46 EFFECT OF LINES ON INVERTEBRATES. 



which crowd, throughout the greater part of the year, the 

 region over the bottom, and ascend to the surface. Swarms 

 of purely pelagic forms, such as Spirialis, which, small though 

 it be, is often eaten by ducks at the surface, and more abun- 

 dantly by many young fishes near the bottom, are mingled 

 with these and the larval nudibranchs, and occasionally even 

 with Glione. The latter does not attain the bulk of the Arctic 

 examples, but is by no means infrequent at certain seasons. 

 Finally, the proximity of a mussel-bed, or the presence of an 

 extensive coating of small mussels on the rocks, fills the water 

 (June and July) with myriads of pelagic mussels, which by- 

 and-by adhere to everything affording a surface, and form a 

 favourite food of young fishes, and even of some of the 

 adults. 



Irrespective of its direct relation to fish-food, this unceasing 

 wealth of pelagic life has a close connection with the susten- 

 ance of the bottom-fauna. Every invertebrate group, mentioned 

 in the foregoing paragraphs, feeds on the pelagic fauna or its 

 debris ; for, even the highest — viz., the cuttle-fishes — frequently 

 devour the pelagic fishes. The whole system forms a wonderful 

 cycle, and is far more important, from a fisheries' point of view, 

 than at first sight appears. 



In returning the contents of the trawl to the water, many 

 forms are doubtless devoured by fishes in their descent to the 

 bottom, just as the gulls which follow the herring-boats in the 

 western lochs, or the wake of a trawler on the eastern coasts, 

 swoop on the offal thrown overboard, or on the injured fishes 

 which escape from the net at the surface when hauling. The 

 same remark applies to the invertebrates thrown overboard by 

 the liners. 



b. Effects of the Hooks of the Liners on the same Ground. 



In considering the effect of the trawl on the animals 

 frequenting the bottom of the so-called fishing banks, it must 



