Overfishing Began 1000 Years Ago: Study

Monday, 25 May 2009 Alister Doyle Reuters

The study examined records ranging from Russian monastery purchases to US schooner logs (Source: Kira Paulli Pravato) Europeans started over-exploiting freshwater fish at least 1000 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 once totalled tens of thousands of tonnes a year, according to historical records.

Records reconstructed from everything from Russian monastery purchases to US schooner logs indicate that overfishing 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," says Dr 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, will be presented this week at the Oceans Past conference in Vancouver.

Out to sea

In Europe, a shift to eating marine fish species from locally caught freshwater fish happened about 1000 years ago.

"The size of freshwater fish caught by Europeans started shrinking in medieval times ... likely caused by increased exploitation and pollution," says an HMAP statement, 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 approximately 1000.

Recovery

Poul Holm, professor at Trinity College in Dublin and global chair of HMAP, says 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 says.

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 3000 tonnes," he says. "When we talk about rebuilding the fishery in the Gulf of Maine people are talking about 5000 to 10000 tonnes."

He says 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 from 20 kg.

Source: ABC Science News