208 Fishing and Natural Mortality 



Angling mortality is probably far less important in the dynamics of 

 sport fish populations than most fishermen are led to believe. 



Restrictions and Mortality 



The history of the fisheries resom*ces of North America follows the 

 pattern of man's use of other renewable natural resources. At first there 

 is unrestricted use, followed by a gradual increase in restrictions until 

 a maximum number has been imposed. Then as more information becomes 

 available on the correct management of a resource, unnecessary or useless 

 restrictions are gradually removed. 



A maximum of restrictions were imposed upon the warm-water fisheries 

 resources by about 1935; since then, a gradual understanding of fish popu- 

 lation dynamics has resulted in an almost complete reversal, once it 

 became appreciated that fish would hatch, spawn, and die in spite of how 

 man restricted himself. 



Under conditions of rapid "turnover," it is of some interest to consider 

 size limits, bag limits, seasons, and other restrictions which man has 

 developed to control himself. 



Size Limits. There are several assumptions upon which the idea of a 

 minimum size limit is based. One of the most common is that each fish 

 should have an opportunity to reproduce before it is caught. This assump- 

 tion might be valid if one could demonstrate a shortage of spawn or 

 show a relationship between abundance of spawn and number of 

 spawners. When growth rate shows an inverse relationship to population 

 numbers, a size-limit restriction on a short-lived species may make certain 

 that most of a crowded population of these fish will die of senility before 

 they are large enough to be taken legally. For example, an 8-inch minimum 

 limit governing the take of crappies would allow from 50 to 90 per cent 

 of them to die unused. 



When Escanaba Lake (northeastern Wisconsin) was opened to un- 

 restricted hook-and-line fishing, 1946 to 1956, there was no evidence of 

 depletion after 10 years. ^-^ More than 50 per cent of the fishes taken from 

 this lake by anglers during the test were illegal elsewhere in Wisconsin 

 because of their size. Eighty per cent of the catch consisted of walleyes 

 and perch. 



In contrast to the uselessness of size limits in the management of most 

 warm-water lake fishes, Allen - cites the catch of marked hatchery -reared 

 trout liberated just before the angling season in American trout streams 

 where the return may be 80 per cent or more in the current season. 

 Shetter, Whalls, and Corbett ^''-^ were able to demonstrate that protection 

 of brook trout in a part of the Au Sable River ( Michigan ) by a length 

 limit that allowed them to spawn at least once was followed by an increase 

 in fingerlings present. This protection, plus a "flies only" regulation, al- 



