Alewife abundance, growth, and mortality in Otsego Lake 1996-2002

Alewife abundance in Otsego Lake has been monitored in 11 of the last 14 years using littoral trap netting efforts. Hydroacoustic surveys of alewife (Alosa pseudoharengus) density have been conducted in Otsego Lake since 1996 (except for 1998). Alewife density during this period ranged from a low of 968 fish/ha in May 2002 to a high of 14,797 fish/ha in August 2002. The lowest density (May 2002) followed the second highest density (October 2001) and the lowest winter water temperatures ever recorded, suggesting that the effects of low water temperatures (1.6 ° C throughout water column) and intraspecific competition are important in regulating alewife survival and abundance. Comparisons of fall density with density in the following spring were used to estimate overwinter mortality during three years of this study. These mortality estimates were compared with alewife (ages 1-4) mortality estimated from catch curve analysis. Both methods revealed high mortality relative to alewife populations in other lakes. High mortality is further supported by slow growth and short life span (4 years) of alewives in Otsego Lake. However, our findings also suggest that alewives exhibit a compensatory increase in survival of young-of-year (and potentially fecundity) when adult abundance is low. This compensation may be the result of reduced cannibalism of young-of-year alewives when adult densities are low, as in May 2002