Overview
The purpose of testing is to determine the optimum spacing between monitors to effectively detect tagged fish as they pass through the system.
Four factors affect the ability of monitors to detect a tagged fish:
- Number of tagged fish simultaneously present
- Tag delay – how frequently the tags transmit their code scheme
- Fish swimming speed
- Minimum receiver detection range
Of the four factors we can really only control two, the tag delay and the minimum receiver detection range. For 2007 we have chosen a random tag delay between 30-90 seconds. This was based on a compromise between long battery life and ability to detect a fish that may be moving with very fast currents (5knts). The minimum receiver detection range can only be determined by testing in the location of interest and over a wide range of weather and sea conditions. Because VR2 are affected by broadband noise, many noise sources can negatively impact a VR2 ability to detect a tagged fish. These include, wind waves, rain, tidal rips, passing motor boats, currents, water column stratification, and water turbidity. Therefore, we are conducting range testing under varied weather and water conditions.
The test array was designed to identify the distance between a transmitter and VR2 where the percentage of total tag transmissions detected falls below a certain threshold, or the minimum receiver detection range.
In the top photograph are tags ready to be used for range testing. The bottom photographs are of range tests in the San Francisco Bay (left) and in the Sacramento River (right).