558 BULLETIIf OF THE BUKEAU OP FISHERIES 



May temperatures. In 1925, for instance, the surface temperature at a line of sta- 

 tions from Cape Ann to Cape Cod rose from 4.3° to 4.4° on April 21 to 23 to 8.3° 

 to 9.4° on May 20 to 22 (Fish Eawlc cruise 13); and vernal warming proceeded 

 at about this same rate there in 1920, when the surface reading rose from 2.5° off 

 Gloucester on March 1 (station 20050) and 3.3° on April 9 (station 20090) to 6.39° 

 on May 4 (station 20120) and 9.72° on May 16 (station 20124). 



This thermal change is accompanied by an alteration in the regional distribution 

 of surface temperature over the bay. Cape Cod Bay continues to be its warmest 

 center, the immediate vicinity of its northern coast line its coldest, reflecting local 

 stirring by the tide or some upwelling, as is the case in April (fig. 22). In 1925, 

 however, the summer state was foreshadowed, as early as the last week in May, by 

 slightly higher surface readings (9°) at the outer stations than between Stellwagen 

 Bank and the shore (fig. 28). 



The surface of Ipswich Bay, just north of Cape Ann, warms as rapidly from 

 April through May as does Massachusetts Bay, judging from readings of 3.05° on 

 April 9, 1920 (station 20092) and 7.22° on May 7 and 8 (station 20122). 



Similarly, the surface temperature of the basin abreast of northern Cape Cod rose 

 from 3.61° on April 19 (station 20116) to 9.17° on May 16 (station 20125); the sur- 

 face of Gloucester and Boothbay Harbors rose from about 4° to about 9° between 

 April 15 and May 15, and Lubec Channel from about 2° to about 5° during this same 

 interval (figs. 29 to 31). As Doctor McMurrich'" records arise from about— 1.67° 

 at vSt. Andrews, on March 3, to about 5° to 6° in mid-May after the very cold and 

 snowy winter of 1916, when the water was about 1° colder there than it was in 1917 

 (Willey, 1921) or than it is likely to be again for some years to come, the surface 

 may be expected to warm by about 5° to 6° between the middle of AprU and 

 the middle of May all along the western and northern shores of the gulf and out over 

 the southwestern part of the basin generally. This warming, however, is made 

 irregular, no doubt, or even intermittent, by local fluctuations in the weather (e. g., 

 belated snowstorms) and by the cold freshets from the rivers. 



The rise in surface temperature proceeds somewhat less rapidly out across 

 Georges Bank, on the southwestern side of which we found the surface only about 3° 

 warmer on May 17, 1920 (stations 20128 and 20129), than it had been there on 

 February 22 (stations 20045 and 20046) . Vernal warming is also less and less rapid 

 from west to east across the gulf (fig. 32), with readings only fractionally higher along 

 the coast of Maine east of Mount Desert Island on May 10 and 11, 1915, than on 

 April 12, 1920, or between Grand Manan and Nova Scotia in 1917.'' 



Whether the surface stratum is warmer or colder in May than in April, from 

 southern Nova Scotia out across German Bank (where the Nova Scotian current 

 from the eastward exerts its chief effect), depends on the date when this curreilt 

 reaches its maximum and slackens again, events that certainly fall several weeks 

 earlier in some years than in others. In 1919, as noted above (p. 553), icy water from 

 this source was pouring into the gulf as early as the last week of March in volume 

 sufficient to chUl the surface to 0° as far west as the eastern side of the basin; but 



"Plankton ILsts (p. 513). 



" Mavor (1923, p. 375) rccor.ls tbc surlace at Prince station 3 as 2.27° on Apr. 9, 1917, and 2.9G° on May 4. 



