SEA-FISHERIES LABORATORY. 279 
The general effect of the flood tides will be to carry 
more southern, or even oceanic forms, from St. George's 
Channel into our area. Ne doubt, on occasions, organisms 
from the Atlantic water will also be carried in by the 
northern tide, and may get driven over “ the head of the 
tide’ at Contrary Head and at Maughold Head so as to 
enter our area. 
The general effect of the ebb tides will be to bring the 
less pure coastal waters of lower salinity, with some of 
their contained organisms, from the shallower eastern 
parts of the Irish Sea, such as Morecambe Bay, into the 
purer, salter and deeper water west of the Isle of Man. 
Most of such coastal water, no doubt, runs clear of the 
south end of the Calf Island in the ebb tide setting 
past the Chicken Rock towards St. George's Channel. An 
inspection of the arrows on the Charts (figs. 8 and 9) 
will show the trend and influence of these various tidal] 
streams. 
The effect of these strong currents, especially at the 
time of spring tides, upon the influence of the prevalent 
winds must be very great, and is very difficult to estimate, 
as the influence is reciprocal, and there are all gradations 
between high springs and low neaps in the tides and 
between calms and gales in the winds; and yet all these 
conditions must play their part in modifying the 
distribution of the plankton, either by mixing waters 
and organisms of different source or by driving a 
planktonic assemblage from or to some area. Swarms 
may conceivably be sometimes caused and sometimes 
dispersed by such combined influences of tide and wind. 
Finally, we must emphasise once more the marked 
contrast in physical conditions—and possibly in plank- 
tonic contents, although this has not yet been sufficiently 
demonstrated——_between the part of the Irish Sea that lies 
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