they never ended up near Brisbane?

Anyway, I wonder this because of a short report in Science:

Stranded or orphaned baby sea otters have been given a new lease on life—and a mission: restoring damaged ecosystems along the California coast.

Sea otters are a keystone species in their native coastal environments. They prey on small herbivorous sea creatures like sea urchins, which can lead to more kelp and healthier seagrass in an area. But after being hunted for their fur to near extinction in the 19th and 20th centuries, otter populations along the California coast are still struggling. Restoring populations is not as simple as bringing in new otters, though. The animals often have strong ties to their homes, and some relocated otters have made journeys of more than 100 kilometers to return to their birthplaces.

To solve this problem, scientists at the Monterey Bay Aquarium in California created the sea otter surrogacy program in 2002. So far, they have rescued 37 stranded or orphaned otters, many of which were suffering from dehydration or hypothermia. The researchers placed the pups with surrogate mothers—captive female otters at the aquarium—until they fully recovered. When the pups were 6 months to 1 year old (the typical age an otter is weaned), the researchers released them into Elkhorn Slough (shown above), a tidal wetland about 1.5 hours south of San Francisco, California. Because the orphaned otters were very young when they were rescued, they did not have strong ties to their home ranges and most thrived in the new environment, the researchers report today in Oryx–The International Journal of Conservation.