COD EGGS IN MASSACHUSETTS BAY, 1924-1925 



287 



and Finmark and, although admitting that currents are important as transporting 

 agents, believes that the greatest attention should be paid to the wastage caused by 

 other animals. Bigelow (1926) has also called attention to the importance of enemies 

 in limiting the numbers of fish. In 1925 Tima formosa, a large hydromedusa, was 

 everywhere abundant during the height of the cod season at Plymouth, and many 

 of the specimens taken contained one or more young fishes of various species. One 

 was taken with six postlarval herring entangled by its manubrium. As these fish 

 were 40 millimeters in length and capable of rapid movement, the helpless larvae of 

 such species as the cod must fall an easy prey and be destroyed in large numbers. 

 Beroe cucumis, another arch enemy of young fish, also was abundant. There can be 

 little doubt that enemies of this type could destroy large quantities of fish fry; but 

 here, again, contradictory evidence is encountered, for larvas of pollock were at times 

 rather numerous, even about Plymouth, although this species spawns in very limited 

 numbers in the inner parts of the bay. Were enemies the controlling factor, larval 

 cod could hardly be completely destroyed at all times while specimens of such a 

 closely related species survive in abundance. The following is a record of pollock 

 larvse taken on the Plymouth grounds on trip 1. 



Other species of larval fishes, particularly sand eels, also were abundant at times. 

 On trips 5 to 12 sand eels swarmed along the inner arm of Massachusetts Bay. At 

 station 22 (trip 9) 375 appeared in a single haul. The distribution of this species is 

 not exactly comparable to that of the cod and pollock, because, having demersal eggs, 

 the young hatch and enter the surface waters in precisely the same spot where the 

 eggs were deposited; but it is mentioned to show another species, the young of which 

 escapes annihilation by enemies. 



5. Drift. — The evidence of drift is overwhelming. In several other localities 

 investigators have found that ocean currents play an important part in the dis- 

 tribution of cod eggs. Schmidt (1909) studied the drift of eggs about Iceland; 

 Hjort (1914) and Damas (1909) reported similar migrations off Norway, and Petersen 

 (1892) in Danish waters. Dannevig (1919) found that cod eggs disappear with 

 greatest rapidity in the outer waters off Lofoten and Finmarken. An interesting 

 account of the movements of eggs in English waters also has been published by 

 Graham (1925). 



In Massachusetts Bay both the drift bottles and the charts on egg distribution 

 show very well the general movement of the circulatory drift in the bay. 



Special attention was devoted to the incubation period of cod eggs as affected 

 by fluctuating water temperature and the consequent variations in the interval 

 during which they would drift before hatching. These data were then applied with 

 the rates, as indicated by bottle drifts, to determine the probable distance that eggs 

 leaving Massachusetts Bay would be carried before hatching. 



Station 



8„ 

 9_. 

 10 

 11. 

 12 

 17. 



Pollock 

 larvae 



35 



29 



68 



42 



2 



5 



