May 25, 2009

Ocean’s History Being Unlocked By Researchers

According to a recent study, medieval fishermen first took to the sea around AD 1,000 in search of food after a sharp decline in freshwater fish.

The decline was likely caused by rising population and pollution levels.

The study, which will be presented at a Census of Marine Life (CoML) conference in Canada, focuses on the human impact on life beneath the waves throughout history.

"Fish bones are found in archaeological sites... all around the north-western part of Europe," said James Barrett, of Cambridge University's McDonald Institute for Archaeological Research, and co-author of the study.

"What we have done is to start to piece together some of the information that has been gathered."

Piecing the information together required looking at fish bones to determine their species, and what time period they came from.

One hypothesis says that freshwater fish were no longer able to satisfy demand.
"At the end of the first millennium AD there is this wholesale shift in emphasis from reliance on freshwater fish towards marine species," said Barrett.

"It is not rocket science, it is just literally looking at the proportion of species that are obligatory freshwater ones, such as pike... and which ones are obligatory sea fish, such as cod and herring."

According to Barrett, the cause of the shift can not be pinpointed to one single item.

"But when you look very carefully at the freshwater fish bones from the York site, where a big collection was gathered, you can see that the length of the fish are decreasing through time," Barrett told BBC News.

"Certainly, one of the straightforward hypotheses is that freshwater fish were no longer sufficient to satisfy demand. This was likely to have been for two reasons; one was because there had been a reduction in the availability of freshwater fish as a result of overfishing, or from things such as people building dams for water mills."

"The second thing would have been that there would have simply been more people."

According to Barrett, there was also rapid population expansion near this time in north-western Europe.

"So this meant that there was an increased pressure on freshwater fish, and there was an increase in demand that probably could not have been satisfied even if the supply had remained stable."

Barrett's study is one of a number of projects being shown as a part of the CoML's History of Marine Animal Populations (HMAP).

The showcase addresses a number of questions, including how the distribution of marine animals has changed over the past 2,000 years, and what caused those changes.

Professor Poul Holm, global chairman of the HMAP project, said that the history of marine animals has widely been unknown, but recent advances helped scientists gain a better understanding.

"We now know that the distribution and abundance of marine animal populations change dramatically over time.  Climate and humanity forces changes and while few marine species have gone extinct, entire marine ecosystems have been depleted beyond recovery."

"Understanding historical patterns of resources exploitation and identifying what has actually been lost in the habitat is essential to develop and implement recovery plans for depleted marine ecosystems." he explained.

According to Ian Poiner, Chair of the Census Scientific Steering Committee, "we're only just starting to fully realize what the planet once had."
"The insights emerging from this research of the past provide a new context for contemporary ocean management. Understanding the magnitude and drivers of change long ago is essential to accurately interpret today's trends and to make future projections."

Much of the HMAP findings will be presented at the Oceans Past II Conference, which begins on Tuesday in Vancouver, Canada.

The goal of the decade-long COML is to explain the diversity and distribution of marine life in the world's oceans.  Thousands of researchers contribute to the international project.

The first complete global Census of Marine Life is scheduled to be published in October 2010.


Image 1: This Byzantine image from the 11th century shows night fishing with a lamp and a net. Credit: International Journal of Nautical Archaeology / CoML

Image 2: This reproduction from an 1887 paper by A. Howard Clark shows the processing of a right whale carcass. Credit: HMAP / CoML


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