COLTON: TEMPERATURE TRENDS AND GROUNDFISH DISTRIBUTION 



throughout their entire range (Caldwell, 1961). 

 In the Gulf of Maine spawning occurs from June 

 through August (Bigelow and Schroeder, 1953). 

 In general, the first arrivals at any point along 

 the coast are in spawning condition, and it would 

 appear that the summer poleward boundary is 

 governed by the minimum temperature suitable 

 for reproduction. Although one can only gen- 

 eralize as to temperature dependence, the timing 

 of arrival of butterfish at various points along 

 the coast of New England and the Maritime 

 Provinces suggests that the minimum spawning 

 temperature is approximately 15°C. The time 

 at which butterfish leave the coastal waters and 

 their distribution in deep water along the conti- 

 nental slope during the winter months indicate 

 a minimum temperature for survival of about 

 10°C. These temperature approximations are 

 based on average values given by Colton and 

 Stoddard (1972 and In press). 



Bigelow and Schroeder (1953) state that the 

 American plaice spawns throughout the Gulf of 

 Maine, but principally in water shoaler than 

 100 m. More recent observations (Marak and 

 Colton, 1961; Marak, Colton, and Foster, 1962; 

 Marak, Colton, Foster, and Miller, 1962) con- 

 firm that the plaice has no well-defined spawning 

 area, although plaice eggs were most abundant 

 in the western Gulf of Maine and over the south- 

 eastern part of Georges Bank. Plaice spawn 

 from March through May (Bigelow and Schroe- 

 der, 1953). Long-term temperature data in the 

 areas of maximum spawning (Colton and Stod- 

 dard, In press) suggest an optimum spawning 

 temperature of 3°-6°C. During the spawning 

 period such bottom-water temperature condi- 

 tions prevail over most of the area within the 

 100-m isobath from Cape Cod to New Jersey. 

 Thus, the equatorward boundary of plaice ap- 

 pears to be limited by summer and fall temper- 

 atures too high for survival rather than temper- 

 atures during the spawning season that are too 

 high for reproduction. As noted previously, 

 plaice were not caught in the Georges Shoal area 

 during the summer and fall. The long-term tem- 

 perature distribution in this area indicates a 

 maximum temperature for survival of about 

 12°C. Bigelow and Schroeder (1953) give a 

 range of 10°-13°C as the upper limit of regular 



occurrence of American plaice. 



In contrast to the American plaice, the spawn- 

 ing of haddock is restricted to limited areas with- 

 in the Gulf of Maine. The most productive 

 spawning grounds are in depths ranging from 

 40 to 100 m on the northeastern part of Georges 

 Bank and on Browns Bank (Walford, 1938; 

 Bigelow and Schroeder, 1953; Colton and Tem- 

 ple, 1961). Limited and less consistent spawn- 

 ing occurs in the South Channel, Stellwagen 

 Bank, and Jeffreys Ledge areas. Haddock 

 spawn from February through May with the 

 height of spawning occurring on Georges Bank 

 during March and April and on Browns Bank 

 during April and May. Long-term temperature 

 data in the areas of maximum spawning suggest 

 an optimum spawning temperature of 4°-6°C, 

 although spawning does take place at temper- 

 atures below and above this range (2°-7°C). 

 There is no evidence that haddock spawn west 

 of Cape Cod, although favorable temperature 

 conditions exist over most of this area during 

 the spawning season. 



It is not apparent why haddock select restrict- 

 ed spawning areas, but this limitation may gov- 

 ern in part the extent of their seasonal diffusion 

 into waters west of Cape Cod. Bigelow and 

 Schroeder (1953) give 11°C as the upper tem- 

 perature limit of the normal range of occurrence 

 of haddock, but the fact that haddock are caught 

 in the Georges Shoal area during the warmest 

 part of the year indicates that haddock can sur- 

 vive temperatures at least as high as 15 °C for 

 limited periods. Bottom-water temperatures 

 well below this upper limit occur over much of 

 the area between Cape Cod and Long Island dur- 

 ing the summer and fall. 



Although seasonal shifts in depth distribution 

 and the timing of spawning of haddock appear 

 to be regulated in part by temperature (Bigelow 

 and Schroeder, 1953; Colton, 1968a), the fact 

 that there was no appreciable change in the geo- 

 graphic distribution of haddock coincident with 

 the downward trend in temperature suggests 

 that factors other than temperature are also 

 critical in the geographic zonation of this spe- 

 cies. Bigelow and Schroeder (1953) note that 

 haddock are selective as to substrate type. Had- 

 dock avoid areas of rock, kelp, and exceptionally 



653 



