Big lures catch big fish?

[Tim Smith]

The question of whether or you need to use big lures to catch big fish seems to be a favorite on this forum. I've been meaning to dig out this old data for some time to contribute to that discussion.

 

The data presented here are from Smith and Wahl 1993, Development of Reservoir Shad Assessment Methods (IDOC report). The graphs show largemouth bass diet data (collected with smooth edged acrylic tubes without harming the fish) from boat electrofishing in Lake Shelbyville, Illinois. The comparisons are all total length of the bass (x axis) vs. total length of gizzard shad found in the stomachs of the bass (y axis).

 

 

This graph was from data collected in electrofishing runs near Bo Woods (station 3) at the upper end of the lake where the three year average CPUE (catch per unit effort) for gizzard shad was about 9 fish a minute.

 

 

This graph was collected in electrofishing runs near the COE boat ram at the dam (station 6) where gizzard shad CPUE was around 4 fish a minute.

 

 

This graph is from data collected throughtout the lake in 1988, the big drought year with a lakewide annual gizzard shad CPUE of 3 fish per minute.

 

 

This graph is from data collected throughout the lake in 1989, a year with an average gizzard shad CPUE over 10 fish per minute.

[Steve S.]

so, what does the data tell us?

[Mike Clifford]

I think it's telling us big bass like big shad. = )

Or big rats, even-

we can make believe the little squares in the graphs are anything we want them to be.

That's my theory and I'm stickin' to it.

 

Think I'm kidding?

Go ahead- take a closer look at the graph here!

 

 

[Tim Smith]

Mike, I was just wondering...when the Dr. shows you ink blots, how many of them look like rats?

 

Steve,

 

There are actually quite a few nice trends in these graphs, but look first at the big bass in the 500 mm area. In years and places with abundant shad forage, big fish ate both big prey and small prey. When shad were not as abundant, big fish took only big shad.

 

Other data show that big bass also had fewer alternative diet items in their guts when shad were abundant. When shad were less abundant, they had higher proportions of bluegill in their diet, probably indicating a shift in foraging strategy and search patterns.

 

So the answer (in this case) to "Do bass prefer larger prey" is "Yes, but less so if there's a strong foraging focus on one specific prey type."

 

So does this apply to smallmouth?

[jamie shard]

Yup, small bass like mice, big bass like rats.... but when a lake contains mostly mice a big bass will eat enough mice to make up for a lack of rats.

 

Can I get a MS degree for that thesis paper, uh, paragraph?

 

 

Tim,

 

When shad were not as abundant, big fish took only big shad.

 

I'm curious, how do you deduce this from the graphs? Serious question, I'm trying to learn.

 

-j

[Tim Smith]

Tim,

I'm curious, how do you deduce this from the graphs? Serious question, I'm trying to learn.

 

-j

 

 

I would have to post all the diet data from the report to show you the bluegill-shad trends, that part isn't in these particular graphs. I'm deducing a shift in foraging strategies because bluegill behave very differently from gizzard shad, using more cover and less open water.

 

The main thing to look at here is that prey size increases more predictably with predator size when the prey are abundant. Focus on the bigger bass...400mm to 500mm (16-20 inches) and up. Look at the sizes of shad that were in their guts in the low shad abundance graphs (1988 and Station 6) vs. the high shad abundance graphs (1989 and Station 3). There aren't any or many small shad (i.e. <100mm) in the guts of big bass in the low shad abundance years. You can also see the pattern of stronger linear relationships between prey size and bass size in the R2 values. When those are higher, the stronger the relationship.

[Steve S.]

Tim

 

I thought that is what I saw, but I wasn't sure.

 

Now, does it say if the shad were single or tandem spin?

[Mike Clifford]

I'd be interested in seeing what else the bass are eating- i.e. Crawdads, macros, etc......as it applies to their "opportunistic" nature.

I read somewhere years ago that they will eat a Craw before anything else, but have never seen any scientific data to support this claim.

[Tim Smith]

I'd be interested in seeing what else the bass are eating- i.e. Crawdads, macros, etc......as it applies to their "opportunistic" nature.

I read somewhere years ago that they will eat a Craw before anything else, but have never seen any scientific data to support this claim.

 

Bass do pursue crayfish but they also focus on soft-rayed fish like minnows and shad. Fathead minnows, for instance, can't even live in the same system with them for very long. Bass outstrip their reproduction and drive them to extinction or near to extinction. Gizzard shad are easy pickings while they're small, but eventually become too large to be consumed. Bluegill are tougher prey. Spiny, with a lower energetic return and a size refuge for adults, bass eat them but would prefer to go after just about anything other than bluegill.

 

Maybe I can dig out some of my pond data sometime that shows how bass almost eliminated some species of crayfish in experimental ponds, but didn't even put a dent in the bluegill populations.

 

Let me see if I can find some citations, Mike.

[Steve S.]

Tim

 

Okay, thinking like a fish, how often would I "make the choice" to pursue my select forage? Would a smallie pass on a juicy nightcrawler that drifts by to forage for a crayfish? What about a fat (and soft) creek chub?

 

I always think of fish as being opportunistic first and discretionary second, but maybe I need to alter my thinking.

 

BTW, I love seeing this data, as long as I can interpret it.

 

Thanks!

[Tim Smith]

Tim

 

Okay, thinking like a fish, how often would I "make the choice" to pursue my select forage? Would a smallie pass on a juicy nightcrawler that drifts by to forage for a crayfish? What about a fat (and soft) creek chub?

 

I always think of fish as being opportunistic first and discretionary second, but maybe I need to alter my thinking.

 

BTW, I love seeing this data, as long as I can interpret it.

 

Thanks!

 

 

I wouldn't modify your opinion too much. Trends can be suggestive, but without a controlled experiment, it's all guessing. Certainly there are good guesses and bad guesses and clearly impossibly wrong guesses, but at the end of the day, there are assumptions buried in these interpretations and they're still guesses. You can comb through data and find things that are pretty obvious (for instance, in 1989, you can see the 1+ gizzard shad in the largemouth diet by the gap between the smaller and larger fish), but other things are more speculative.

 

Maybe the large bass would have eaten small shad if they could in '88 and at the dam, but the small shad were all offshore (there's no data to support that idea, but it COULD be true). Maybe feeding on shad in schools in open water makes this trend unique. Maybe this, maybe that...The exact processes that led to these trends aren't known. This kind of data lends itself to hypothesis formation, but my "interpretation" (and all observational data) is only that, a hypothesis. You could make your own as well.

 

In general, fish would try to optimize your energetic intake, but balance that against exposure to predators, breeding status, and habitat requirements such as temperature and oxygen. Their level of hunger will also influence their foraging choices.

 

I am guessing that in this case the bass were pursuing a hunting strategy that included things other than gizzard shad when the gizzard shad were less abundant. In those conditions they were less likely to initiate an attack on smaller, less profitable prey because they had search images or habitat use that focused on different prey. It took a stronger inducement to get them to attack smaller gizzard shad. When the shad were abundant, the bass shifted to a forage strategy that focused specifically on shad and their "opportunistic" nature kicked in. The smaller shad were closer to their search image or habitat use and they didn't hesitate to take them.

[jim bielecki]

I think it's telling us big bass like big shad. = )

Or big rats, even-

we can make believe the little squares in the graphs are anything we want them to be.

That's my theory and I'm stickin' to it.

 

Think I'm kidding?

Go ahead- take a closer look at the graph here!

 

 

 

I think mike is right. Big bass like big rats...unless the rat is from Chicago.