40 Part II1.—Twenty-first Annual Report 
TL. Tue Distrinution AND Mi1GRATIONS OF THE Foop FIsHEs. 
The investigations on board trawlers have also furnished a considerable 
body of evidence with regard to the distribution of both young and adult 
fishes on the deep-water grounds and on those inshore. The experiments 
made by fixing on a small-meshed net around the cod-end of the otter- 
trawl, in order to capture the smaller fishes which escape through the 
meshes of the latter, give much important information as to the presence 
at the time on the ground when the haul was made of the very young 
forms of the food fishes, as described below. But the records of the 
marketable and unmarketable fishes taken with the ordinary net are 
likewise of importance, both in regard to the distribution of the fish 
and to the action of the trawl in capturing immature individuals. It 
will be found that the proportion of these taken differs largely with 
different species. 
In most cases the classification of the fishes adopted by the trawler, 
into marketable and unmarketable, represents roughly the difference in 
the size, since the value of most of those taken depends upon the size. 
Thus, whether or not codling, whiting, haddocks, witches, &c., be taken 
to market or thrown overboard depends upon the size, for there is 
always a market for them. But the selection may be somewhat different 
at different times, or even by different men; for example, if prices rule 
high smaller fish than usual may be brought ashore ; if prices are low it 
may be considered not worth while to take thesmallest. Moreover, the 
selection in the case of some of the cheaper kinds, as gurnards and dabs, 
is very variable, and with some other forms usually considered inedible, 
as anglers, the larger only are made use of, and it may be not at all. 
The following sizes may be given as generally ruling whether the fish 
are marketable or unmarketable:—Codling 114 inches, haddock 9-94 
inches, whiting 9-94 inches, lemon sole 8-84 inches, witch 9-10 inches, 
megrim 9-10 inches, brill and turbot 8-9 inches, cat-fish 14-15 inches, 
ling 15-16 inches, tusk 14-15 inches, hake 15 inches. These limits are 
derived from measurements on board the vessels, but the number of 
small forms obtained of the four last is small. 
A study of the facts shows that the proportions of the marketable and 
unmarketable varies very considerably with different species, and 
furnishes evidence of the presence or absence of the younger fishes on 
the ground. 
Puatce (Pleuronectes platessa). 
The distribution of the young of this fish is well known, the very 
young stages, following the assumption of the adult form, being found 
at the margin of the beach or in shallow tidal estuaries as the Solway ; 
and as they increase in size they move further out into somewhat deeper 
water. In the hauls made on board the steam-trawlers the proportion 
present varied very much according to the prevailing depth of water in 
which the drag was made. In the foregoing pages and in the Tables 
appended particulars are given showing this proportion in different 
cases. But if all plaice must begin their bottom-life quite at the margin 
of the sea, the cases where the larger plaice are taken is deep water at 
considerable distances from shore acquire some interest as showing the 
extent of the migration of this fish from its original habitat when 
young. I have tabulated the hauls with this object in view, and 
beginning with those nearest shore, and in least depths, I find that in 
the Moray Firth, from about two and a half to four miles from shore, 
in depths from eighteen to twenty-seven fathoms, sixteen or seventeen 
