In an effort to determine whether hatching can take place at the pre- 

 vailing temperatures in Delaware Bay, Prof, Parr and the writer found that 

 artificially-fertilized eggs held at controlled temperatures hatched at all 

 temperatures within the range observed in the bay. 



On the other hand, juveniles as small as 18 millimeters were taken by 

 Parr in otter trawls in early July and subsequently. Their presence can be 

 explained by either of two hypotheses: 1) They are the result of local 

 spawning and are to be connected with larvae which in some unknoim manner 

 escaped the intensive search made for them. 2) They are immigrants from 

 other spawning areas, presumably from southern spawning areas. 



Idth respect to the first hypothesis, the juveniles taken in early July 

 are rather smaller than would be expected if they were produced at the height 

 of spawning observed by Parr in late May and early June, Moreover, the 

 length frequency distributions of the summer and autumn collections suggest 

 that either most of the young fish in Delaware Bay grow very slowly (cf . 

 Hildebrand and Cable, 193U; Pearson 19^1) ; or the young fish taken there are 

 transients for the most part, the stock being added to either by belated 

 spawning in the bay or by immigration of juveniles from elsewhere while 

 losing most of the larger sizes by emigration or mortality. 



In addition to these difficulties in connecting the juveniles in 

 Delaware Bay and elsewhere in New Jersey and New York with the egg collec- 

 tions reported, it is also difficult to account for them satisfactorily in 

 any other way, ITie inshore drift along the coast is southerly so that they 

 cannot be involuntary immigrants from southern spawning. Since both eggs 

 and larvae are absent from the offshore collections, they cannot be carried 

 northward by an offshore drift as appears to be true for mackerel, bluefish, 

 and eel larvae. The only remaining possibility is that after attaining the 

 power of independent locomotion, larvae hatched in the South swim northward. 

 The principal consideration in favor of this suggestion is the presence in 

 the North of large numbers of very small juveniles of at least two other 

 species which, if they spawn at all in the North, must do so sparingly — 

 mullet, Mugil cephalus , and spot, Leiostomus xanthurus. Prof. Parr finds 

 the juveniles of both species abundantly represented in his New Jersey col- 

 lections and both are common as juveniles as far north and east as Woods 

 Hole. Both are known to be winter spawners. Adult mullet are rare in the 

 North at all seasons and spot disappear from New Jersey in November. A 

 single record indicates the movement of a tagged spot from Delaware Bay to 

 the vicinity of Ocracoke Inlet, N. C, between October, 1930, and December 

 1930. It is possible, however, that these species may spawn so far off- 

 shore that the young are carried northward by the offshore drift. 



76 



