Longevity and Mortality Rates of Fish in Nature 177 



Taylor, C. C. (1958). J. Cons. int. Explor. Mer, 23, 366. 

 Templeman, W. (1948). Bull. Newf. Govn. Lab., 17. 

 Tester, A. L. (1937). J. biol. Bd Can., 3, 108. * 



Thompson, W. F., and Bell, F. H. (1934). Rep. int. Fish. Comm., 8. 

 Thompson, W. F., and Herrington, W. C. (1930). Rep. int. Fish. 



Comm., 2. 

 TiBBO, S. N. (1957). Bull. Fish. Res. Bd Can., Ill, 85. 

 TiEWS, K. (1957). Ber. Dtsch. Komm. Meeresforsch., 14, 192. 

 Tucker, D. W. (1959). Nature (Loud.), 183, 495. 

 Vaas, K. F. (1952). Proc. Indo-Pacif. Fish. Coun., 3, 119. 

 VivES, F., and Suau, P. (1956). Invest. Pesq., 5, 17. 

 VNIRO (1949). Ministry of Industrial Fisheries, Moscow. 

 Walford, L. a. (1946). Biol. Bull, Wood's Hole, 90, 141. 

 WoHLSCHLAG, D. E. (1954a). Ecology, 35, 388. • 

 WoHLSCHLAG, D. E. (19546). Stanf. ichthyol. Bull., 4, 189. 

 YoKOTA, T. (1951). Bull. Jap. Soc. sci. Fish., 16, 188. 



DISCUSSION 



Rotblat: Have you also plotted 1/jK" against T^jax? IjKhas the dimen- 

 sions of time and is proportional to the time it takes to grow to half 

 size. This may also be a linear function of the span of life. 



Beverton: No, we have not yet done that; so far we have examined 

 only the relationships between K and M and between Loo and T,^^. 



Rotblat: The combination of these two factors is of special interest 

 because you relate, then, time to time. This also agrees with what 

 Sacher said about low metabolic rate. 



BeveHon: In fish the natural mortality coefficient and the maxi- 

 mum age are closely correlated, because most of the logarithmic 

 survival curves tend to be rather straight. We do not have curves of 

 nearly the same slope which suddenly dip to very diff'erent maximum 

 ages. 



Danielli: These growth-rate limitations may be entirely due to 

 differences in natural conditions. Have you any data from fish 

 which have been exposed to toxic substances in the water ? 



Beverton : The only paper on exposure of fish to toxic substances 

 that I can recall offhand is on Gambusia (Geiser, S. W. (1924). Biol. 

 Bull. {Wood's Hole), 47, 175). There the investigation was to show 

 that males not only died off more quickly than the females after 

 reproduction but were also more susceptible to a range of toxic sub- 

 stances. In other words, their balance with the environment seemed 

 more precarious than that of the females, with respect to artificially 

 induced hazards as well as natural ones such as reproduction. On the 

 first point, growth is undoubtedly very flexible in fish. Nevertheless, 



