†S. v. glaucus
|†Sander vitreus glaucus|
The blue walleye (Sander vitreus var. glaucus), also called the blue pike, was a unique color morph (formerly considered a subspecies) of walleye which was endemic to the Great Lakes of North America. Morphometric studies led biologists to classify the blue walleye as a separate species in 1926, although it was later downgraded to a subspecies. Listed as an endangered species by the United States in 1967, it was declared extinct in 1983.
Genetic analyses conducted in the 21st century show that the blue walleye was not genetically different from the yellow walleye (Sander vitreus), rendering the taxon invalid.
The blue walleye was long considered to be different from the yellow walleye. Based on morphological study, Carl Leavitt Hubbs declared the blue walleye to be a separate species in 1926. The species was later downgraded to a subspecies.
The blue walleye was a commercially valuable fish in the Great Lakes. Populations appeared to collapse quickly in the 1950s. Between 1950 and 1957, catches in the U.S. and Canada fluctuated between 2,000,000 pounds (910,000 kg) and 26,000,000 pounds (12,000,000 kg) a year. In 1959, however, just 79,000 pounds (36,000 kg) were caught, and in 1964 only 200 pounds (91 kg). The United States declared blue walleye an endangered species in 1967, and extinct in 1983.
A 2014 genetic study of 1,181 preserved "historic" walleye (70 to 90 years old), blue walleye/blue pike, and modern walleye found no evidence for concluding that blue walleye/blue pike was a subspecies of walleye. This rendered the taxon invalid.
A turquoise-colored walleye exists in some waters of the Canadian Shield. A mucosal pigment, named "sandercyanin", was hypothesized to be the source of the color, but this has not been confirmed. This fish was also thought to be a separate subspecies of walleye, but genetic testing showed there is no difference between the turquoise walleye and yellow walleye.
Sander vitreus "glaucus" also known as the "blue pike" is endemic to Lakes Erie and Ontario and co-occurred with Sander vitreus vitreus. It is compared to the walleye in many aspects however, the "blue pike" inhabits the deeper and cooler areas of Lake Erie but was also seen in shallow and warmer areas alongside the walleye. In comparison to the walleye the "blue pike" has a steel blue color, larger eyes placed bit higher than the walleyes eye placement, and the eye distance is smaller as well. 
- Bolsenga, S.J.; Herdendorf, Charles E., eds. (1993). Lake Erie and Lake St. Clair Handbook. Detroit: Wayne State University Press. p. 323. ISBN 9780814324707.
- Wallus, Robert; Scott, Edwin M. (2004). "Genus: Sander (Rafinesque)". In Simon, Thomas P.; Wallus, Robert (eds.). Reproductive Biology and Early Life History of Fishes in the Ohio River Drainage. Vol. 4: Percidae - Perch, Pikeperch and Darters. Boca Raton, Fla.: CRC Press. p. 570. ISBN 084931920X.
- Bennett, David Henry (1979). Probable Walleye (Stizostedion Vitreum) Habitation in the Snake River and Tributaries of Idaho: Research Technical Completion Report (Report). Boise, Idaho: Idaho Water Resources Research Institute, University of Idaho. p. 4. OCLC 5525598.
- Trautman, Milton B. (1981). The Fishes of Ohio. Columbus, Ohio: Ohio State University Press. p. 613. ISBN 9780814202135.
- Wilcove, David Samuel (2000). The Condor's Shadow: The Loss and Recovery of Wildlife in America. New York: Anchor Books. p. 129. ISBN 9780385498814.
- Weidensaul, Scott (2002). The Ghost With Trembling Wings: Science, Wishful Thinking, and the Search for Lost Species. New York: North Point Press. p. 72. ISBN 9780374246648.
- Haponski, Amanda E.; Stepien, Carol A. (2014). "A population genetic window into the past and future of the walleye Sander vitreus: relation to historic walleye and the extinct 'blue pike' S. v. 'glaucus'". BMC Evolutionary Biology. 14 (133): 133. doi:10.1186/1471-2148-14-133. PMC 4229939. PMID 24941945.
