By Terry Knight
Last week the Department of Fish and Game (DFG) did their annual fish electro-shocking at Clear Lake.
The DFG calls it “electrofishing.” A number of lakeside residents came out on their docks to observe the procedure but most didn”t really understand the purpose of the event.
Electrofishing is a tool biologists use to check on the state of a fishery. The reason being that it”s an easy way to obtain large numbers of fish without harming them.
It can be used as a backpack shocker or mounted on a boat. At Clear Lake the DFG normally uses three specially equipped boats.
The boats have generators to produce the needed electricity and a large livewell to hold the fish.
The way it works is that the boat is equipped with a set of large metal electrodes that are mounted on long arms in the front of the boat and suspended into the water.
The electrodes are insulated from the boat and are called anodes.
A electrical current is generated through the anodes into the water which sets up an electric field between the anodes and the boat. The boat acts as a cathode. The electrical field causes galvanotaxis in the fish.
It is an uncontrolled muscular convulsion, which makes the fish swim toward the anode.
The fish will normally swim in circles and then float to the surface where it is netted by an individual standing on a platform at the front of the boat.
The fish is then placed in the livewell where it recovers in a matter of minutes.
At Clear Lake the DFG has been electrofishing for more than 20 years. They do it at least once per year and many times twice a year and it”s always done at night because bass and other game fish tend move into the shallow water to feed after dark.
The electric field can only penetrate to a depth of about seven feet. The DFG has established designated areas where they electrofish.
These areas are situated around the lake and have been used for the entire time the DFG has been taking fish samples. At the end of each stretch of shoreline where they have been shocked, a distance of about 200 yards, the fish are weighed, measured and checked for sores and other conditions.
The data is logged in and the fish are released. Using this information and comparing it with previous years, the biologists can check on population trends, sizes and physical conditions of the fish. At Clear Lake it”s not only the bass that are sampled but all species of fish except carp. Even the tiny silverside minnows are measured and weighed.
On Tuesday evening I had the opportunity to accompany one of the electrofishing boats. We started at the Skylark Shores Motel in Lakeport and ran as far as Land”s End.
The area was divided into four zones and we shocked more than 200 bass plus a large number of bluegill, a few catfish and some sculpin.
In one area near the Lakeport Lagoons we shocked more than 70 bass in a stretch that covered approximately 10 docks.
Our largest bass for the evening weighed a little more than 4 pounds. We didn”t get a single crappie, no threadfin shad and no silversides. We did shock a few catfish and black fish. Of the three DFG electrofishing boats one went to Rodman Slough and the other worked the Nice-Lucerne area. On Wednesday night the boats covered the south end of the lake.
Whereas the results of the two-day electrofishing experiment haven”t yet been completed, the preliminary results show the overall bass population to be healthy although there was lack of juvenile fish in the 3-5 inch class.
What was surprising was the complete lack of silverside minnows. The same applied to crappie. Although one biologist said they could have been out in the deeper water where there is more plankton.
The south end of the lake did produce a good number of juvenile crappie. Biological data can help the DFG to set limits and judge the overall effects of pollution and fishing pressure on the fish population.
It is just part of a wide range of tools and other information that the DFG uses in managing the state”s fisheries.
