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 Clallam Home Page
 Revised B-IBI Grading System

HOW AND WHY STREAMKEEPERS OF CLALLAM COUNTY REVISED THE GRADING SYSTEM FOR THE B-IBI FOR THE PUGET SOUND LOWLANDS

 

To provide a richer and more descriptive biological context for the various B-IBI grading levels, Streamkeepers has refined and revised the system of grades originally used by the University of Washington and SalmonWeb (see links elsewhere on this site).  These organizations used a report-card-style system of five grades which were intuitive and undefined:

ORIGINAL B-IBI GRADING SYSTEM

 

Score

Grade

50-46

Excellent

44-38

Good

36-28

Fair

26-18

Poor

16-10

Very Poor

 

 

 

 

 

Since that time, further research has indicated correlations between B-IBI scores and other signs of ecosystem health, to the point where more meaningful descriptions can be made of score-clusters.

REVISED B-IBI GRADING SYSTEM:

Score

Grade

Definition

50-46

Healthy

Ecologically intact, supporting the most sensitive lifeforms.

44-36

Compromised

Showing signs of ecological degradation. Impacts expected to one or more salmon life-stages.

34-28

Impaired

Healthy ecosystem functions demonstrably impaired. Cannot support self-sustaining salmon populations.

26-18

Highly impaired

Highly adverse to salmon and other lifeforms.

16-10

Critically impaired

Unable to support a large proportion of once-native lifeforms.

 

 

 

 

 

Dr. James Karr, professor of aquatic sciences at the University of Washington and the developer of the B-IBI grading system for the Puget Sound lowlands, has approved of this revision.  On 12/31/2003, he made the following comment about the revised grading system:  "I agree in all respects to your logic in the message and in the documents you sent.  Your points about the original 5 class system names are all correct and I like your solution as well."  On 6/24/04, he said, "I think they are excellent, even used them as an example of a recent advance in a talk I gave at EPA in Corvallis yesterday."

In the old system,  the levels were misleading because streams labeled "good" showed signs of degradation, streams labeled "fair" could not sustain viable salmon populations, and those labeled "poor" could be better differentiated by dividing them between the new grade levels of " highly impaired"  and "critically impaired."

Printed below are responses made on 8/20/2003 by Dr. Karr and Dr. Sarah Morley (NOAA Northwest Fisheries Science Center) to questions posed by Steve Butkus of the Washington State Department of Ecology concerning the use of B-IBI metrics to help make "impaired water body" [303(d)] determinations under the federal Clean Water Act:

Mr. Butkus asked the following question:

We need an established basis upon which to call a given result either "impaired," "unimpaired," or "of concern"; as far as the latter goes, Rob Plotnikoff [Dept. of Ecology Environmental Assessment Program] recommends that we call the Poors & Very Poors "impaired," the Excellents and Goods "unimpaired," and the Fairs "of concern."  That makes intuitive sense; would you agree?

Morley's response:  "I'd be inclined to include good in the ‘of concern'."

Karr's response:  "In my opinion we need to better connect the numeric score of an IBI to a specific context of biological condition.  I have suggested based on my experience in the region that a B-IBI of about 35 is necessary to support a self sustaining population of anadromous salmonids.  That is a soft conclusion however because of the general lack of knowledge of the condition of fish assemblages in PAC NW rivers."

Further support for Karr's suggestion that B-IBI scores below 35 represent biological impairment from a salmonid point-of-view is provided in the following references:

Karr, J.R.  2003.  Vignette 11.1.  Biological integrity and ecological health.  Pages 245-249 in M.C. Newman and M.A. Unger, Fundamentals of Ecotoxicology, Second Edition.  Lewis Publishers, Boca Raton, FL.

Karr, J.R., R.H. Horner, and C.R. Horner.  2003.  EPA's review of Washington's water quality criteria:  An evaluation of whether Washington's criteria proposal protects stream health and designated uses.  National Wildlife Federation, Seattle.  25 p.  Available here.