this could hardly happen without the herring having some orientation with the sea bottom . it means that the crowding is caused during the daytime , and that the herring must continue to migrate over the ground as well as in midwater and during the swim ( the swim at East Anglia is always from the north ) . thus we can see that herring movements , although primarily instinctive perhaps , and certainly helped and hindered by water flow , are also closely related to the sea-bed geography . geography , too , names the great fisheries that depend on them : the Fladen Ground ( where again most big shots are taken on the edges ) , the Gut , a deep-water channel to the Dogger where the herring spawn along the northern edge ; a good contour map will almost define the migrations of these summer herring . the effect of bottom congestion due to the light pressure is inevitably mixed with that of the suitability of ground for spawning . both result in crowding , so there is no need to try to separate them - thank heaven ! a good picture of this is seen on the 150 miles of spawning grounds from the Viking in the north down to the Klondykes and the Reef along the western edge of the Norwegian deep . in this 200-fathom trench the herring do not touch the bottom . their descent stops at the end of the light pressure . but they migrate easterly to the Norwegian side , or westerly , until in the shallower water the mile wide layers disappear from the echo-sounders . bottom crowding comes when they can not reach their optimum depth ; and this coincides with the suitable gravelly soil of these many roughs where the spring-spawning herring are always found . the joint evidence of echo-sounders and fishing gear leads to an overall though somewhat dim picture . the details are harder still to see . drift effects . at East Anglia , for instance , shoals that gather at the Knoll or other banks are most of them going to travel a hundred miles farther south before they spawn . some will spawn at the Hinder banks , which are half-way ; and it may be that in their southerly march the herring will spawn wherever the suitable gravelly bottom soil coincides with their final ripeness . so the arrival of any particular shoal fish at a certain spawning ground may be accidental . yet there will always be some that find it if enough are travelling , just as the robin who gets back exactly may be only one among thousands who do not . but this southerly migration is not accidental . being contranatant or against the drift , it probably has a survival value in ensuring that the fry after hatching are drifted back into the normal home of the adults , by the water flow through the English Channel into the North Sea . drift in another form probably explains how these migrating herring are biased to east or west by the different winds . strong westerlies are well known to bring good longshore fishings . the surface water that is blown offshore must be replaced by an underflow bringing with it the herring to the Norfolk and Suffolk beaches . easterly winds , on the other hand , mean no herring along the shore , as recent years have shown . a succession of winds is needed for this effect of course - one breeze will not do it , though a very hard westerly will often start off the local herring ; but quite apart from this wind effect there is an easterly drift special to this rump of coastline , caused by the meeting of water from north and south . herring fishermen call this the outset . it is strongest at spring tides , when without wind you will set out - or drift to the eastward , the length of half a fleet of nets - almost a mile on every tide at the Smith &apos;s Knoll . without an explanation of how it works , it may well be that this outset , akin to the mouth of a great salmon river , has been the biggest factor through the ages in the constancy of this great herring fishery . the East Anglian behaviour ( see p 82 ) has always differed from that of the summer fisheries . there is the swim at slack waters , even in daylight sometimes ; and the high swimming , when fish are caught only in the top few yards of netting . these and other fascinating behaviour mysteries are peculiar to this fishery , which unfortunately seems to be dying out ; but a full discussion of them is beyond the present scope . 2 . reaction to fishing gear . the bow-wave theory . this assumes that all fishing gear , when moving , sends before it a kind of scaring effect , probably through waves or vibrations in the water or along the ground . underwater films suggest that the footrope of a trawl does this . films have also shown plaice moving before a seine net in just the same way after being gathered inwards by the ropes . ( just how the seine ropes do this is not yet proved ; it may be by actual contact , or by sight reaction to the disturbed sand ; or even in the case of flat fish , by vibrations through or along the bottom . ) but given such a bow wave of disturbance , it is obvious that without something to overcome its effect , very few fish would be caught . let us consider first what would appear to be the simplest case - that of flat fish on the bottom . the evidence suggest that the fish are aware of the moving footrope before it reaches them . they move away before it , swimming at the same speed for an unknown period of time , until they become ( 1 ) tired , or ( 2 ) more used to the disturbance . then they stop swimming and are caught . in the seine-net film this usually seemed to happen just after the fish had risen above the footrope , and presumably out of its field of disturbance , or bow wave . this suggests that the wave might be transmitted