Tidal Fish Community Indicators

a photo of fish caught in a seine
A typical beach seine haul.

Tidal fish community data are collected in tributaries throughout the Chesapeake Bay. These data are evaluated to assess the condition of the resident fish community at each of the sampling sites. Data are applied to a numeric index that accounts for the number of different types of fish, the total number of fish, and other important community measures. This Index is referred to as the Index of Biotic Integrity (IBI).

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a photo of DNR biologists pulling a beach seine




DNR Biologists pull a beach seine.

Fish are sampled monthly from July through September. Two beach seines and one bottom trawl are pulled at each site. The fish captured (above) are generally small including the typical bay forage species and juvenile game fish. Water Quality information is measured to assess fish habitat conditions.


The Index of Biotic Integrity helps identify where fish communities may be suffering from habitat impacts, such as low dissolved oxygen, so that appropriate management action can be taken. For example, data have shown that areas with persistent low dissolved oxygen concentrations in the bottom waters show reduced species diversity in this habitat. A graph showing lowered species diversity with increasing amounts of habitat where bottom dissolved oxygen concentrrations are less than 3 mg/L.






The average number of species decreases as the number of low oxygen events increases.

Dissolved oxygen concentrations below 3.0 mg/l can be lethal to some fish species and therefore fish tend to avoid areas with inadequate dissolved oxygen. New monitoring technologies are now allowing us to assess habitat on a more spatially and temporally extensive scale. This information is being incorporated into our fish assessments to better understand the relationship between habitat suitability and fish presence in a river, so that fisheries managers can incorporate habitat effects into management decisions.

a photo of DNR biologists sorting fish and recording data
Biologists sort fish and record data.

Biologist Calvin Jordan takes water quality measurements.
Biologist, Calvin Jordan takes water quality measurements.


If you would like to learn more about fish, please visit the Chesapeake and Coastal Bay Life Guide.

photo of a biologist deploying a trawl
Deploying a trawl.

Learn more about:

For more information, please contact Margaret McGinty (mmcginty@dnr.state.md.us) of the Maryland Department of Natural Resources at (410)260-8630.

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