Yellow perch, Perc4 flavescens (Mitchill), were sampled by bottom trawling and gillnetting in Indiana waters of Lake Michigan near Michigan City, Indiana during the months of June, July and August, 1988.Length-frequency analysis of trawl-caught fish revealed that fish older than age 1 were represented by a single large aggregate in monthly length frequency distributions. Opercular ages were validated by establishing that opercular bone annulus formation occurred from late spring to early summer and was completed by late July.Percent agreement of age determinations by age class between the methods ranged from 0X to 100X for males and OZ to 89X for 'Females for combined months. There was a tendency for percent agreement to decrease with increasing age in both males and females. The majority of the age discrepancies were a difference of plus or minus one year for both males and females.The body-scale length relationship was determined to be linear with data points close to the regression line for both sexes by month and for months combined. Coefficients of determination values ranged from 0.92 to 0.96 for male body-scale length regression by month with a value of 0.93 for months combined . Coefficients of determination values for females ranged from 0.92 to 0.94 by month with a value of 0.93 for months combined. Combining all data for months and sexes yielded a coefficient of determination value of 0.93 for body-scale length regression.The a-values determined for the body-scale length relationship were variable from June through August for both sexes. Male avalues ranged from 30.58 to * 44.15 monthly with a months combined value of 37.63. Female a-values ranged from 25.55 to 43.30 monthly with a combined months value of 34.83. Combining all data for months and sexes yielded an a-value of 35.78.The body-opercular length relationship was determined to be linear with data points close to the regression line. Coefficients of determination values for males ranged from 0.94 to 0.98 by month with a value of 0.96 for months combined. Coefficients of determination for females ranged from 0.97 to 0.98 by month with a value of 0.97 for months combined. The combined data for sexes and months resulted in a coefficient of determination value of 0.97.The a-values determined for the body-opercular length relationship demonstrated variability from month to month. Male a-values ranged from 9.19 to 14.47 monthly with a combined months value of 11.69. Female a-values ranged from 8.83 to 12.26 monthly with a combined value of 11.57. Combining the data for months and sexes yielded an a-value of 11.59.Growth determinations based on scale and opercular data for all aged fish demonstrated a high degree of agreement between the methods for both sexes and all age classes. No significant differences were found between 95X confidence intervals for mean length at formation of last annulus for any age class. The largest observed difference in length at formation of last annulus was 23 mm in the age 3+ females in June. Growth determined from opercular bones was found to be slightly greater than growth determined from scales in both sexes. Females grew faster than males after age 2 based both on scale and on opercular data. Monthly length increment determined from scale and opercular data was determined to be small or non-existent after age 2 for both sexes.Growth determined from scales and opercular bones for only those fish with agreed age between the methods demonstrated a high degree of agreement between methods by month for both sexes. No significant differences were found between 95X confidence intervals of mean length at last annulus in any age class. Data for months combined and sexes separate revealed that growth determinations were virtually identical between the methods. Females were shown to grow faster than males after age 2 for both methods. Monthly length increment was again found to be small or non-existent after age 2.Based on these results, it is concluded that the opercular bone method is an acceptable procedure for assessing age and growth of the yellow perch in Indiana waters of Lake Michigan. Since false annuli were more readily recognized in the opercular bone than in the scales and, since there was the decreasing agreement between the methods with increasing age of fish it is concluded the opercular method is probably a more accurate method for age and growth analysis in the yellow perch from Indiana waters of Lake Michigan. / Department of Biology

Relative weight (Wr) of yellow perch (Perca flavescens) was evaluated for fish collected from the Indiana waters of Lake Michigan in June, July and August of 1976 and 1984-1991. Computation of Wr was completed for individual fish in 20 mm intervals over the size range from 100-219 mm using Wr = (W/Ws) 100 where W=weight of a fish in grams and Ws=standard weight for a fish of the same length. Length was highly correlated with weight in all years for males, females and sexes combined (r=0.97-0.99). Distributions of predicted weights for fish at 130 mm and 250 mm were at or near modes of the populations used to construct the Ws equation for yellow perch. Relative weights consistently decreased with increasing size in all years for males, females and sexes combined. Using 1976 length-weight data when the yellow perch population was sparse and fast growing as a standard (100%) for comparison, relative condition factors (Q) increased with increasing size in some years and decreased with increasing size in others for males females and sexes combined and it did not appear to be length dependent. When comparing Wr at 100 mm and 200 mm by sex and month, f hales had higher Wr than males at 100 mm in seven of nine years in June, six of nine years in July and only four of nine years in August. Female fish also had higher Wr than males at 200 mm in eight of nine years in June and July and six of nine years in August. There appeared to be no consistent pattern or trend of Wr increasing or decreasing by month for males, females or sexes combined. When Kn was evaluated for 100 mm and 200 mm fish by sex and year, male fish had higher Kn than females at 100 mm in all eight years. Male and female fish at 200 mm were more similar; male fish had higher Kn in three years, lower Kn in three years and equal Kn in two years. No relationships were found at 200 mm comparing Wr or Kn and CPE (quality/ h) for males (r=0.43; r=0.42), females (r=0.12; r=0.13) or sexes combined (r=0.28; r=0.22). Simple linear correlations of proportional stock density (PSD) with Wr and Kn revealed relative weights increased with PSD for 100 mm (r=0.51) and 200 mm (r=0.72) fish. Relative condition factors also increased with PSD for 100 mm fish, however the relationship was weak (r=0.30) but a strong correlation was found between Kn and PSD (r=0.81) for 200 mm fish. Based on these results, it appears that either Kn or Wr may be used inassessing the condition of yellow perch from the Indiana waters of Lake Michigan. / Department of Biology

The yellow perch, (Perca flavescens), is an important commercial and sport fish in Indiana waters of Lake Michigan. The population is currently managed by temporary restrictions of commercial harvest. A computer simulation model was developed to examine the effects of various constant harvest quotas and alewife densities on yellow perch relative numbers.Model design is based on the SLAM II simulation language incorporating a FORTRAN biological subroutine. The age-structured population model includes measured or predicted biological characteristics of the dynamic pool model. Recruitment is based on a preestablished three-dimensional Ricker stock-recruitment function including alewife (Alosa pseudoharengus) species interaction as a constant or stochastic factor. Sex-specific natural mortality rates were established through life history parameter analysis and the von Bertalanffy growth factors. Density-dependent growth is incorporated into each year of a model run and fluctuates with the simultaneous density of fish. Constant levels of commercial harvest ranging from 0 to 700,000 kg were used in 20-year forecasts. Initial conditions for model runs were 1984 and 1994 trawl CPUE levels when yellow perch were at high and low levels, respectively according to standardized sampling. Response variables were examined as mean catches over each forecast length and included: age 2 fish, spawning stock (z 190 mm), and total catch > age 1.Alewife densities had a tremendous impact on mean catches of the response variables. Highest catches under any forecast period occurred when alewife was considered absent from the system. Catches declined as alewife density was increased as a 20-year constant under each harvest regimen.Catches of spawning size fish were maintained at highest levels for all forecast periods when harvest was set to zero. Catches of young fish were moderate with this harvest regimen if initial catch conditions were high such as in 1984. Catches of young fish were always higher in the absence of a commercial fishery if initial catch conditions were low such as in 1994. Low to moderate harvest quotas could maintain moderate levels of young fish for the forecast length if initial model conditions were high. However, these quota levels for the 1984-2004 forecast length resulted in lower mean catches of spawning size fish as compared to the no commercial fishery regimen. The best case scenario for all response variables when initial catch conditions were low was under a no commercial harvest regimen. / 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