Dr. Arthur Davis Hasler, an internationally recognized authority on freshwater ecology who is credited with explaining the salmon's homing instinct, died on March 23 in Madison, Wis. He was 93.
Dr. Hasler was on the faculty of the University of Wisconsin for 41 years and built it into a hub for lake research. At his death he was an emeritus professor of limnology, a science dealing with the physical, chemical and biological properties of fresh waters.
He recognized early on that lake ecosystems were too complex to study piecemeal in a laboratory. To overcome that problem, he devised novel controlled experiments to deal with the ecosystems of entire lakes.
He introduced the concept of "whole lake manipulation" in the 1950s at two connected, hourglass-shaped lakes. He built a barrier between them and, leaving one side as a control, used the other to gauge the effects of water chemistry on aquatic life.
Such experiments have since come widely into use in lakes, streams, forests and even oceans.
Dr. Hasler helped define the importance of interplay between land and water as a primary variable in the water quality and ecological health of freshwater bodies. He tackled conditions like the excessive loading of nutrients into lakes bordered by urban and agricultural land in an effort to protect the water from sewage and fertilizer runoffs and from soil erosion.
His research became a basis for better freshwater management on an international scale.
Dr. Hasler was born in Lehi, Utah, and graduated from Brigham Young University in 1932. He received a doctorate in zoology from the University of Wisconsin in 1937.
Dr. Hasler wrote seven textbooks -- notably Olfactory Imprinting and Homing in Salmon (1983) -- and more than 200 other publications.
In addition to his wife of 29 years, Hatheway Minton Brooks Hasler, he is survived by a daughter and five sons.