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Conservation lessons: Marine Mammal Act shifts burden of proof
Imagine trying to count the number of dolphins between California and Hawaii.
Determining the abundance and distribution of species is particularly difficult in marine environments, which are often remote and inaccessible.
But lack of concrete data should not hinder species conservation, according to a recent report in the October issue of Conservation Biology.
"Getting an exact scientific number is almost impossible and the burden of proof usually ends up on the scientists who must prove that a population is in trouble before anything happens," said lead author of the report, Barbara Taylor, a conservation biologist at the National Marine Fisheries Service's Southwest Fisheries Science Center.
Citing the management approach of the Marine Mammal Protection Act, the report describes how to incorporate uncertainty into management decisions.
In 1994 the Marine Mammal Protection Act was amended to incorporate uncertainty about the status of a particular species. Now the less managers know about the status of a marine mammal stock, the fewer the number of kills that are allowed by commerical fisheries.
Prior to the amendment the data requirements of the Marine Mammal Protection Act were so strict that only 12 of the 153 marine mammals in U.S. waters were assessed. "It was so difficult to obtain evidence that the law did nothing," Taylor said. "Entire species were falling through the cracks under the old system."
Only a year after the act was revised, 112 stocks had been accounted for.
To understand how many marine mammals can be killed by marine fisheries, biologists must know the number of members within a certain species, how many are being killed by the fisheries and how fast a population can rebound.
Problems arise when the data is not conclusive.
The Marine Mammal Protection Act takes a precautionary approach when faced with uncertainty, Taylor explains. "The less we know about a species, the more conservation we incorporate in our management decisions."
The act works like this:
If wildlife managers know that they have a population of 100 whales and that the population grows by four members each year, the act allows the incidental take of two whales a year, or half of the population growth. But if wildlife managers can only estimate that between 50 and 130 whales exist, the population growth estimate is based on 50 whales, and only half of that number can be incidental catch.
If the species is listed under the Endangered Species Act, further restrictions are put in place.
"We feel that this management approach has worked so well that it could be used as a model for species on land," Taylor said. "The Marine Mammal Protection Act encourages management action when populations are still healthy. Most conservation laws such as the Endangered Species Act are geared toward emergency action. It is much more economical to treat a patient before it gets to the emergency room."
In addition to providing better protection for marine mammals, the researchers suggest that the management style might encourage fisheries to help researchers collect more data. Since more data means less uncertainty, the fisherman could be allowed a higher take for healthy stocks of marine mammals.
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