Urban Lakes/ General Ponds Foodweb Question

[Haris122]

Just been wondering if the MDC stocks any smaller minnow-like fish or other food species that would be even below bluegills on the foodweb, in the artificial ponds/lakes like the ones in the St. Louis area urban lakes, or even Bush wildlife area lakes. Or how they take care of essentially preventing the fish higher up on the foodweb, from starving. And additionally, how they prevent the larger fish from eating them all up in short order, if they do stock them. I know they figure part of the problem will be taken care off by people keeping legal size fish, but just been wondering if there's any "deeper" approach to that issue.

[Tim Smith]

Just been wondering if the MDC stocks any smaller minnow-like fish or other food species that would be even below bluegills on the foodweb, in the artificial ponds/lakes like the ones in the St. Louis area urban lakes, or even Bush wildlife area lakes. Or how they take care of essentially preventing the fish higher up on the foodweb, from starving. And additionally, how they prevent the larger fish from eating them all up in short order, if they do stock them. I know they figure part of the problem will be taken care off by people keeping legal size fish, but just been wondering if there's any "deeper" approach to that issue.

Good question.

In general, forage issues are a lower priority for lake managers. Even if no forage species are available, a fishery can often persist on cannibalism and terrestrial forage (although that's usually far less than ideal for bass growth). There are often higher pay-offs for stocking effort than fooling around with forage fish.

You put your finger on the key issue when you mentioned the need to keep the forage in the system. Very high quality forage is full of fat and protein relative to body weight, but many of the species that fit this description don't do well when large predators like bass are also abundant. The expense of stocking forage that will all immediately be eaten is prohibitive (although ironically many of the quality bass fisheries in California are fueled in part by consumption of stocked rainbow trout). So for the MDC or any conservation agency to bother with forage stocking, they need something that will reproduce effectively in a system with predators before they're all eaten, but not be so resistant to predators that they don't end up competing with the predators or eating their juveniles. It's a tricky prospect because to do forage introductions well, the goal is a long term (permanent) introduction to the food web.

Bluegill or bluegill hybrids are typically the forage species of choice. They are not ideal for growth of bass as they are spiny with less energy content, they can at least avoid the bass well enough to stay in the system and produce a sustainable forage base. These systems have to be kept in balance or they can end up with many small bluegill and only a very few large bass (the bluegill eat and outcompete the bass juveniles), or a few very large bluegill and many small bass.

Gizzard shad have been stocked for forage in the past but that's usually a big mistake. They have a high energy content and produce good bass growth but they can get out of control and crush the zooplankton populations in lakes. That impairs survival of almost all larval fish and eventually harms the fishery. Threadfin shad never grow to a size that escapes predators so they're less of a problem, but they normally can't overwinter unless a heat source like a power plant discharge is on the lake.

Minnows will occasionally establish in a lake but it's pretty hit or miss and many species just can't sustain themselves (especially in small systems) in the presence of bass.

One sucker species that can persist in a system with bass and has been looked at closely as an alternative forage is the lake chubsucker. They reach a larger size as adults and have a high energy content and produce faster growth in bass than bluegill. That particular idea hasn't been used very often. I'm not sure why, exactly.

One indirect way to manage forage is to manage refuge for forage. The best way to do that is to keep about 20% to 30% of a lake vegetated with a high quality submersed aquatic plant (such as coontail or Val).

[Haris122]

Wow, very informative answer. Thanks Tim. I have seen 1 or 2 local ponds/lakes with a fenced in, small protected refuge area, which I assume was for a purpose like that, but never much else. So that got me wondering, especially with all the fish-imitation lures like roostertails and crankbaits I use, and what effect no prey fish in a given lake might have on the frequency that a predatory fish might still fall for those types of lures if they never experienced such a thing as smaller food fish in the area. I know instinct to some extent trumps that, but I figured there is almost certainly some learned aspect to it as well.

[Tim Smith]

Wow, very informative answer. Thanks Tim. I have seen 1 or 2 local ponds/lakes with a fenced in, small protected refuge area, which I assume was for a purpose like that, but never much else. So that got me wondering, especially with all the fish-imitation lures like roostertails and crankbaits I use, and what effect no prey fish in a given lake might have on the frequency that a predatory fish might still fall for those types of lures if they never experienced such a thing as smaller food fish in the area. I know instinct to some extent trumps that, but I figured there is almost certainly some learned aspect to it as well.

Prey selection is a pretty complicated topic.

Fish defintely select habitats and develop search images with particular prey in mind. How long those patterns last and how quickly they switch to new patterns is still open for debate (at least it is as far as I know, I haven't looked at the scientific literature on this topic in quite a while).

There's a notion that fish will try to forage "optimally" and maximize their intake of calories per unit time. That assumes the fish are aware of their options and able to percieve them in a way they can exploit them. Things like the risk of being eaten themselves or the level of predator hunger weigh in and affect the way fish choose how and where and what to eat.

It does seem pretty clear that if you're in a lake where the dominant forage is crayfish (for instance), you're better off selecting baits that resemble crayfish in some way.

It also seems clear that if you're in a lake where there are limited numbers of forage fish, the predator fish are pretty desperate and they'll jump anything that moves.

I'd be curious to learn more about any systems that were using fencing for prey refuge. In my own experience, I've only used fencing to protect newly planted water plants from water fowl.

[Haris122]

I'd be curious to learn more about any systems that were using fencing for prey refuge. In my own experience, I've only used fencing to protect newly planted water plants from water fowl.

I can't say precisely what they were protecting it from, but I got the impression the fencing was protecting some water plant that certain species like to use for laying eggs, or maybe that juveniles of that same species or several, use to more effectively escape predation. I can't remember exactly how fine the mesh of the fencing was, and if smaller bass could make their way through it for example, but I think the plaque near it suggested it to be some type of refuge/sanctuary. It wasn't anything impressive, the space within the fencing was barely 5 feet in diameter if I recall correctly, and there were maybe 2 or 3 of these "refuges" total. It was in a small urban pond here in St. Louis. It seemed like some quick fix measure to improve survival of something within that small lake. What, that I can't recall.

[ozark trout fisher]

This is an interesting topic that relates to one of the lakes I spend a lot of time fishing. It's an (approximately) 100 acre body of water that has plenty of dead-fall, aquatic vegetation, and excellent water quality. Simply put, it has the appearance of perfect largemouth bass habitat, and everyone who fishes it the first time thinks it just has to be a trophy factory. But there just isn't much of a forage base, so while bass are present in fairly respectable numbers, anything much over about 17 inches is considered quite a large fish. Bluegill and green sunfish are the only available forage. A good effort to alleviate the problem has certainly been made by those who manage the lake. Several forage species from shiners to shad have been stocked, and everyone has had high hopes each time... but none of these efforts have been successful in establishing even low density populations of baitfish. At a certain point, I have to wonder if there is simply no good solution for some of the lakes with this sort of problem.

[Tim Smith]

Shad need a certain sized system to really get established. Once they have good open water habitat, they're pretty dangerous in a lake as they can get out of hand.

If you want more baitfish, let the aquatic veg fill in a bit. If you can get about 20% coverage, you should have enough refuge to let the juvenile bluegill hang around long enough to provide a forage base.

Haris, that is a unique use of those enclosures. Even small ones like you're describing might be of some use. You can get really high densities of juvenile bluegill inside vegetated habitat. I'd really be curious to see data from those systems. It's an idea I've wondered about and if it were cost effective, it might be one that would be worthwhile in other systems.