A HISTORY OF NORFOLK 



ities of the marine zoology of Norfolk waters ; and although a detailed 

 analysis of the Norfolk marine fauna from this point of view would be 

 premature in the present state of knowledge, it is nevertheless probable 

 that, as suggested by Metzger for the southern North Sea fauna in 

 general, the paucity of the shore fauna is largely attributable to the 

 excessive seasonal alterations of temperature, which render the summers 

 too hot for purely northern species and the winters too cold for the per- 

 manent residence of purely southern types. Indirectly this view receives 

 corroboration from the exceptional numbers of migratory species which 

 frequent East Anglian waters in the summer and autumn months, but 

 retire either to north or south with the approach of winter. Thus the 

 herring, an essentially northern fish, does not arrive until the excessive 

 summer heat has begun to wane in September, and retires to deeper 

 water towards the end of November, when a rapid fall of temperature 

 usually takes place off Norfolk and Suffolk. On the other hand, the 

 mackerel, an essentially southern ' fish, invades Norfolk waters from the 

 English Channel in May, when the local temperature has begun to ex- 

 ceed the winter temperature at the mouth of the English Channel ; and 

 the same fish finally retires in October or November, when the temper- 

 ature has begun to fall markedly below the temperature then prevalent 

 in the Channel. 



The following record of average monthly temperatures off the north 

 and east coasts of Norfolk will enable the student, by careful use of the 

 thermometer, to tell whether in any particular year the sea is warmer or 

 colder than usual, and thus perhaps to trace the causes of any exceptional 

 phenomena which may occur in the migrations or abundance of particu- 

 lar members of the Norfolk fauna. The figures are derived from Mr. 

 H. N. Dickson's valuable paper in the Quart. Journ. Roy. Met. Soc. (vol. 

 xxv., October, 1899), and are computed from the regular observations 

 for eighteen years of men employed on the lightships mentioned. The 

 temperatures taken further inshore on the Newarp light -vessel are 

 practically identical with those recorded from the Leman and Ower 

 light-vessel. The scale is that of Fahrenheit : — 



Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. 

 Outer Dowsing L. V. 416 40-8 410 432 463 52-5 556 57-2 567 532 488 451 

 Leman and Ower L. V. 409 399 40-5 431 476 531 573 591 579 537 489 443 



Another factor, equally important in determining the character of 

 the Norfolk fauna, is the nature of the ground and coast-line. The ex- 

 posed coast, and the lack of sheltered creeks and inlets, render the fauna 

 of Norfolk less rich than that of Essex, although the latter region is sub- 

 ject to temperature changes closely resembling those of Norfolk. The 

 scarcity of rocks also deprives the region of great numbers of fixed and 

 climbing forms which would otherwise be present. 



The fauna thus consists principally of those sand- or mud-loving 

 types which are capable of withstanding an exceptionally wide range of 



* Other examples of southern immigrants in summer are the red mullet, anchovy, and latchet 

 {Trigla hirundo), which are sometimes caught in large numbers. 



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