60 DEPARTMENT OF THE NAVAL SERVICE 



6 GEORGE V, A. 1916 



third stage in six days longer. The reason we were unable to rear any to the fourth 

 stage was that they became so greatly infected with parasites that they were unable to 

 eat, and consequently died. 



It will thus be seen that cold water retards the growth and development of larvic, 

 whereas warm weather promotes them. If, therefore, the policy of rearing lobsters 

 is decided on as a permanent one for the Dominion, it will be essential that the plant 

 be placed in the warmest sea-water along our Canadian coast. 



LIGHT. 



Light is another influence which profoundly affects the life of both larvae and 

 adult lobsters. 



How quick and invariable the response to light is in the case of the young was 

 frequently demonstrated to visitors. By transferring a number of larvae to a basin 

 containing sea-water and then placing the basin on a table so that direct sunlight 

 might fall upon a small part of the water the newly hatched larvae at once swam into 

 the sunlight. This experiment was repeated again and again with the same results. 



The conclusion to be drawn from it is clear enough. The newly hatched larvae 

 should be impounded in rearing boxes to which sunlight has free access. Cloudy or 

 foggy weather in the earliest stage is unfavourable, and consequently in the selection 

 of a locality in which to place a permanent rearing plant, careful consideration should 

 be given to the amount of sunshine prevalent in the place. 



But the young lobster does- not seem to enjoy bright sunshine for any lengthened 

 period. After it has moulted twice, and especially after it has moulted three times, 

 the habit of basking in the sunshine changes to some extent to that of retiring from 

 the light. In other words, it begins to take on the habit of the adult. As is well 

 known, full-grown lobsters avoid the light. During the day they hide in burrows or 

 under ledges of rock. In the evening they come out and roam about seeking food. 

 Probably they move about all night, for those in sanctuaries are usually seen veiy 

 early in the morning returning to their habitual haunts or shelters for the day. 



It follows from the foregoing observations that as soon as larval lobsters reach 

 tbe fourth or fifth stage, and adopt the habit of the adult of avoiding the light and 

 hiding on the bottom in the mud or among the weeds, the rearing operation may cease. 

 During the transition period between stage one, when they delight in sunshine, and 

 stage four when they begin to avoid it, that is, during the third stage, the rearing 

 boxes are shaded from the direct rays of the s\in by a canvas covering stretched over 

 the boxes. 



It must not be imagined that cold water, cloudy weather, and microbes were the 

 only enemies with which young lobsters had to contend in Long Beach. Eels, stickle- 

 bacKP and various species of Crustacea were prefeent, the latter in vast numbers ; Alysis 

 stenolepis were also abimdant; but above all Idotea irrorata, a species of isopod. All 

 of these animals are enemies of lobster larvse. As regards the last-named animal, an 

 experiment which I suggested to A. E. Dawson shows that larvae which were hatched 

 in the pond would have but a poor chance to avoid being eaten. Mr. Dawson reports 

 as follows: — 



" On July 4, ten lobster larvae, one day old, were placed in a basin of water, with 

 one isopod. This was at 11 a.m. At 1 p.m. the isopod had killed eight larvae. Only 

 the cephalo-thorax was eaten. At one time the isopod held two lobster larvae, one in 

 the first and second pairs of the thoracic feet, the other in the third and fourth pairs. 

 When the isopod had eaten the desired part of larva No. 1, it was released and allowed 

 to float away, while larva No. 2, held in the third and fourth pairs of feet, was passed 

 forward to be in a suitable position for being eaten. 



"Almost invariably the isopods sank to the bottom of the basin as soon as they 

 had taken their prey and rested on their backs while eating." 



