284 DISCOVERY REPORTS 



by direct biological comparison alone. Peculiar economic and even political considerations — in fact, 

 the bionomics of the prospective human producers and consumers — play at least an equal part in 

 the determination of industrial possibilities. At the same time, some knowledge of the natural history 

 of the Patagonian species is obviously a basic necessity in any attempt to deal with the problem. 

 Our data are therefore considered here from the biological point of view, while suggestions as to com- 

 mercial prospects are deferred to a later section of this report where the summarized weight data 

 allow one to take into account the possible value of other less important species. 



Table lo. Figures illustrating the size and relative values of the principal 

 fisheries for Merluccius spp. 



THE SIZES OF PATAGONIAN AND EUROPEAN HAKE COMPARED 



First, it is desirable to establish the sizes of the hake we captured and to see how they compare with 

 the sizes of better-known species captured with similar gear. 



If it were possible to obtain ' ideal samples ' of a slow-growing fish like hake, whose length increases 

 almost as a Imear function of age, the length frequencies, when plotted graphically, would approximate 

 to the Ix curve of a life table (a curve like a left-handed ogive, but with the curvature reversed and 

 enormously produced at the very beginning, because of the high infant mortality rate). An imaginary 

 curve of this nature is shown by the solid Ime in Fig. 19. It would begin with astronomical numbers 

 of newly-hatched larvae, and end with the largest hake caught. Departures from this curve would, in 

 part, be due to slight changes in growth rate. Such fish grow rather faster than usual early in life and 

 slower near the end of their lives. The straight line of the age-length relationship becomes slightly 

 bent at the ends, approaching a parabola. 



But the ideal length-frequency distribution would show other more important deviations about the 

 smoothed curve if considered with small class intervals (say i-ocm.): there would be modes or 

 shoulders whose magnitude would reflect the difl^erential survival of hake hatched in successive years 

 the resultant of all the environmental factors, animate and inanimate, that influenced their lives An 

 imaginary distribution of this type is shown by the pecked line in Fig. 19. Hake have a prolonged 

 spawning season, and the changing environmental conditions would not have favoured early- and late- 

 hatched fry equally in successive years. This would be a further source of variation in the modes or 

 shoulders in our imaginary curve, for it is their dispersion that helps in age determination, and this 

 even more than their magnitude, may thus be distorted. In actual hake samples this factor so com- 

 plicates the length-frequency distribution that Pettersen's method of age determination is rendered 

 unsatisfactory except for the younger (smaller) fish. 



