28 
the second for concluding that the immigration takes place later 
usually than that of Alnmouth Bay. This is apparently the case also 
with regard to Cambois Bay and Blyth Bay. 
Attention has been drawn before, in previous reports, to the 
increase in numbers of the common flat fish during the short period 
of the experimental season, and that such an increase was some- 
times correlated with the appearance so near the shore as our 
trawling stations of off-shore mature plaice. This is rendered all the 
more evident when the results are brought together for the first two 
months and the last two months of the season. (Table IX. and 
Chart 3.) 
The experiments thus demonstrate that an enrichment and sub- 
sequent loss occurs every season, that in fact there is emigration to the 
offshore grounds, followed by an immigration, and that the intensity 
of the immigration, and the period when it takes place, varies with 
the season. It has to be noted, likewise, that the two dominant 
species are not always similarly affected. In some cases both may 
show an increase or decrease, and in other cases one may have 
improved in numbers and the other decreased. 
When the results are combined, as they have been in Table VIII., 
seasonal variation is more or less masked from the fact that the 
experiments have been made at different times during the season in 
successive years. In the case of plaice this is so markedly the case 
that the large number of experiments taken together may reasonably 
be held to be typical of the Northumberland area. Furthermore, it 
has to be stated that in no case can a variation in the form of the 
experiment be appealed to in explanation of returns which 
are much above or below the mean. I have no hesitation in con- 
cluding that on these occasions the plaice or the dabs were actually 
present in excessive or small numbers. As was pointed out in the 
report for 1902, p. 23, the experiments are not liable to be aiiected 
by such circumstances as may be suggested would produce variation. 
Because "(1) They have been conducted for over ten years [now 
for fourteen years]. (2) The season during which they are 
made is short, — from about the end of June to the beginning of 
September. (3) The experiment is made long enough to cover at 
least one phase of the tide. By the latter statement is meant that 
during the time the experiment is being conducted the tide more or 
less ebbs and flows. (4) Very little line fishing takes place in these 
bays, and practically none at all during the season of our experi- 
ments, and trawling is prohibited." In short, the elements of 
variation which may be suggested would affect the results are covered 
by the conditions of the experiment. 
