304 



NA TURE 



[July 29, 1897 



The Influence of Beam Trawling. 

 The results of the trawling experiments carried on in 1896, 

 together with the tables embodying the details of the observa- 

 tions, are given in a special report. The trawling experiments 

 have for the present been suspended in the Firth of Forth and 

 St. Andrews Bay, where they were most systematically and 

 regularly conducted for a number of years. The general results, 

 so far as concerns the most important subject of the experiments 

 in these waters, the increase or decrease in the abundance of 

 the food fishes since beam trawling was prohibited, showed that 

 while the relative numbers of most of the round-fishes, such as 

 cod and haddock, and the unimportant flat-fishes, the dabs, had 

 slightly increased, there was a decrease among the more valuable 

 flat-fishes, the plaice and lemon sole, a circumstance probably 

 due to the increased trawling in the offshore areas where these 

 fishes spawn. 



The Hatching and Rearing of Food Fishes. 



In previous reports, detailed descriptions were given of the 

 methods and processes adopted at the Dunbar Hatchery in con- 

 nection with the artificial propagation of marine food fishes. 

 Operations have been conducted for the most part with the 

 valuable flat-fishes, especially the plaice, but also the turbot, 

 sole, and lemon sole, and also on a lesser scale with certain 

 round-fishes, such as the cod and haddock. The total number 

 of the various species which have been hatched and placed on 

 the fishing grounds since the work was begun in 1894 is 

 92,920,000. 



During the current season (1897) the artificial propagation of 

 plaice is being proceeded with on a large scale, but owing to the 

 earlier publication of the annual report this year, it was not 

 possible to give a statement of the results of the work, which is 

 still in progress. As mentioned in last year's report, the fry pro- 

 duced in the hatchery are being transferred to certain sea-lochs, 

 which are, to a large extent, cut off" from free communication 

 with the open sea, and observations are being made to test the 

 results on the relative abundance of the same species within the 

 areas selected. 



The hatching work has hitherto been much impeded by the 

 want of suitable ponds or enclosures of sea-water in which, the 

 adult spawners could be retained from one season to another, 

 and by means of which it would be possible to retain the fry until 

 towards the close of the post-larval stage, when they begin to 

 assume the form and habits of the adult, and are in a much 

 better condition to successfully meet the influences tending to- 

 wards their destruction. The present report contains a paper 

 by Mr. Harald Dannevig, giving the results of experiments he 

 has made with the view of ascertaining the methods by which 

 this may be accomplished. Some of the fry of the plaice which 

 were hatched in the establishment were kept in suitable vessels 

 of unfiltered water, to which tow-net collections — that is to say, 

 the gatherings of minute organisms found naturally in sea-water 

 — were added. By this means the fry were reared through their 

 post-larval stages, until they had undergone their transformation 

 into little plaice and settled on the bottom. Their food con- 

 sisted to a small extent of diatoms, and chiefly of minute 

 crustacese and larval molluscs. 



These experiments point to a method by which the utility of 

 artificial propagation might be considerably extended, namely, 

 by retaining the fry for a few weeks in suitable enclosures of 

 sea-water before they are transferred to the sea. 



The Currents in the North Sea and their Relation 

 TO Fisheries. 



In recent years, the attention of a number of investigators has 

 been directed to the hydrography of the North Sea, and several 

 inquiries and series of observations have been made with the 

 object of determining its principal physical conditions with 

 especial relation to the movement of its waters. During the 

 last two years and a half some thousands of drift-bottles have 

 been thrown into various parts of the North Sea, about five 

 hundred of which have been recovered, and from careful com- 

 parison of the course taken, combined with a study of the 

 prevailing winds throughout the period, it has been possible to 

 ascertain the general circulation of the surface water. The 

 results are given in a paper in the present report by Dr. 

 Wemyss Fulton, who shows (i) that surface water passes into 

 the North Sea from the Atlantic round the north of Scotland 

 and in the neighbourhood of the Orkney and Shetland Isles, 



NO. 1448, VOL. 56] 



and then moves southwards along the east coast of Scotland and 

 England to the neighbourhood of the Wash ; (2) that it then 

 travels in an easterly direction towards the coast of Denmark, 

 and then northwards to the Skagerak, which it may or may not 

 enter, and finally passes northwards along the west coast of 

 Norway, at least as far as the Loff"oden Islands. 



