OF THE GRIMSBY TRAWL FISHERY. 389° 
fishery matters, a lamentable tendency towards generalisation. The 
fish form an enormous class, composed of species and families, of 
which some are so far distinguished from others, not only in 
conformation but in habit, that it is hardly possible to say that they 
have much in common beyond that they live in the sea, and 
breathe by gills. Yet the amateur exponent seems mentally to 
assign to the most widely distinct kinds a degree of relationship 
which he would probably be loth to admit as existing between 
himself and his next-door neighbour. 
As a matter of fact, every species of fish requires separate 
consideration, or at the most, only a few kinds can be grouped 
together, and that only in relation to a part of their life-history and 
habit, and not to the whole. It will, perhaps, be no waste of space 
if, before entering on the question of their destruction, I endeavour 
to sketch briefly the facts that are known with regard to the life- 
history of some of the more important kinds.* 
Even in dealing with fish of one kind one cannot make sweeping 
conclusions with regard to locality, since a species often differs con- 
siderably in habit, at distances so little remote as are the opposite 
coasts of this country. ‘There is little or no difference in the 
temperature in such cases, but there may be a great deal of 
difference in the coast itself and the soundings at sea. Thus on 
the west of Ireland we have a very bold coast, rocky in most places, 
and everywhere with deep water at no great distance from land. 
One may literally step from land into 40 fathoms of water, and fish 
in 80 fathoms in sight of some outlying island. For a great part of 
the coast-line the territorial limit is not far from coincident with the 
40-fathom line. When we turn to the North Sea, we find that part 
of the area with which we have most to do almost entirely devoid 
of rocks, and everywhere comparatively shallow. Indeed, south of 
the Fisher Bank the maximum depth is about 60 fathoms, and that 
is found only in a very limited part. 
Yet much the same kinds of fish occur in the two districts, and, 
of course, their habits, in adaptation to the available physical 
conditions, show corresponding modifications. So far as there is 
constancy of habit in relation to physical conditions, it is found to 
* In explanation of the terms used in this chapter, it may be said that some fish deposit 
their spawn on the bottom; it is then termed “demersal.” In the case of other fish, the 
spawn floats to the top of the water, and is then called“ pelagic.’ When first hatched 
the little fish or “larve ” appear to be always “ pelagic,” 7. e. swimming at the surface; in 
the case of flat-fish the pelagic larva undergoes a “ metamorphosis” or change of shape 
into the flattened form, at or near the time when it adopts the habits of adult fish by 
sinking to the bottom. 
+ See chart at the end of this paper. 
