HYDROGRAPHY OF THE MARINE WATERS 



29 



coastal distribution northward to Cape Hatteras and little or no farther. 

 Those that require cooler waters would encounter such north of this cape.^^ 

 Though the above are theoretical considerations and the ecological role of 

 temperature is known for but few species, it is obvious from the literature 

 and from discussions with students of the area that many known distributions 

 of non-migratory forms fit these expectations. 



90 



80 



70 



60 



50 



40 



Fig. II. Average annual temperature curves at (i) Cape Lookout Lightship, (2) Cape Look- 

 out Lighthouse, and (3) Beaufort Harbor. Source of data and method of smoothing as follows: 

 (i) average annual range by 2S-day periods plotted on Fig. 22 of Parr (1933); (2) average 

 annual range by lo-day period from the temperature charts of Rathbun (1887) as plotted on 

 Fig. 17 by Parr (1933); (3) average annual cycle by S-day periods smoothed by hand. 



Most of the known migrators that frequent our coast seem to prefer warm 

 waters or at least to avoid cooling waters. There is a group of typically south- 

 eastern fishes, like the striped mullet, Mugil cephalus, the Spanish mackerel, 

 Scomberomorus maculatus, and various shrimps, which are more or less 

 restricted to high temperatures, that do not extend far north of Hatteras. This 

 fauna is said to retreat southward along the coast for the winter, though it is 

 possible that some take an offshore retreat to warmer waters at the edge of 

 the continental shelf near the Florida Current or even a northeastward 

 coastal migration toward the warm Hatteras region. 



II. All these non-migrators must be considered in terms of the suitability of temperatures 

 not only for the survival of adults but also for reproduction. It is not implied, however, that 

 without reproduction the populations will not continue, for the conditions which first introduced 

 an organism may repeatedly stock any area in question. 



