Last updated at 1:38 PM on 25th May 2009
Medieval fishermen first went to sea 1,000 years ago because of a steep decline in freshwater fish, according to scientists.
Researchers from Cambridge and York University studied and dated fish bones found in archaeological sites around the north-western part of Europe and compared historical records.
They found there were fewer species of freshwater fish, which became smaller over time. Both over-fishing and pollution are thought to be to blame for the decline which caused a major change in the diet of our ancestors.
'At the end of the first millennium AD there is this wholesale shift in emphasis from reliance on freshwater fish towards marine species,' study co-author Dr Barrett told the BBC.
'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.'The study forms just one part of a huge international project that will be discussed at the Census of Marine Life (CoML) conference in Canada this week.The project called 'History of Marine Animal Populations', aims to look at the diversity and distribution of marine animals in the past and present and the implications this could have in the future.
Trophy fish caught in 1958 (above) are far bigger than those caught in 2007 (below)
Another paper from the University of Bologna has revealed that new fishing boats and equipment invented in the 1500s then allowed Europeans to venture from coastal to deep sea fishing.
However study author Maria Lucia De Nicolo said that the biggest fishing revolution happened in the mid-1600s when pairs of boats began dragging a net.
Diverse sources have been used by census researchers including old ship logs, tax accounts and literary texts.
They reveal that large pods of blue whales and orcas, blue sharks and thresher sharks darkened the waters off Cornwall in the 1800s, while herds of harbour porpoise pursued fish upriver.
Processing of a right whale in 1887. There were 30 times as many whales off New Zealand in the 1800s than today
At the same time oil hunters in New Zealand decimated the southern right whales off its coast which once teemed with 27,000 creatures - 30 times as many as today.
One novel technique used by American researchers compared mounted trophies from sport fishermen between 1956 to 2007 in the Key West area of Florida.
They found the average fish size shrank from 20kg to 2.3kg and sharks and predatory fish were replaced by small snappers.
Chair of the Census Scientific Steering Committee Ian Poiner said: 'When it comes to marine life, we're only just starting to realise 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.'
News source: http://www.dailymail.co.uk
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