So far, we have seen that the ways in which the fishermen attempt to connect the trawl-net with the decrease of fish as cause and effect, have scarcely succeeded in establishing their contention. The last and most serious count of their indictment is "disturbance and exhaustion of the fishing-grounds." By "disturbance" is meant the driving away of the fish for a longer or shorter time; by "exhaustion," the working out of any particular ground by over-fishing.
The evidence for and against this charge is, unfortunately, of the same indefinite character as that with which we have had to deal all along, rendering only approximate results possible. And if this be true as regards the existence of any particular state of things, such as the increase or diminution of fish on a particular bank, much more does it apply to any attempt to ascertain the causes that have produced such a result.
This difficulty is strongly felt in tho case of disturbance. As the Commissioners say, "Several cases of a specific character were mentioned to us, where shoals of herring and haddock were alleged to have disappeared from particular fishing-grounds after the trawlers had begun to work there. We have had no satisfactory proof that trawling was the cause of this disappearance."
A fisherman may come with a story that a shoal of herring has been frightened away in a night by the trawlers, and it may be the fact that the fish have disappeared; but until we can say that no other causes affect the movements of herring but fear of a trawl-net, we cannot safely ascribe their departure to the working of that implement. It is perfectly possible that the moving of the fish may be only a step in a process of whose course we are ignorant. It may be the result of scarcity of food, change of temperature, presence of enemies, or some other alteration of the natural conditions. Still more difficult it is to say whether repeated disturbance could ever, in any case, have the effect of permanently causing fish to desert any particular area. There have been undoubted instances of fish abandoning grounds without any assignable cause – viz., the disappearance of haddock from Dublin Bay, and the extraordinary fluctuations of the Bohuslän herring-fisheries in Sweden.
The question of "disturbance" would seem in reality to be really one of degree. The amount of disturbance that would scare fish from a small fishing-bank, would have no effect when distributed over a large one. Trawling has gone on at Brixham on the same grounds for over 100 years without affecting the large offshore banks, but some of the Brixham witnesses before the Commission thought that the increase in the number of trawlers was beginning to tell on the smaller grounds near the shore. On the Dogger Bank, or the fishing-grounds off the mouth of the Firth of Forth, disturbance is an unknown word; but in St Andrews Bay, or in the Firth itself, its effects are stated to be plainly visible. And as the whole question is one of degree, so is the part played by the trawler in the matter. If herrings are scared by the passage of a trawl-net of 100 feet by 50, surely they will not be indifferent to the presence of two miles of drift-net filled with struggling members of their species. The blame due to the trawlers in alarming the fish must depend "on the proportion their operations bear in any particular locality to those of other modes of fishing." Perhaps, too, the fishing-boats,
