224 CoUcyc of Forestry 



examination of the digestive tracts of fish caught in trap nets, 

 examined after intervals of 24, 48, and yi hours indicate that 

 digestion is rather rapid in summer and that it is possible that 

 the stomach may be emptied in 24 hours and the intestine in 

 4<S hours. llie percentage of fish with emjity stomachs 

 increased rapidly with the time interval of emi)tying the net, 

 50 percent had full stomachs in the 24 hour interval, 12.9 

 ])ercent in the 48 hour interval, and all had empty stomachs 

 in the ^2 hour interval, lliis data is not conclusive but adds 

 weight to the belief that in the summer months the stomach 

 may be emptied in about 24 hours. It is estimated that the 

 invertebrate animals on the bottom of the 1,164 acres examined 

 would feed 407,425 fish for one year. 



It is important to consider some of the conclusions of the 

 investigators of marine life, and although the life of the sea 

 and of the inland waters are not strictly comparable, there is 

 yet much in the hnal analysis of the results that is common 

 to both. Johnstotie ('08, p. 178) wisely warns against inter- 

 preting the phrase " census of the sea " too literally. Census 

 figures that are based on some quantitative plankton investi- 

 gations and all commercial fishery statistics and lishing experi- 

 ments Johnstone criticizes as but very rough ai)proximations 

 to the truth. 1 hey have but relative value. With the methods 

 used by Petersen a census, however, becomes much more 

 accurate for sea areas and in the case of fresh-water areas 

 may be made fairly accurate, so as to give a true i)icture of 

 the life on the bottom, [)articularly in shallow waters. 



Johnstone ('08, p. i/t)) further says: " Ikit when we have 

 obtained these approximate figures for the population of the 

 sea it is not enough, for such populations are continually 

 changing. Organisms die and fall to the sea liottom and 

 decompose, or are devoured by their enemies or are captured 

 by man. Birth-rates in the sea vary with each kind- of 

 organism and change with the season, and the rates of growth 

 undergo corresjxMiding fluctuations. Death-rates, too, change 

 with the season, and with changes in the density (jf inimical 

 organisms. Not only must we attemi)t to estimate the density 

 of the population in the sea at a given time, but wc must also 



