"It is crucial in the future that this lesson not be ignored," they admonish.
In an example of recovery, the authors describe the situation of the eastern North Pacific population of gray whale. Removed from the Endangered Species Act (ESA) List of Endangered and Threatened Wildlife in June 1994, and the only large whale so far "delisted," this whale population is approximately 26,635 individuals, up 2.5 percent each year over the last three decades.
To address the question of how much monitoring is necessary to detect recovery of this whale population, the authors sampled different sets of data from 19 years. "We then applied a model to determine ESA status for each subset of survey data and found that a quantitative decision to delist is unambiguously supported by 11 years of data, but precariously uncertain with fewer than 10 years of data," said the authors.
Depletion of whale populations is mainly the result of commercial whaling ending sometime between the 30s and 80s. The authors state that "only the eastern North Pacific population of gray whales seems to have fully recovered."
The rest are still classified as endangered under the U.S. Endangered Species Act.
"The lesson here seems to be that at least some large whale populations can recover from overexploitation, but only if their numbers are not reduced to some level, beyond which the "extinction vortex" reaches out and starts pulling them inexorably towards extinction," they state.
They go on to explain that "moratoria on harvest alone are insufficient to guarantee adequate conservation. Without adequate monitoring, it is not clear to what extent management objectives have been or will be achieved. Adequate monitoring programs, such as that for the eastern North Pacific gray whale, will not be inexpensive and will not be brief."
The authors conclude with a call for better objective criteria in asse
'"/>
Contact: Gail Brown
gbrown@instadv.ucsb.edu
805-893-7220
University of California - Santa Barbara
27-Jun-2000