INVESTIGATION OF OYSTER SPAWNING, ETC., MILFORD, CONN. 



483 



Table 14. — Verlica! distrihition nf oyster larvae in Milford Harbor in relation to the stage of tide, 



August 11 to 13, 19S6> 



' Figures refer only to number of "lunbo" larvse collected diu'ing three tidal cycles. 



One thing the table clearly shows is the general scarcity of swimming oyster 

 larvae in this small harbor, where later many hundred thousands were found attached 

 as spat . It can be seen that the vertical distribution of the larvse during the low-water 

 period as a whole was comparatively uniform, and approximately the same number 

 was found in each sample taken from the surface to the bottom. However, upon 

 •further examination of each stage of this period, a noticeable variation in the distribu- 

 tion according to tidal movement was found at the time the sample was taken. On 

 the last of ebb tide the larvse were found to be most abundant in the bottom and 

 mid-zone samples; at low slack water there was practically no difference in the num- 

 bers of larvaj at each depth; while in the first of flood stage the larvas were most 

 abundant in the surface samples. During the intermediate period only a few larvae 

 were found, and these were chiefly small larvae that occurred most frequently in the 

 bottom samples. In the samples taken during the high-water period the larvse were 

 also much less abundant than at low water and occurred mostly in the bottom and 

 middle zone. The results obtained from this series of plankton collections are 

 presented graphically in Figure 31, which shows the distribution and abundance of 

 the oyster larvse in relation to the height and stage of the tide. 



If we classify all the plankton collections made in the harbor in 1925 and 1926 

 according to the stage of tide, and include also the straight-hinge larvae, we find that 

 the distribution of the larvse is similar to that shown in the previous table. In the 

 collections as a whole the straight-hinge larvse were the most abundant, and, though a 

 certain number were collected at nearly all stages of the tide and at all depths, they 

 also were found to be most numerous during the low-water period, and their abundance 

 in any zone was much the same as that of the older or "umbo" larvae. One thing 

 in Figure 31 that deserves notice is that the oyster larva are extremely scarce during 

 the intermediate period or at the times when the vertical movement of the water is 

 greatest. 



By means of the second quantitative method employed the concentration of the 

 larvae at the level of the oyster bed — that is, 1 foot below low-water mark — was deter- 

 mined hourly according to the stage and height of the tide. In the following record 

 for August 11, 12, and 13, 1926, the number of larvse collected in each hourly sample 

 of 200 gallons is given, together with the tidal data. 



