274 FOUNDERS OF OCEANOGRAPHY 



absorbed their food-yolk and started feeding on Diatoms. 

 If, however, we take the case of one important fish — the 

 plaice — we can get some data from our hatching experiments 

 at the Port Erin Biological Station, which have now been 

 carried on for a period of nearly twenty years. An examina- 

 tion of the hatchery records for these years in comparison 

 with the plankton records of the neighbom*ing sea, which 

 have been kept systematically for the fifteen years from 1907 

 to 1921 inclusive, shows that in most of these years the 

 Diatoms were present in abundance in the sea a few days at 

 least before the fish larvae from the hatchery were set free, and 

 that it was only in four years (1908, '09, '13, and '14) that 



Fig. 18 — Young Labval Plaice with supply or Food-yolk, x 16. 



there was apparently some risk of the larvae finding no phyto- 

 plankton food, or very httle. The evidence so far seems to 

 show that if fish larvse (Fig. 18) are set free in the sea as late 

 as March 20, they are fairly sure of finding suitable food ; ^ 

 but if they are hatched as early as February, they run some 

 chance of being starved. 



But this does not exhaust the risks to the future fishery. 

 C. G. Joh. Petersen and Boysen- Jensen, in their valuation of 

 the Limf jord, in Denmark, have shown that in the case not 

 only of some fish, but also of the larger invertebrates on 



1 All dates and statements as to occurrence refer to the Irish Sea 

 round the south end of the Isle of Man. For further details see 

 Report Lanes. Sea-Fish, Lab. for 1919. 



