By Deborah Zabarenko, Environment Correspondent

WASHINGTON, Oct 19 (Reuters) - Pirates seeking Chilean sea bass and fishing vessels that vacuum up tiny shrimp-like creatures that are a staple for whales, seals and penguins are menacing Antarctic waters, environmentalists said on Thursday.

Both kinds of fishing could undermine the complex ecosystem of the Southern Ocean around Antarctica, the U.S. conservation experts said in a telephone news conference, and will be on the agenda next week at a meeting of the Conservation of Antarctic Marine Living Resources in Hobart, Australia.

The antarctic conservation group, which includes the United States and 23 other countries, has been working to end piracy in the area for more than a decade, according to Mark Stevens of the U.S.-based National Environmental Trust.

One problem is the rising demand for Chilean sea bass, also known as toothfish and not really a genuine sea bass at all, Stevens said on the conference call.

"It's a deep-living, slow-growing, long-lived predator fish found in the Southern Ocean around Antarctica ... It's important for the survival of Weddel seals, killer whales and sperm whales," Stevens said.

Prized for its mild, white flesh, Chilean sea bass brings high prices for those who catch them illegally in rough southern waters that are rarely patrolled, he said. To stop this trade, conservationists are working to block access to ports where the pirates offload their catch.

Many of these vessels fly the flags of Togo, North Korea and Equatorial Guinea, Stevens said.

The vacuum-fishing of the little crustaceans known as krill has not reached a crisis yet, and conservationists want to keep it that way, said Clifton Curtis, director of the Antarctic Conservation Project.

Krill are at the bottom of a marine food chain that includes fish, birds, seals and whales, Curtis said.

Current fishing for krill is below mandated limits, but there is localized depletion, he said. New regulations could ensure continued sustainable fishing, but two factors may make this difficult, he said.

First, there is a growing demand for krill, which can be used as feed for farmed salmon, and second, the latest technology for catching krill, with ships that continuously vacuum them up, could deplete their numbers.

Some members of the Antarctic marine conservation group -- Australia, New Zealand, the United Kingdom, Chile, the United States, Norway and South Africa -- favor reformed requirements on krill, but fishing nations -- including Japan, Ukraine, Russia, South Korea and possibly Poland -- could derail this, Curtis said.

More information is available online at http://www.krillcount.org and http://www.ccamlr.org.

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