Ryan:

FYI a PB thread and excerpts from 2 studies (and there are more) on GSD.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=5;t=000214#000001


EXPERIMENTS WITH COMBINATIONS OF LARGEMOUTH

BLACK BASS, BLUEGILLS, AND MINNOWS IN PONDS

by H. S. Swingle

In this experiment , a pond was stocked with 1,000 bluegills and 48 shad per acrein October 1941, and 200 bass fry per acre were added the following May. The pond was drained in November 1943. In 1942 gizzard shad began to hatch in the middle of March and continued into July. The first bluegills hatched in early May and spawning occurred at intervals the rest of the season. No shad hatched in 1943 but bluegills spawned lightly from July until fall. Largemouth bass grew rapidly, reaching a size of 7 ounces by August 8, 1942. At that time the young gizzard shad were still small enough to be eaten by the bass. In 1943, the shad reached a size of 1.5 to 2 ounces by the middle of the summer, and when the pond was drained in November, there were 516 pounds of gizzard shad per acre, the smallest being too large for the largest bass to eat. This combination produced 101 pounds of largemouth bass, 173 pounds of bluegills, and 516 pounds of gizzard shad, or a total of 790 pounds of fish per acre. Of this total weight, 65.3 percent was shad, 12.7 percent bass, 13.5 percent adult bluegills and 8.5 percent young bluegills.

During the second year, gizzard shad reproduced only sparingly or not at all, apparently due to overcrowding by large shad, bluegills, or both.


Management of Forage Fishes in Impoundments of the

Southern United States

by RICHARD L. NOBLE

They frequently become overpopulated and affect other species. For example, Jenkins (1957a) com-
pared fish populations in two nearby lakes, one having 560 kg/hectare of gizzard shad, the oth-
er lacking this species; in the presence of gizzard shad, game fish had a lower standing crop,and centrarchids had slower growth, poorer condition, and smaller average size than where
gizzard shad were absent. Swingle (1950) found that when gizzard shad became overpopulated
at sizes larger than those readily vulnerable to predation, they reduced or prevented produc-
tion of forage-size bluegills and gizzard shad, thereby reducing growth and survival of young
largemouth bass. In spite of its major contribution to food of predators, the gizzard shad remains a problematic species due to its propensity to develop high biomass of large individuals with the potential to interfere with production of other species.