Fishint^ Mortality 189 



The fact that fish can hve indefinitely on a maintenance diet practically 

 eliminates mass mortality through starvation; barring some catastrophe, 

 such as the drying up of a pond or the freezing of the water to the bottom, 

 stunted populations of fishes remain so indefinitely. These populations are 

 rather easily identified, because individuals usually are thin and their 

 eyes are disproportionately large for the size of the body. Apparently the 

 eyes of a fish continue to grow even when the bodv stops growing. 



Overfishing 



When more pounds of fish are removed from a hodij of water in a 

 single season than can he replaced through food gathering, assimilation, 

 growth, and recruitment, the hodij of ivater is said to he oveiiished 

 (Figure 7.1). According to James, Meehan, and Douglass,-'' waters located 

 near centers of population frequently are overfished, but their concept of 

 overfishing may deal with selected species rather than the complex of all 

 species present in a body of water. 



Fish populations show considerable resistance to intensive angling and 

 are not easily decimated. This point was made by Viosca ^^ who stated: 

 ". . . when a body of water is said to have been fished out by angling, 

 only a relatively small percentage of the fish have actually been removed. 

 . . . Apparently, the majority of fish in a body of water cannot be taken by 

 angling because of the automatic increase in their prey resulting from 

 the removal of part of the stock by the very act of angling." Swingle and 

 Smith ^^ made essentially the same statement. Through fishing experi- 

 ments using largemouth bass populations of known numbers per acre, 

 Lagler and DeRoth ^- concluded that fishermen angling in experimental 

 ponds could scarcely be induced to fish for this species when it was 

 represented by a population density as low as 6 legal bass per acre (be- 

 cause the rate of catch was only 0.04 legal fish per man-hour ) ; the interest 

 in fishing had waned completely among cooperating fishermen and the 

 impression was general that the ponds had been "fished out." 



One of the first comprehensive studies of the overfishing of warm-water 

 fishes in ponds became possible because of a complex of several favorable 

 circumstances. A conscientious custodian at the Owens-Illinois Glass 

 Company recreation area collected information on the fish yield of Onized 

 Lake (Illinois), a two-acre pond that was overfished, largely because 

 picnicking and fishing could be combined.^ Here family groups came for 

 picnics, but brough fishing equipment and baits, too, because it was 

 possible to watch a bobbing cork while otherwise occupied at the picnic 

 table. With these "double" recreation facilities, many man-hours of fishing 

 were logged because, with the stimulus of the hamburger and hot dog, 

 the low catch rate lost its importance as a fishing deterrent. The result 

 was that during two successive years the fishing pressure on Onized Lake 



