In last month’s column, I shared what biologists know about largemouth bass spawning, emphasizing those aspects that may help anglers intercept spawning bass and habitat conditions that are needed for successful spawning. Largemouth bass are, compared to other fishes, pretty flexible in their spawning requirements.
Although sedimentation from erosion and incompletely decomposed aquatic plants cause problems, sufficient areas of spawning habitat allow bass to spawn successfully in all of Mississippi’s public reservoirs and most lakes.
It’s what happens to the young bass after the spawn that determines the abundance of bass that recruit to the catchable population — those fish that you and I are looking for.
Given a good spawn, good recruitment depends on high survival and fast growth of the young bass. The small bass are prey for a myriad of predators in their aquatic world, and often the major predator is other bass. Suitable cover to provide refuge from predation is important to high survival.
Growth rate also affects survival — the faster the young bass grow, the fewer are the predators that can consume them. The small bass initially feed on aquatic invertebrates, and then transition to fish. The sooner they can start feeding on fish, the faster the young bass will grow.
Shad are an important food for young bass in most Mississippi waters. But the young shad grow quickly, and soon are too large for the bass. Fast growth of the young bass requires ample supply of other, slower-growing forage fish, such as sunfish and minnows.
Fast growth, in addition to helping the young bass survive the net of predators, provides important energy reserves to help bass survive their first winter. Food is scarce, and the young bass must live off their own energy reserves. Larger bass have greater energy reserves and fewer predators.
Cover in the form of rooted aquatic plants (macrophytes) or inundated terrestrial vegetation provides refuge from predation and positively affects the survival of young bass. Aquatic macrophytes provide abundant invertebrates like insect larvae that attract sunfish and other small fish that are important food for young bass.
It stands to reason that habitats with macrophytes, by providing both cover and abundant food, would benefit the growth and survival of young largemouth bass. Research by Dr. Steve Miranda at the U.S. Geological Survey Mississippi Cooperative Fish and Wildlife Research Unit and graduate student Larry Pugh, who is now assistant fisheries director for MDWFP, supports this notion, but also indicates that there can be too much of a good thing.
Miranda and Pugh estimated macrophyte coverage and abundance of young-of-the-year largemouth bass in 13 coves in Aliceville Lake. The abundance of age-0 bass was little affected by macrophyte coverage in October, but abundance peaked at around 20 percent area coverage of plants in March. The overwinter survival of young bass was greatest at about 15-20 percent macrophyte coverage.
Total length of the young bass was greatest in coves lacking vegetation and decreased with increasing macrophyte coverage in both October and March. Overwinter fish-length increases were greatest in coves with about 20 percent macrophyte coverage.
Putting these results together, coves lacking macrophytes produced the largest age-0 bass, but coves with about 20-percent macrophyte coverage produced the most bass. As the size of the young bass differed little between no macrophytes and 20-percent macrophyte coverage (average total length in March was 6.0 inches at 0-percent coverage and 5.8 inches at 20-percent coverage), 20-percent macrophyte coverage, or at least some intermediate macrophyte coverage, would be a good management target for producing strong year-classes of largemouth bass.
The results of the Miranda and Pugh study indicate that providing an intermediate level of macrophytes may be good medicine for a bass population where recruitment is ailing. But the results of this study, when coupled with information from other investigations of largemouth recruitment, provide some interesting insights into largemouth bass recruitment.
The fewest but largest and fastest-growing bass occurred in the absence of macrophyte coverage. Lacking cover, predation probably reduced the abundance of smaller age-0 bass. These open-water bass also ate the most fish because the prey fish were vulnerable to the small bass. Just as the macrophytes provide cover for the young bass, the plants also provide cover for the prey of the young bass and reduce the foraging efficiency of the young bass.
In other words, dense vegetation may hold a lot of forage for the young bass, but if they can’t catch it and eat it, they don’t grow much.
The greater overwinter survival and increase in length at 20 to 30-percent macrophyte coverage may be the consequence of the availability of invertebrate forage that provided energy for survival and growth while at the same time providing refuge from predation. The invertebrates may not be the preferred forage, but they do provide energy during times of scarcity of fish.
Aquatic vegetation benefits bass recruitment, but the amount of vegetation can be critical to achieving that benefit.
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