June, lyub.j 



KN OWLEDGE 



137 



appear to intermiugle. Similarity in size has also been 

 observed to l)e usual in the shoals oE grey mullet. It is, 

 iu fact, not well ascertained whether these mackerel 

 schools are formed by chauce assueiation, or are due to the 

 selective association of fish, having some characteristic in 

 common. Such evidence as is to hand in the case of other 

 fishes, in that of the grey mullet, for instance, points to 

 the conclusion that the principle of selective association 

 j>lays a considei-able jjart in the formation of shoals, and 

 tliat similarity of size is one of the points selected. 



As to the manner in which mackerel keep together in 

 shoals little is known. Grrey mullet probably follow each 

 other by sight The shoal seems to have no definite 

 leader, but follows any individual that makes a dart in a 

 particular direction. At night they lie on the surface of 

 the water, their heads not all pointing one way, as they 

 generally do by day, and they do not move as a shoal. It 

 may be doubted whether other shoal fishes, as pilchards, 

 habitually travel about as a shoal at night. The iridescent 

 colouring of many fishes may assist them in keeping 

 together in shoals. 



The migrations of these shoaling mackerel have long 

 lieeu a suliject of speculation among naturalists, and 

 though much is known that was formerly obscure, it is a 

 subject, in its various aspects, that presents peculiar 

 difficvilties to arriving at certain or definite information. 

 It is not long since the value of statistics showing the 

 quantities of the fish landed at various ports at different 

 times of the year has been recognised, and from these, 

 English and foreign, a number of tables have been con- 

 structed which give an insight into the distribution of the 

 mackerel on the coasts in question during the different 

 nK>nths of the year. Of this seasonal distribution as a 

 whole it may be premised that, while the same general 

 systematic movements can be observed, considerable 

 variation takeg place from year to year as to the exact 

 date of the appearance of the shoals in a particular locality. 



During the first two mouths of the year few mackerel 

 are taken in any locality, the cold period being presumably 

 the time when the fish are farthest from the coast. The 

 few caught are chiefly found in the western part of the 

 English Channel — at a distance of thirty to forty miles out 

 at sea, south of Start Point and south of Plymouth — off 

 the south-west coast of Ireland, off the west of France, 

 and iu small numbers in the Grulf of Marseille. Often 

 during the greater part of March the conditions of 

 February do uot. materially alter. Throughout that month, 

 ami in April, the mackerel in the English Channel continue 

 a long way off-shore, becoming, however, more abiuidaut. 

 Towards the end of March, or early in April, generally 

 speaking, large schools approach the south-west coasts of 

 Ireland and the west coast of France, and the great si)ring 

 mackerel fishery commences. At about the same time 

 mackerel fishing l)egins in the Mediterranean In the 

 eastern portion of the English Channel mackerel are not 

 yet (April) taken in numbers, unless in exceptional years : 

 at Dieppe souk; are taken in April. 



The sjiring mackerel fishing rciichcs its height in May. 

 and continues into June, becoming considerably less 

 pi-oductive towards the end of that montli. In the 

 Mediterranean, on the west coast of Fram-e, on t he south- 

 west of Ireland, and in the western portion of tlie English 

 Channel, during both May and June, the fish draw close 

 inshore in great al)undance, the fishing in all these districts 

 attaining its maxinuuu iu May. In the eastern part of 

 the English Channel, c.;/., St. Varloy-sur-Somme, tlie fish 

 are seldom ])lentifnl before Jiuie; in the southern part of 

 the North Sea a small fishery on thi> Danish coast begins 

 in May ; but at the English North Se;i ports practically no 

 mackerel are lauded until June, and then thev do uot, in 



any measure, approach the numbers taken later in the 

 year. Large shoals appear on the southern Noi'wegian 

 coast, ahmg the Swedish coast, and in the Kattegat, 

 towards the end of May, and the principal fishery on these 

 coasts is at its height in .lune. 



At all the large fi.shing centres, as a general rule, a 

 season of scarcity exists during July and August, between 

 the great spring and autumn fisheries. Of this season on 

 the south and west coasts of Ireland one of the inspectors 

 says, there is a sharply-defined interval " l>etween the two 

 visitations of fish." It is true that at this time of the year 

 mackerel in large numbers enter Plymouth Sound and in- 

 shore waters, where they are taken by whiffing lines and 

 with the seine ; but the mackerel appear to be scattered, 

 and drift-net fishing is practically suspended. In Norway 

 the summer fishing practically ceases about the middle of 

 July. In the Mediterranean, at Cette, and at the majority 

 of "the ports, the great fishing is over iu June, but to this 

 Marseilles is an exception, the fish being generally plentiful 

 until September. 



Septemlier and October are the season of the great 

 autumn fisheries. Immense schools visit the west coast of 

 France and the south-west of Ireland, the quantities 

 landed in some years equalling those of the spring 

 fishery — a remark, perhaps, applying more strictly to 

 Ireland. But as regards the west coast of England, 

 practically an autumn fishery does not exist, and although 

 on the south coast in most years the numbers landed 

 increase in September as compared with August, they are 

 by no means large, and show a decided falling off in 

 October. After the beginning of September the mackerel 

 leave Plymouth Sound, and are then caught in open water 

 a few miles south of Eddystone Light, and south of Start 

 Point. On the other hand, in the eastern ]3art of tlie 

 English Channel, and in the southern part of the North 

 Sea — at the east ports of England and Graveliues — the 

 most valualde fishery of the year is carried on at this time. 

 During the last two mouths of the year, as during the 

 first two months, mackerel fishing may be said to be 

 closed on all the European coasts, though a few fish are 

 still caught south of Start Point and the Eddystone, in 

 the English Channel, and elsewhere. 



The causes which bring about these periodic migrations 

 are not by any means well understood. Study of the 

 physical and biological conditions prevailing at different 

 seasons of the year in the waters in which the shoals swim 

 is being now undertaken, in order to throw light upon 

 this important jjoint. Thei'e can lie little doubt that the 

 temperature of the sea-water may be looked upon as one 

 of the most important influenc»!s which determine — which 

 may retard or accelerate — the inovements of the fish ; 

 though Some have sup]iosed the influence to be an indirect 

 one, by cU'tenniuing the presence or absence of the organisms 

 which ciinstitute the mackerel's food in the several locali- 

 ties. When the fish first visit the coast iu spring and early 

 summer it is chiefly in order to spawn, and, plainly, tlie 

 demands made by the needs of the young aiv met by 

 proximity to the land, where the smaller organisms of the 

 ])lanktou abound, besides all the numerous larval forms of 

 the creatures whose home is the coastal waters. During 

 the latter part of sununer, and in the autumn, however, 

 when the mackerel are in the inshore waters, small fish of 

 other species become abundant, which then furnish the 

 mackerel with a generous food sup[>ly. On their first 

 coming to the coast to spawn they are not readily taken 

 with bait, l^ecause at this ]ieriod they take less food, 

 es]iecially the females, which for a time indeed cease to 

 fetnl. Thus, we may roughly term the first migration the 

 ■'sjiawiiing inigr.itiou " : the approach to the coast in the 

 summer and autumn is a " feeding migration." 



