Effects of climate and global warming on year-class strength and relative abundance of smallmouth bass in eastern Lake Ontario

Predicting the effects of climate and global warming on fisheries necessitates understanding the effects of temperature on fish. For more than two decades, index gill netting in the Ontario and New York waters of eastern Lake Ontario has provided catch statistics and age data to assess the population dynamics of smallmouth bass, an important warm-water sport species. The relationship between log year-class strength and July-August water temperatures was positively correlated and highly significant, explaining 34 to 48 percent of the variance. From 1973 to 1996 the strongest year-classes came from the El Nino years-of 1973, 1983, 1987-1988, and 1995, with some weak year-classes in the La Nina years, 1985,1989, and 1976, and the weakest from the cool 1992 to 1993 period, which were associated with the Mount Pinatubo eruption. Proportional year-class strength and survival rate (67% for ages less than 4 and 62% for ages 4-10) were used to assess relative abundance of the fishable stock (ages 4-10). Relative abundance of older fish was greatest in the mid- to late 1980s, approximately 4-fold higher than when it was weakest, from 1996 to 1998. The strong 1995 and 1994 year-classes initiated a resurgence of older fish in 1999. Relative abundance from 2001 to 2003 was projected to be very close to average and threefold higher than during the lowest period. A 1degreesC increase in global warming will increase year-class strength almost 2.5-fold and a 2degreesC increase 6-fold. Although many factors, including cormorant predation, affect smallmouth bass in eastern Lake Ontario, temperature and year-class strength substantially influenced recent fluctuations in abundance, and the relationship now exists to remove the effects of temperature on recruitment dynamics.