Building a little bit upon our discussion from the other day, I'd like to take a minute and describe how some of these fishery statistics relate to what anglers actually experience when out on the water.
One of the stats you'll see repeated in this post is the CPUE of both bass and bluegill in the form of numbers of fish captured via electrofishing per hour. The other is Proportional Stock Density (PSD). Proportional Stock Density is calculated as a number based upon percent of fish over a quality length, divided by the percentage that are over a stock length, times 100. The lake in this example will be West Boggs.
In this first graph dealing with largemouth bass, you'll see the CPUE in blue and labeled on the right, with the PSD in magenta and labeled on the left. In particular, notice the red circled values around the recent and contined low (~50) CPUE values, and the trend arrow for CPUE continuing to rise, and now up around 90. What this means is that the overall population of bass has dropped, most likely due to poor recruitment, so that anglers are catching fewer fish overall. However, the tradeoff is that the remaining bass tend to grow large, hence the really high PSD numbers. In the case of W. Boggs, electrofishing surveys have shown that more than 55% of all bass surveyed are over the 14" minimum length limit, a much higher than normal number.
In this next graph, the same stats are applied to the lake's bluegill population. Here the trends are exactly reversed (see red arrows), with the CPUE of over 1000, and the PSD now down to less than 10. So you have a large population of bluegills that have become slow growing due to their numbers relative to the amount of food available. What's this all mean?
What has most likely happened is that as shad got introduced into the lake after the renovation, bass started to preferentially feed on them over the bluegill, and the bluegill population could no longer be kept in check. Bluegill are best managed by a very high population of small bass, and what you now actually have is a very low population of large bass. Part of this problem is also likely exacerbated by high shad biomass that tends to negatively affect recruitment of bass, though there is some mixed opinions on this in the literature. The kicker is that once this happens, it is very hard to reverse, and the word I've heard is that the liklihood of another renovation at Boggs in the next couple years is high.
From a more practical standpoint, anglers can get a very good idea of the fishing potential of a lake by studying this type of information before ever visiting. If you're a bass angler, by looking at this data, you could expect to not catch a lot of fish if you were to make a trip, but the ones you did catch are likely to be a very good size. Tournament anglers can then make a good guess as to game plan or strategy based upon this information. On the other hand, if you're a pan fisherman, it probably wouldn't be worth your time to go, because while you would most likely catch a ton of fish, very few of them are going to be of a harvestable size.
Don't be like most anglers and overlook this valuable information. It's all easily accessable via the IDNR website, with much of the information in downloadable .PDF files that you can ultimately save to your computer for future reference.
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