Marine ecologists conducting field research employ a broad cross-section of tools to help them better understand ocean environments, from nets to microscopes to cameras and video equipment. One of the items not at their disposal is a time machine that would allow researchers to go back in time to study marine environments before they were altered by human interactions.
Without stepping into a time travel device, scientists are now employing the next best thing. Part of a burgeoning field known as historical marine ecology, scientists at Scripps Institution of Oceanography at UC San Diego are diving into archives of yesteryear to help paint a picture of the past. Historical photographs, maps, news accounts, library records, and other documentation are helping marine ecologists fill in gaps of days before formal scientific field surveys were conducted.
Scripps graduate student Loren McClenachan recently conducted such a study that concentrated on the fish of the coral reefs surrounding Key West, Florida.
While researching material for her doctoral thesis on coral reef ecosystems, McClenachan came across what she describes as a goldmine of photographic data at the Monroe County Library in Key West. Hundreds of archived photographs, snapped by professional photographer Charles Anderson over five decades, depict sportfishers posed next to a hanging board used to determine the largest “trophy fish” 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 and weight of the fish over the years. In her paper published in the scientific journal Conservation Biology, McClenachan describes a stark 88 percent decline in the estimated weight of large predatory fish imaged in black-and-white 1950s photos compared to the relatively diminutive catches photographed in modern pictures.
“While the photographs in this study do not provide a direct measurement, they clearly demonstrate that large fish were more abundant in the past,” said McClenachan.
McClenachan determined the mean size of the prize catches—including sharks, large groupers, and other hefty fish in early photographs—and their decline from nearly two meters (6.5 feet) in length in the 1950s to contemporary catches of small fish such as snappers measuring a mere 34 centimeters (approximately one foot) on average. From 1956 to 2007, the fishes’ average estimated weight dropped from nearly 19.9 kilograms (43.8 pounds) to 2.3 kilograms (5 pounds). Additionally, the photographs revealed that the average length of sharks declined by more than 50 percent in 50 years, the photographs revealed.
“These results provide evidence of major changes over the last half century and a window into an earlier, less disturbed fish community,” McClenachan said about the study, which was funded by the National Oceanic and Atmospheric Administration.
Yet while McClenachan’s research depicts significant changes over the last 50 years, she indicates in the paper that evidence exists showing that even the Florida Keys ecosystems of the 1950s were not pristine. Commercial fishing in the 1930s and 40s reduced populations of sharks, while numbers of large groupers declined through commercial fishing since at least the 1880s.
“The ongoing debate about the status of fisheries in the Florida Keys is a classic problem of the shifting baselines syndrome,” said Scripps oceanographer Jeremy Jackson, McClenachan’s advisor. “Managers mistakenly assume that what they saw in the 1980s was pristine, but most prized fish species had been reduced to a small fraction of their pristine abundance long before. Historical ecology provides the critical missing data to evaluate what we lost before modern scientific surveys began.”
—Mario C. Aguilera