has been criticized from a statistical point of 

 view because c/f and / are obviously correlated. 

 A measure of the magnitude of this correlation 

 is clearly implied by (3) or (4). 



Finally we should point out that our allusion 

 to considering these indices as expressing rela- 

 tion among organisms was not careless because 

 it seems to us that predator-prey relationships 

 might be further elucidated through examina- 

 tion of concentration indices. For example, it 

 would be interesting to relate the catch ( in num- 

 ber of prey organisms) per predator stomach to 

 the number of predator stomachs. This, how- 

 ever, is just a special case of the wealth of fish- 

 ery-fish interaction models which could be ap- 

 plied to the prey-predator situation. 



Acknowledgments 



We would like to thank D. G. Chapman, Di- 

 rector, Center for Quantitative Science, Univer- 

 sity of Washington, for reading this note and J. 

 Joseph of the Inter-American Tropical Tuna 

 Commission for stimulating our writing this 

 note. 



Literature Cited 



Calkins, T. P. 



1963. An examination of fluctuations in the "con- 

 centration index" of purse-seiners and baitboats 

 in the fishery for tropical tunas in the eastern 

 Pacific, 1951-1961. [In English and Spanish.] 

 Inter-Am. Trop. Tuna Comm., Bull. 8:255-316. 



Paloheimo, J. E., AND L. M. Dickie. 



1964. Abundance and fishing success. In J. A. 

 Gulland (editor), Contributions to symposium 

 1963, On the measurement of abundance of fish 

 stocks, p. 152-163. Cons. Perm. Int. Explor. Mer., 

 Rapp. P.-V. Reun. 160. 



Gulland, J. A. 



1955. Estimation of growth and mortality in com- 

 mercial fish populations. Fish. Invest. Minist. 

 Agric. Fish. (G. B.) Ser. II, 18(9), 46 p. 



B. J. Rothschild 



National Marine Fisheries Service 

 Northwest Fisheries Center 

 2725 Montlake Boulevard East 

 Seattle, WA 98102 



Biometrics Unit 

 Cornell University 

 Ithaca, NY 1U850 



D. S. ROBSON 



SUITABILITY OF INTERNAL TAGS 

 FOR ATLANTIC MENHADEN 



Investigations of the Atlantic menhaden re- 

 source depend primarily on sampling and anal- 

 yses of the commercial landings and studies of 

 menhaden biology and ecology. Results of these 

 studies give a broad understanding of the re- 

 source but sometimes lack the reliability of more 

 direct evidence. Tagging and recovery of men- 

 haden help provide the reliable information on 

 movements, population size, availability, mortal- 

 ity, and growth rates required to better under- 

 stand the resource. 



The methods by which menhaden are caught, 

 handled, and processed determine some of the 

 requirements for tagging. Menhaden are cap- 

 tured in purse seines and are transferred by 

 suction pumps from the nets to the vessels and 

 from the vessels to the reduction plants. In 

 the plant, the fish are cooked, pressed, dried, and 

 ground into meal. From the time the fish are 

 caught until they are processed into oil and meal, 

 there is little opportunity to handle or see an 

 individual menhaden. Consequently tags or 

 tagged fish must be recovered by mechanical or 

 electronic means. Internal ferromagnetic tags 

 that are mechanically or electronically recover- 

 able have been developed for Atlantic and Pacific 

 herring, Pacific sardine, and anchoveta. 



We conducted a series of experiments at Beau- 

 fort, N.C., to find a mark suitable for Atlantic 

 menhaden. In 1959 we tagged young menhaden 

 with a nickel-plated, steel tag, (Type A in Fig- 

 ure 1). The tagged menhaden died within a 

 week, terminating the experiment. During 1960 

 we attempted to mark menhaden with fluores- 

 cent pigments and to develop a photoelectric 

 detector. The occurrence of natural fluorescence 

 in menhaden and other marine organisms made 

 discrimination of marked fish impractical (Rein- 

 tjes, 1963). In 1961-62 we resumed tests with 

 internal tags to select a type suitable for men- 

 haden and to demonstrate its recovery with mag- 

 nets in a menhaden reduction plant. 



Tagging Experiments and Tag Selection 



We selected four ferromagnetic tags (Table 1 

 and Figure 1) for insertion in young Atlantic 



514 



