Bias in Estimates of Maximum Life Span, With an Example of the Edible Cockle, Cerastoderma Ed Ule

Abstract

The assessment of maximum life span in a natural population of a species ("ecological longevity") meets with several difficulties. Using as an example a long-term data series of a tidal-flat population of the edible cockle, Cerastoderma (Cardium) edule, it is shown that the age of the oldest individual found depends on the sampling effort (both sizc of area sampled and duration of sampling period), on the numbers of cohorts studied and on their size. All of these factors enhance the number of (old) specimens examined and, thus, the chance that a very old individual is encountered. Even in a relatively short-living species such as the cockle, low-effort or low-density estimates were biassed by one or more years. It is argued that the available data on longevity may all be considered underestimates and thus should be used with caution. An example of incautious use is discussed.