210 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



curred in a year wlien the officials failed to enforce 

 the law on size limits. 



Economic conditions doubtless have had an 

 effect on the annual fluctuations in the yield of 

 perch, but the relation is too obscure to point 

 to any major change in the annual catch as the 

 result of changes in the price of or demand for 

 perch. 



The discussion of the relation of production to 

 fishing intensity, to fishery laws and enforcement 

 of laws, and to market conditions, has been given 

 in advance of the treatment of the relation between 

 the catch and the abundance of perch, not with 

 the intent to imply that abimdance is not of great 

 importance in determining the yield, but rather 

 to bring out the dangers of interpreting too freely 

 fluctuation in production as the result of fluctua- 

 tion in abundance. To be sure, abundance and 

 catch are closely related; but careful recognition 

 also must be given to other factors that affect the 

 annual yield. 



Abimdance may be considered in terms of long- 

 period changes such as those brought about bj^ 

 the prosecution of the fishery or by gradual changes 

 in the environment, or in terms of the short-period 

 fluctuations traceable to variations from year to 

 year in the success of natural reproduction. Both 

 types of changes are reflected in fluctuations in the 

 annual catch. Many of the variations in annual 

 yield as recorded in table 1 are probably to a large 

 extent the result of relative strength or weakness 

 of year classes. Age determinations have shown, 

 for example, that the increases in production in 

 1928 and 1929 were not exclusively the result of 

 increased fishing intensity and the reduction of 

 the legal size for perch, but were furthered also by 

 the phenomenal richness of the 1926 year class. 



The fluctuations in abundance that arise from 

 variations in the strength of year classes must be 

 accepted by fishermen as part of the natural course 

 of events, since at present very little can be done 

 to increase the survival of young. The environ- 

 ment may be improved by such measures as the 

 control of poflution and erosion. The value of 

 such measures to the Lake Erie fisheries is open 

 to question, since it has been shown that no ex- 

 tensive areas of heavy pollution e.xist that would 

 be inimical to fish life (Wright and Tidd 19.33, 

 Fish 1929), and that turbidity is not a factor in 

 either the survival of the young or their subse- 

 quent growth in Lake Eric (Van Oosten 1948). 



In fact, the causes underlying annual variations 

 in the success of natural reproduction are little 

 understood. Although a knowledge of the fluc- 

 tuations that occur in the strength of year classes 

 may contribute to an understanding of changes in 

 the fishery, a knowledge of the general level of 

 abundance and of long-period trends in abundance 

 is more pertinent to the solution of administrative 

 problems than is information on short-period fluc- 

 tuations. 



The abundance of yellow perch in the early 

 period of the United States fishery (1885-99) must 

 have been at a relatively high level, since good 

 production was maintained in spite of low fishing 

 intensity and inefficient methods. On the other 

 hand, the reduced yields of the 1900-1927 period — 

 one of expanding fishing intensity and increasing 

 efficiency in fishing methods — indicate a sharp 

 reduction in the general level of abimdance. The 

 greatly increased production in 1928-35 must be 

 considered the result, in part at least, of the 

 increase in intensity of the fishery for perch that 

 followed the collapse of the cisco fishery. The 

 known abundance in 1928 and 1929 of perch of the 

 big 1926 year class and the virtual removal of the 

 size limit in Ohio in 1934 undoubtedly contributed 

 to the large yields in those years. It seems 

 unlikely, however, that a production of over 14 

 million pounds could have been reached in 1934, 

 even without a size limit, unless the population 

 had reached an enormous size that year. Like- 

 wise, the yields of more than 9 million pounds in 

 1931, 1932, and 1935 indicate tremendous abund- 

 ance. Evidence will be presented later (p. 245) 

 which shows that normally the perch of a year 

 class dominate the fall fishery in their third year 

 and the spring fishery in their fourth year of life. 

 Thus, two year classes of perch make up the bulk 

 of the commercial catch each calendar year. On 

 the basis of that evidence, it may be assumed that 

 the year classes of 1928 to 1932 or 1933, inclusive, 

 were of exceptional strength to have been able to 

 produce the high yields during the period 1931-35. 



The statistics (table 1) suggest strongly that the 

 abundance of yellow perch was reduced greatly 

 during the years 1936-47. The fishing intensity 

 may have decreased in United States waters when 

 some of the operators quit business, but it is 

 known also that some new outfits started opera- 

 tions during this period. Increase in size of the 

 mesh in the Ohio trap nets probably did not 