by the sea-bed , though the footrope in this case was actually just off the bottom and was indeed passing over some fish . it is natural to assume that flat fish being in actual contact with the bottom would react and be aware of the approach of anything like a footrope . and only the continuous progress of the net ensures that the fish are captured . recent research on the swimming speeds of fish shows that they soon get tired , hence the success of the trawl . the lifting reaction is interesting since it seems in a way to be the last resource . the flat fish does not want to rise . its instinct is to hide on the bottom . when disturbed , most flat fish will swim rapidly away for a short distance and then ground again , turning to face the disturbance and flirting up the sand or mud as they do so . before a trawl they have not time for this ; and the flight becomes a steady swim ahead of the wave until lifting is the only thing left to do . this behaviour will probably be corroborated by future films . if so , it will be a remarkable vindication of the basic trawl design , for the earliest beam trawls had what we call cover - that is the headline running ahead of the ground rope . actually the seine net has little or no cover . and in this film the rise of the fish was small , a matter of a foot or two . with round fish like haddock , which would hardly find safety on the bottom , this cover would seem to be even more essential ; but more films are needed to prove this . cover in the fast-moving trawl is considered essential to catch round fish whose reaction to disturbance would be upwards . in seine nets it might be less important . the fish before the net have been gathered more slowly : the reaction of bottom feeding haddocks while being chevied inwards by the slowly closing arms of rope would be to swim away from the disturbance and then downwards again to resume feeding . if they swam upwards for any distance they would get above the disturbance and escape . it may well be that the efficiency of seineing on haddocks depends a lot on what the fish happen to be doing . when working the Cleaver Bank years ago we used to get good hauls , 12 to 15 baskets at opening and close of day , and nothing , except a basket or two of whiting , during the high day . this might be explained by a change in behaviour of the fish ; or even indirectly of the feed animals on the bottom . the point is , however , that once round fish are persuaded into the path of the seine net they would probably be less disturbed than they would be by the faster-moving trawl . whether or not they would be moving slowly before the seine net like the flats , we do not know . but the fact that they are caught proves that they do not lift above the headline . it may be that some of them do , though . and this would explain why the Vinge trawls are now being found more efficient than seine nets when used with seine ropes . on this subject of cover , my father could remember 40 baskets of haddock in beam trawl hauls at Smith &apos;s Knoll . this suggests that cover might be more important than speed . but we should realise that a smack with a strong wind and tide could move a trawl fast over the ground . if we take note of the action and results of seineing gear , it becomes fairly obvious that the creeping ropes can have very little bow-wave effect . if they moved fast enough to produce a continuous swim the fish would eventually lift and be lost ; but the slow heaving taught us by the Danes , like the dog s careful driving of the sheep , drives the flat fish without scaring them . as it seems to be the rule to heave fast , as well as to tow , for round fish we may expect the cameras to show a different reaction on the part of these : being rather more active than flats one would expect them to avoid a slow-moving trawl more easily . the more we think about trawling and seineing the more we realise how different they are . the seine net can be likened to a dustpan , with brushes - the ropes - sweeping things into its path , and if the fish are swept too vigorously they will rise , like the dust , and be lost . the trawl , however , is more like the dustpan without a brush and has to move a bit faster . we can assume that the bow wave will become greater as the speed of the gear increases . in the case of herring trawling great emphasis is placed on the need for fast towing . the Germans , who are the recognised experts at this , have been using bigger and bigger ships towing at over 4 knots . their main difficulty seems to be to get netting that will stand the weight of the great catches . but if there is anything in the bow wave theory there must be something more than just speed to consider . herring are more lively than the white fish , which we have seen react to the bow wave of trawl footropes . and the herring can probably swim faster , for short periods anyway , than the trawl moves . if the herring react to the disturbance ahead of the trawl like other fish , then increased speed alone is not the answer . you can not catch a bow wave . I remember seeing the bow wave of herring from a trawl on the Fladen Ground over twenty years ago . herring trawling . one calm summer day in 1937 we lay waiting to shoot our drift nets . that morning the drifters had hauled good shots and gone to market , leaving us alone on the ground . yet our systematic echo-sounding over the area had yielded no fish traces . at about midday an Aberdeen trawler came towing along , and passed us some hundred yards off . I pictured her trawl trundling over the bottom ; and I thought of the herring we could not find though knowing they were present . 