261 



Tabic III indicates, overall, that black crappie are the lowest in mercury concentration while 

 channel catfish are the highest. A more quantitative and accurate comparison may be 

 accomplished, though, by taking into account fish size and location. Both of these factors 

 have been shown in other studies (e.g. Sorensen et al., 1990) to strongly influence fish 

 mercury concentrations . In order to address these dependencies, we determine or 

 mathematically model the relationship between mercury concentration and fish size for each 

 sampling site. 



Table III. Statistical Summary of Mercury in Fish for Each 

 Species Across All Sampling Sites 



Table IV. Statistical Summary of Fish Size Parameters for Each Species Across All Sampling Sites 



*Ages were not determined for all fish; the n value for the age statistics are 2, 83, 10, 3. 6, 9, 20, and 41 for black 

 crappie through walleye, respectively. 



Before modeling the fish mercury concentration data we must resolve two issues: 1) can fish 

 mercury concentration data from two sampling years (1990 and 1991) be merged? and 2) 

 which fish size parameter is the most appropriate? Figure 5 shows the relationships between 

 mercury levels in catfish and fish length for two sampling regions along the river with the two 

 sampling years delineated. With the exception of three outliers (all firom 1991) there is no 

 significant difference between the two years. 



10 



