PARIS, May 24 (Reuters) - Europeans started over-exploiting freshwater fish at least 1,000 years ago, according to historical studies that could help manage depleted modern fish stocks worldwide.

Whales teemed in waters off New Zealand in the 19th century and a now almost non-existent cod stock in the Gulf of Maine totalled a huge 70,000 tonnes a year in the mid-19th century, according to historical records.

Records reconstructed from everything from Russian monastery purchases to U.S. schooner logs indicate that over-fishing has been happening in many parts of the world for centuries and that fish used to be more abundant, and bigger, than now.

"We see similar patterns of human impacts on the oceans pretty much everywhere, and in many cases real depletion," said Andy Rosenberg of the University of New Hampshire, a leader of a project called the History of Marine Animal Population (HMAP).

The findings, part of a 10-year Census of Marine Life due for completion in 2010, have widened from a few local anecdotes about fish abundance in past centuries, he told Reuters. He will chair a HMAP "Oceans Past" conference in Vancouver on May 26-28.

In Europe, a shift to eating marine fish species from locally caught freshwater fish happened about 1,000 years ago.

"The size of freshwater fish caught by Europeans started shrinking in medieval times ... likely caused by increased exploitation and pollution," an HMAP statement said, based on freshwater fish remains dumped in northwest Europe and England.

New fishing boats in the 16th century made it possible to fish in deeper seas and a "real revolution" came in the mid-17th century when pairs of boats started dragging much bigger nets.

Blue whales, orcas and dolphins used to be common off Cornwall in southwest England.

Examination of records including log books of whalers indicated that populations of the southern right whale off New Zealand totalled 22,000 to 32,000 in the early 19th century. They now total perhaps 1,000 after over-hunting.

RECOVERY

Poul Holm, professor at Trinity College in Dublin and global chair of HMAP, said that the history of stocks could help work out recovery plans. New threats such as climate change are also emerging.

"We need to have better biological information and HMAP is providing some of the solution," he told Reuters.

Rosenberg led a 2005 report that showed schooners used to land 70,000 tonnes of cod a year in the 1860s in the Gulf of Maine.

"Now a mechanised fleet lands 3,000 tonnes," he said. "When we talk about rebuilding the fishery in the Gulf of Maine people are talking about 5-10,000 tonnes."

He said governments including Australia, New Zealand and Canada were starting to build a historical perspective in planning stock management.

Among other examples, a comparison of 13 photos of "trophy" reef fish caught between 1956 and 2007 in Key West, Florida, showed that the average fish size shrank to an estimated 2.3 kg (5 lb) from 20 kg.

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