TEMPERATURE TRENDS AND THE DISTRIBUTION OF GROUNDFISH 

 IN CONTINENTAL SHELF WATERS, NOVA SCOTIA TO LONG ISLAND 



John B. Colton, Jr/ 

 ABSTRACT 



The 1953 to 1967 downward trend in seawater temperature in continental shelf waters 

 between Nova Scotia and Long Island did not significantly alter the distribution of four 

 species of groundfish. There was an extension of the southern range of American plaice 

 and a contraction of the northern range of butterfish. These shifts in distribution were 

 not extensive. The equatorward boundary of American plaice appears to be limited by 

 summer temperatures too high for survival and the poleward boundary of butterfish by 

 summer temperatures too low for reproduction. There was no obvious alteration in 

 the geographic distribution of haddock and yellowtail flounder. The distribution and 

 movements of haddock and yellowtail flounder appear to be influenced more by restrictive 

 spawning area and bottom type conditions than by temperature. 



An alternation in sea-surface temperature has 

 been observed at Atlantic coast stations from 

 Nova Scotia to Cape Hatteras (Lauzier, 1965; 

 Stearns, 1965; Welch, 1967). Coastal warming 

 and cooling trends have been pronounced in the 

 waters between Cape Sable and Long Island. 

 A warming trend began in the early 1940's and 

 reached a maximum during 1952-53. This rise 

 in temperature was followed by a cooling period 

 which continued with only minor checks through 

 1967. Since 1967 there has been an increase in 

 sea-surface temperature, the 1969 annual mean 

 being only slightly lower than the long-term 

 mean. An example of these temperature trends 

 is shown in Figure 1 in which the annual devi- 

 ations from the 1940-1959 mean sea-surface tem- 

 perature at Boothbay Harbor, Maine are plotted 

 for the period 1940-1968. The base period 1940- 

 1959 was chosen for it included approximately 

 equal numbers of years in periods of warming 

 and cooling. 



In Figure 2 seasonal sea-surface-temperature 

 curves at Boothbay Harbor based on monthly 

 mean values for each year between 1940 and 

 1968 are compared with the 1940-1959 mean 



' National Marine Fisheries Service, Northeast Fish- 

 eries Center, Woods Hole, MA 02543. 



Manuscript accepted February 1972. 



FISHERY BULLETIN: VOL. 70, NO. 3, 1972. 



seasonal temperature curve. As would be ex- 

 pected, there were marked fluctuations in the 

 seasonal temperature cycle due to variations in 

 runoff and meteorological conditions, but for the 

 most part, the monthly deviations reflected the 

 annual deviations in both periods of warming 

 and cooling. 



Similar warming and cooling trends have oc- 

 curred off"shore, both at the surface and at depth 

 (Taylor, Bigelow, and Graham, 1957; Lauzier, 

 1965, 1967; Colton, 1968a, 1968b, 1969). 

 Though off'shore temperatures varied less sea- 

 sonally than those inshore, in general, the mag- 

 nitude of both surface and subsurface temper- 

 ature anomalies were greater offshore than along 

 the coast. These warming and cooling trends 

 are associated with changes in the composition 

 of the subsurface water (Colton, 1968b, 1969). 

 Cold years occur when slope water is displaced 

 or modified by coastal water of Labrador origin. 

 Warm years occur when slope water borders 

 upon the 200-m isobath and the ratio of coastal 

 to central Atlantic water is low. 



Taylor et al, (1957) concluded that although 

 there was evidence of northward shifts in the 

 abundance and distribution of some marine ani- 

 mals as a consequence of the warming trend 

 which commenced in the early 1940's, these 



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