BULLETIN OF THE UNITED STATES FISH COMMISSION. 393 



69.— CAST WE DO ANYTHING TO DECREASE, PRESERVE, OR IN- 

 CREASE THE IV UMBER OE OUR USEFUL MARINE ANIMALS?* 



By KARL. MOBIUS. 



The fishermen of the Prussian coast have for a long time complained 

 of the decrease of the flounders (Pleuronectes flesus). It is also alleged 

 that, on the Baltic coast of Schleswig-Holstein, the flat fish, especially 

 the golden flounders {Pleuronectes platessa), are on the decrease. Ac- 

 coding to the statement of a Kiel eel-smoker, the net-fishery for summer 

 eels (with yellow belly) is said not to produce as much as in former times. 

 These complaints suggest the question whether man is really able to 

 change the number of animals in the sea. On land man has extermi- 

 nated wild animals and substituted useful ones; and by changing the 

 character of the vegetation he has driven away from various localities 

 many insects, birds, and small mammals. By raising different kinds of 

 good food-fish he has also extended his dominion over the inhabitants of 

 fresh water. Why should not man also be able to increase the useful 

 marine animals? This question lies so near that I was not in the least 

 astonished when, last year, the directors of our Fishery Association re- 

 quested me to make it the subject of a paper to be read at the general 

 meeting. 



Although I am fully aware of the fact that we are far less acquainted 

 with the various conditions of life of the useful marine animals than 

 with those of the fresh- water fish and the laud animals, and that con- 

 sequently we are not yet prepared to make as well-founded rules for the 

 preservation and increase of the useful marine animals as for the in- 

 crease of fresh-water fish, I considered it my duty to comply with the 

 request of our directors, with the view of making more generally known 

 the great truth that the preservation and increase of marine animals is 

 subject to the same general laws as that of the land animals and fresh- 

 water fish ; and of stimulating our fishermen to carry on their business 

 in such a manner as not to decrease, to their own loss, the number of use- 

 ful marine animals. 



In every territory — both land and water — where animals are able to 

 live, an average number of animals is developed per season, or per year, 

 which is duly proportioned to the conditions of food and propagation 

 within that territory. The entire inhabitable portion of our globe is 

 therefore fully occupied by plants and animals. The truth of these 

 assertions can easily be proved by examples from agriculture. Every 

 farmer knows, from his own experience, how many grains of seed will 



* Konncn icir dazu beitragen, den Bestand unserer nutzbaren Seetiere su vermindern, su 

 erhalten, oder su vermehrenV von Karl Mobius, Bendsburg, 1883. Paper read at the 

 general meeting of the Schleswig-Holstein Fishery Association, at Neuniiinster, March 

 1, 1883. Translated from the German by Herman Jacobson. 



