SILLIMAN: EXPERIMENTAL EXPLOITATION OF FISH POPULATIONS 



Table 3. -Mean temperatures, °C, 3-wk periods, competing 

 populations. Daily readings (21) to period 70, Sunday to Friday 

 (18) from period' 72 on. 



Competing populations 



Tank 



Tank 



Period 



38 

 39 

 40 

 41 

 42 

 43 

 44 

 45 

 46 

 47 

 48 

 49 

 50 

 51 

 52 

 53 

 54 

 55 

 56 

 57 

 58 

 59 

 60 

 61 

 62 

 63 

 64 

 65 

 66 

 67 

 68 

 69 

 70 

 71 

 72 

 73 

 74 

 75 



23.6 

 23.8 

 23.9 

 23.5 

 23.3 

 24.1 

 24.5 

 24.1 

 24.9 

 24.9 

 24.3 

 24.8 

 24.1 

 24.1 

 23.7 

 23.7 

 23.5 

 23.4 

 23.7 

 23.9 

 23.6 

 23.5 

 23.2 

 24.3 

 24.5 

 24.9 

 24.7 

 23.8 

 23.9 

 24.4 

 21.5 

 24.0 

 24.0 

 '23.9 

 23.7 

 23.8 

 23.9 

 23.9 



23.9 

 24.2 

 24.4 

 23.8 

 23.5 

 24.4 

 24.7 

 24.7 

 25.2 

 25.1 

 23.5 

 24.9 

 24.3 

 24.4 

 23.9 

 23.8 

 23.6 

 23.9 

 23.9 

 23.8 

 23.6 

 23.7 

 23.5 

 24.5 

 24.5 

 24.9 

 24.9 

 23.8 

 23.8 

 24.3 

 21.4 

 24.0 

 23.8 

 '23.8 

 23.4 

 23.5 

 23.5 

 23.5 



'One Friday and two Saturday readings missing, period 71. 

 ^Based on 1 wk only. 



Table 4. -Mean temperatures, °C, 3-wk periods, independent 

 populations. Sunday to Friday readings (18). 



BIdg. 

 heat failure 





"1 I I I I 1 1 1 1 1 1 T r 



10 20 30 40 50 60 70 



3-week periods 



Aquarium: 



'Last three readings missing. 



Figure 1. -Water temperatures (3-wk means). "S" indicates 

 summer periods (approximately 20 June to 20 September). 



Heaters were placed in tanks during periods 

 1-32 (Figure 1) but caused excessive temperature 

 fluctuation and one instance of mortality from a 

 nonfunctioning thermostat. During periods 33-174 

 the tank water was at room temperature. This was 

 thermostatically controlled except that no cooling 

 was available in the summer. Summer tempera- 

 tures were thus somewhat higher than during the 

 balance of the year (Figure 1), but the change was 

 the same for all tanks. 



Measurements of dissolved oxygen and carbon 

 dioxide concentrations and pH were made at 

 irregular intervals during the course of the 

 experiment (Table 5). All Og readings were within 

 or above the 3-5 ppm range considered satisfactory 

 for warmwater fishes by Lewis (1963), and the COg 

 and pH readings were within the range he con- 

 sidered safe (CO2<30 ppm., pH 5.0-9.0). 



Light was provided from overhead fluorescent 

 fixtures with standard tubes to period 11. After 

 period 11, pink tinted tubes were used. 



Handling, Enumeration, Exploitation, and 

 Weighing 



Areas behind the refuge fences described under 

 "Aquarium Tanks" were inspected daily. If any 

 newborn fish were found there or in other corners 

 of the tanks, they were removed by netting or 

 siphoning, counted, and placed in the nursery 



875 



