COLTON: TEMPERATURE TRENDS AND GROUNDFISH DISTRIBUTION 



which ranges as far south as Cape Hatteras in 

 the winter, were not representatively sampled by 

 the otter trawl. Studies undertaken on the dis- 

 tribution of tunas (Blackburn, 1965, 1969) in- 

 dicate that, in general, pelagic species are much 

 more sensitive to temperature than groundfish 

 species. 



There is some evidence to the effect that sen- 

 sitivity to temperature varies with age of fish. 

 Rollefsen (1949) noted that immature cod can 

 tolerate lower temperatures than mature cod. 

 It is only during the spawning season that ap- 

 preciable numbers of the older year classes of 

 haddock are caught on Georges Bank (Colton, 

 1955) . In summer these older fish move off" into 

 deeper and cooler water, and the Georges Bank 

 population is made up principally of the younger 

 year classes of haddock (1- to 3-year-olds). It 

 would appear that young haddock can withstand 

 higher temperatures than older haddock. The 

 fact that we grouped all age fish in this study 

 may have concealed shifts in distribution asso- 

 ciated with specific age-groups. 



Any attempt to relate geographic distribution 

 to the direct result of physical processes involves 

 gross oversimplification. It is apparent, how- 

 ever, that there was no major change in the 

 distribution of groundfish coincident with the 

 cooling trend, i.e., the establishment of resident 

 populations south of Cape Cod of species that 

 were formerly winter migrants or a northern 

 diminution of the range of southern migrants. 

 It would appear that the magnitude and rate 

 of temperature change were not sufficient to sig- 

 nificantly alter the groundfish composition in the 

 area between Nova Scotia and Long Island. A 

 similar conclusion was reached by Taylor et al. 

 (1957) in their study of changes in the distribu- 

 tion and abundance of marine animals in the 

 same area during a period of warming. 



SUMMARY 



An alternation in seawater temperature has 

 been observed in coastal and off"shore waters in 

 the area between Nova Scotia and Cape Hatter- 

 as. There have been a number of reports of 

 southward extensions of range and shifts in 

 distribution of fish and invertebrate fauna dur- 



ing the cooling trend which commenced during 

 1952-53. 



Research vessel survey data is presented to 

 determine what eff"ect the cooling trend has had 

 on the distribution of some important commer- 

 cial groundfish species in continental shelf wa- 

 ters between Nova Scotia and Long Island, Four 

 species representative of the basic types of geo- 

 graphic zonation characteristic of the area are 

 considered in this paper: American plaice, had- 

 dock, yellowtail flounder, and butterfish. 



The American plaice and the butterfish showed 

 a change in distribution coincident with the 

 downward trend in temperature, but these shifts 

 were not extensive. During both summer and 

 fall there was an extension of the southern and 

 western limits of the area of occurrence of Amer- 

 ican plaice and a contraction of the northern 

 and eastern limits of the area of occurrence of 

 butterfish. The equatorward boundary of plaice 

 appears to be limited by summer temperatures 

 too high for survival and the poleward bound- 

 ary of butterfish by summer temperatures too 

 low for reproduction. 



There was no change in the general distribu- 

 tion of haddock and yellowtail flounder. In all 

 years and seasons the catches of haddock were 

 confined for the most part to the area east of 

 Cape Cod. Restricted spawning areas and com- 

 petition for food may govern, in part, the sea- 

 sonal difl!"usion of haddock into waters west of 

 Cape Cod. 



Yellowtail flounder occurred both to the east 

 and west of Cape Cod at all seasons. Their dis- 

 tribution was limited to depths shoaler than 

 100 m and to areas of sand bottom. The re- 

 stricted depth range, long spawning season, ex- 

 tensive spawning area, and nonmigratory habit 

 of the yellowtail flounder indicate that this spe- 

 cies can tolerate a wide range of temperature. 

 It appears that except at the extreme northerly 

 and southerly limits of its range, the geographic 

 distribution of yellowtail flounder is more in- 

 fluenced by bottom type than by temperature. 

 Although it is possible that changes in distri- 

 bution did occur which were not evident from 

 the survey data, it appears that the magnitude 

 and rate of temperature change during the cool- 

 ing period were not sufficient to significantly 



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