OCEAN TEMPERATURES OF THE EASTERN COAST OF THE UNITED STATES, 

 FROM OBSERVATIONS MADE AT TWENTY-FOUR LIGHTHOUSES AND 

 LIGHT-SHIPS. 



[With thirty-two charts.] 



By RiCHAKD Rathbun. 



INTRODUCTION. 



Temijerature has loug been recognized as having an imijortant influence upon the general 

 movements of fishes, and especially of those species that migrate periodically from one region to 

 another. The salmon, shad, and alewives ascend the rivers in the spring, and at about the same 

 time large schools of mackerel and menhaden approach the coast from the direction of the Gulf 

 Stream, and, to some extent at least; work northward as the season advances. Cod are abundant 

 near shore only during the colder months, while lobsters retreat into deeper water at the begin- 

 ning of winter, and return again in the spring. Whatever may be the impelliug power that 

 incites these and other species to cliange their grounds at stated periods, whether the necessity of 

 seeking new sources of food or more congenial waters for the purposes of breeding, it has gener- 

 ally been observed that their migrations coincide more or less closely with certain changes in 

 temperature, and the latter, therefore, appears to exert a controlling or restraining influence upon 

 their movements. Until recently, however, very little has been published respecting the precise 

 relations of temperature to fish migrations, and the subject is but little understood. 



In a history of the menhaden, published in 1879,* Mr. G. Brown Goode discusses the water 

 temperatures taken at several stations along the Atlantic coast of the United States for a period 

 of three years, in connection with such information as was then obtainable respecting the move- 

 ments of menhaden during their spring migrations. In prefacing this subject, Mr. Goode remarks 

 that "the date of the earliest appearance of the schools of menhaden at any given point upon 

 the coast corresponds very closely with that of the arrival of scup, shad, bluefish, and other of 

 the non-resident species. It depends i)rimarily upon the temperature of the water, [and the 

 departure of the schools] is regulated by the same causes. At the approach of settled warm 

 weather the schools make their appearance in the coast waters. They remain in the bays and 

 near the shores until they ai'e warned away by the breath of coming winter. The date of their 

 appearance is earlier in the more southern waters, and the length of Uieir sojourn longer. It is 

 manifestly impracticable [from the data he then possessed] to give anything but approximate 

 dates to indicate the time of their movements. In fact, the comparison of two localities, distant 

 apart 100 or 200 miles, would indicate very little. When wider ranges are compared there 

 becomes perceptible a proportion in the relations of the general averages. There is always a 

 balance in favor of earlier arrivals at the more southern localities. Thus it becomes apparent 



* The Natural and Economical History of the American Menhaden, by G. Brown Goode. U. S. Commission of 

 Fish and Fisheries. Report of the Commissioner for 1877, Appendix A, 529 pp., 31 plates. AVashington, 1879. 



157 



