14 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



of a dominant year-class of striped bass is in no way dependent on the presence of a 

 great number of mature individuals. It is thus necessary to look to other factors 

 for the explanation of this phenomenon. Russell (1932) has pointed out that especially 

 large dominant year-classes were produced in the North Sea in 1904 simultaneously 

 by three different species — herring (Clupea harengus), cod (Gadus morhua 6 ), and 

 haddock (Melanogrammus aeglefinus) . It would seem from this evidence that environ- 

 mental factors apparently play some part in producing these exceptional year-classes. 

 Russell (loc. cit.) has also mentioned the fact that "... there is no necessary con- 

 nection between the number of eggs produced in a particular spawning season and the 

 amount of fry which survives," and it is apparent that environmental factors are most 

 effective in determining the percentage of survival. This is probably especially true 

 in a species with pelagic eggs, a category to which the striped bass essentially belongs 

 (see p. 18). Since the striped bass is anadromous, anything that might affect the 

 rivers in which this species spawns, and the areas in which the eggs hatch and the 

 larvae develop, is worthy of consideration. Unfortunately, the only records that are 

 available are meteorological. Attempts have been made to correlate both tempera- 

 ture and precipitation, since either is capable of seriously influencing the regions where 

 spawning and early development take place, with the prominent peaks shown in the 

 catch records in figure 4. Such a correlation necessarily assumes that the peaks at 

 1894 and 1895, 1906, and 1922, represent dominant year-classes, and, as has already 

 been mentioned, it is impossible to test the validity of such an assumption. It also 

 takes for granted that these dominant year-classes were produced 2 years before, since 

 striped bass first make their appearance in the commercial catch as 2-year-olds. In 

 the case of the peak at 1936, it is definitely known tbat a dominant year-class was 

 present, and it is further known that the fish that produced this peak were born 2 years 

 before in 1934. Figure 9 shows the deviations from the mean temperature from 1880 

 to 1935 at Washington, D. C, for February, March, April, and May. Washington 



DEVIATIONS FROM THE MEAN TEMPERATURES FOR 

 FEB. MARCH. APRIL, AND MAY. IB80-I935. AT WASHINGTON. DC. 



Figure 9-The deviations from the mean temperature for February, March, April, and May, 1880-1935, at Washington. D. C. 

 The black columns on the base line indicate the years when exceptionally good catches of striped bass were made, and the arrows 

 connect them with the temperatures 2 years before, when in all probability, dominant year-classes were produced. 



D. C, was chosen because it is in the general latitude of the majority of the important 

 spawning areas for striped bass. The 4 months from February to May were chosen 

 because May is the main spawning season (see below), and because temperatures over 

 this period may well affect the river temperatures as late as May and thereafter. It 

 will be seen from figure 9 that the peak years in the catch record in figure 4 invariably 

 correspond with a below-the-mean temperature 2 years before. It seems likely, there- 

 fore, that dominant year-classes in the striped bass are produced only on a subnormal 

 temperature. On the other hand, a low temperature during the late winter and sprmg 

 months does not necessarily cause the production of a dominant year-class. There are 

 undoubtedly other factors which must concatenate with a subnormal temperature to 

 bring about such a production. It is impossible to state what these factors are, 

 but examination of the precipitation records shows that there is no correlation between 

 rainfall and the dates 2 years before the peaks at 1884 and 1885, 1906, and 1922 shown 

 in figure 4. The inverse correlation between temperature and this catch record, how- 

 ever^ is good. The coefficient of correlation for the entire catch record (1884-1937) 

 and the temperature over this whole period is —.354, which is significant to the 1- 

 percent level. It is thus highly probable that the production of dominant year-classes 

 in the striped bass is quite closely associated with low temperatures. 



6 The spelling "morhua," instead of "morrhua" as used by most recent authors, is in keeping with Schultz and Welander (1935) . 



