• Individual humans that consume species other than the 

 dominant component of the diet for the entire exposed popula- 

 tion may not be protected when the results of the risk assess- 

 ment are used in risk management 



• Which species are dominant often varies spatially, making it 

 difficult to compare risk estimates for different sites 



• Extensive species-specific data on catch, consumption, and 

 contamination patterns are needed to select target species 

 (these data are costly to obtain if not already available) 



• If samples are obtained directly from harvesters, a major com- 

 ponent of the catch may be unidentifiable because the catch is 

 sometimes cleaned before being surveyed. Moreover, the loca- 

 tion of harvest by boat anglers often cannot be verified. 



Indicator Species— The use of selected indicator species is an alterna- 

 tive to the use of dominant harvested species. Indicator species can be 

 chosen to represent the average (or maximum) contamination levels in 

 the harvest, as determined from available data or from a pilot survey. 

 Use of indicator species may be appropriate for investigations with 

 multiple objectives (e.g., assessment of bioaccumulation in fishery 

 species and human health risks for specific areas within a water body). 

 Indicator species may include both highly mobile and relatively seden- 

 tary species. If small-scale discrimination of spatial patterns of con- 

 tamination is a concern, indicator species should include nonmigratory 

 biota or species that exhibit minimal movement within the aquatic 

 habitat (e.g., bivalve molluscs and English sole in nearshore marine 

 areas; mussels and sculpins in streams). 



The use of a few indicator species for exposure assessment is appro- 

 priate for initial screening of geographic areas before more detailed 

 exposure assessments are conducted. If no potential health problems 

 are identified in an initial risk analysis, further data collection may not 

 be warranted, unless long-term monitoring is desired. If, on the other 

 hand, analysis of tissues from indicator species reveals substantial 

 health risks, further field surveys may be needed to perform a detailed 

 exposure assessment. The latter should include data on consumption 

 patterns and contaminant concentrations for a wider variety of har- 

 vested species and size classes. 



The use of indicator species for exposure assessment offers the follow- 

 ing advantages: 



• Field surveys based on indicator species are cost-effective 

 because efforts can be focused on collecting large sample sizes 

 of one or a few species rather than minimally adequate sample 

 sizes of many species 



• Background information on the distribution, abundance, and 

 contamination of indicator species may be available 



• Indicator species can be selected to represent the average or 

 maximum level of contamination expected for all harvested 

 species (assuming background or pilot data are available) 



38 



