Saugeye are stocked by the IDNR in the large flood control reservoirs because they do better in those types of waters than either walleye or sauger. Many of the “walleye” caught out of the lower Iowa River are actually saugeye.
In the Mississippi, where both walleye and sauger occur naturally, saugeye are the result of crossbreeding between walleye and sauger in the wild. Sauger spawn when the water temps. are a couple degrees warmer than walleye do, but male sauger are often ready to spawn when female walleyes are, and fertilize walleye eggs when the females drop them. This is how wild saugeye are made.
The saugeye is unusual among hybrid fish in that it is fertile, and can mate succesfully with walleye, sauger, or other saugeye. (This is not true of tiger muskie, wiper, or tiger trout, all of which are sterile.) I mention this because the various resulting 3/4, 7/8, or 15/16 walleye/sauger mixes can be difficult to identify with certainty. Every year on the Mississippi I catch “sauger” with a rather large white patch on their tail, and “walleye” with noticeble dark patches on their body. According to In-Fisherman , 20% of the sauger in the Missouri river system carry walleye genes, and this is probably true of the Mississippi sauger population as well. As other people have said, when in doubt, treat it as a walleye in regards to regulation restrictions.