in inidwestern Nortli American reservoirs almost 400 

 lbs/acre (45 mg/m'-), in other reservoirs and ponds 

 200-3(.X) lbs/acre (23-24 mg/m-), in warm-water 

 lakes 123-150 lbs/acre (14-17 mg/m-). and in trout 

 lakes less than 50 lb/acre (5.7 mg/m-). There is no 

 tendency for the standing crop to decrease with in- 

 crease in size of the body of water (Carlander 1955). 

 Biomass varies with the fertility of the pond and the 

 food supply. Ponds and lakes receiving water that 

 drains over fertile soil will have more basic food sub- 

 stances than drainage from poor soils brings. The 

 presence of certain species depends also on suitable 

 breeding sites (Shelford 1911). 



Biomass is further affected by the food habits of 

 the fish species present. In fertile ponds in Alabama 

 containing species feeding largely on phytoplankton, 

 the median biomass of fish was 925 lbs/acre (105 

 ing/m-) : in ponds with fish feeding largely on in- 

 sects, 550 lbs /acre (62 mg/m-) : and in ponds with 

 fish feeding largely on other fish, 175 lb/acre (20 

 mg/m-) (Swingle and Smith 1941). It was esti- 

 mated that about five pounds of food (2.26 kg) are 

 required to produce one pound of fish (0.45 kg). 

 The same ratio has been found characteristic of ponds 

 in Michigaiv (Hayne and Ball 1956). Hence, the 

 biomass of animal life decreases with each additional 

 link in the food chain. 



In two small Michigan ponds where it was pos- 

 sible to tabulate the entire fish population, the benthic 

 production (at least, that portion used as fish food) 

 during one growing season was calculated at about 

 17 times the standing crop when fish were present. 

 This equalled 811 lbs/acre (92.0 g/m-). The pro- 

 ductivity of the fish during the same period was 181 

 lbs/acre (20.5 g/m-), giving a ratio of 4.5 :1 (Hayne 

 and Ball 1956). 



When the standing crop of fish remains the same 

 year after year, its productivity is indicated by the 

 number or biomass harvested. In northern Wiscon- 

 sin the maximum annual yield of desirable food fishes 

 is about 21 per cent of the mean standing crop: in 

 central Illinois it is about 50 per cent : in southern 

 Louisiana, 118 per cent (Thompson 1941). 



The productivity of ponds and marshes for verte- 

 brates other than fish has been measured in a few 

 localities. In northwest Iowa, redhead ducks annually 

 produce about 1.4 young per hectare (56/lOOacre) ; 

 ruddy ducks, 0.6 young (24/lOOacre) ; (Low 1941, 

 1945). Xine species of ducks in the Bear River 

 marshes of L'tah average 16 voung per hectare (640/ 

 lOOacre) (Williams and Marshall 1938). In Idaho, 

 nine species of ducks produce over 22 young per 

 hectare (880/lOOacre) and Canada geese about 0.1 

 young (Steel et al. 1956, 1957). On a well-developed 

 marsh, it is generally possible to remove two-thirds 

 of the muskrats each year and still reserve sufficient 

 brood stock for a sustained annual crop. This is 

 about 2.5 muskrats per lodge (Dozier 1953). 



POND AND MARSH MANAGEMENT 



The maintenance and control, throughout 

 the year, of the water level of ])onds and marshes is 

 important for increased productivity. This may often 

 be accomi)lished by danuning the outlet. It is also 

 im|)ortant to retard the plant succession which, if left 

 alone, will eventually bring alxjut the total disap- 

 jiearance of the habitat. This may be done by cutting, 

 burning, use of chemical sprays, flooding, and ditch- 

 ing. Small ponds, called pot holes, with a good mar- 

 gin of marsh vegetation, or a marsh interspersed with 

 numerous small areas of open water, give the highest 

 yield of waterfowl and other birds, and muskrats. 

 The abundance of waterfowl is often proportional to 

 the extent of the pond margin rather than the acre- 

 age of emergent vegetation. In the Louisiana coastal 

 marshes, the highest sustained yield of muskrats 

 (14.5/hectare/yr or 580/lOOacre/yr) is in areas with 

 Scirpits amcricaniis (O'Neil 1949). 



Artificial ponds are easily constructed (Ander- 

 son 1950, Musser 1948) and are an asset to farms 

 as a source of food and recreation as well as water 

 for domestic animals. Such ponds are commonly 

 stocked with bluegill and largemouth bass, although 

 other combinations may be used. High rates of re- 

 production bring the fish population up to full carry- 

 ing capacity within one or two years. If the pond 

 were stocked with an herbivorous fish only, such as 

 bluegills, normal reproduction would soon become so 

 excessive that a dense population of stunted fish 

 would be present. Using a prey-predator combina- 

 tion in proper proportions, the predator (largemouth 

 bass, for instance) will consume the excessive ofT- 

 spring of the prey species, and the average size of 

 the remaining fish will be increased. The develop- 

 ment of aquatic vegetation in these farm ponds is dis- 

 couraged since it allows too many prey individuals 

 to escape the predator. The fertility of poor ponds 

 can be increased by applying fertilizer encouraging 

 the abundant growth of bacteria, plankton, and bot- 

 tom organisms providing fish food (Howell 1941). 

 The control of turbidity is also important. Clear 

 ponds with less than 25 ppm turbidity may have 12.8 

 times more plankton and 5.5 times more fish than 

 ponds with a turbidity exceeding 100 ppm (Buck 

 1956). 



Repeated stocking of ponds with artificially prop- 

 agated fish is undesirable as there is more trouble 

 in controlling overpopulation than underpopulation. 

 The productivity of a pond is determined not by the 

 number of fish introduced but by available food sup- 

 ply. The available food supply is divided between the 

 individuals present. One study showed that 6500 

 bluegills per acre (16,250 per hectare) averaged 25.5 

 grams each, 3200 per acre (8000 per hectare) aver- 

 aged 51.0 grams each, and 1300 per acre (3250 per 

 hectare) averaged 104.9 grams each (Swingle and 



Ponds, marshes, swamps, and bogs 91 



