Sampling Sites
Sampling sites are the locations where fish and shellfish are collected. Ideally, a fish or shellfish contaminant monitoring program should include all water bodies where commercial, recreational or subsistence fishing or shellfish harvesting occur. However, when resources are limited, target the sites suspected of having the highest levels of contamination and of posing the greatest potential health risk to local fish and shellfish consumers.
Selection of Sampling Sites
Sampling site selection is detailed for the two sampling approaches strategies:
Sampling Site Selection Considerations
Information about the presence of contamination or potential pollutant sources
Contamination in waterbodies may be due to direct discharges, runoff, precipitation, atmospheric deposition, or seepage from septic systems. Discharges of chemicals, pathogens, nutrients, and other contaminants to waterbodies may be from industry, combined sewer overflows or municipal storm sewer systems. Runoff from rainfall or snowmelt can pick up natural and human-made pollutants depositing them into lakes, rivers, wetlands, coastal waters and groundwaters. These pollutants can include fertilizers, herbicides, insecticides, oil, grease, toxic chemicals, salt, and pathogens. Different types of land use (developed lands, agriculture, forestry, marinas, roads, urban areas, and wetlands) will determine what pollutants could potentially impact a given waterbody.
Historical and Observational Information from Frequently Fished Sites
Fish and shellfish contaminant monitoring programs should be conducted in waterbodies commonly used by recreational or subsistence fishers since this is where consumed fish are harvested. Specific sampling sites should include areas where various types of fishing are conducted routinely (e.g., from a pier, from shore, or from locations frequented by private and commercial boats).
Range of Prevalent Species of Fish and Shellfish
Biological Community Information
Availability of data on the fish and shellfish community structure should be considered in site selection. Information on preferred feeding areas and migration patterns is valuable in locating populations of the target species and conserves resources. Knowledge of habitat preference provided by fisheries biologists or commercial fishers may significantly reduce the time required to locate a suitable population of the target species at a given site.
Bottom Condition/Habitat Information
Bottom condition is a site-specific factor closely related to the ecology of a target fish or shellfish population. For example, if only soft-bottom areas are available at an estuarine site, neither oysters (Crassostrea virginica) nor mussels (Mytilus edulis and M. californianus) would likely be present since these species need hard substrates. However, an aquaculture operation could use off-bottom floating cages and suspended lines to mitigate bottom condition (lack of substrate, low DO).
Migratory Species
Many Great Lakes fish species, as well as riverine, estuarine, and marine species, migrate considerable distances during spawning periods. For many marine species, such as Atlantic Salmon, estuaries are the spawning areas for the adults and nursery areas for the developing juveniles, which eventually travel offshore as adults and return to the estuaries to spawn. For these species, migratory or seasonal movements both from inshore to offshore areas and north and south migrations along the coasts can take place. These migrations should be considered when selecting sites.
Immobile Species
Bivalve mollusks, such as oysters or mussels, cement themselves to hard substrate as young spat and are unable to move away from pollution effects after they have settled out of the water column. Although clams and scallops are slightly more mobile, they also typically stay in the general area in which they first settled out of the water column. For crustaceans like the blue crab and lobster, however, movements both into and out of estuaries as well as into deeper water offshore are species- and locality-specific.
As the complexity of an ecosystem increases and the mobility of the target species likely increases, so too do the number of samples and the number of sampling stations required to delineate the area where contaminated fish may be present.
Threatened or Endangered Species
While harvesting threatened or endangered species for consumption is illegal, agencies may need to sample fish from waters also inhabited by threatened or endangered species. In some of these waterbodies under study, threatened or endangered species may be collected incidental to the primary sampling objective. For incidental take permits, authorizations, and other related information contact your nearest USFWS Ecological Services Office or visit these webpages.
- U.S. Fish and Wildlife Service:
- National Marine Fisheries Service:
It is also necessary to obtain fish sample collection permits from the appropriate Tribal or state permitting authority or wildlife agency. These permits may impose additional restrictions. Coordination is necessary among local partners, among fish and game departments, environmental and/or water quality agencies, and power authorities or owners of impoundments. The permitting process may take months; start early.
Site Accessibility and Equipment Requirements
Site accessibility should be considered because it affects equipment selection, sampling time, and other cost-related factors. Remote or otherwise less accessible locations are more costly to assess, both initially and for follow-up monitoring over time. These characteristics should be considered:
- Type of vegetation and local topography that could make transport of collection equipment difficult
- Location of boat ramps and marinas
- Depth of water and bottom condition required to deploy the selected sampling gear efficiently and to operate the boat safely
- Locations of underwater obstacles in coastal areas and larger navigable rivers, mapped in navigation charts
- Information from commercial fishers familiar with the candidate site to identify areas where the target species congregate and the appropriate sampling equipment to use
- Federal, Tribal, or state permit restrictions on sampling locations and equipment
Site Size and Corresponding Sample Collection Size
The larger the waterbody, the more samples are needed to determine whether the contaminant concentration in fish at a particular site is likely to exceed the human health screening level. Typically, the contaminant concentration among fish from a larger or more complex water body is likely be more variable and will require a greater sampling effort and cost. As the size of a waterbody increases (from small lakes to larger lakes to the Great Lakes, or from streams to rivers to estuaries to coastal marine waters), the number of samples that need to be collected to maintain a selected statistical power and the number of sampling stations needed to define the area that should be under advisory both increase. Small lakes are likely to be exposed to a relatively homogeneous aquatic environment of contaminant concentrations. Large waterbodies may have more complex hydrodynamics which can greatly affect both the magnitude and nature of contamination in fish populations as well as the location of the fish. Streams may have pools and sizeable still waters as well as rapids and shallows, depending on the geology that the stream traverses.
Proximity to Sites with Environmental Data
The most important benefit of locating fish or shellfish sampling sites near sites otherwise selected for water, sediment, and other related studies is the possibility of correlating contaminant concentrations in different environmental media (e.g., water, sediment, and fish). Selecting sampling sites near another sampling location is also more cost-effective because it provides opportunities to combine sampling trips for different media and to compare data over time.
Least disturbed areas that could be reference sites for unrestricted consumption
Due to atmospheric deposition of certain contaminants (most predominantly mercury), it is usually not possible to find pristine sites. It is, however, important for program managers to identify and document a few “least disturbed” sites. This will vary according to the specific contaminant. For instance, PCBs are likely to be associated with former industrial sites, and agricultural pesticide residues are likely to be associated with agricultural land use and certain crops.
Least disturbed sites may be needed for use as reference sites in subsequent monitoring studies. the site-selection methodology and the assumptions about primary sources of pollution.
After Sampling Site Selection
Coordinate the selection of sampling sites with other agencies and programs when appropriate.
Once the sites have been selected:
- Geolocate the sites’ latitude and longitude (waypoints) using a portable global positioning system (GPS). A large-scale map should be available as a backup and annotated as the assessment progresses.
- Note the estimated travel time to the sampling site from an access point, as well as any relevant waterbody features, such as water depth or tidal cycle.
- Indicate the availability of landmarks for visual or range fixes, the biological trawl paths (or other sampling gear transects), and the navigational hazards for each site.
- Record sampling site locations accurately because fish and shellfish contaminant monitoring data may be stored in a public database like the Water Quality Portal. This information should be documented in the Project Work Plan as well as the Field Record Form for the field crew.