590 REPORT OF THE COMMISSIONER OF FISHERIES. 



to him the aquatic vegetation in the Potomac River has not been 

 damaged by carp, although these fish are abundant there. He says: 



The carp is very numerous ami prolific in the Potomac River. There are speci- 

 mens from 20 to 30 pounds, but that they go for the water celery has not been noticed 

 here as yet. Water celery grows in abundance in places where the river flows 

 slowly, especially about the so-called flats, but any injury to its growth, or a reduc- 

 tion of its density, not to speak of its total destruction, has not been heard of, as far 

 as I know, with two exceptions only, not attributable, however, to the carp, but to 

 high water in the spring of 1882 and 1889, when every kind of vegetation was swept 

 away by the floods, and consequently water celery disappeared from the river dur- 

 ing the two years Mil (sequent to those freshets. 



I must not forget to call your attention to the fact that turtles, too, are not averse to 

 a meal of water celery. Frequently I have seen "red-bellies" and "yellow bellies" 

 feasting in the dense growth of Potomac celery upon that plant. Another point: For 

 years I have kept quite a number of these species of turtles for ornamental purposes in 

 a small pond about this station and fed them with water celery taken fresh from two 

 ponds stocked with a great number of old and young carp, which never touched the 

 celery, though it must be admitted they did loosen the roots in their hunt for animal 

 food. 



In conclusion, I reiterate that I am not familiar with the fauna of the Suisun 

 Marches, but my impression is that, upon closer investigation, there may perhaps be 

 found additional causes for the disappearance of the water celery and other vegeta- 

 tion therein, besides the undeservedly much-abused carp. 



Even if Mr. HesseFs contention that the uprooting- of the plants is 

 a secondary result as the carp is searching- about in the mud for animal 

 food should be found to be true, the nature of the damage done would 

 be the same. It seems, however, from the facts brought forward in 

 the discussion of the food of the carp, that we should not be too hasty 

 in concluding that it is altogether for animal matter that they dig up 

 these plants; knowing as we do that they eat a large quantity of vege- 

 table matter, it seems likely that they would take it whenever there is 

 opportunity, so that in the case of the wild celery they probably eat 

 the softer parts of the plant as well as the Crustacea, insect larva?, etc., 

 dug up in the mud. 



The fact that the wild celery in the Potomac was not being destroyed 

 is a matter of more weight, but if the damage in other places is really 

 perpetrated by the carp it merely goes to show that under certain con- 

 ditions the fish does not harm the vegetation to a marked extent, while 

 in other cases it does. This perhaps depends upon the relative abun- 

 dance of other food. Furthermore, as Mr. Hessel suggests, there 

 should be further investigation as to whether the carp is the sole factor 

 in causing the rapid disappearance of these water plants. It must be 

 remembered that we know very little of the obscure ecological forces 

 at work which may cause great changes in the aquatic flora of a region. 

 Since these reports come from such widely separated areas, however, 

 the factor which is causing the destruction must be a very general one. 

 If the damage were confined to the Great Lakes basin, for instance, it 

 might be expected that some general phenomenon, such as a gradual 



