Pond Boss Forums INTRO Questions & Observations grass carp

Hi Shan – I wasn’t sure, but it seems that some of your last questions were directed to a couple of my original points. I’ll try to provide a little more input.

First, please realize that I would never say that submergent vegetation is necessary in southern pond management. I’ve never worked any place south of Kansas!! Also, Mike Maceina of Auburn University told me that grass carp removal of vegetation in Alabama and Florida essentially had no effect on largemouth bass recruitment. So, he certainly is supportive of what you have said.

So, let me try to answer your questions. First, I think that “literature” on the more northern waters is pretty clear. I’ll provide some information below. However, if you want copies of any of the papers, you’ll need to give me a mailing address. I found your web page, but it did not have a mailing address.

I suppose the “biggie” paper on this is Wiley et al. 1984 (North American Journal of Fisheries Management [NAJFM]), who worked on Illinois ponds. Maximum production (pounds of flesh “grown” by the population in one growing season) occurred at a submergent vegetation coverage of about 36%. Below that, largemouth bass recruitment was lower, and production declined. At 0% coverage, they found about half the largemouth bass production as they did at 36% coverage. Above 36%, there was too much cover for small sunfishes, largemouth bass could not keep them in check, and production also declined. Over the years, I have heard many discussions about the “magic” level of coverage. I chose 30% as a good, reasonable number that most Midwestern biologists would agree on. In fact, there was one study by the Central States Small Impoundment Work Group (never published) where coverage up to 50 or 60% was still OK. I was surprised by that, and still believe that much coverage is a problem. However, my point is to pass some of this information on to you.

In South Dakota, we looked at the influence of habitat on largemouth bass abundance in 20 ponds. The only two variables that influenced bass density were submerged vegetation coverage and water transparency. When vegetation coverage was down near 0%, we typically collected about 10 largemouth bass (8-in and longer) per hour of night electrofishing. When vegetation coverage was near 30%, we averaged just under 100/hr. These results were not especially surprising, and we only put them in a SD Academy of Science publication. Again, I’d be glad to send a copy if you want it.

Have you seen the NAJFM paper by Durocher et al. (1984)? In Texas reservoirs (80-36,000 ha), they found that largemouth bass abundance increased as submergent vegetation increased from 0 to 20%. While this is not the Midwest, Texas reservoirs probably have some of our same problems with wind, waves, water turbidity, fluctuating water levels, etc. Those are the big negatives for largemouth bass recruitment in the Midwest (the wind blows “once in a while” here). The vegetation probably provides a refuge and food supply for the young largemouth bass. In fact, the big Lake Conroe grass carp study was done in TX (Bettoli et al. 1993 in the NAJFM). The reservoir had about 40% vegetation coverage before grass carp were added, and largemouth bass biomass was 11-14 kilograms/hectare. After the vegetation was eliminated, the bass biomass averaged 2-6 kg/ha.

I guess those are my best citations for you. Please realize that I say all of this realizing that higher bass density is not always good if you are trying to manage for large bass. Too many small largemouth bass is a very common pond management occurrence up here. Reduction in recruitment can actually lead to increased sizes of bass in the pond.

Now, on to your ice cover question. You made a darn good point! Actually, in eastern SD, our winters are so long and the ice cover can get so thick that it takes a truly high quality pond, with lots of depth (= lots of water volume), to make the winter. The only ponds that I actively manage right around here in the east-central part of the state are either very deep (most are 25-30 ft) or are gravel pit lakes in which we have constant ground water movement throughout the winter. In the central and western part of the state, we have much more mild winters, and ponds that are shallower can make the winters. We still try to get at least 20 ft of water, because we can expect periodic droughts.

I really don’t know what to say about the vegetation causing winterkills. Obviously, it does, but we need the vegetation to provide habitat for our largemouth bass. On the other hand, we are working in some pretty darn fertile waters here (fertile soils). So, if grass carp strip the vegetation, we will simply get massive algae blooms, and I assume they must also add quite a bit of oxygen demand during their decomposition. I guess I really don’t know what else to say. Winterkill is the limiting factor for our pond management program. North Dakota has almost no pond management, except in the southwestern corner of the state. So, we’re sort of on the borderline here in SD. There is more and more interest in the windmill aerators as a result.

I hope this was not overly technical for the general readers. I know the Pond Boss web page/front page indicates plain language!! I also realize that this got long, but Shan certainly asked some legitimate questions.

Dave Willis