A Comparison of Four Eastern Smallmouth Bass Streams

Four smallmouth bass streams in the Potomac River watershed are compared. In the largest stream, the Shenandoah River near Berryville, Virginia, the fingerling bass (Micropterus dolomieu) grew to an average length of 4.25 inches during 1936, whereas in the South Branch of the Potomac near Romney, West Virginia, fingerlings attained a length of 2.75 inches by the end of the summer. In the Shenandoah River and probably also in its North Fork, bass grow rapidly and attain the legal size of 10 inches in three years, but in the South Branch of the Potomac and in the Cacapon River from four to six years or more are required for the fish to grow to legal size. The muddy condition of the Shenandoah and North Fork for long periods during the summer affects the success of natural propagation. These streams also have extensive riffle areas over limestone ledges where bass find shelter while feeding. In the South Branch of the Potomac and in the Cacapon River the riffles are short and little shelter is available. Bottom samples collected in riffles of the four streams failed to show any marked difference in the abundance of organisms. Samples from pools of the South Branch, however, contained approximately twice as much potential bass food as pools of the Shenandoah River. A number of faunal differences in these streams are pointed out. In the clear streams such insect larvae as Eriocera, Atherix, and Chauliodes and the mayfiy nymphs of Isonychia and Iron are more abundant than in the muddy streams where Sphaeriidae, Oligochaeta, larvae of Elophila and parnid beetles, and nymphs of Potamanthus are more abundant. The extent of natural propagation in the four rivers was studied quantitatively. The smaller, clearer streams have the most extensive natural propagation. In the small, clear streams, there are many bass but their slow growth indicates serious food competition. In the South Branch of the Potomac the extent of natural propagation is probably about five times greater per mile length of stream than in the Shenandoah River which produces the fastest growing fish of any of the four streams studied. A seasonal study of the food of fry and fingerling smallmouth bass was made from monthly collections during 1936 in the Shenandoah River and South Branch of the Potomac. The chief items of food were mayfiy nymphs of the genus Baetis and chironomid larvae. Entomostraca (chiefly Cyclops) played a minor role in the food of bass in both streams. In the Shenandoah River, 9.9 per cent of the fry which averaged 10.0 millimeters in length on May 13, 1936, had consumed fish. The livers of the South Branch fingerling bass contained large numbers of trematode cysts but relatively few were found in the livers of the Shenandoah River bass. There was no evidence that the presence of trematode cysts affected the growth rate, since infested and uninfested fish were very nearly the same size. Minnow censuses were made on the four rivers. The data given in part, although to a certain extent inaccurate, at least afford some idea of the relative abundance of the more important forage fishes. These studies indicate that much information of very practical value can be gained by actual field studies of bass streams. In some of these streams it is evident that the stocking of bass is a mistake.