One of the many things that make a stream, a great stream for fish, is the presence of fish food.

Some of that food, researchers have recently found, are insects from land and the air. However, any fly fisherman will tell you the most important fish food are aquatic insects. They are what ecologists call “benthic invertebrates.” The word “benthic” refers to the creek bottom or on rocks and debris in a stream or a lake. Invertebrates are animals with no back bone or bony skeleton.

Aquatic invertebrates in our freshwater streams experience changing water depths and temperature during the year. Some have relatively long life cycles (taking one whole year to mature and reproduce); others have very short lives (just a few days). Others go through many life stages before becoming that little flying creature that a fish or a frog will snap up quickly.

Some are called “clingers,” since they have adapted physical features to grip onto the sides of rocks while water flows by. Some are very sensitive to pollution and others are very tolerant to the oil, sediment and the other kinds of chemicals that might be washed into the stream from stormwater. Some even have life stages where they are the predator, eating other bugs in the waterway.

While Stillwaters does water flow and chemical monitoring to assess the health and quality of the riparian environment in Carpenter Creek, another way to monitor its health is with biological monitoring. While water management focuses on water quality, human activity near streams can also alter the habitat structure and the flow regime, and in turn affect the trophic base and biotic interactions (who’s eating who) in the stream. Each one of those aspects of stream dynamics, added together, describes the biological integrity of the stream.

To try to assess a stream’s health, scientists developed a method of sampling the stream for benthic critters to allow them to calculate called the Benthic Index of Biological Integrity, or BIBI. The BIBI number is called an “index,” because it is a combination of measurements of each of the aspects of the physical, chemical and biological structure of the stream. In that way, it takes diverse information about the types of bugs found, what kind of creatures they are, and how they live, and add them all up to get a score.

For example, are they clingers, house builders (like stone flies) or worms; are they tolerant of pollutants or not; are they mayflies, caddisflies or stoneflies — especially important insect groups.

This work has been going on throughout the Puget Lowland Streams for many years.  Kitsap County has undertaken BIBI since 1998. Twenty five locations have been samples within 20 Kitsap creeks. Some locations have been sampled yearly from 1998-2006, and again in 2010 and 2012. Others have been sampled less frequently. It is sometimes difficult to make the case to cash-strapped government agencies that funding these efforts is important. Therefore cuts in this and other types of ecological sampling are frequent and diminishes the validity of the data when the sampling cannot be repeated enough times to reveal reliable characterization or trend information.

Carpenter Creek’s BIBI index has been evaluated for site 1 – a stream segment just above the salt marsh in a wooded area on the Stillwaters campus. Its Index has been in the Low category but appears to be improving. This may be due to many influences such as stormwater pollution, proximity to salt water, variable flows. Carpenter creek’s site 3 – a segment just north (above) State Route 104, over the 7 years of sampling undertaken so far, appears to exhibit a moderate to good index. Next month more about the components of the index and what could be expected to be found in low, moderate and high biotic integrity.

— Betsy Cooper is a board member and stream monitor at Stillwaters Environmental Education Center.