34 BULLETIN OF THE BUREAU OF FISHERIES. 



3. CURRENTS AND TIDES. 



The first currents which concern us are two of the great permanent streams which 

 maintain the circulation of the ocean, namely, the Gulf Stream and the southwardly 

 flowing Labrador Current. Off the Massachusetts coast, the Gulf Stream is first encoun- 

 tered at a distance of about 85 nautical miles south of Marthas Vineyard and Nantucket ; 

 that is, just beyond the edge of the continental shelf. Its distance from shore varies from 

 year to year, and even during lesser periods. It has been shown by Libbey (1895) that 

 the Gulf Stream, during this part of its course, at least, presents by no means a regular 

 outline in crosssection, but exhibits, on its coastal side, a wall having very roughly the 

 contour of an inverted S. Its lower boundary, which Libbey identifies approximately 

 with the 50 (F.) curve, sends a projection coastward between the adjacent colder zone 

 and the bottom, while at a higher level the cold stratum referred to projects seaward 

 into the midst of the warmer water of the Gulf Stream. (See Libbey's fig. 1-2 1.) 

 This brings about the result that throughout a narrow strip along the continental declivity 

 the latter is bathed by warmer water than it would otherwise be exposed to, and con- 

 sequently supports a different fauna. 



A not wholly convincing illustration of the dependence of the fauna of this section 

 of the ocean upon the chance relations of these temperature zones is offered by the case 

 of the well-known tilefish, which suddenly disappeared from the edge of the continental 

 platform for a period of about 10 years. (See Collins, 1884; Verrill, 1884; Libbey, 1895; 

 Bumpus, 1899.) Its extermination was first revealed by the presence, during the spring 

 of 1882, of enormous numbers of the dead fishes floating upon the surface of the sea 

 throughout a belt parallel to the coast and about 170 miles in length. At the same time 

 Verrill (1884, p. 656) reported the "scarcity or absence of many of the species, especially 

 of Crustacea, that were taken in the two previous years, in essentially the same localities 

 and depths in vast numbers — several thousand at a time." Verrill accounted for this 

 wholesale destruction of life by the occurrence of a heavy storm, which he believed to 

 have "forced outward the very cold water that, even in summer, occupies the wide area 

 of shallower sea, in less than 60 fathoms, along the coast, and thus caused a sudden 

 lowering of the temperature along this narrow, comparatively warm zone, where the 

 tilefish and the Crustacea referred to were formerly found." Libbey has endeavored to 

 correlate the reappearance of the tilefish, about 1892, with a change in the position of the 

 50 curve; and, indeed, the first successful search for the fish after the catastrophe of 

 1882 was suggested by the discovery of changed temperature conditions. 



But the influence of the Gulf Stream extends much nearer to the coast than the 

 edge of the continental shelf, and without doubt affects our local faunal conditions. 

 The presence nearly every 3>ear in Vineyard Sound of considerable masses of the Sar- 

 gassum bacciferum, with its attendant fauna, shows that strong southerly winds may 

 drive the surface water of the Gulf Stream as far as the mainland of Massachusetts." 

 And, apart from these occasional and obvious effects, it is probable that the warm current 

 exerts a constant influence upon the coastal waters of southern New England, the two 

 undergoing a certain degree of intermingling as a result of winds and tides. Indirectly, 



a The prevailing wind during the summer months blows from the southwest quadrant. From records kept for five years 

 on the Vineyard Sound Lightship (Rathbun, 1887). southwesterly winds are found to be the most frequent ones during the months 

 of April to September, inclusive. At Nantucket, also, according to the report of the Chief of the Weather Bureau for 1909-10, 

 the prevailing direction of the wind from May to September, inclusive, is southwest. 



