NATURAL CAUSES AFFECTING THE FISHERIES. 75 
Tay, and the still more extensive ponds belonging to Sir 
James Gibson Maitland, Bart., at Howietoun, near Stirling, 
have in our own country done what the “ hatcheries” belong- 
ing to the United States and Canadian Fishery Commis- 
sioners have done on a larger scale on the other side of the 
Atlantic. By their assistance several disputed points in the 
history of Salmonide have been cleared up, notably the 
identineation of the “parr” of different Sspeciess” But 
many important problems have yet to be solved before 
we can claim to have an accurate knowledge of the habits 
of salmon. 
How often, for instance, are we at a loss to account for 
the strange fluctuations in the harvest of our salmon 
fisheries. We have yet to ascertain the full effects of 
floods, of droughts, of severe winters, of hot summers, and 
of storms at sea, not only on the fish themselves, but on their 
enemies and on their food; how far their migrations are 
affected by changes of temperature, by rainfall, by elec- 
tricity ; what conditions favour an abundance of their 
natural food; what laws govern their periods of spawn- 
ing; what is their average period of life—these are pro- 
blems, hitherto unsolved, which artificial culture may help 
us to answer ; and their solution is no less necessary in a 
practical sense than desirable from the point of view of 
abstract science. Legislation, to be effective, must be 
based upon accurate knowledge ; to be beneficial it must 
be shown to be necessary. To blindly restrict fishing in 
order to check a diminished productiveness caused by 
natural causes is to misapply legislation. Fluctuations in 
the harvest of the water are as natural as fluctuations in 
the harvest of the land. When we have learned whether 
to attribute a falling-off in a particular fishery to natural 
or to artificial causes, we shall have got the essence 
