Longevity and Mortality Rates of Fish in Nature 165 



values of ikf , and in several instances it has been necessary to 

 draw an arrow indicating the direction in which the true value 

 of M is thought to lie. However, when the remaining values 

 are superimposed on those for the four main groups (Fig. 7), 

 a rather more ordered picture is produced than that of Fig. 5. 

 Of the previously aberrant species, the Thunniformes now fall 



2-5 



20 



SALMONOIDEI 



PLEURONECTOIDEI 



175 



Fig. 7. Relation between natural mortality coefficient (M) and rate of curva- 

 ture of growth curve {K) in various species not included in Fig. 6 (from Table I). 

 The lines are those for the four groups shown in Fig. 6. 



into line, because although they grow to a relatively large size 

 they approach it rapidly, i.e. they have a high K, The same 

 is true for the Atlantic salmon (Salmo solar \ Nail, 1927) since 

 this also has a relatively high value of ^; so indeed have the 

 Pacific salmons {Oncorhynchus spp.), although the trend of 

 mortality with age is so abruptly discontinuous in these 

 species that a single value of M cannot be assigned to all of 

 them. 



