56 



DEPARTMENT OF THE NAVAL SERVICE 



8 GEORGE V, A. 1918 



once. Of the 20,000 to 22,000 fry which we tried to rear at a second trial, beginning 

 August 2, only 146 were alive on August 17, and these also were all in the second stage. 



In the August rearing the larvae were shaded from the sunlight by heavy painted 

 canvas screens lying close over the boxes; in July they were not. The effect of the 

 shading appeared to be to reduce the first stage from thirteen days to nine days, and 

 to lessen the number of diatoms; but the larvae died just the same. 



It is, of course, true that the warmer water in August (about one degree) may 

 have had more to do with the shortening of the first stage than the exclusion of light. 

 Indeed, the influence of direct sunlight upon larvae is still an open question. To be 

 sure, the fry, when left to themselves, swim straight into the light, but it does not 

 follow that because they do so, the result to themselves is necessarily beneficial. 



Fig. 3. — Showing the interior of the cement pound. The six latticed compartments are for 

 retaining lobsters so that they can be studied at close range. 



Leaving out for the present the influence of light, it may well be asked: "What 

 favourable conditions exist at Wickford, that enable the operators there to raise 40 

 per cent of their fry to the crawling or fourth stage, which do not exist at Long 

 Beach pond?" And the answer is: first, too slight a depth of water under our rearing 

 boxes, thus favouring the entrance of mud and diatoms from the bottom; secondly, 

 the presence in the water of an unusual number of diatoms not generally found in 

 open sea-water;* thirdly, too low a temperature of water. While the temperature at 

 Wickford varies during the rearing season from 68° to 75°, the mean average temper- 

 ature at Long Beach this season was only 58-09° for July, and 58-9° for August. 

 The two following tables give the daily temperatures at Long Beach for July and 

 August, respectively: — 



• Professor McClement's Report " Diatoms and Lobster Rearing" — Contributions to Cana- 

 dian Biology, 1915-16. Supp. 6th Ann. Rep. Dept. Naval Service (Fisheries), Ottawa. 1917. 



