Tenneson, M., and C. Wellenstein. 1983. Population decline of the mink frog, Rana septentrionalis (Anura:Ranidae) in northwest Minnesota. Final report submitted to the Minnesota Department of Natural Resources. 20+ pp.
Mink frog populations at all sites investigated showed marked declines in population levels. At two sites in Itasca State Park, Schoolcraft Island and West Twin Lake, mink frog populations declined an order of magnitude over a period of 25 and 15 y, respectively. In addition, the overall sex ratio was female skewed, perhaps due to differential predation of males. Of a variety of potential causes of the decline investigated, none were thought to have singly caused the decline. The decline may have been related to redleg disease, caused by the bacterium Aeromonas hydrophila. Redleg symptoms were found in 19% of all frogs in 1982, whereas only two dead frogs with redleg symptoms were reported in the late 1960's. Juvenile mink frogs showed signs of the disease more frequently than adults. Possibly redleg, combined with some other factor such as severe winters, was an important cause of mink frog mortality.