FISHERY BULLETIN: VOL. 70, NO. 3 



related to the coefficient of conversion of food 

 (in terms of material). Certainly the upper 

 value of fc is limited to the total trace substance 

 intake "diluted" by the new grov^rth and hence, 



^''^ l^f 



(17)* 



This argues that a creature with a low coefficient 

 of conversion for food can show high concentra- 

 tions of trace elements or pollutants for this 

 reason alone. 



Such lower coefficients of conversion and high 

 concentration of trace elements may result from 

 definitive growth, sickness or abnormality or, as 

 probably in the case of the mullet, when food is 

 converted into a more energetic form. Conclu- 

 sions as to cause and effect of pollutant trace ele- 

 ment concentrations in creatures with abnormal- 

 ities must thus be considered with caution. 



eral, and hence into the existing or potential 

 distribution of pollutants. 



ADDENDUM 



Several reviewers of this paper have suggest- 

 ed that I expand the treatment of trophic types 

 in an unstructured food web. Dominance of any 

 highly complex trophic types is incompatible 

 with an unstructured food web hypothesis. 

 However, the following may be considered com- 

 patible (from equations 4, 6, or 7 as appropri- 

 ate) : 



Strict herbivores 



(19) 



CONCLUSIONS 



The assumption and analysis of an unstruc- 

 tured food web is reasonably consistent with 

 findings on the concentration of the element 

 cesium (in respect to potassium) in the Gulf of 

 California. It suggests that unstructured ma- 

 rine food webs may be common and that the dis- 

 tribution of natural trace elements, such as 

 cesium, may give insight into food webs in gen- 



* This can be derived more formally as follows : let Cf 

 be the concentration in the food; then 



9/ 



where q^ is quantity of the substance and q^ is total 

 quantity of food material. 



Then the concentration in the organism. 



since 



/c = 



C„ = 



Co 



QcK 



\c 



K, 



WTi-^'^^i 





, and 



Kic ]^ 1 , then 



/c}> 



^ 



Omnivores 



Kt 



M. = Mo i_(^;^^3) (20) 



Particle feeders 



(detritus + phytoplankton) 



* = ^»T^Hfc^^ <21) 



Detrital feeders 



Ma - Mo 



1 — (^1 + Ks) 



Strict predators 



/Ti^ 



Non-herbivorous omnivores 



M„ = Mo 



1— {Ki + Ks) 



(14) 



Feeders on the detrital 



milieu (detritus and detrital feeders) 



M... = M. ff -,]/. X ^f^ (22) 



^- = ^» T^TTTrrrKT ^^s) 



(10) 



'' Equation 20 could well have been employed instead of eauation (10) 

 in the previous treatment. Differences in results would be small, however. 



1058 



