IB What?

The barge electrofishing unit is used for larger streams

What is an IBI? The ESD uses the Cold Water Index of Biotic Integrity (IBI) assessment method to calculate a water quality score for streams on the reservation. The basis of an IBI is to use either the fish community or the macroinvertebrate community to aid in determining the “health” of the stream. In our case, we are using the fish community for our assessments. So how is an IBI calculated? The process of calculating an IBI is fairly simple. A sample reach is established on each stream to be sampled. The stream reach is 35 times the mean stream width. A stream that averages 20 feet wide would have a 700 feet long sample reach. Two different electrofishing gear types are used to sample reservation streams. In larger streams a barge electrofishing unit is used and in smaller streams backpack units are used. During the sample collection an effort is made to capture all fish. All fish captured are identified to species and counted. Game fish (primarily trout) are also measured and weighed. The trout are marked with an upper caudal (tail) clip and released back into the sample reach. Five metrics are used to calculate the IBI for each stream. These are as follows:

1) number of intolerant species (intolerant species can only persist in waters of high quality, e.g. trout)

A brook trout is measured prior to weighing

2) percent of all individuals that are tolerant species (tolerant species can survive in a wide variety of conditions, e.g. minnow species)

3) percent of all individuals that are top carnivore species

4) percent of individuals that are native or exotic stenothermal coldwater or coolwater species (fish that require cold water)

5) percent of salmonid individuals that are brook trout Salvelinus fontinalis( a native species that requires clean cold water)

A score is then determined for each category using the table below.

Table for calculating the coldwater IBI

Metric	Criteria for assigning scores of:
	20 (good)	10 (fair)	0 (poor)
(1) Number of intolerant species	≥ 2	1	0
(2) Percent of all individuals that are tolerant species	0-5	6-22	23-100
(3) Percent of all individuals that are top carnivore species	46-100	15-45	0-14
(4) Percent of all individuals that are stenothermal coolwater and coldwater species (native and exotic)	86-100	43-85	0-42
(5) Percent of salmonid individuals that are brook trout	96-100	5-95	0-4

A score of 100 – 90 is considered excellent, 80 – 60 good, 50 – 30 fair, 20 – 10 poor, and 0 or no score very poor.

This brook trout has been fin clipped on the tail

The sample reach is also fished on a subsequent day to capture trout. Trout that were marked with a caudal fin clip can be identified. A population estimate for the sample reach can be derived based on the number of marked and unmarked fish that are captured during this second sampling event. The population estimate is then extrapolated out and reported as trout per mile. This has been a basic overview of the IBI process we are using as part of our assessments on the reservation streams. We will be giving more information on other parts of the overall fish community assessment in future posts.