6 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



perch {Perca flavescens) , snnfLsh {Eupomotis gibhosus) , catfish {Ameiurus nebulosus) , 

 fresh water dogfish {Amia calva), top-minnow {Fundulus diaphanus), blunt-nosed 

 minnow {Pimephales notatus), bream (Abramis crysoleucas) , six species of common 

 minnows {Notropis cornutus, N. hudsonius, N. cayuga, N. blennius, N. heterodon, 

 and N. atherinoides) , mud-minnow (Umbra limi), and brook-stickleback (Eucalia 

 inconstans) . This list does not include the young of the small-mouthed bass, rock- 

 bass, or common sucker, which temporarily inhabit such areas, or any species also 

 found on sand beaches. 



Swamp areas appear to offer very favorable conditions, as indicated by the 

 large proportion of species inhabiting them. It will be seen, however, that eleven 

 of these species are insignificant forms, doubtless seeking the protection afforded by 

 such situations, other places being more or less barred to them. Noth withstanding 

 their diminutive size, these species are relatively of great importance, since the 

 existence of the larger, predatory forms, desirable as food or game fishes, depends 

 at all times on an adequate food supply provided by smaller fishes. 



The conditions which prevail in swamp areas are undoubtedly selected by 

 certain species according to certain factors, but it is not clear how these factors are 

 to be differentiated. Natural protection, provided by the shape and size of the 

 body, as in the common sunfish and rock-bass, doubtless enable such species to 

 occupy a situation where food is abundant more or less in the face of predatory 

 forms. The foregoing species and also the common perch and catfish have in ad- 

 dition the natural protection of spines. The environmental protection afforded 

 by weeds or by less transparent water enables a variety of smaller fishes such as 

 minnows, top-minnows, mud-minnows, and the young of larger types to maintain 

 themselves also against predatory fishes. Predatory forms themselves find in 

 swamp situations an abundant and convenient food supply. Some of them, how- 

 ever, as a result of the deterrent factors mentioned below, are apparently able to 

 select this environment only within certain limits. Forms such as the green bass 

 and pike, for example, tend to inliabit only the clearer portions of such areas, while 

 the dogfish readily accepts the more confined situations. By way of comparison, 

 small-mouthed bass and pickerel tend to avoid such situations entirely, or resort 

 to them only temporarily for feeding purposes, nothwithstanding the fact that these 

 areas contain an abundance of their favorite food. 



This distinction of habitat, which also applies to many smaller species, must 

 be based on conditions existing to a greater or less extent in swamp areas according 

 to their more open or closed character. They possibly include excessive light, in- 

 creased temperature in summer or cold in winter, deficiency of oxygen circulation 

 pollution of the water with dissolved materials or mechanical pollution by organic 

 detritus, stems of water plants or filamentous algae. 



The fact that swamp areas of all types are present within this region makes it 

 possible to institute comparisons as to their habitability for different species. For 

 example, the smallest inland ponds habitable to fishes at all are as a rule occupied 

 only by two insignificant forms, sticklebacks and mud-minnows. Somewhat larger 

 ponds may contain in addition breams and sunfish. Swamp lakes will probably 

 contain the latter two species, together with the commoner minnows, rock-bass. 



