Extinction considerations for diadromous fishes

Among diadromous fishes, the sturgeons are particularly threatened with 13 of 15 species considered endangered or vulnerable to extinction worldwide. These species have low intrinsic rate of growth and specialized habitat requirements making them sensitive to environmental changes and human exploitation. Habitat destruction, degradation, and alternations are probably prime causes of extinction in diadromous fishes. The spread of alien species, naturally or transported by humans to new environments, may be the second most important cause. Harvest is a contributing factor to extinction risk for many diadromous populations, although there is no known example where overfishing has led directly to the extinction of species. Population viability analysis is a method which may be used for evaluating extinction risk. However, uncertainties associated with parameter estimation and model choice limit its usefulness. Avoiding short-term extinctions is difficult enough, but restoration and recovery of natural populations present a whole new array of challenges. The understanding of the genetic population structure of the species is essential in this context. Captive rearing has some use as tool to assist stock restoration. However, artificial propagation will not lead to recovery unless the fundamental problems that caused the population declines are addressed. (C) 1999 International Council for the Exploration of the Sea.