Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations CC Mouths vs GShiner & Bluegill Sizes: My Summer Term Paper

This all started with a question on how big CC have to be to eat GShiners: Channel Cat Prey Sizing thread

I now think I have enough info to present the answer to Prof. Cody and the rest of the students.

I have measured the mouth sizes and body lengths of 31 CC this Spring/Summer. These are the results:


The interesting part of this info is that CC (appear to) have two different mouths sizes for body length. "Regulars" have a mouth size (major opening diameter, side to side) that is very nearly 10% of their body length. "Bigmouths," on the other hand, have a mouth size that is very nearly 15% of their body length, as well as a thicker, heavier head. Based on secondary sexual characteristics info from NRAC CC Culture I am pretty darn sure the the "Bigmouths" are males and the "Regulars" are females.

I also measured the lengths and heights of 25 GShiners. Combining these with info on 9 smaller GShiners thoughtfully provided by Bill Cody gives this plot of GShiner sizing:



These GShiners were, in Bill & my respective opinions, healthy and in good condition. As a rule of thumb, GShiner body height is just under 30% of their body length.

I also happened to save the height and length of 8 of the small BG which were harvested. The height measurement for the BG (and the GShiners above) does not include their dorsal fin. The BG body sizing plots as:



As all reports indicate, it is probably easier for a predator to swallow a 10" GShiner than a 6" BG, especially when the BG sticks out that spiny dorsal fin.

As a result of these findings, I have changed my CC harvest plan for the year (which is intended to remove CC to eat and to make room for the remainder to grow, support the predation of GShiners, and eventually get a couple of "General Sherman" sized CC left in the pond) from harvesting the smallest edible size CC to removing the smallmouthed females. I theorize that the bigmouthed males will be able to eat larger prey and function better as predators. By keeping the males I hope to maximize predation by CC with a smaller total mass of CC in the pond.

Comments, especially those gracefully pointing out how I screwed something up, are welcome.

That might be about the coolest post I've ever seen. Somebody contact Lusk. I think we've got the makings of a story.

Good job, Theo!

Oh, Lusk, I summon thee.

Geez...and I only thought channel cat were the stepchildren of southern fishing ponds, periodically donating their omnivorous bodies only to palates of science. Theo Gallus, fisheries philosopher and seer of bigger things has brought new information to the table. Well done. It has never entered my mind to measure the mouths of channel cat.
Theo, would you like to write a story for PB? If so, let's do it. I'll help. Heck, if you hurry up, we'll put it in the Sept-October issue.
You are right on the money deducing the larger mouths belong to males. But, it's because females are larger of the species. They tend to be longer and heavier, while males of similar length are lighter weight, with wider, more flattened heads. Depending when you measure, females are much heavier, especially when their ovaries are full and the males have one thing on their minds.
Another twist to your theory, though. Think about this. Even though a given size shiner will fit into a given channel cat mouth, that doesn't mean channel cat will be effective predators. One of the most fun things about fisheries management is to take solid science such as Theo and Cody's stuff, then put it to work in a pond. I love to eat oranges, but I ain't drivin' to Florida to get an orange. Golden shiners are fast, and quick. They live in open water, near shore, normally in the top few feet. Channel cat are typically skittish, nocturnal, hanging deep as they can. I love Theo's fact finding. Let's take it to the next step and answer the follow up question. Will channel catfish effectively prey on golden shiners in Theo's pond, based on mouth size of catfish and length of shiners? When we take solid scientific evidence and mix it with a behavioral study, now we have the makings of a great story.
Theo, why don't we write a story based on your current findings, with a hypothesis, then a follow up on the behavioral aspects?

Have there been studies done which indicate whether male or female CC have a higher top end growth potential? In other words, if you were to ID sex of all twenty pounders caught in U.S. ponds in a given year, would they be mostly females? If so would we not make efforts to harvest the sex with less growth potential? Knowing from an early age which CC are males or females could be a great benefit in boosting average size of CC in a particular pond. Extremely interesting thread.

Bob:

I am flattered by the invitation to write a story and will see what I can come up with fairly quickly. Fortunately my webmaster is spending 2 weeks at Fort A. P. Hill for the Boy Scout Jamboree, which frees up a lot of computer time for everyone else. When I have what I feel is a decent draft (requiring no more than 2 out of every 3 words being replaced ), I should E-Mail it?

Bruce:

This is all your doing. Thanks (I think)!

Theo :

I was out a few days and missed your post. Ditto Bruce's comment. Great job !!!! Miss. State Univ. because it services the commercial catfish industry { a huge industry here} has lots of info on CC . I think most of the info is online. ewest