July 2005

POSSIBLE DAM STOCKING

Following the interest shown recently by the Fisheries department, for a possible stocking of some of our dams with new species, and the suggestions by some people for specific species, we have spent quite a long time gathering information and search results from the USA, that took years to complete, through the internet.  What follows, is not the opinion of any "amateur", but what the scientists and experts suggest.

1. Gizzard Shad are not generally recommended for stocking in dams due to the fact that they grow quickly, attain very big sizes for most predators to eat and they can become overcrowded.  They are useful as forage fish for bass only in the early stages of their life (1-2 months).  After that, they are too big to be eaten by bass and due to their really huge reproductive rate (they reproduce from the first months of their lives at about 4 cm long) they create serious problems.  In the United States, where Gizzard Shad are naturally present, there exist also the Striped Bass (their diet consists mainly of large gizzard shad) or even other big fish like muskie or pike.  The experts suggest that 25% of predators be large enough to consume 90% of Gizzard Shad.  In lakes or reservoirs where Gizzard shad have been stocked along with only Largemouth Bass as a predator, every 2-3 years restructuring or reducing the populations with a fish toxicant is necessary to reduce the problem.

2. Threadfin Shad. Even though they are of smaller size they are not recommended for stocking in dams similar to ours, due to their high reproductive rate which the Bass cannot control.  While threadfin do not grow too big for predators to eat like gizzard shad, they can still make up most of the fish biomass in a body of water due to their filter feeding ability and high reproductive rates.   The first food of shad (and most game fish species) is microscopic animals called zooplankton and protozoa.  Shad quickly supplement their diet with free-floating algae, called phytoplankton, and insect larvae.  Shad have a distinct advantage over other fish species because of their ability to filter large amounts of water through long, closely set gill rakers.  As the water passes through the gill rakers, free-floating plants and animals are filtered out as food.  This enables shad to compete much more effectively for food with other fish that rely on the same diet, such as sunfish and recently hatched bass and crappie.  Shad also graze for algae and small insects over logs and other underwater objects, but their main way of feeding is simply swimming and pumping water through their mouths and out their gills. This results in huge reduction of young bass populations.  However, once the few bass left grow to a size they can prey on the shad, bass growth rates are extremely high, but I don't think this is what we want for our dams.

Gizzard and Threadfin Shad are not edible,  therefore they are no good for fishing and their numbers will not reduce by being caught by anglers.  In lakes or dams in the United States where Gizzard Shad have been introduced, adult shad (20 cm or longer) comprise up to 80% of the total fish population. Where Threadfin Shad is stocked, in 2-4 years their density is so big, that all available food resources are needed for their survival.

Shad are efficient at feeding on zooplankton (microscopic animals) and may reduce the availability of these organisms that are also necessary food items for juvenile sport fishes. In addition, unlike most juvenile fishes, shad of both species can switch to alternate food sources after stripping a body of water of available zooplankton. Therefore, in part, shad owe their great numbers to adaptability. They are able to switch to alternate food sources that other fish species cannot utilize.

The above would be catastrophic to our fish populations.  All new born bass would just die due to lack of food.

3. Βluegill do not present the above problems, and are therefore suggested to be used as forage fish in dams or lakes stocked with Largemouth Bass.  They are extremely nutritional and contribute to the maximum in Bass growth.  Largemouth Bass can control the bluegill numbers and therefore overpopulation is definitely not likely to occur.  Bluegill is a very tasty fish with excellent quality flesh and will be fished by many anglers (lives near the shore), so it will be rather difficult to increase in sufficient numbers let alone overpopulating.   Bluegills are density dependent, meaning that as their numbers increase (within limits), their relative sizes decrease.  This means that in the remote case of overpopulation (lets say due to bass over fishing), then their size will remain small making it easy pray for younger bass.  Even in the remote event of overpopulation, the American experts suggest that about 1/3 of the water of the lake or dam is removed (something that happens in our dams every year anyway), so the bluegill will loose their hiding places and become again easy prey for bass.

Some people say that bluegill eat other fish's eggs.  Maybe rarely they do.  But would a bass allow a bluegill to even come close to its nest and try to eat the eggs? Bluegill diet consists mainly of aquatic insects and their larvae, crayfish, snails, algae and rarely small fish.  They are not built to chase fish (they do not have hydrodynamic shape).  What can initially happen is that bluegill will affect roach population until a balance is reached.  This is not a problem though, because the bluegill has a lot more to offer and their presence in a dam is much more essential both as a forage fish as well as a sport fish.

4. Some people have suggested stocking our dams with brown trout.  Brown trout has similar temperature needs as rainbow trout (70-75 ^oF for short periods).  However, they are territorial, active usually at night, do not put up as good a fight as the rainbow trout, slow growing, do not taste as good as the rainbow, very difficult to catch and exhibit cannibalistic behaviour  (they eat small trout, therefore when they grow too large to catch, they will attack small rainbows released in dams - something similar to the situation in Lefkara dam where the zander almost eliminates young rainbows). Their diet also consists of frogs, lizards etc.

5. As far as Crappie is concerned, it is not advisable to release in dams smaller than 5 acres (0.02 sq.kms), that is the size of Lympia dam or smaller, turbid waters, very low visibility waters, and where there are no bluegills or shad.  In waters where bass is already established, crappie will not effect its reproduction and growth.  The opposite will rather happen.  Bass will control the crappie numbers by hunting it, something not really necessary as crappie will be fished in numbers by anglers as it is a great sport fish.  Crappie hunt bluegill or shad and therefore do not bother young bass.  There are two kinds of crappie, white and black.  Maybe white crappie will fit Cyprus conditions better.

6. The introduction of the Florida Largemouth Bass  (Micropterus salmoides floridanus) and the proper reproduction and stocking in our dams would help in having record size fish.  The reason is that this subspecies grows at much higher rates than the northern bass (Micropterus salmoides).  Scientists even suggest that the hybrid of the two subspecies, grows at an even better rate.  Of course this requires the proper forage fish (bluegill and crappie).

7.  A major problem seen at Kalavasos dam, is that there are some really big bass and some seasons small bass show up as well which later disappear instead of grow.  What possibly happens is that due to the fact that forage fish (roach) is limited, bass turn to cannibalism to survive, eating their own species.  The clarity of the water which is usually a few meters certainly contributes as small bass find it very difficult to escape.  Rumors say that the dam was illegally stocked with Tilapia.  If tilapia survive and multiply, which I doubt, then maybe the problem will be solved.  Bluegill could be the ideal solution to the problem.  (Lefkara dam also desperately needs bluegill or tilapia since zander eliminates the small trout released every year by the fisheries department).

8. Tilapia, which we already have in some of our dams, has similar qualities as the bluegill, with the disadvantage that it cannot survive in water temperatures lower than 10 ^οC.

Introducing bluegill and crappie in our dams, will greatly improve freshwater fishing in Cyprus, offering two very popular new species (just like bass).  More important, the bass numbers will increase a lot and sizes will reach world record levels, never seen in Cyprus before.

Thank you for your time.