40 



Part III, — Twenty-first Annual Report 



III. The Distribution and Migrations of the Food 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 

 mat ketable 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 diflfers 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, (tc, 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 diff'erent 

 at diff'erent 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 the smallest. 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 11| inches, haddock 9-9 1 

 inches, whiting 9-9 1 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. 



Plaice (Pleuronectes plcitessa). 



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 



