Target Species and Size Classes

Target species are the fish and shellfish collected for the contaminant monitoring program. These species are distributed widely enough to allow for comparison of contaminant data across a wide geographic area. The age of a fish or shellfish correlates with its size and in many cases with the amount of contaminants in tissue. By collecting data on different size classes of target species, a more nuanced and accurate fish or shellfish consumption advisory can be developed.

• Creating a Target Species List
• EPA Target Species List - Fish
• EPA Target Species List - Shellfish
• Size Classes

Target Species Selection and Size Class Considerations

Creating a Target Species List

Ideally, all fish and shellfish species consumed from a given waterbody by the local population should be monitored. However, not all programs have the resources to sample all routinely consumed fish and shellfish. If your jurisdiction is only able to collect a few species, select the most frequently consumed species. For fresh waters, consider selecting at least two fish species (including one bottom feeder) as primary target species and one mollusk if appropriate for the waterbody. For marine/estuarine waters, consider selecting at least two fish species (including one bottom feeder and one pelagic species), one mollusk, and one crustacean as appropriate for local conditions. Alternate target species should be identified and included in the sampling only if a primary species is not caught.

You can use the EPA target species list and supplement it with or substitute other more appropriate species for your sampling location. Local fisheries biologists, with knowledge of site-specific fisheries and human consumption patterns, should be consulted when selecting target species for use in fish contaminant monitoring programs within their jurisdiction.

EPA Target Species List - Fish

Download as an Excel file:  EPA Target Species List – Fish (xlsx) (42.72 KB)

The U.S. Environmental Protection Agency developed the target fish species list to provide guidance to fish monitoring programs on species commonly consumed by the general population. The EPA selected these species as a representative list using state, territory, and Tribal input on currently monitored fish species. This is a thorough, but not an all-inclusive list of target species. The program manager and field sampling staff should identify primary and alternate target species. The target species list should be based on the selection considerations:

1. Commonly caught and consumed locally; commercial, recreational, or subsistence value
2. Abundant, easy to capture, and large enough to provide adequate tissue samples for chemical analyses Sample Type Fish and Sample Type Shellfish
3. Potential to bioaccumulate contaminants if present
4. Easy to identify taxonomically
5. Wide geographic distribution

These considerations provide a reliable comparison of sampling information and the magnitude and geographic extent of contamination can be assessed. Then it is possible to cost-effectively compare contaminant concentrations in waterbodies and prioritize sites where tissue contaminant levels are a risk to human health.

Fish species with these following characteristics are generally not acceptable target species:

1. Not consumed by humans, including forage species that are small in size
2. Threatened and endangered species – shouldn’t be fished or consumed by humans
3. Herbivorous fish – no commercial fisheries support their consumption, cannot be caught by hook and line since they eat algae
4. Limited geographic distributions

The following types of fish are not typically target species, but there are some examples on the EPA’s target species list. The study objectives should be considered before accepting or rejecting these fish; however, these fish could still be representative of potential health risks to fishers or consumers who harvest them.

1. Migratory Fish Species
2. Stocked Fish Species
3. Invasive Species

EPA Target Species List - Shellfish

Download as an Excel file:  EPA Target Species List – Shellfish (xlsx) (17 KB)

The target shellfish species list contains species that have commercial, recreation and subsistence value in coastal areas of the U.S. They also have the potential to bioaccumulate contaminants and are monitored for pathogens and HAB biotoxins as required by the National Shellfish Sanitation Program.

Bivalve mollusks (e.g., oysters, mussels, scallops, and clams) are filter feeders that accumulate contaminants directly from the water column or via ingestion of contaminants adsorbed to phytoplankton, detritus, and sediment particles. Bivalves bioaccumulate heavy metals (Cunningham, 1979) and polycyclic aromatic hydrocarbons (PAHs) and other organic compounds (Phillips, 1980; NOAA, 1987) and, because they are sessile, they may reflect local contaminant concentrations more accurately than more mobile crustacean or finfish species.

Three bivalve species—the blue mussel (Mytilus edulis), the California mussel (Mytilus californianus), and the American oyster (Crassostrea virginica)—are recommended as target species as they are known to bioaccumulate a variety of environmental contaminants (Phillips, 1988). The wide distribution of these three species makes them useful for comparison within a state or between states sharing coastal waters. Because these three species meet all of the selection criteria, they are recommended as target species for use in geographic areas in which they occur.

In addition, several species of edible clams were added to the various estuarine/marine target species lists based on recommendations received from specific state and regional fisheries experts.

Crustaceans are also recommended as target species in states, territories or tribes where they are commonly consumed for estuarine/marine sampling sites. Many crustaceans are bottom-dwelling and bottom-feeding predator and/or scavenger species that are good indicators of contaminants that may be biomagnified through several trophic levels of the food web.

Size Classes

The age of a fish or shellfish correlates with its size. Size is determined by measuring the length of fish and most shellfish or the width for crabs. Some contaminants bioaccumulate in tissue and therefore, the older and larger the organism, the higher the contaminant concentration and potential harm to consumers.

To determine an accurate and not overly conservative fish or shellfish consumption advisory, it is recommended that two or three size classes of legally harvestable size should be included in the data collection. The size class parameters (length categories) are dependent upon the size range of target species caught in the field. A sample of 10 individuals is generally sufficient to determine whether a relationship between sizes and contaminant concentration exists. A regression analysis can then be used to set a size threshold, that relates to a contaminant concentration, for an advisory.

With size class data, there may be a restriction on larger (more contaminated) organisms and no restriction on smaller organisms (less contaminated) of the same species. Advisory programs can tailor an advisory to protect human health and still allow use of the fishery resource.

The relationship between increasing size and contaminant tissue concentration observed for some freshwater finfish species may be much less evident in estuarine and marine fish species. Some estuarine and marine species migrate as they mature and this may change their contaminant exposure. Larger fish may not necessarily have a significantly greater level of contamination and thus, class size distinctions may not be necessary for a fishing advisory.