184 EIGHTH PACIFIC SCIENCE CONGRESS 



been determined to the satisfaction of all concerned (California Marine 

 Research Committee, in press). 



The Japanese data include only the landings made in the Japanese 

 islands; they do not include landings in continental Asia. In some 

 years the latter were as large or larger than the Japanese landings. In 

 addition, it is not certain that the data include all Japanese landings, 

 nor that they refer entirely to the sardine. Nevertheless, and on a big- 

 ger scale, the curve of annual catches in the Japanese fishery is remark- 

 ably similar to that of the North American fishery. The peak catch 

 was obtained in the same year, but the decline started about two years 

 earlier. In 1951 there was a partial recovery. 



The Portuguese data include only the landings made in Portugal. 

 Obviously this fishery has never attained the magnitude of the other 

 two. Properly, this curve should include the catches of Sardina pilchar- 

 dus landed in all European and North African countries, but these data 

 are not available to us at the moment. The Portuguese landings are 

 therefore used as an example of the northeastern Atlantic sardine catch- 

 es. There is a peak, although not a pronounced one, in the Portuguese 

 catches occurring at about the same time as in the other two fisheries. 

 There is a decline occurring slightly later than in the North American 

 fishery. We understand that more recent seasons have shown a recovery 

 of the Portuguese fishery, but have thus far been unable to secure exact 

 data. 



These same catch data are also shown in Figure 2, but here, for 

 each fishery, the catch in each year has been expressed as a percentage 

 of the largest annual catch made in that fishery during the period re- 

 ported. This shows the relative fluctuations in the three fisheries with- 

 out respect to their absolute magnitudes. The similarities already men- 

 tioned are even more strikingly shown in this figure, especially the rela- 

 tive magnitudes of the declines in catches and their close relation in 

 time, even though not simultaneous. 



It is often inferred that when the catch of a particular species be- 

 comes less, the absolute size of the population is also reduced. This 

 is not necessarily true and it should be remembered that the data just 

 presented refer only to catches. The relation of these catches to the 

 size of the populations from which they were drawn is not known. 



The reasons for a major decline in catch in any fishery must be 

 found among one or more of the following: (1) a decrease in the amount 

 of fishing effort expended per unit of time; (2) an increase in the 

 rate of natural mortality; (3) a decrease in the rate of recruitment 

 (i.e., a decrease in year-class size); or (4) a decrease in the availability 

 of the fish to the fishery, through a change in behavior or distribution. 



