Tidal Fish -
Index of Biotic Integrity (IBI)

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A striped bass captured on the South River, Anne Arundel County.  This fish represents one of the carnivorous species that are frequently captured.

An Index of Biotic Integrity (IBI) is a tool (index) which we use to determine the health (integrity) of the fish community (biotic) in a given river.  Webster's defines an index as "a ratio or other number derived from a series of observations and used as an indicator or measure".  Biotic is defined as "of or relating to life".  And integrity is defined as "the quality or state of completeness".  Thus, we can say that an IBI is a numerical measure of the biological completeness of a system. 

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An IBI allows us to easily compare communities among river systems because it is a numerical measure.  Once the health of the biological system is known, inferences about habitat quality can be made, and where problems exist, they can be corrected.

Fish captured in a seine conducted on Mattawoman Creek, Charles County, Maryland
Fish captured in a seine conducted on Mattawoman Creek, Charles County, Maryland

IBI has several characteristics which make it a desirable tool.  It is a comprehensive, rapid bioassessment technique which can be applied on a relatively large scale.

Comprehensive means that when we apply IBI, we are looking at the fish community as a whole.  The IBI examines three components of the fish community to determine its health.  By knowing the abundance (total number of fish), the diversity (number of different species), and trophic (food chain) interactions, we get an idea of how healthy the fish community is in a given area.

Rapid bioassessment technique refers to the fact the IBI is a relatively quick and easy technique.  The monitoring is done, and the data recorded on site.  The data are input into the data system, and analyzed.  There is no post processing or long laboratory testing.  Data are collected and used.

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Striped and bay anchovies are small fish that feed on microscopic plants and animals.  They are a forage species for larger carnivorous fish, like the striped bass pictured above

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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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