Drift-bottles were found scattered along a stretch of about 

 1700 miles of coast, in Scotland, England, Holland, Germany, 

 Denmark, Sweden, and Norway, between 53° and 69° N. 

 latitude. 



A detailed study of the winds prevailing during the time the 

 experiments were in progress, based upon over 12,000 observa- 

 tions, appears to show that this circulation of the surface water 

 in the North Sea is principally due to the preponderance of 

 south-westerly and westerly winds, which tend to heap up the 

 surface water on the western or continental coasts, when, as it 

 cannot escape southwards owing to the shallows and the narrow 

 orifice of the Channel, it passes to the north ; but subsidiary 

 influences may aid the movement. For some weeks last winter, 

 owing to prolonged gales and strong winds, first from a south- 

 easterly and then from a north-easterly direction, the circulatiorv 

 was reversed, the surface water passing rapidly northwards along 

 our east coast, from Norfolk to the Shetlands. 



The main object of the experiments was to determine the part 

 taken by the surface currents in transporting the floating eggs 

 and larvae of the food fishes from the great spawning areas lying 

 off" the coast to the territorial waters and inshore grounds. It is 

 shown that as the normal current moves along our east coast in 

 a southerly direction at a mean rate of about two or three geo- 

 graphical miles a day, and as the floating eggs, according to the 

 species and the season, take from about a week to over three 

 weeks to hatch, and the larvae are exposed for some weeks 

 additional to the action of the current, they may be carried for 

 very considerable distances from the place where they are 

 spawned. 



From a study of the mean temperature of the .surface waters 

 off the east coast of Scotland in each month throughout the 

 spawning season, namely, from January to August, and of the 

 duration of ihe development of the- embryonic fishes within the 

 eggs of the various species at such temperature, it is shown that 

 the spawning grounds of early spawners, as the cod, haddock, 

 and especially the plaice, may be normally situated more thar> 

 fifty or sixty miles to the north of the locality where the young 

 fishes are found. "With summer spawners, on the other hand, 

 whose eggs develop with much greater rapidity, owing to the 

 higher temperature of the surface waters, the distance between 

 the spawning area and the "nurseries" of the young fishes is 

 much less. The spawning areas off a particular part of the coast 

 do not normally supply the inshore waters opposite to them, but 

 those situated further south ; thus, for example, the breeding 

 grounds off" the coasts of Forfarshire and Kincardine stand in 

 relation to St. Andrews Bay and the Firth of Forth, while the 

 breeding grounds situated to the east of the latter stand in 

 relation to the coasts of Berwickshire and Northumberland. 



It is shown that the southward drift of the floating eggs and 

 larvae of the plaice is in agreement with the migratory movement 

 of the adults and growing fish, which is in the opposite, or 

 northerly, direction. 



The easterly surface drift from the neighbourhood of the 

 Dogger Bank also tends to explain the enormous aggregation of 

 immature flat-fishes in the great bight between the north coast 

 of Holland and the coast of Denmark. The southerly drift is 

 not improbably related to the movements of the herring shoals 

 during summer and autumn, but the connection has not yet been 

 thoroughly investigated. 



The Life-Histories and Development of the Food 



Fishes. 

 Prof. M'Intosh describes the life-histories of the cod, haddock, 

 and whiting from very early stages. It is shown that, while the 

 spawning grounds of the cod are off"shore, the eggs and larvae- 

 are wafted inshore, or that the post-larval stage is attained in 

 the former region, the young fish moving shorewards subse- 

 quently, when from about half an inch to three-quarters of an 

 inch in length. During June and July they frequent the shallow 

 rock-pools at ebb-tide in company with the green-cod or saithe, 

 and as they grow older many of them pass outwards again to 

 the off"-shore waters. Young haddocks have a diff"erent distri- 

 bution from the young cod, and are found in the deeper water 

 at a distance from shore, as appears also to be the case with the 



