. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 40 CALIFORNIA PISH AND GAME. These results when considered as yearly averages would be indicative of the yearly fluctuations in abundance, or at least the availability to the fishermen of the species studied, if no changes in economic, weather or biological conditions had taken place during the time included in the boat catch study. However, some change, such as adverse weather for the best catches, or a great demand for another fish,
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 40 CALIFORNIA PISH AND GAME. These results when considered as yearly averages would be indicative of the yearly fluctuations in abundance, or at least the availability to the fishermen of the species studied, if no changes in economic, weather or biological conditions had taken place during the time included in the boat catch study. However, some change, such as adverse weather for the best catches, or a great demand for another fish, taken perhaps with the same gear as the one studied, may have caused the fishermen to make only small incidental catches of the one in question, and fluctuations would result in the average boat catch so that it is not an absolutely accurate measure of the abundance or availability of the fish to the fishermen. Also the appearance of the offspring of an unusually successful spawning season in the commercial catch may cause a tempo- rary increase in abundance, which would not be especially significant if the study of abundance extended over a long period of time. Therefore, when the average daily catch per year has been computed, the problem of a person undertaking a boat catch analysis is by no means completed. All available data on economic, weather and. Fig. 22. Graph showing the average daily boat catch of shad of twenty boats fishing in the San Francisco bay district for the years 1920—1925, inclusive. biological conditions that may affect the fishery should be carefully analyzed and applied to the boat catch analysis results, before the final result is said to be indicative of the state of abundance or availability of the fish in question. When there is added to this the fact that different fisheries may require different statistical methods of deriving the boat catch averages, it can at once be seen that a boat catch analysis is not a simple problem. The solid line in
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