Silversides Family (ATHERINIDAE)
The inland silversides was introduced to some the Blue Lakes and Clear Lake, California in 1967 in an effort to control midge populations. It first appeared in Black Butte Reservoir in 1995, perhaps transported there in an angler's bait bucket. In Fall 95, we found only a few. By Spring 96, they were one of the more common fish captured by beach seining. In Fall, 1996, silversides were so abundant that each seine haul brought in thousands. While earlier data include all silversides captured in about two hours of beach seining, the 96 data represents a random subsample.
Silversides feed on zooplankton and some insects. Development of such a large population is certain to affect the food availability for other planktivores (including at least the fry stage of most fish in the lake.) Since silversides seldom exceed 100 mm in length, they will also provide an additional food source for adult predatory fish and piscivorous birds.
Bluegill Sunfish, Lepomis macrochirus
Sunfish & Black Bass Family (CENTRARCHIDAE)
The bluegill sunfish was native to the eastern US but has been introduced around the world as a pan fish While common in Black Butte, it is not abundant where we sample, probably due to lack of cover. Young-of-the-year bluegills school in open water, feeding on zooplankton, but larger ones work weed beds for invertebrates.
Sunfish & Black Bass Family (CENTRARCHIDAE)
The largemouth bass was introduced to California as a warm water game fish and has been widely distributed within the state. Largemouths are exclusively carnivorous, eating anything that will fit into their mouths as long as it tries to get away. Such planktivores as threadfin shad and inland silversides provide excellent food for bass from fingerlings to adults. However the bass fry totally depend upon zooplankton for food and presence of abundant planktivores may reduce their survival.
Sunfish & Black Bass Family (CENTRARCHIDAE)
White crappies have been the best known game fish in Black Butte Reservoir. Fall beach seining seldom yielded many crappie, probably because they stayed in deeper water than was being sampled. Spring seining produced many more, chiefly young -of-the-year. Crappies have long, fine gill rakers which enable them to filter out zooplankton as a major source of food, but larger ones also take small fish. As with the largemouth, adult crappies benefit from planktivorous bait fish, but the juveniles may come into severe competition. Black crappies, Pomoxus nigromaculatus, while less abundant than whites, are also common in Black Butte. They feed in much the same way as white crappies so would be affected by populations of planktivorous bait fish in the same manner.
Herring Family (CLUPEIDAE)
Prior to 1996, threadfin shad were by far the most abundant fish captured by beach seine in Black Butte and size distributions were based on subsamples of the hundreds collected in each seine haul. However, in Spring 1996, only a few were captured and in Fall, 1996, only five threadfins were captured in about two hours of beach seining. It seems likely that competition with the silversides has already depressed the threadfin population.