on a nationwide basis, and independent of specific treatments, the levels 

 and trends of selected environmental contaminants in freshwater fishes and 

 selected bird species. In addition to monitoring trends in contaminants, 

 the Fish and Wildlife Service also investigates the sources and impacts of 

 contaminants on natural resources. The Columbia National Fisheries Research 

 Laboratory (CNFRL) is responsible for monitoring residue trends in fresh- 

 water fishes and Patuxent Wildlife Research Center, Laurel, Maryland is re- 

 sponsible for monitoring residues in tissues of selected waterfowl and star- 

 lings ( Sturnus vulgaris ). 



FRESHWATER FISH FROM LAKES AND STREAMS 



Monitoring contaminants in freshwater fish has undergone a series of 

 changes since collections began in 1967. At first, fish were collected 

 from 50 sampling stations in the Great Lakes and major rivers throughout the 

 United States (Stations 1-50, Figure 1). Five adult fish of each of three 

 predominant species were collected in the spring and again in the fall of 

 both 1967 and 1968. In 1969, and each year since then, collections have 

 been made only in the fall. In 1970 the number of collection stations was 

 increased to 100 with the addition of Stations 51-100 (Figure 1). Deter- 

 minations have always been based on composited, whole-body samples of five 

 fish each. From 1967 through 1971 all sample analyses were contracted to a 

 private laboratory; in 1972, for economic and administrative reasons, the 

 analytical work was shifted to the Fish and Wildlife Service Laboratory in 

 Denver, Colorado; and in 1976 the program was relocated to CNFRL, where it 

 remains today. Collections were suspended for one year in 1975 when fresh- 

 water fish monitoring was undergoing an internal review and reorganization. 



There are now 117 stations in the United States where fish are collected 

 for analysis of contaminant residues (Figure 1). About half of the stations 

 are sampled in the Fall of even-numbered years and the other half during 

 odd-numbered years. At each trend monitoring station three samples of five 

 fish each are taken: two samples of a predominant bottom-dwelling species 

 and one sample of a predator species. The preferred species to be collected 

 vary geographically and according to habitat (Table 2). 



The number of contaminants studied has increased over the years from 

 eight in 1967 to more than 20 today (Table 3). At CNFRL there is a strong 

 research emphasis on improving methods and developing the technology neces- 

 sary to quantify toxic chemical contaminants that are difficult to analyze 

 in biological tissues. 



PROCEDURES 



Fish are collected by non-chemical means (i.e., by electroshocking, net- 

 ting or hook and line) according to specified instructions. Sometimes fish 

 must be purchased from local commercial fishermen known to Fish in the vi- 

 cinity of the collection site. All specimens are adult fish, preferably of 

 uniform size, and weighing no more than 22.7 kg (5 lb) each. 



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