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Wild Math: How Many Fish are in this Lake?

The weight in pounds removed was equal for both bluegill and largemouth bass. Would this result mean that there were equal numbers of fishes for each of these species? 
It is very doubtful that equal numbers of these species were removed. Bluegill are smaller than largemouth bass, and it would take more of them to equal the same weight of largemouth bass, even with a variety of individual sizes present.

Why do you think the standing crop of carp was so large? 
Carp can live a long time, and they can grow fairly large. Their reproduction rates are very high. Each female can produce tens of thousands of eggs each year. They scavenge on the bottom of the lake. No other fishes prey on large carp.

Why are gizzard shad important to the lake?
Gizzard shad are small fish that many predators feed on.

Is stocking an aquarium the same as stocking a pond?
If you want it to be sustainable, then the same techniques apply. Most aquaria must be provided with outside food sources, however, so the balance between species can be unnatural.

Why do you think that some of the species removed were not added back to the lake?
This lake is used mainly for recreational fishing. For it to be successful, there need to be fishes present that people enjoy catching and/or eating. Bluegill, largemouth bass, channel catfish and white crappie were present for these purposes originally and were added back to the lake. Redear sunfish and hybrid striped bass also fit these criteria and were also added to the lake. Common carp, gizzard shad, bullheads and green sunfish are not often desired by anglers. Green sunfish can outcompete other sunfish species, too. There are pros and cons when considering stocking of gizzard shad. While serving as a forage fish, gizzard shad can also cause problems to the fishery depending upon what is determined to be the goal of the sport fishery. Yellow bass can be taken by anglers, but it is not as popular as the four species restocked in this lake, and this lake can only support a small variety of species.

Why do you think it was not necessary to restock gizzard shad in the lake?
The species returned to the lake will support each other as food sources. There is no need for additional forage species.

If the fishes in the lake were all removed now (many years after the restocking discussed in this activity), do you think that fish species other than the six that were restocked would be found?
Yes, there would probably be additional species present in the lake.

How would other fish species enter the lake?
Humans are the most likely source. People sometimes use fish species as bait. While this is a legal practice as long as all regulations are followed, people sometimes obtain bait fishes at one location and release them into the lake, river or pond where they were fishing. It is not legal to transport live bait, or any fish for that matter, between water bodies. This practice greatly increases the chance of the spread of invasive species and diseases. People also sometimes release fish species that they once obtained for use in an aquarium. Many of them will not live for long periods of time, but some will survive and spread. People also sometimes catch fishes at one water body and release them into another water body. Fish may occasionally wash into a lake from upstream or from other bodies in the watershed, if flooding occurs.

Why do hybrid striped bass and channel catfish need to be added regularly to the lake?
These are popular species that people remove from the lake in great numbers. Hybrid striped bass are raised in hatcheries for release. Channel catfish do reproduce in the lake, but not in numbers great enough to meet the demand.

What do you predict would happen to this lake in 10 years if stocking and other management strategies were stopped today?
The fishes that are regularly stocked would disappear from the lake quickly due to fishing. Fishing would again become poor quality in this lake, and the variety of species present would be very low. The predator/prey balance could be adversely affected.