476 C. O'D. IsELiN 



a fairly constant rate, while the second is Hkely to be intermittent in character and to 

 be triggered off by the offshore currents. It is the intermittent large-scale losses of 

 coastal water that are probably the important events from the standpoint of a fisheries 

 biologist. If physical processes are an important factor in the widely fluctuating 

 annual recruitment of young fish, then it seems likely that major changes in the 

 environment must be involved. Presumably the fish, even very young ones, are able 

 to deal with the normal, small-scale mixing mechanisms. Thus we can ask the 

 question: from the standpoint of a fish, what constitutes a physical catastrophy? 

 The answer may be somewhat different for each species of fish. 



The two primary variables in coastal circulation are undoubtedly the river inflow 

 and the weather. The former supplies most of the energy, and the latter is important 

 both in maintaining the small-scale mixing processes and also in causing the mass 

 movements of considerable bodies of water, especially in winter. How great a varia- 

 tion from the normal can be produced by either factor? The larger eddying motions 

 of an intermittent character occurring near the edge of the continental shelf are a 

 third factor capable of producing considerable variations in the coastal environment. 

 South of New England the available evidence indicates that these are most likely 

 to take place along the southern edge of Georges Banks and off Chesapeake Bay. 

 In both cases the currents of the Gulf Stream System are relatively close to the 100 

 fathom curve. If it is true that the offshore currents can sometimes cause relatively 

 large eddies to form, and thus remove considerable masses of coastal water, then 

 these events are probably not unrelated to the variations in transport of the Gulf 

 Stream System. 



If the above summary of the problem is reasonably correct, a physical oceano- 

 grapher, in order to be of help to his friends concerned with fluctuations in the 

 fisheries, needs to find answers to the following questions. By how much does land 

 drainage have to change before the normal environment of coastal water is seriously 

 affected ? How abnormal does the weather have to become before the winds produce 

 a corresponding change ? How important to the larger-scale exchange of coastal and 

 oceanic waters are the variations of the deep, offshore currents ? 



The available observations of temperature and salinity cannot be expected to yield 

 clear-cut answers to these questions. The data consist of spot observations, separated 

 widely in time and usually also in space. Observations from some of the extreme 

 winters, for example 1918 and 1934, are entirely lacking. While the winds and the 

 inflow of several of the rivers are known continuously for a good many years back, 

 the only reasonably continuous oceanographic data are some temperature records 

 close to the beach, and these of course mainly reflect the local weather. OflFshore on 

 the bottom where the main commercial fisheries are located we have no continuous 

 information, nor do we have records of the variations in the offshore component 

 of the upper half of the water column. 



Why have we at Woods Hole seemingly so long avoided problems in coastal cir- 

 culation ? In the first place, of course, the more spectacular problems of the Gulf 

 Stream System were close at hand. In 1933 and 1934 we did survey the Gulf of Maine 

 on 17 occasions. Not a single paper dealing with the dynamics of the system appeared. 

 None of us interested primarily in the causes of the circulation were able to use these 

 extensive data to add anything of significance to Dr. Bigelow's classical studies. 

 Tidal currents and internal waves so compHcated the picture that one could draw no 



