Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Population Assessment info

OK, I think I know what you are asking Ewest.

First of all, I assume you realize that Figure 1 has nothing to do with Ross Barnett Reservoir? I looked through Steve’s methods, and he used summary papers based on broad geographic ranges for the largemouth bass, white crappie, and bluegill growth rates to develop those hypothetical length frequencies in Figure 1. The references for the three sources of growth data are in his citations.

Figure 4 in that paper has the actual length-frequency data for Ross Barnett Reservoir. I could not find the sampling time, but I’m sure it was either fall or spring, so let’s progress with that thought. Let’s start with LMB, which had a PSD of 54. Whether this is a fall or spring sample, the fall age-0 or spring age-1 LMB look to average about 8 inches long (20 cm). Does that sound right to you for established populations? I’d say yes. When I look at this length frequency from a northern biologist’s perspective, it looks darn good to me. We like a mid-range PSD, and there are many, many fish that exceed 15 inches (38 cm; Dick Anderson’s RSD-P). In fact, some of the bass exceed 25 inches, which is trophy stuff to me! I don’t see many peaks and valleys in the length information, meaning that reproduction and year-class strength must be pretty consistent. Growth must be moderate to high by the standards of your region, or the fish would not reach those large sizes.

Next, let’s look at the crappies. The PSD is 79, which borders on too high. However, too high typically means low recruitment, and there a nice year class of fall age-0 or spring age-1 crappies right at 4 inches. I also like to see such a good number of fish over 12 inches (30 cm); again, growth probably is pretty good for that locale. I have a sneaking suspicion that you can see the three younger age groups in this length frequency. If this is a spring sample, the age 1 fish are 4 inches, the age 2 fish are 8-9 inches, and the age 3 fish are that bump in lengths near 13 inches. There could be a missing year class between 4 and 9 inches, but I sort of doubt it. I’ve heard that southern crappies grow fast and die young; if my guess is right about the year classes, then that story would hold true.

What about bluegills? First of all, we’ve got some sampling bias probably happening. A rookie might think that the past year’s reproduction and recruitment was poor, as there are too few small fish in this sample. However, we typically underestimate the very small bluegills. I see no reason to suspect a weak year class of fall age 0 or spring age 1 fish, but could be wrong. I really would only know by working there long term and following the catches by age group over time in my annual samples with the trap nets. Bluegill size structure is ok, but not great. Would that sum up the fishery down there? In the upper Midwest, we often don’t see the quality of bluegills in larger reservoirs that we see in ponds and small impoundments. Here at Ross Barnett, there is a moderate PSD (good), and a few fish make 8 inches (20 cm). So, I’d rank it ok, but not great. In these large waters with lots of shad (you mentioned the threadfin; are gizzards also present?), we typically don’t see bluegill quality as good as the small waters. However, I’ve never been to this reservoir, and I’m not experienced in southern waters. Just making educated guesses.

I’d like to fish for both crappies and largemouth bass in this reservoir. It is a quality fishery!!

To more fully interpret the population samples for largemouth bass, bluegill, and white crappie, I’d sure like to see more information: catch per hour of electrofishing or per trap net night; growth; and age frequency. However, we of ten have to make suppositions based on just the length frequency, just as I did in the last paragraph.

Here’s a final thought on “balance.” The balance concepts “work” much better in ponds and small impoundments. In a 33,000 acre reservoir, the fishery is often driven by recruitment (i.e., year-class strength in the various fish species). However, I can see why you say “balance” for this reservoir – guessing from the length-frequency information in Figure 4, recruitment has been pretty darn consistent for largemouth bass, white crappie, and bluegill.