In all, she measured and analyzed some 1,275 fish from photographs.
McClenachan calculated the mean size of the prize catchesincluding sharks, large groupers and other hefty fish in early photographsand 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. The fishes' average estimated weight dropped from nearly 19.9 kilograms (43.8 pounds) to 2.3 kilograms (5 pounds) from 1956 to 2007. The average length of sharks declined by more than 50 percent in 50 years, the photographs revealed.
"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.
Yet while McClenachan's study 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," says Scripps Professor Jeremy Jackson. "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 evalua
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University of California - San Diego