OCT 1 )<^eji 



Report on the Present State of Knowledge with 



regard to the Habits and Migrations of the 



Mackerel (Scomber scomber). 



By 



E. J. Allen, B.Sc, 



Director of the Plymouth Laboratory. 



Prepared by order of the Council of the Marine Biological Association for the use of 



H.M. Inspectors of Irish Fisheries. 



The mackerel {Scomher scomber) is a pelagic* and migratory fish, which 

 during the warmer months of the year frequents the coastal waters 

 in the northern temperate region of the Atlantic. The whole form 

 of the fish is evidently well fitted for swift motion and the free- 

 swimming mode of life. The spindle-shaped outline of the body, 

 its perfect curves and rounded surfaces, the absence of all irregular 

 projections which would tend to retard forward movement, the great 

 muscular development of the tail, and the deep forking of the caudal 

 fin, combine to produce an almost ideal adaptation for propulsion at 

 high speed through the water, t 



The mackerel may be called also a pelagic-feeding fish, in con- 

 tradistinction to fishes such as many of the family of the Gadidae, 

 which are " ground " feeders ; that is to say, the mackerel feeds entirely 

 upon free-swimming organisms, whilst the ground-feeders hunt at the 

 bottom and amongst rocks, capturing prey which is not pelagic. The 

 difference is an important one in considering the habits of the fish. 



During, at any rate, a great portion of the year mackerel swim in 

 shoals or schools. These shoals often contain an immense number 

 of fish, and the fish belonging to any particular shoal are usually 

 of about the same size. Schools of small fish and schools of large 

 may be found in the same neighbourhood at the same time, but they 

 appear to remain separate. Little is known as to the manner in which 

 fish keep together in shoals. From observations made in the Aquarium 

 at the Plymouth Laboratory, Bateson j concludes that grey mullet keep 

 together by sight. In this case also the shoals appear to arrange them- 



* The term lieluglc is used in the sense in which it was originally employed by Johannes 

 Mliller, and subsequently by Haeckel. The mackerel is not a pelagic fish in the restricted 

 sense adopted by Giinther, who employs this term to include only such free-swimming 

 fishes as inhabit the open ocean at a great distance from land. 



t Cf. Bashfort) Dean, Fishes, Living and Fossil, pp. 2-6. 



X Journ. Mar. Biol. Assoc, N.S., vol. i. pp. 249-250. 



NEW SERIES. — VOL. V. NO. 1. A 



