Friday, March 12, 2010

Shifting Baselines: what is the appropriate measurement of a healthy ocean?

When we examine a marine ecosystem or the population of a particular species and observe that "it's not what it once was," we are, in simple terms, observing a shifting baseline. The use of shifting baselines, or what has sometimes been called Shifting Baseline Syndrome (SBS), has become a common but controversial tool in evaluating fishery management, species population, and general ocean vitality. In fact, it has been used as the basis of study for a variety of scientific and societal conditions - from ocean conservation to Hollywood entertainment.

One of the challenges in using SBS is in determining what the fundamental baseline is - what is the baseline that represents a fully healthy, functioning marine ecosystem or species population? Is it what it was 10 years ago? A century? Or before the arrival of mankind? To determine such an ultimate starting point, scientists often have to take a variety of empirical and anecdotal data and work backwards. Sometimes this works, sometimes not.

As an example, one study in the late 1990's determined that the appropriate baseline population for green sea turtles in the Caribbean was 660 million, based on an extrapolation of the extent of a particular sea grass that figured prominently in the turtle's diet. Several years later, based on a reevaluation of the sea grass growth, that number was scaled back to 16 to 33 million - quite a reduction but still, given today's population of less than 200,000, what can we realistically expect as a conservation goal?

In other situations, SBS gets oversimplified in its application regarding policy. When research determined that over-fishing was the primary cause of a drop in Canadian cod fisheries, a moratorium was put in place in the early 90's. However, the cod population has failed to recover and the moratorium remains in place. What may have been missed is some unforeseen cascade effect, some other component to a healthy cod population that is missing or altered, perhaps triggered by the over-fishing, perhaps not.

Many scientists see value in using SBS but there are some who feel that it must be utilized in a more comprehensive fashion that also incorporates other theoretical approaches including resilience and social-ecological systems (SES) which introduce variables of human involvement or impact while trying to determine an appropriate future baseline.

In the end, it can be a vexing question: as we consider the health of marine species or ecosystems, what is the ideal goal that we can truly expect to strive for, regardless of how things were in the past? Can science accurately and reliably make that determination? Hopefully, it can but it will require a broad spectrum of scientific approaches to do so.

Click here for a proponent web site that explains shifting baselines.
Click here to read a scientific paper on SBS weaknesses and solutions.

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