weight) in the harvest may be selected to represent a typical exposure 

 level. However, this approach has the major disadvantage that highly 

 contaminated species may be overlooked (see Dominant Harvested 

 Species below). For the third objective (worst-case species analysis), 

 the target species should be among the most contaminated species in 

 the harvest. If the worst-case assessment is species-specific (i.e., the 

 consumption rate for a single species is used to estimate exposure), 

 then the target species should also be one of the dominant species in 

 the harvest. When the dominant component of the diet differs among 

 subpopulations of concern, then specific dietary information for sub- 

 populations should be used to select the worst-case target species. The 

 target species may be the most contaminated species regardless of its 

 status in the diet of the entire exposed population. For the last objec- 

 tive (site-specific analyses of the spatial distribution of contamination), 

 an indicator species with a small home range that is expected to have 

 high concentrations of contaminants in edible tissue would be selected. 

 Note that an indicator species could be a species that is relatively rare 

 in the harvest. Although home range size and degree of contamination 

 of species may not constrain the selection of species to meet the first 

 two objectives listed above, selecting species without regard to con- 

 tamination levels will not necessarily ensure that the overall purpose 

 of performing an exposure assessment will be met. 



TABLE 4. Criteria for Selecting Target Species^ 



Alternative Design Objeclives 



Species 

 Characteristics 



Comprehensive Typical Worst-Case Spatial Pattern 

 Species Eixposure Species Indicator 



Analysis Case Species 



Harvest ranking Species forming Dominanl Dominanl Variable 



95% of catch species in catch species in catch 



Home range size Variable Variable Variable Small 



Contamination level Variable Variable High High 



Criteria for selecting target species to meet a given objective are shown in bold. 

 A full statement of each objective is given in the text. 



Dominant Harvested Species-If available, data on fisheries catches or 

 consumption from field surveys (e.g., Finch 1973; Puffer et al. 1982; 

 Landolt et al. 1987; McCallum 1985) can be used to select species for 

 analysis that are dominant members of the catch on a wet-weight basis. 

 The advantages of choosing the dominant harvested species for ex- 

 posure assessment are that: 



• Exposure estimates will be based on realistic conditions in 

 terms of relative contribution of species to the diet, providing 

 that catch data reflect consumption patterns or that consump- 

 tion data are used for the selection of species 



• Adequate numbers of organisms for chemical analyses should 

 be relatively easy to obtain. 



The disadvantages of this approach are that: 



• Species that are minor components of the diet by weight but 

 that are highly contaminated may be overlooked 



37 



