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resolution lo Tish consumption concerns in addition to providing information on mercury 

 contamination sources. 



Because fish may in some cases be highly mobile and slow to change mercui7 levels in 

 response to new surroundings, results must be interpreted carefully. That is. some areas may 

 show both high and low fish mercury levels indicating a mixture of both local and transient 

 fish. For those areas as well as "upstream input areas" additional measurements of mercury in 

 medium (such as water, plankton, and sediment) that respond differently (temporally) to 

 mercury contamination are needed. For this purpose we chose to sample water (fast mercury 

 response), plankton (intermediate response), and sediment (slow response; downstream 

 mobility only). Appendix A describes each sampling site and indicates fish movement 

 constraints resulting from various dams. 



Methods and Materials 



Fish Sampling. During the summer of 1990, personnel from the FDLIR made several 

 sampling visits to two sites on the St. Louis River (near Brookston and Cloquet) to collect 

 various game fish for mercury analysis. A total of 62 fish were collected using both trotlines 

 and gillnets as follows: black crappie (1), channel catfish (26), northern pike (3), northern 

 redhorse sucker (3), white sucker (6), rock bass (7), smaUmouth bass (11). and walleye (5). 



In 1991 additional sites on the St. Louis River were added to the survey started in 1990. A 

 total of 152 fish were collected in 1991 as follows: black crappie (1), bluegill sunfish (1), 

 channel catfish (64), nonhem pike (15), northern redhorse sucker (2),white sucker (2), rock 

 bass (2), smallmouth bass (29), and walleye (36). A summary of the fish collection inventory 

 is shown in Table I; site locations are defined in Figure 1 and Appendix A; and sampling 

 dates and raw data are given in the Appendix B. 



Immediately after the fish were collected, weights and lengths were measured and fillets were 

 removed and frozen. The samples were sent to the UMD/ERL-D (University of Minnesota- 

 Duluth / Environmental Research Laboratory-Duluth) mercury laboratory and kept frozen 

 until analyzed. 



