PROGRESS IN BIOLOGICAL INQUIRIES, 1931 453 



influence the catch of these small mackerel, and because of the diffi- 

 culties of getting a measure of abundance of young mackerel before 

 they are large enough to be caught commercially, the forecast was 

 limited to the sizes larger than blinks or tinkers. In the forecast it 

 was estimated that the abundance of mackerel would be such as to 

 produce a catch of 35,000,000 pounds exclusive of yearlings (pro- 

 vided the fishing was approximately as intensive as in the previous 

 year). Actually, the 1931 catch slightly exceeded 32,000,000 pounds, 

 exclusive of yearlings. Thus the forecast was within Y per cent 

 of the realization. There has not yet been opportunity to analyze the 

 statistics, but we are under the impression that the fleet was approxi- 

 mately the same size and as active as in the previous year. When it is 

 recalled that the catch of mackerel is sometimes subject to fluctua- 

 tions of the order of 50 or 100 per cent, the closeness of the prediction 

 may be appreciated. 



The satisfactory outcome of the 1931 prediction must not be re- 

 ceived as an indication that forecasting is established on a sound 

 basis ; on the contrary, there are elements in the behavior of various 

 contingents of mackerel which may easily prove disconcerting in 

 future predictions. For instance, the 1928 class of mackerel appears 

 to have had a much higher loss rate than the 1923 class at a similar 

 age. It remains to be determined whether this was due, in fact, to a 

 difference in death rate or to an artifact traceable to a more intensive 

 fishery at one time than the other. There is also the additional pos- 

 sibility that neither was the case, for the same effect might be pro- 

 duced by an intrinsic difference in the habits of the 2-year classes 

 which might render them susceptible to larger catches at one stage 

 of their life history than at another. A notable difference in the 

 areas frequented by these year classes strongly hints at this possi- 

 bility. Continued observations and more intensive analysis of the 

 data are in order. 



An equally serious weakness in the observations from the stand- 

 point of forecasting methods is the inability to get a measure of 

 abundance before a year class is first old enough to be an important 

 component of the commercial catch. This difficulty may be overcome 

 by discovering the cause of variations in the size of the year classes 

 so as to estimate the abundance independently of the commercial 

 fishery, and in advance of the earliest exploitation. To this end the 

 fisheries-research steamer. Albatross II, has periodically cruised the 

 spawning and nursery areas of the mackerel in order to collect data 

 as to the abundance of the eggs and young stages, and as to the 

 physical, chemical, and biological conditions in the environment 

 which might have an influence on the number surviving the hazards 

 of their early existence. While it is yet too early for conclusive re- 

 sults, differences in the abundance of late larval stages have been 

 discovered that may prove useful to indicate the numerical strength 

 of the year classes. Particularly noteworthy was the widespread 

 presence of late larvae in 1931, the significance of which will be 

 established when these mackerel become of commercial size in 1932 

 and 1933. 



The work on the spawning grounds should not only aid in arriv- 

 ing at more reliable forecasts but should also provide information 

 as to the conditions that control the production of successful year 



