r,j,,r 8— WVefr?!/ weiphls and food-level means for each ta,ik dunnq period of exploit 

 ',«!.■ Ze obtained hy sublLlin, ^eei,hts removed (table 9) ; expo,,aUon rales are 

 las started week ^9 for 1.0 d,et, week JO for 0.5 diet and week .A for l.o diet 



alion; postremoval weights for removal 

 indicated in parentheses. Exploitation 



0.5 diet 



1.0 diet 



1.5 diet 



Week No. 



TankB 

 (0.25) 



Tank F 

 (0.33) 



TankH 

 (0.50) 



Tank 

 mean 



Tank A 

 (0.25) 



29.. 

 30.. 

 31.. 

 32.. 

 33.. 

 34.. 

 35.. 

 36.. 

 37.. 



39- 



40..- 



41... 



42... 



43.. 



44... 



45.. 



46.- 



47... 



48... 



49... 



60... 



61... 



62... 



63... 



54... 



56... 



66... 



67... 



58... 



59- 



60.. 



61.- 



62.. 



63 . 



64.- 



66.. 



66.. 



67.- 



68..- 



70.. 

 71.. 

 72.. 



G. 



14.2 



14.6 



11.5 



11.9 



12.1 



9.6 



10.3 



10.9 



8.7 



9.4 



9.7 



7.8 



8.7 



10.2 



8.6 



8.6 



10.1 



9.1 



9.8 



10.1 



7.6 



8.5 



9.3 



8.4 



9.0 



9.7 



7.9 



8.5 



9.4 



8.6 



10.3 



10.8 



9.2 



9.5 



10.3 



8.8 



9.6 



10.3 



8.2 



8.8 



■ Aberrant datum discarded. 



a. 



15.3 



15.5 



10.1 



11.3 



12.0 



8.3 



9.0 



9.4 



8.1 



7.9 



8.6 



7.0 



7.8 



8.6 



7.1 



8.2 



9.3 



8.2 



9.3 



9.1 



7.3 



8.1 



9.3 



6.9 



7.9 



8.8 



6.9 



7.5 



8.4 



6.9 



7.9 



8.1 



6.6 



7.2 



7.9 



6.4 



7.6 



8.0 



6.0 



6.2 



7.0 



6.6 



6.6 



6.9 



a. 



17.5 



14.7 



8.2 



8.9 



9.4 



5.9 



6.8 



7.3 



4.9 



6.1 



6.1 



4.5 



6.5 



6.8 



7.2 



6.5 



7.2 



6.1 



6.6 



7.1 



4.2 



6.3 



5.6 



3.7 



4.6 



.5.7 



4.3 



4.4 



5.9 



3.6 



4.7 



6.6 



3.6 



4.4 



4.3 



2.9 



3.8 



4.6 



2.6 



3.2 



3.8 



2.5 



4.0 



4.6 



a. 



16.7 

 14.9 



9.9 

 10.7 

 11.2 



7.9 



7.5 



8.1 



6.4 



7.3 



8.5 



7.6 



7.8 



8.9 



7.8 



8.6 



8.8 



6.4 



7.3 



8.1 



6.3 



7.2 



8.1 



6.4 



6.8 



7.9 



6.4 



7.6 



8.2 



6.4 



7.0 



7.6 



6.0 



7.0 



7.6 



6.6 



6.1 



6.5 



5.3 



6.3 



7.1 



and 1.5 diet levels, respectively. Amounts of food 

 consumed at these levels were 8.55, 17.10, and 

 25.65 g. per 3 weel.s (sum of weekly totals for 

 Daphnia and dry ood plus 6 [0.000125 X diet 

 ratio] for Artemin, all multiplied by 3, table 1); 

 thus, conversior efficiencies were 0.28, 0.23, and 

 0.23. Again, the small difference at the 0.5 diet 

 level ])robably is not significant. For practical 

 purposes the conversions at all three diet levels 

 are identical and are close to the 0.20 reported by 

 Silfiman and Outsell (195S). 



I conclude that efficiency of food conversion, as 

 well as relation between exploitation rate and 

 yield, is independent of amount of food a\ailat)le 

 "for the laboratory populations within the range of 

 observation. Management strategies for commer- 

 cially fished i^opulations that behave in this man- 

 ner "can be apjilied with the e.xpectation of the 

 same conversion efficiency regardless of the abun- 

 (hmce of available food organisms. 



This finding seems to be contrary to that re- 



c. 



26.1 



19.9 



21.0 



22.0 



16.6 



17.2 



17.6 



14.0 



15.3 



16.8 



12.8 



14.2 



16.0 



13.8 



16.3 



16.5 



12.9 



13.6 



16.0 



11.6 



12.5 



14.0 



13.3 



14.0 



15.8 



12.2 



13.2 



16.2 



12.2 



13.1 



14.9 



13.1 



14.7 



15.8 



12.1 



13.5 



14.5 



11.6 



13.0 



13.7 



11.6 



12.5 



13.1 



11.6 



Tank D Tank G 

 (0.50) (0.33) 



a. 



