In addition to the millions of crappie, bass and other gamefish found in Clear Lake, one of this year’s most numerous species is the threadfin shad. Fishermen report seeing huge schools of shad, some stretching more than a mile. The shad also can be seen schooling around the docks. They are an important food source for the bass, crappie and other gamefish.
Threadfin shad get their name from the long, threadlike final ray of the dorsal fin. They also can be distinguished by the black spot on their side just behind the gills. They are a member of herring family.
Threadfins are not native to California. The Department of Fish and Wildlife (DFW) first introduced the shad into San Vincente Reservoir in San Diego County in 1953. The purpose of the stocking was to provide an open water forage fish for bass and trout. Since then the shad have spread across the state and now just about every low level lake has threadfin shad. It is thought that the threadfin shad found in Clear Lake were transplanted here by fishermen from Lake Mendocino. The DFW originally stocked the shad in Lake Mendocino as food for the striped bass.
They first appeared at Clear Lake in 1986 and within two years the shad had multiplied by the millions. They are a fast-growing but short-lived fish, rarely living long than three years. A threadfin can grow as much as an inch per month and can reach lengths of six inches. Some of the shad found in the lake have been five inches or longer.
Shad feed on plankton, which puts them in direct competition with other fish in Clear Lake such as the silverside minnows, blackfish and hitch. They also compete with bass and crappie fingerlings. In fact, threadfin shad were blamed for the demise of the bass fishery in Clear Lake during the period of 1989-91.
Shad spawn when the water temperature reaches 65 degrees. They have an unusual method of spawning, which most often occurs at dawn and centers around floating or partially submerged objects such as logs, brush, aquatic plants and docks. Small compact groups of shad swimming near the surface will approach an object at a fast speed and at the last moment will veer away, spewing their eggs and sperm onto the object. The eggs contain an adhesive which allows them to stick to logs and other debris. The eggs hatch in three to six days. Each female shad produces 900-21,000 eggs. In 1989 when the shad were at their peak in Clear Lake, outboard motors that were left in the water would have huge globs of the jelly-like eggs stuck to the lower units.
Threadfin shad are a delicate fish. They have a low tolerance for cold water and when the surface temperature drops to 45-48 degrees, most will die. They also can’t tolerate sudden changes in water temperature.
It was thought that the cold winter of 1991 killed off all the shad in Clear Lake, but in 1997 they reappeared and DFG biologists feel they were either restocked in the lake by fishermen or there was a small population that survived from 1991. Why the shad have appeared in such great numbers this year in Clear Lake is unknown. Biologists say one possibility is that since the silverside minnow population is down and since both species compete for the same type plankton, the availability of food has caused the shad explosion.
Threadfin shad are an excellent forage fish for adult bass and catfish. However, most biologists feel it was a mistake to introduce them into California because they compete with other game and native fish for food.
The shad can be used as bait for catfish but there are certain rules that a fisherman has to follow to obtain them. They cannot be snagged. Throw nets are also not allowed to obtain the shad. What can be used is a dip net and several of the local tackle shops stock a special dip net that is made solely for obtaining shad. When placed in a boat’s livewell or in an ice chest they will only live a short time. Threadfin shad can be seen schooling around the docks at Library Park in Lakeport, Lakeside County Park, the docks at Redbud Park in Clearlake and anywhere along the Nice-Lucerne shoreline. They are an important food source for the birds living at the lake. Western grebes feed heavily on the shad as do osprey, cormorants, herons, pelicans and even bald eagles.
The explosion of the threadfin shad population in Clear Lake is just another mystery revolving around the oldest lake in North America.
