FISHERIES IN MICHIGAN WATERS OF GREEN BAY 



19 



FLUCTUATIONS IN ABUNDANCE OF 



THE PRINCIPAL SPECIES OF 



GREEN BAY, 1929-49 



The abundance, or availability, indices u of table 

 10 were derived from the records of catch per 

 unit of effort of tables 11 to 16 by methods de- 

 scribed in publications listed in the introduction of 

 this paper (Ilile, 1937, gave an example of the 

 actual computations). Information on the catch 

 per unit of effort is given for smelt in table 17, 

 but no attempt has been made to compute abun- 

 dance percentages for the species. The compara- 

 tively recent development of the smelt fishery and 

 the disruption occasioned by the 1943 mortality 



Table 10. — Abundance indices of six commercially im- 

 portant fish in Green Bay, 1929-49 



[Expressed as percentages of the 1929-43 mean] 



i Probably too high; see text, p. 22. 



11 In using the terms "abundance" and "availability" Inter- 

 changeably 111 references to our Indices we follow Hile, Eschmeyer, 

 and Lunger (1951a), rather than Marr (1951), when they stated : 



Arguments about which of the two words should be employed 

 would constitute a futile quibbling over terminology. These esti- 

 mates are based on the fishing experience of the fishermen — the 

 records of their catch of legal-sized lake trout per standard unit 

 of fishing effort. They offer no information on the abundance of 

 undersized lake trout and are affected by such factors as mete- 

 orological conditions, annual differences In the time of spawning 

 in relation to the fixed closed season, and annual differences in the 

 distribution of fish. Yet, for all these obvious weaknesses they 

 offer the best estlmutes of abundance to be had at the present time. 

 Accordingly, we do not hesitate to use "availability" and "abun- 

 dance" interchangeably. 



have prevented the establishment of satisfactory 

 norms. 



Table 11. — Catch, in pounds, of lake trout per unit of 

 effort in Green Bay, by gear, 1929-49 



' When data were lacking for one or more years the 15-year average was 

 estimated by dividing the mean of the available annual averages by the 

 mean of the abundance percentages for the same years. See Van Oosten, 

 Hile, and Jobes (1946) for comments on the estimation of a normal catch 

 when data are not available for all years. 



Table 12. — Catch, in pounds, of whiteflsh per unit of 

 effort in Green Bay, by gear, 1929-49 



i Became illegal during the 1935 season. 

 'Estimated. See footnote 1, table 11. 



