What Does Mt. Pinatubo Have to Do with Walleyes?

Abstract

The eruption of Mt. Pinatubo in the Philippine Islands during June 1991 was followed by a global temperature decline of 1°F through 1993. May to July temperatures in Minnesota during 1992 and 1993 were 3°F below the 1979–1998 average. The 1992 and 1993 year-classes of walleyes Stizostedion vitreum from Minnesota's nine largest walleye lakes, which are gillnetted annually, were the two weakest since 1979. Mean June temperature explained more than 40% of the variation in year-class strength. Mean statewide walleye gill-net catch per unit effort (CPUE) from lake surveys increased at a rate of 1.3% annually after 1979 and was positively related to rising June temperatures, which explains 57% of the variation from lakes in glacial drift and 28% of the variation from Precambrian shield lakes. Walleye fry stocking was also positively related to increased walleye gill-net CPUE, but fingerling stocking was not. Chaotic events, such as large volcanic eruptions, may negatively affect walleye recruitment, and these effects may be evident to anglers several years later.