Fisheries Classics: Ryder’s Morphoedaphic Index

Jeff Schaeffer | AFS Co-Chief Science Editor. E-mail: [email protected]

Photo credit: wikimedia.org

Photo credit: wikimedia.org

This work by Richard Ryder represents an important paper because it was one of the first widely accepted papers that promoted the idea that groups of freshwater lakes were comparable and that fish yields could be predicted based on physical and chemical attributes. The morphoedaphic index (MEI) was simple to calculate by dividing total dissolved solids (T, ppm) by mean depth (D, feet) and ranged from 0.12 in deep oligotrophic lakes to 20.8 in shallow eutrophic lakes. While not the first attempt to achieve this, this manuscript generated a lot of discussion at conferences, and many educators began to include discussions of MEI in their classes. Since that time, advances in spatial ecology and computational techniques have produced far more refined models of fish production, but this was the paper that got the discussion started widely. Ryder’s model worked well in its time, was objective rather than subjective, and got a lot of people thinking about the idea that lakes with similar physical characteristics could be managed in similar ways. This was transformative because at that time many fisheries scientists viewed lakes as individual and unique and there was far less recognition of landscape-scale patterns in aquatic environments. This year is the 50th anniversary of his publication, but it is still a good read. REFERENCE Ryder, R. A. 1965. A method for estimating the potential fish production of north-temperate lakes. Transactions of the American Fisheries Society 94:214-218. dx.doi.org/10.1577/1548-8659(1965)94[214:AMFETP]2.0.CO;2