102 NORTH SEA INVESTIGATIONS. 
mature soles in the river, if it did not abolish it altogether. This may 
seem, as it were, an academic discussion, since it is allowed that the 
same or nearly the same end is attained by either means; but the 
method I favour would be an effectual safeguard against the abuse 
of shrimp-trawls for catching small plaice on grounds where neither 
prawns nor shrimps are to be had. I have found such a practice to 
be quite feasible, and have no doubt it might be occasionally re- 
munerative, but I must confess that I have no knowledge that the 
possessors of shrimp-trawls ever divert them from their legitimate prey. 
Migrations and spawnings of shrimps and prawns.—Shrimps and 
prawns seem to arrive at about the same time, viz. the beginning of 
April, on those grounds in the Humber which they respectively 
frequent, but the time of arrival, as of departure, is said to vary 
according to the weather. My own experience is too short to enable 
me to offer any comments on this point. 
The shrimp season for shove-nets usually closes about November, 
though in very open winters it is said to last longer. The quantity 
present on the sandy margin, so far as this can be gauged by the 
takes, is at all times subject to rather sudden variation, and becomes, 
I believe, especially variable after the end of September. Any 
diminution in the normal turbidity of the water, more readily per- 
ceived by those engaged in the industry than others, is regarded as 
prejudicial to good catches. The variation of the trawling grounds 
appears to be even greater than on the margin. Some few shrimps 
are found in all parts of the river throughout the year, but I do not 
know what becomes of the remainder in the winter. In digging for 
lugworms, in February, near high water mark I have found a shrimp, 
living but very torpid, some few inches below the surface of the 
sand, at a time when none were obtainable in the shove-net ; but it 
would be unwarrantable to conjecture from this single instance that 
any considerable number take refuge in this manner during the 
winter months. 
I have made no effort to ascertain the chief spawning period ; 
here, as elsewhere, some shrimps are found carrying ova at all 
seasons. 
Prawns are certainly most abundant in the Humber in summer. 
Tt is commonly asserted that a north-westerly gale in autumn has the 
effect of driving large numbers of them out of the river, and I had 
the opportunity of observing last year that the number obtainable 
certainly decreases after such weather. It is also said that once 
their bellies turn green they begin to leave the river. The green 
colour is that of the ova attached to the abdominal appendages. 
We found only a few with spawn at the beginning of October, but 
later in the same month and in the early part of November the 
