Modern Fish Live Fast and Die Young

June 24, 2011

An archaeological study by a WCS marine researcher in Kenya compares fish communities from modern times with those from the Middle Ages. The scientist finds that the modern fish are overwhelmingly smaller, lower on the food chain, and shorter-lived.

The human life expectancy has trended up over the last century. For fish, it’s a different story. A recent study by WCS researchers found that fish communities in the 21st century live fast and die young.

The scientists compared fish recently caught in coastal Kenya with fish bones dug from ancient Swahili refuse heaps, in order to understand how to rebuild current fisheries. They found that modern fish communities contain more species with shorter life spans, faster growth rates, smaller average sizes, and lower ranks on the food chain. By contrast, ancient communities had a high percentage of top predators—species that prey on fish and large invertebrates such as snails, sea urchins, and clams.

The cause of this downward trend is overfishing, which has impacted the ecosystem in ways that may not be easily reversible, according to the study. Over the centuries, fishing has greatly reduced or eliminated larger and longer-lived species that were more commonly caught in the Middle Ages.

The study, which utilized more than 5,000 samples of ancient fish remains dating between 750 and 1400 AD, approximately, appears in the current online edition of the journal Conservation Biology. WCS’s Tim R. McClanahan and Johnstone O. Omukoto authored the paper.

“The ancient Swahili middens represent a time capsule of data, containing information on the composition of the region’s fish assemblages and how human communities influenced the marine environment,” said McClanahan, who leads WCS’s coral reef research and conservation program.

The researchers also found that the number of fish bones in the middens peaked between 1000 and 1100 AD before declining, while the bones of sheep and goats become more prevalent in the higher levels of substrate, suggesting a shift in human diet to domesticated animals.

“The archeological evidence demonstrates the incredible longevity of humanity’s utilization of coastal fisheries, while emphasizing the critical need to actively manage slower growing, longer-lived species within an ecosystem approach,” said Dr. Caleb McClennen, Director of WCS Marine Programs. “The evidence from Kenya aligns with findings from around the world that for millennia, humanity has relied on the world’s oceans for our basic needs—but has more recently failed to do so in a manner that also will sufficiently sustain that resource.”

Dr. McClanahan’s research has been supported by the John D. and Catherine T. MacArthur Foundation and The Tiffany & Co. Foundation.

For more information, see the press release.

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