28.4 



20.2 



21.5 



22.6 



16.6 



18.0 



19.2 



14.8 



16.0 



17.0 



13.2 



14.7 



16.7 



14.5 



15.2 



16.8 



12.2 



13.7 



14.3 



9.8 



11.2 



13.0 



10.3 



11.5 



12.8 



11.1 



12.9 



13.6 



11.3 



12. n 



14.3 



10.6 



11.7 



12.1 



9.6 



10.7 



11.2 



8.6 



10.0 



10.9 



8.2 



Tank 

 mean 



Tank C Tank E 

 (0.60) (0.26) 



Tank I 

 (0.33) 



Tank 

 mean 



r,. 



26.8 



14.9 



16.9 



17.4 



10.1 



11.7 



13.2 



9.0 



10.1 



11.3 



9.2 



11.0 



12.6 



10.6 



12.6 



13.8 



8.6 



9.6 



11.6 



8.3 



9.0 



10.7 



6.8 



8.0 



9.2 



4.8 



6.9 



6.6 



5.0 



6.4 



7. 7 



6.5 



7.6 



8.5 



5.6 



6.7 



8.2 



5.7 



6.4 



6.0 



4.3 



4.9 



5.3 



3.1 



10.4 



G. 



27.1 



18.3 



19.8 



20.7 



14.1 



16.6 



16.7 



12.6 



13.8 



14.7 



11.7 



13.3 



16.1 



12.9 



14.3 



15.7 



11.2 



12.3 



13.6 



9.9 



in. 9 



12.6 



10.1 



11.2 



12.6 



9.4 



10.7 



11.8 



9.6 



10.6 



12.3 



10.1 



11.3 



12.1 



9.1 



10.3 



11.3 



10.2 

 8.0 

 8.7 

 9.6 

 8.0 



G. 



45.2 



42.2 



(>) 



42. 2 



43.7 



46.7 



23.6 



26.8 



30.0 



14.3 



16.3 



17.2 



12.6 



16.7 



9.5 



7.6 



9.6 



12.2 



14.2 



14.6 



16.2 



12. 2 



11.3 



12. 6 



8.6 



10.2 



12.3 



7.5 



9.6 



11.3 



8.4 



10.9 



12.6 



8.2 



10.6 



12.3 



8.6 



8.4 



9.6 



6.6 



6.6 



8.0 



6.9 



6.4 



G. 



37.6 



38.1 



41.0 



39.6 



40.8 



42.7 



30.8 



19.8 



20.5 



21.6 



23.4 



25. 4 



26.0 



28.3 



30.4 



17.1 



18.5 



19.8 



14.1 



14.6 



15.7 



16.9 



19.0 



21.3 



17.7 



19.6 



22.3 



13.6 



16.0 



16.1 



18.0 



20.0 



21.6 



17.5 



18.3 



19.5 



15.6 



17.3 



18.2 



14.8 



16.0 



18.3 



14.6 



15.7 



G. 



35.9 



37.4 



37.6 . 



39.0 



38.6 



39,1 



27.7 



28.4 



30.6 



21.9 



23.4 



25.4 



19.0 



21.3 



22.4 



18.7 



20.2 



21.3 



15.0 



16.1 



18.2 



16.6 



19.5 



21.5 



17.1 



19.6 



21.6 



17.3 



20.6 



22.0 



16.6 



18.9 



20.7 



16.3 



16.6 



20.1 



14.7 



16.6 



18.0 



13.6 



14.6 



16.7 



12.6 



13.6 



n. 



39.5 

 39.2 



40.2 



41.0 



42. 6 



27.4 



24.7 



27.0 



19.2 



21.0 



22.7 



19.2 



21.8 



20.8 



14.4 



16.1 



17.8 



14.4 



15.1 



16.7 



16.2 



16.6 



18.4 



14.4 



16.5 



18.7 



12.8 



15.4 



16.6 



14.3 



16.6 



18.3 



14.0 



15.2 



17.3 



13.0 



14.1 



15.2 



11.3 



12.4 



14.0 



11-0 



11-9 



ported under "Initial Growth of Populations." It 

 is noteworthy, however, that the lesser efficiency 

 at the two higher diet levels, mentioned there, 

 occurred when the populations were stabihzed at 

 near asymptotic levels. Composition of sucli 

 stabihzed populations is difterent from that ol 

 exploited populations, and the growth reactions 

 could well be iliffei-ent also. 



The relation of food conversion efficiency to 

 average size of individual fish can be examined by 

 comparing the average weights with the food con- 

 versions for eac.li of the nine populations during 

 the exploitation i)eriod (weeks 59-72, data from 

 tables 10 and 6, plus food amounts quoted above), 

 L. M. Dickie (personal communication) has 

 pointed out t(. me that if conversion efficiency be 

 plotted as a regression on average body weight, 

 there is a significant negative correlation (line is 

 E = 0.317 — 0.667W, where E is conversion effi- 

 ciency as above, W is average body weight, and 

 ,.=,_"0.90 and P<0.01). This determinatiim sup- 



FOOD LEVEL .\XD EXPLOITATION IN FISH POPULATIONS 



437 



