SEA-FISHERIES LABORATORY. 269 



On the whole, these results will be seen to agree with 

 those of Basset t,* which have been carried out over a more 

 extended area. In 14 cases out of 21 series the difference 

 between the surface and bottom is 0'05%oOr less, and since 

 the experimental error may be O02%o> it will be seen that 

 the actual difference between surface and bottom water 

 is but small. In 8 cases it is only 0'02 o / O o or ^ ess - The 

 greatest differences, as might be expected, are at the deep 

 Stat. A in mid-channel, and are 0*24 %o aim 0*33 °/ 0O 

 respectively. In seven cases the surface is more salt than 

 the bottom, in eleven cases less salt, and in three cases 

 the same, though, as before mentioned, where the 

 difference is only 0'02 °/ 00 it is too small to allow any 

 deduction to be made. The salinities are on the whole 

 high, but agree with Bassett's figures for the Gulf Stream 

 water at his Stats. 5, 6 and T (spring '08, and for the May 

 observations '09). One might infer from this that Port 

 Erin was one of the places nearing the northern limit of 

 this current to the West of the Isle of Man, since two 

 samples of water which came from a place North of Peel 

 in the northern tide were very different from any taken 

 off Port Erin. The salinity was only 33*73%o- I do not 

 think that the small differences, either in vertical 

 distribution or from day to day throughout the month, 

 would cause any great changes in the distribution of the 

 plankton, but a sudden lowering of the surface salinity 

 by heavy rain, which would affect the plankton of the 

 upper layers only, might cause a descent. The influence 

 of light and the alternation of day and night will 

 probably produce far greater changes, f With regard to 

 temperatures, a prolonged period of cold weather will 



* Lancash. Sea-Fisheries Labor. Report for 1908, p. 44. 



fin a series of tow-nettings taken at intervals of three hours 

 during 24 hours at Port Erin a great difference is noticed between the 

 surface catches taken at night and those during the day. 



