Fishing Mortality 187 



Underfishing 



In artificial ponds and lakes \\ licre natural predators are limited, severe 

 competition among fishes may take place because of a scarcity of ade- 

 quate mortality factors (Figure 7.1). This competition results in poor 

 growth and eventual stunting and often causes a gradual change in popu- 

 lation composition. 



Most artificial impoundments, large or small, are underfished, i.e., 

 usually hook-and-line fishing is not intensive or diversified enough to 

 replace the normal system of natural predation which is usual for "wild" 

 waters beyond the influence of human populations. Also, some individuals 

 of certain species apparently become wary of baited hooks or artificial 

 lures. 



Fishing pressures and the degree of stunting caused from overpopula- 

 tion may vary from one body of water to another. The advent of stunting 

 is purely arbitrary, and has been defined on the basis (and perhaps 

 falsely) of average growth rates of a selected species taken from specific 

 waters in a limited region. One might determine that the average rate of 

 growth of largemouth bass in northern Illinois and southern Wisconsin 

 produced fish that were 4.0 inches the first year, 8.3 inches the second, 

 10.6 inches the third, and 12.0 inches the fourth. These averages might 

 not be at all representative of bass growth in this region if the popula- 

 tions of bass inhabiting the lakes from which samples were taken were 

 unusually fast-growing. Yet, it would seem logical to assume that fish that 

 grew faster than these averages were living in a very satisfactory en- 

 vironment and those that grew more slowly were stunted. 



Underfishing can be defined as all levels of fishing pressure that, when 

 operating with the forces of natural mortality, cause insufficient total 

 mortality to prevent excessive survival of juveniles and moderate to 

 severe food competition among adults. It becomes obvious that fishing 

 mortality and natural mortality combine to define total mortality, and, 

 where natural mortality is high or variable, underfishing cannot be de- 

 fined in specific terms. For example, the seasonal fishing pressure exerted 

 by resident Indians on a Canadian lake might be no more than 2 man- 

 hours per acre, while that of farm families on an Ozark hill pond was 

 30 man-hours per acre. In spite of the fact that the Ozark pond received 

 15 times the fishing pressure of the Canadian lake, the former could be 

 underfished while the latter was not. This can be explained only through 

 a consideration of all mortality factors. In the Canadian situation, Indians 

 might be a mortality factor of minor importance compared to predatory 

 fish and fish-eating birds. On the Ozark pond, perhaps fish predation was 

 limited largely to humans engaged in fishing. 



