Research Highlight: Going Down in History

Marine ecologists conducting field research employ a broadcross-section of tools to help them better understand oceanenvironments, from nets to microscopes to cameras and videoequipment. One of the items not at their disposal is a time machinethat would allow researchers to go back in time to study marineenvironments before they were altered by human interactions.

Without stepping into a time travel device, scientists are nowemploying the next best thing. Part of a burgeoning field known ashistorical marine ecology, scientists at Scripps Institution ofOceanography at UC San Diego are diving into archives of yesteryearto help paint a picture of the past. Historical photographs, maps,news accounts, library records, and other documentation are helpingmarine ecologists fill in gaps of days before formal scientificfield surveys were conducted.

Scripps graduate student Loren McClenachan recently conducted such astudy that concentrated on the fish of the coral reefs surroundingKey West, Florida.

While researching material for her doctoral thesis on coral reefecosystems, McClenachan came across what she describes as a goldmineof photographic data at the Monroe County Library in Key West.Hundreds of archived photographs, snapped by professionalphotographer Charles Anderson over five decades, depict sportfishersposed next to a hanging board used to determine the largest "trophyfish" catches of the day.

By analyzing the photos, which depict some 1,275 fish in all,McClenachan was able to calculate a drastic decline in the size andweight of the fish over the years. In her paper published in thescientific journal Conservation Biology, McClenachan describes astark 88 percent decline in the estimated weight of large predatoryfish imaged in black-and-white 1950s photos compared to therelatively diminutive catches photographed in modern pictures.

"While the photographs in this study do not provide a directmeasurement, they clearly demonstrate that large fish were moreabundant in the past," said McClenachan.

McClenachan determined the mean size of the prize catches — includingsharks, large groupers, and other hefty fish in earlyphotographs—and their decline from nearly two meters (6.5 feet) inlength in the 1950s to contemporary catches of small fish such assnappers measuring a mere 34 centimeters (approximately one foot) onaverage. From 1956 to 2007, the fishes’ average estimated weightdropped from nearly 19.9 kilograms (43.8 pounds) to 2.3 kilograms (5pounds). Additionally, the photographs revealed that the averagelength of sharks declined by more than 50 percent in 50 years.

"These results provide evidence of major changes over the last halfcentury and a window into an earlier, less disturbed fishcommunity," McClenachan said about the study, which was funded bythe National Oceanic and Atmospheric Administration.

Yet while McClenachan’s research depicts significant changes overthe last 50 years, she indicates in the paper that evidence existsshowing that even the Florida Keys ecosystems of the 1950s were notpristine. Commercial fishing in the 1930s and 40s reducedpopulations of sharks, while numbers of large groupers declinedthrough commercial fishing since at least the 1880s.

"The ongoing debate about the status of fisheries in the FloridaKeys is a classic problem of the shifting baselines syndrome," saidScripps oceanographer Jeremy Jackson, McClenachan’s advisor."Managers mistakenly assume that what they saw in the 1980s waspristine, but most prized fish species had been reduced to a smallfraction of their pristine abundance long before. Historical ecologyprovides the critical missing data to evaluate what we lost beforemodern scientific surveys began."

—Mario C. Aguilera

March 2009