September 3, 2009

Freshwater fish reductions overlooked

U.S. and Canadian scientists say natural resource managers are overlooking steep historical reductions in the numbers of freshwater fish.

Kirk Winemiller of Texas A&M University and Paul Humphries, of Charles Sturt University in New South Wales, Australia, argue a result of that neglect of historical records has led to watershed planning often built on estimates of baseline abundances of fish, freshwater mussels, beavers and other aquatic fauna that are much lower than actual past numbers.

The scientists said written accounts of travelers and diarists dating from the 1600s report rivers so full of fish that a spear thrown into the water only rarely missed one, salmon runs that spanned the whole width of a river, and fish so plentiful they were used as pig feed.

Humphries and Winemiller said European colonizers in North America and Australia moved inland and started constructing dams and mills that impeded the migration of fishes. Subsequently stocks of fish and shellfish declined rapidly. Humphries and Winemiller said the affects of that early loss of river wildlife has not been adequately considered.

The scientists say they support reintroduction of top freshwater predators and keystone species and urge the creation of freshwater protected areas. Some of those protected areas, they said, could be used for restoration experiments in which the effects of reintroduced species could be explored.

The study is reported in the journal BioScience.