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Michael Esgro

What is a Pristine Ocean Environment?

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A Loss of Perception

Human overexploitation of marine resources is one of the most serious threats to our oceans. There are many obvious consequences of overexploitation: species are being driven to extinction, global rates of biodiversity are in sharp decline, and ecosystems are being irreversibly damaged. But overexploitation is also causing us to slowly lose our perception of what pristine marine environments look like, a slippery slope of reduced expectations with serious implications for ocean conservation. Scientists call this problem “shifting baselines syndrome”.

A New Reference Point

Although shifting baselines syndrome applies to entire ecosystems, it has garnered the most attention in fisheries science. Global fish populations have plummeted drastically over the last fifty years with the industrialization of fisheries and the introduction of new fishing technologies. Many once-abundant species have been fished to extinction, and the species that have survived are steadily declining in terms of both numbers and average size. Yet our perception of the scale of this loss is blunted by the fact that all too often, each successive generation of fisheries scientists “accepts as a baseline the stock size and species composition that occurred at the beginning of their careers, and uses this to evaluate changes”. Using an ever-shifting reference point masks the extent to which ecosystems have actually changed over multi-generational periods of time.

Anne Randall and Pier Thiret

Losing Our Sense of Reality

This problem is particularly dangerous for conservation efforts because lowered expectations make it almost impossible to accurately assess anthropogenic effects on marine ecosystems and set appropriate goals for recovery. For example, one recent study compared 1950s and 1990s catch rates of pelagic sharks in the Gulf of Mexico and found a staggering 99% decline in oceanic whitetip sharks over the last fifty years. This was the first study to examine trends in shark abundance in the Gulf over such a large time scale, which may explain why the International Union for Conservation of Nature, the world organization tasked with monitoring biodiversity levels and identifying threatened or endangered species, currently places oceanic whitetips only at “lower risk/near threatened” status. Because of shifting baselines, the gradual decimation of this once-abundant shark species has gone largely unnoticed.

Demand Studies Over Longer Time Periods

Thankfully, some marine scientists are aware of shifting baselines and are taking steps to combat this insidious problem. Several recent studies have attempted to establish objective, historically accurate baselines for populations of marine organisms by carefully examining decades-old data from fisheries all over the world. Some of these studies have even incorporated archaeological and paleontological evidence. The California Cooperative Oceanic Fisheries Investigations, or CalCOFI, is currently gathering long-term data on pelagic ecosystems to prevent baselines from being shifted even further in the future. And several conservationists, filmmakers, and bloggers have banded together to create the Shifting Baselines Ocean Media Project ( in an attempt to draw much-needed public attention to the issue. Hopefully, increased awareness of shifting baselines will soon result in a more objective understanding of the damage that overexploitation is doing to our oceans, and more realistic goals for conservation.

About the Author

Michael Esgro is a marine biologist, conservationist, educator, surfer, and nature lover. He received his B.S. in Biology from UCLA and has worked on projects ranging from the design of marine protected areas in Indonesia to the identification of new coral reef fish species. He is looking forward to going back to school to earn an advanced degree in marine science and hopes to eventually work as a researcher, professor, and science writer.