The Problem with Shifting Baselines

“Yellowbanks—good spot for abalone” my fading and barely legible printing in a terse, 32-year-old logbook entry indicates.  It was a fine day of diving on the southeast side of Santa Cruz Island. The log entry fades, but the memory of abundant pink abalone stays in my mind.  A few years later, the “withering foot disease” decimates the abalone populations of the northern Channel Islands, bringing the species to the brink of local extinction.  A new diver visiting Yellowbanks for the first time in the mid-1990s finds a healthy kelp forest ecosystem albeit one that is devoid of abalone.  Since that diver never experienced the area with abalone, that diver’s “baseline” of a healthy ecosystem does not include abalone. Only the scattered abalone shell fragments in the seabed indicate the species was ever present.

The above phenomenon is known as the “shifting baseline syndrome.” Identified in 1995 by Daniel Pauly, a shifting baselines syndrome posits that people measure ecosystem change against their personal recollections of the past and, based on this decidedly short-term view, unknowingly tolerate gradual and incremental change in the ecosystem.

Divers continually establish baselines, a point driven home for me a few years ago while diving the Kona Coast of the Big Island of Hawaii with a freshly-minted teenage diver.  The coral reef with all its life fascinates us.  Our baselines are the same.  While I know from historical accounts that the coral reefs around the island once were more abundant, this condition is counterfactual to my experience.  One is textbook knowledge, the other is experiential, with the latter being the more powerful of the two. 

A recent study examines the loss of coral reefs in the Florida Keys by comparing  240-year-old  British Admiralty nautical charts of the area against satellite data.  The study found overall loss of 52% (Standard Error, 6.4%) of the area of the seafloor occupied by corals.  The study notes

The near-complete elimination of the spatial coverage of nearshore coral represents an underappreciated spatial component of the shifting baseline syndrome, with important lessons for other species and ecosystems. That is, modern surveys are typically designed to assess change only within the species’ known, extant range. For species ranging from corals to sea turtles, this approach may overlook spatial loss over longer time frames, resulting in both overly optimistic views of their current conservation status and underestimates of their restoration potential.

The study, “Ghost reefs: Nautical charts document large spatial scale of coral reef loss over 240 years” can be found at http://advances.sciencemag.org/content/3/9/e1603155