The blue walleye owes its cobalt cast to a lack of yellow skin pigment and the presence of a blue protein in the mucus coating its skin.
Anglers can aid his efforts by reporting blue walleye catches on his website.
A lifelong fisherman, Schaefer became interested in blue walleyes more than a decade ago after catching some in a stream near his cabin at Ear Falls, Ontario.
Because biliverdin is known to act as a sunscreen of sorts in some species of animals, it is possible that, in an ironic twist of science, blue walleyes could be protecting themselves from the sun by excreting excess amounts of the very substance caused by its radiation.
An increase in the number of blue walleyes may be due to decreases in the ozone layer that protects Earth from UV radiation.