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Index of Biotic Integrity

Historically, the health of aquatic systems was monitored primarily through chemical means. However, chemical monitoring provides only a "snapshot" of conditions at the time of sampling and may fail to detect acute pollution events (e.g. runoff from heavy rain, spills), non-chemical pollution (e.g. habitat alteration) and non-point source pollution.

In order to address the shortcomings of chemical monitoring, the New Jersey Department of Environmental Protection supplements chemical monitoring with biological monitoring. Biological monitoring is based on the premise that biological communities are shaped by the long-term conditions of their environment and more accurately reflect the health of an ecosystem. Currently, the Bureau of Freshwater and Biological Monitoring (BFBM) monitors benthic macroinvertebrate assemblages (insects, worms, clams etc.) at over 760 non-tidal stream stations throughout New Jersey.

Benthic macroinvertebrate assemblages are generally reflective of short-term and local impairment. In order to assess environmental conditions on a larger spatial and temporal scale, the BFBM began to supplement benthic macroinvertebrate monitoring with an index of biotic integrity (IBI) during the summer of 2000. An IBI is an index that measures the health of a stream based on multiple attributes of the resident fish assemblage. Each site sampled is scored based on its deviation from reference conditions (i.e. what would be found in an unimpacted stream) and classified as poor, fair, good or excellent.

Data provided by the IBI has become another component of the DEP's suite of environmental indicators. The data helps to measure water quality use attainment and the Department's success in attaining the Clean Water Act goal of "fishable" waters as elaborated in the Department's Integrated Water Quality Monitoring & Assessment Report. IBI data will also be used to develop biological criteria, prioritize sites for further studies, provide biological impact assessments, and assess status and trends of the state's freshwater fish assemblages.

In an effort to ensure sensitivity to anthropogenic stressors, the Northern Fish IBI was re-evaluated by the BFBM staff in 2005 using Round 1 data (2000-2004).  This recalibration resulted in modifications in scoring criteria and species lists for several metrics. The current IBI measures the following metrics:

    Species Richness & Composition
    1. Number of Species
    2. Number of Benthic Insectivorous Species (excluding white suckers & bullheads)
    3. Number of Trout and/or Sunfish Species (excluding green sunfish and bluegill)
    4. Number of Intolerant Species
    5. Proportion of Tolerant Individuals
    Trophic Composition
    6. Proportion of Generalists
    7. Proportion of Insectivorous Cyprinids
    8. Proportion of Trout OR Proportion of Piscivores (top carnivores - excluding american eel)
    Fish Abundance & Condition
    9. Number of Fish (excluding tolerant species)
    10. Proportion of Fish with DELT Anomalies (excluding blackspot disease)


The final FIBI network will have 100 established sampling stations in northern New Jersey. Thereafter stations will be visited once every five years as part of the BFBM’s ambient monitoring efforts. Fish IBI reports of results are published by the bureau annually; copies are available from this web site. A summary of the biological and habitat ratings are also available from this web site for Round 1 and Round 2 data. Data are currently being collected for the planned expansion of the network to include both portions of southern New Jersey and the state’s headwater streams with the goal of having a statewide 200 station network. If you are interested in more information about the IBI, please contact John Vile at 609-292-0427.


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Department of Environmental Protection
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Trenton, NJ 08625-0402

Last Updated: September 10, 2012

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