Table 9. — Weights removed (yields) for each diet and exploitation rate; exploitation rates are indicated in parentheses 



Week No. 



0.5 diet 



1.0 diet 



1.6 diet 



Tank B Tank F TankH Tank Tank A Tank G Tank D Tank Tank E Tank I Tank C Tank 

 (0.25) (0.33) (0.50) mean (0.26) (0.33) (0.50) mew (0.25) (0.33) (0.50) mean 



29-..- 



30 



SI- 

 S'.'.- 



33 



34 



35- 



36- 



37. 



3R 



3!!.. 



411 



41.. 



41'-- 



43. 



44-- 



45-. 



46 



47 



48-- 



49.- 



50.. 



51.- 



52-. 



63- 



54-- 



55-- 

 56.. 



57.- 

 58-- 

 59- 

 60-. 

 61.- 

 62.- 



63 



64.. 



65 



66 



67 



68 



69 



70 



71 



72 



Mean 

 29-43.. 

 44-58.. 

 59-72.. 



3.6 



2.9 



.'.3 



2.1 



"2.3 



" i.'9 



"3.4 



" i.'e 



"'2.'4 



"i.'T 



"2.'2 

 '2.3 



'2.'7 

 " f.'g 



' 2.4 



2.6 

 2.2 

 2.3 



4.9 

 "4.'2 



2.6 

 "2V7 



"zo 



"2.8 



"Hi 



"2.7 



"2.6 



"i'i 

 ' '2.2 

 '3.3 

 ' 2.0 



1V5 



3.5 

 2.7 

 2.2 



7.0 

 '4.5 

 "Tb 



'3.2 

 "2V9 



"2A 

 3.8 



"s.i 



"3.0 



"3.6 



" '2.8 



"1.9 



"i"? 

 "i.'i 



"i'.2 



4.2 

 3.1 

 2 '' 



o. 



"i.2 



'3.9 



'2.9 



"i'e 

 '"2.6 

 '2.1 

 "i'.i 

 ' ' i'.i 



c. 7 

 7.3 



'"5.'2 

 3.4 

 3^2 



"5. 5 

 4. 1 



2.4 



'2.4 



" '2V1 



2. 9 



"i.'i 



2.6 



2.3 

 3.3 

 4.9 

 '3.6 

 "4.4 

 4.6 

 "i.\ 



a, 

 9.3 



6. 9 



'"5.8 



' ' '6. '2 

 4.4 



■ ■ 6.2 



11.1 



' ' '4. 



3. 2 



" 3.6 



"4.8 



4. 4 



4.2 



3.6 



■ 2.4 



(I. G. a. 

 14.1 10.0 



a. 



8.5 



" 5.'6 

 3.6 



"3.0 

 7.4 

 4. 6 

 5. 6 



' 5. 6 



3. i 

 ■"2.9 



4.3 

 3. 

 2.'i 

 '2.7 



7.6 



"i'.h 



"i.'i 

 ' 3.5 



"6.4 

 ' '4. 9 

 ' 4.0 

 " "4.0 



3.9 



3. 8 

 4.4 

 3.7 

 3.3 

 2.6 



12.8 



" I'.O 



"' "'.0 



" 7! 4 



"1.3 



' 6.0 

 '10.0 



1.8 



5.2 

 4.0 

 3.7 



6.3 

 4.6 

 3.9 



6.9 

 5.2 

 3.0 



6.2 

 5.8 

 5.0 



4.8 



10.1 

 4.9 

 6.4 



14.2 



"i'.'s 

 "s'.'s 



"6.S 



's.'i 



"3.7 

 "I'.'l 

 6.9 

 ' 7.'i 

 6^1 

 '6.5 



's.i 



'i.2 



9.7 

 6.4 

 5.9 



22.2 

 "i4.'2 

 "¥.3 



•■S.i 

 3.5 



16.4 

 7.9 



'5.'2 



8.7 



V.'o 5.0 



'6.4 3.8 



5^6 6.2 



6.'6 7.3 



5.6 4.3 



ae 6.3 



5.'S ' 5.9 

 4.'5 ,5.1 



2.'7 4.2 



13.9 

 5.8 

 4.8 



'-^ Footnotes on Table 7. 



T.\Bi,E 10. — Average biomass and yield per lank per .3 iveeks 

 for preexploilalion asymptotic levels, and for levels during 

 weeks 59 to 72. Exploitation rates are fractions removed 

 per 3-week brood interval 



counterpart of the "K-curve" which PaloliciiiK 

 nnd Dickie clevelo])ed for iiidi\i(hial fish 



(K,= 



AW 

 'RAt 



= e 



■ Taken as average of tlie weights for tlie three populations during the 3 

 weeks immediately preceding exploitation. Weeks were as follows: 0.5 diet. 

 28-30; 1.0 diet, 27-29: 1.5 diet, 32-34. Data from tables 5 and 8. 



2 Data from table 8. 



2 Data from table 9. 



polls ilie contention (Paloheimo and Dickie, 1965) 

 iliat . . . "within a hfe-liistory stanza a given 

 fcHid ubundance leads to a higher production of 

 rephiceable fi.sh flesli if the ])roducing population 

 consists of the smaller more efficient fish than if it 

 consists of the larger fisli." He further |)ointe(l out 

 that this regression line might he tlie iiopulation 



438 



where W is body weight, R is rations, and a and 

 i) are empirical constants). 



The fact that the "K-curve" is an exponential 

 relation, wiiereas the gup])y relation is linear, may 

 stem from llie wide range of sizes of individual 

 fish in the gujipy populations (about 10 40 mm. 

 in lengtli). It may also result from 1 he chief me I hod 

 of ])opulation control among guppioscannibalism. 

 This beha\ior causes the food of the larger (isii to 

 pass through two or more trophic levels, with a 

 consecjuent lowering of comersion efliciency. 

 ()l)\iously, such an effect would be the more 

 pronounced the larger the average size of indi- 

 vidual fish in the population, as long as smaller 

 fish are present for prey, as was true for all popula- 

 tions during the e.\])loitalion jieriod. 



U.S. FISH .AND WILDLIFE SERVICE 