- Stepien, Carol A.; Haponski, Amanda E. (2015). "Taxonomy, Distribution, and Evolution of the Percidae". In Kestemont, P.; Dabrowski, Konrad; Summerfelt, Robert C. (eds.). Biology and Culture of Percid Fishes: Principles and Practices. New York: Springer. p. 21. ISBN 9789401772266.
- Trautman, Milton B. (1981). The Fishes of Ohio. Columbus, Ohio: Ohio State University Press. pp. 611, 613. ISBN 9780814202135; Scott, William B.; Crossman, Edwin J. (1973). Freshwater Fishes of Canada. Bulletin 184 (PDF). Ottawa: Fisheries Research Board of Canada. p. 768. OCLC 256035728. Retrieved April 27, 2018; "Fish thought extinct caught in Tennessee". United Press International. February 9, 2012. Retrieved September 30, 2018; "Blue pike extinct, but did they ever really exist?". The Coloradoan. March 19, 2014. Retrieved September 30, 2018; Bowman, Dale (July 11, 2016). "Blue pike, silver pike, walleye: Tracking fishing mystery and words". Chicago Sun-Times. Retrieved September 30, 2018.
- Trautman, Milton B. (1981). The Fishes of Ohio. Columbus, Ohio: Ohio State University Press. p. 612. ISBN 9780814202135; Scott, William B.; Crossman, Edwin J. (1973). Freshwater Fishes of Canada. Bulletin 184 (PDF). Ottawa: Fisheries Research Board of Canada. pp. 755–756. OCLC 256035728. Retrieved April 27, 2018.
- Paradis, Yves; Magnan, Pierre (2005). "Phenotypic variation of walleye, Sander vitreus, in Canadian Shield lakes: New insights on percid polymorphism". Environmental Biology of Fishes. 73 (4): 357–366. doi:10.1007/s10641-005-2261-1. S2CID 22471516. Retrieved April 27, 2018.
- Yu, Chi-Li; Ferraro, Daniel; Ramaswamy, S.; Schmitz, Mark H.; Schaefer, Wayne F.; Gibson, David T. (2008). "Purification and properties of sandercyanin, a blue protein secreted in the mucus of blue forms of walleye, Sander vitreus". Environmental Biology of Fishes. 82 (1): 51–58. doi:10.1007/s10641-007-9252-3. S2CID 20912874.
- Schaefer, Wayne F.; Schmitz, Mark H.; Blazer, Vicki S.; Ehlinger, Timothy J.; Bergese, John A. (2015). "Localization and seasonal variation of blue pigment (sandercyanin) in walleye (Sander vitreus)". Canadian Journal of Fisheries and Aquatic Sciences. 72 (2): 281–289. doi:10.1007/s10641-005-2261-1. S2CID 22471516. Retrieved April 27, 2018.
- Hamponski, Amanda; Stepien, Carol (2014). "A population genetic window into the past and future of the walleye Sander vitreus: relation to historic walleye and the extinct "blue pike" S-v. "glaucus"". BMC Evolutionary Biology (published 17 June 2014). 14: 1–21. doi:10.1186/1471-2148-14-133. PMC 4229939. PMID 24941945.
- Hubbs, Carl L. (1926). A Check-List of the Fishes of the Great Lakes and Tributary Waters, with Nomenclatorial Notes and Analytical Keys. University of Michigan Museum of Zoology Special Publications No. 15. Ann Arbor: University of Michigan. 77 pp. + Plates I-IV. (Stizostedion glaucum, new species, pp. 58–59 + Plate IV, figure 2).
- Trautman, Milton B. (1981). The Fishes of Ohio. Columbus, Ohio: Ohio State University Press. 782 pp. ISBN 978-0814202135. (Stizostedion vitreum glaucum, new combination).