The population dynamics of alewives Alosa pseudoharengus and spottail shiners Notropis hudsonius were investigated in Indiana waters of Lake Michigan from 1984-1996. Insights to population dynamics of both species were found by applying age and growth information to length-frequency distributions of index trawl catches within and between years. Both alewife and spottail shiner populations showed general increasing trends over the period, reaching peak levels in 1996. Interaction potential was examined for alewives, spottail shiners, and the yellow perch Perca flavescens, another important nearshore species. Trends in relative catches of these species were correlated to provide insight to possible interactions. There appears to be negative relationships between alewife and yellow perch populations, as well as between yellow perch and spottail shiner populations. No relationships were found between alewife and spottail shiner populations. / Department of Biology

Yellow perch, alewife, spottail shiner and round goby trawl catch per unit effort (CPUE) was evaluated in the Indiana waters of Lake Michigan from 1984-2006 to determine whether spatial or temporal variation in CPUE for these species occurred. Differences in CPUE among sites or periods were not clearly distinguished within a single sampling year. However, when compared over a 23 year time frame, spatial and temporal differences became evident. To determine the minimum number of samples needed to detect differences among sites and periods, we ran a Monte Carlo simulation using 23 years of empirical data. This compared favorably to results obtained from a power analysis that identified the minimum number of samples required to identify statistical differences. Sampling effort needed to distinguish differences in CPUE varied both spatially and temporally among the four species. Differences in sampling only became evident when multi-year efforts were employed. In addition, spatial and temporal differences in male and female (mature and immature) yellow perch proportions was also evaluated among our sample sites and periods from 1993-2006. / Department of Biology

A computer simulation model was developed to examine the effects of various levels of alewife densities, harvest, and bycatch rates on yellow perch Perca flavescens relative densities in Indiana waters of Lake Michigan. The model utilized STELLA® Research software to develop the age-structured population model to include measured or predicted biological characteristics of density-dependent growth, recruitment, and mortality.The model was validated by simulating historically documented yellow perch catch per unit effort (CPUE) from 1984 - 1998. A strong linear relationship (R2= 0.70) between the model predicted CPUE values and the actual CPUE values was found. Twenty year model projections were performed using 1998 yellow perch trawl CPUE as starting values. Alewife abundance was established as either constantly high, constantly low, or allowed to fluctuate randomly and forecasts made used the average of 100 runs. Harvest was imposed on the yellow perch population at 20, 40, and 60% rate levels for fish >_ 200 mm coupled with bycatch at20, 40 and 60% rate levels for fish ranging from 165 - 200 mm.Alewife abundance was the major factor determining the relative abundance of the yellow perch population. On average, constantly high alewife abundance with no harvest or bycatch resulted in projected continuing suppression of yellow perch abundance from 1998 levels. The model predicted the population to rebound using constant low and random alewife abundance with no harvest or bycatch to approximately 1,100 fish/h and 700 fish/h, respectively.The model revealed harvest to have a generally negative impact on the yellow perch population. Increasing harvest and bycatch rate levels resulted in the suppression of projected increases in yellow perch relative abundance. Additionally, increasing harvest and bycatch rates resulted in greater predicted declines in yellow perch abundance. / Department of Biology