In the 18th century, large pods of blue whales, orcas, blue sharks and thresher sharks darkened the waters off Cornwall, herds of harbour porpoise pursued fish upriver, and dolphins regularly played in waters inshore.

Using such diverse sources as old ship logs, literary texts, tax accounts, newly translated legal documents and even mounted trophies, researchers are piecing together images – some flickering, others in high definition – of fish of such sizes, abundance and distribution in ages past that they stagger modern imaginations.

They are also documenting the timelines over which those giant marine life populations declined.

For example, scientists say the size of freshwater fish caught by Europeans started shrinking in medieval times causing a shift from eating locally-caught freshwater to marine fish species around 1000 AD.

Maria Lucia De Nicolò of the Università di Bologna, has established that new fishing boats and equipment invented in the 1500s made it possible to venture from coastal to deep sea fishing. The real revolution in marine fishing, she says, happened in the mid-1600s when pairs of boats began dragging a net.

“Appraising modern marine life through the narrow window of observations during recent decades skews perceptions," says Andy Rosenberg of the University of New Hampshire, and “ that new insights allowed by centuries of information are upending modern notions of "natural" marine life sizes, abundance, habitats and vulnerability, and causing authorities to revisit marine baselines.”

According to Poul Holm, Professor at Trinity College Dublin "While the history of marine animal populations has been one of the great unknowns, recent advances in scientific and historical methodology have enabled the expansion of the realm of the known and the knowable."

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

Comment – we may now know that, but will any of the politicians and fisheries managers take notice ?

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