By digging up and poring over old books and records of Mediterranean marine life, scientists have filled a 200-year gap in fish population data.

The data, generated from from naturalists’ accounts and fish-market records published between 1818 and 2000, shows the clear decline of fishes in the Adriatic Sea (east of Italy) and provides a crucial baseline comparison for the ongoing collapse of today’s fisheries.

“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 Nov. 17 in the journal PLoS ONE. Ignoring old records, they added, has led to a “historical myopia” in fishery science that underestimates the loss of natural resources.

It's no puzzle why. Prior to the mid-20th century, large-scale surveys of marine life didn’t happen and, for that matter, there wasn’t the modern-day level of concern about natural resources or the impetus to conserve them. Back then, there were only fish-catch records and naturalists’ qualitative descriptions of life beneath the waves.

To gather the information, an Italian team of ecologists and marine scientists scoured the libraries, museums and archives of six European cities. In total, the search turned up 36 books by naturalists and dozens of detailed catch records from fish markets spanning almost two centuries.

Using statistical methods to combine and integrate the descriptive naturalist records with fish-catch tallies, the scientists partially reconstructed the rise and fall of 255 fish species in the region.

Sharks in the Adriatic Sea made up about 17 percent of the total fish population in 1800, while bottom-dwellers (such as hake, flounder and anglers) made up 27 percent of all fish. By 1950, the populations had dipped to 11 percent and 20 percent, respectively. Meanwhile, the proportion of smaller and faster-breeding fish rose from about 12 percent of the population to more than 28 percent.

“Chondrichthyes are highly vulnerable to [human] disturbances, and especially to fishery,” the authors wrote, thanks to their large size, slow growth and breeding behavior. 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).

Fish population declines due to human activity since the mid-20th century are established and substantial, with encroachment by non-native fish species, habitat alteration and pollution all contributing to shrinking and more-fragile populations of fish. While it’s not entirely clear how large a role fishing pressure played prior to 1950, the authors say their “results indicate that pre-industrial fisheries had already had significant impacts” on fish populations in the Adriatic.

The study can’t offer a worldwide assessment of fishery health in the past. But turning old records of marine life into useful datasets may prove promising for assessing past fish populations in other regions.

“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.

Image: A naturalist’s catalogue of species used to reconstruct past fish populations. PLoS ONE/Cori C.I.

Citation: "Coding Early Naturalists' Accounts Into Long-Term Fish Community Changes in the Adriatic Sea (1800–2000)." By Tomaso Fortibuoni, Simone Libralato, Saša Raicevich, Otello Giovanardi and Cosimo Solidoro. Nov. 17 PLoS ONE.

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