Components of Utility Indices:

1. Exposure Potential

A measure of the likelihood of an individual encountering a contaminant by oral, dermal, or inhalation routes of exposure.

Specific elements that may affect exposure may include dietary preference, habitat preference, longevity, foraging technique, and other behaviors that result in contact with the physical environment.

Elements for exposure potential will vary among Utility indices.

2. Geographic Occurrence

The range and seasonal occurrence within a particular study area.

Species that are considered more desirable for monitoring occur throughout a greater portion of the study area, spend a greater amount of their life cycle in the study area, and breed, rather than just winter, in the study area.

3. Ease of Collection

Ease of collection is determined by a species’ social structure, accessibility, ease of capture, abundance, and management status. The season during which the collection will occur may influence results (e.g., a population may be highly colonial during the breeding season, yet employ a looser social structure during winter months)

Accessibility is classified in relative terms, simply as “easy,” “moderate,” or difficult.” These loosely defined terms permit users to rate accessibility based on the specific circumstance, taking into account monetary, personnel, equipment, and other logistical constraints.

Abundance and management status includes restrictions on collection or disturbance based upon state or federal regulations protection measures or management protocols.

Species are considered easier to collect if they nest or roost colonially and breed in the study area, making collections of eggs or young for contaminant or biomarker analysis possible (persistent organic pollutants, mercury, and cholinesterase-inhibiting pesticides only).

4. Quantity Of Existing Exposure And Effects Data

The amount of information available for a species in regard to the particular contaminant or contaminant class. Data sources may include hypothesis-driven laboratory or field investigations, or other types of monitoring efforts. Species for which relatively greater amounts of data exist for the contaminant of concern are given more weight as sentinels. The existence of baseline data and historical precedent are considered advantageous for bioindicator species in that such data facilitates comparison to affected conditions.

5. Calculation of Utility Index Scores

The four components are summed, each carrying equal weight regardless of the number of elements:

Utility Index Score = (Exposure Potential) + (Geographic Occurrence) +
(Ease of Collection) + (Quantity of Existing Data)

Each component carries a value between 1 and 5 points. Elements within components are weighted equally (1-5 points), with the exception of “Dietary Preference” and “Foraging Technique” within the Exposure Potential component, which carry a maximum value of 10 points. These two elements are weighted more heavily as they generally represent the principal route of toxicant exposure for terrestrial vertebrates. The final Utility Index score ranges between 4 and 20

Roll over the Index Name with your mouse for specific point values of each element in the table below.

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