FISHERY BULLETIN: VOL. 74, NO. 3 



Fishing at 2200 h at each site failed to yield any 

 stickleback, presumably because of inefficient 

 operations under conditions of total darkness. As a 

 consequence further sampling was suspended 

 until 0630 h 2 October. Fishing during the July 

 series began at 0700 h and was repeated at 1000, 

 1300, 1600, 1900, 2200, 0100, and 0400 h. Gear 

 problems precluded fishing at site B at 1900 h. 

 During each series, the time interval between 

 fishing at the two sites at any time of day was 

 approximately 15 min and for practical purposes 

 can be considered concurrent. 



The target sample size for each site and time of 

 day was 25 fish. Except for sampling times already 

 indicated, this number was achieved or closely 

 approximated. The smallest sample contained 12 

 fish (site B, 1900 h). All fish in the sample were 

 processed in accordance with methods described 

 earlier and 10 fish, selected at random, were 

 examined for stomach contents. A total of 226 

 stickleback were examined for the October series, 

 334 for the July series. The sizes of stickleback by 

 sample are illustrated in Figure 3. 



Mean feeding intensity indices (food weight/ 



body weight X 100) for paired samples were 

 similar, and data for each series were pooled by 

 time of day. 



Daily Ration and Maximum Meal Size 



In this study, daily ration is defined as the 

 weight of food consumed over a 24-h period ex- 

 pressed as a percent of body weight. Daily rations 

 were estimated from the diel feeding rhythm 

 curve, using a modification of the method 

 developed by Keast and Welsh (1968). Essentially, 

 diff'erences between maximal and minimal feed- 

 ing indices during successive periods over a 24-h 

 cycle were determined and these values and the 

 residual content were summed. The method is 

 most applicable to species which completely empty 

 their stomachs between meals. 



Maximum individual meal size was determined 

 from regression analysis of stickleback taken 

 during the maximal feeding period in July and 

 which were judged to have "full" stomachs ac- 

 cording to the subjective "fullness" scale described 

 earlier. 



Table 5. -Seasonal chang-e in the diet of threespine stickleback in Great Central Lake. 1970. 



'% stomachs with item. 



^Mean no. items per stomach examined. 



Mtem = % of total bulk units. T = Trace 



< 1 organism or <1%. 



656 



