Researchers have filled a 200-year gap in fish population data, which indicates a clear decline in the Adriatic Sea (east of Italy).

The data was generated from accounts of naturalists and fish market data between 1818 and 2000 by Italian researchers who scoured libraries, museums and archives of six European cities.

“The understanding of fish communities’ changes over the past centuries has important implications for conservation policy and marine resource management,” the authors wrote in a study published in the journal PLoS ONE.

The authors say ignoring old records has led to a “historical myopia” in fishery science. This underestimates the loss of natural resources over a long period. They partially reconstructed how 255 fish species in the region have fared.

Till 1800, Sharks made up about 17 per cent of the total fish population in the Adriatic Sea, while 27 per cent of all fish were bottom-dwellers such as hake, flounder and anglers.

The population of sharks dipped to 11 percent by 1950 and bottom-dwellers to 20 per cent in the same period.

“Chondrichthyes are highly vulnerable to [human] disturbances, and especially to fishery,” the authors wrote.

As fishermen nabbed such large fish, the smaller and more-nimble species thrived because they weren’t being eaten as readily (by sharks or humans), they wrote.“Naturalists’ eyewitness accounts of fish species, which have long been disregarded by fishery biologists as being ‘anecdotal’ and not ‘science,’ proved to be a useful tool for extending the analysis into the past, well before the onset of field-based monitoring programs,” the authors wrote.