Carrying Capacity and Standing Crop 61 



are usually associated with small individual sizes of those fishes and vice 

 versa). In theory, a body of water in which the fishes represented the 

 greatest range of species and sizes would offer the maximum in efficient 

 utilization of available food (Figure 4.1), although it is conceivable that 

 the kinds and relative numbers of fishes within any given size range 

 might not be paralleled by an equal abundance of acceptable food for 

 this size range. Thus, a part of a population representing a certain size 

 range of one or more species might be stunted, while in the same species, 

 other sizes might be growing rapidly. 



Surface Area 



The carrying capacity ( in pounds ) of a body of water for a specific fish 

 population seems to be largely a function of surface area rather than 

 depth or volume; probably the zone of light penetration at the surface 

 produces the bulk of the food supply (directly or indirectly) for fishes. 

 There seems to be much evidence that carrying capacity is directly related 

 to fish food production, which, in turn, is related to the basic fertility of 

 the water, and conditions allowing the capture of this fertility by the 

 food chain. 



Experimental Testing 



Little is known regarding the carrying capacity of any water for in- 

 dividual species of game or pan fish, although European fish farmers 

 engaged in raising commercial fishes for market have recognized that 

 there are production limits of ponds for carp and other commercial 

 species. It is common practice in fish farming to stock ponds with only 

 a sufficient number of fish to produce a marketable product at the end 

 of one or two growing seasons. Boccius ^^ wrote: "It has been fully proved 

 that a given space of earth can produce only a certain quantity; so only 

 can a given space or quantity of water produce a certain quantity, either 

 of vegetable matter or animalcules; and curious as it may appear, yet it 

 is as true as curious, that by storing only the proper number of fish 

 adapted to the water, the weight in 3 years will prove equal to what 

 would have been had twice the number been placed therein, so that the 

 smaller number produces the same weight as the larger, from a given 

 quantity of water. By overstocking the water, the fish become sickly, lean 

 and bony." 



Swingle and Smith ^^ described an experiment in which two ponds were 

 stocked with 6500 newly hatched bluegill fry per acre in late spring, and 

 when the ponds were drained in November, the fish had grown to an 

 average weight of slightly less than one ounce and the total populations 

 in each of the two ponds amounted to approximately 300 pounds per 

 acre. The fish were returned to the refilled ponds and when the ponds 



