136 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



adults. It lias been observed by ISTortli Carolina porpoise flsberinen 

 tbat as tbe shad swim close along tbe shore tbe porpoises follow and 

 feed on tbem till tliey pass into fresh water. In the rivers the adult 

 shad is comparatively free from enemies. 



To what extent the pollution of the waters has reduced the numbers 

 of shad is not known, but acids, sawdust, garbage, oils, gas tar, and 

 refuse from dye-works all tend to make the water of rivers unsuitable 

 for them. 



FOOD. 



After entering the rivers, the shad takes but little, if any, food 

 previous to spawning, but after casting its eggs it bites at flies or senj 

 small shining object, and has been known to take the artificial fly. 

 The mouth of the adult is practically toothless, and its throat contains 

 no functionally active teeth. The water which passes through the 

 branchial filter — the gillrakers — is deprived of the small animals which 

 are too large to pass through its meshes. It is a common remark with 

 fishermen and others that food is rarely found in the stomach of the 

 adult shad in fresh water, but examinations have shown that the shad 

 does, in some instances, eat small Crustacea, insects, etc. The only 

 substance commonly found in its stomach in fresh water has the 

 appearance of black mud. It is held by some that the shad swims 

 with its mouth open and may unintentionally swallow the small organ- 

 isms found in its stomach under such circumstances, but as far as 

 observation of fish in aquaria and experiences of net fishermen go, the 

 shad does not swim with its mouth open. 



NATURAL SPAWNING. 



Shad are liable to be ripe anywhere above brackish water, and under 

 favorable temiierature conditions spawn wherever they happen to be, 

 but in some river basins they exhibit a well-defined choice of spawning- 

 places, preferring localities below tbe mouths of creeks, where the 

 warmer water of creeks mingles with the colder channel w^ater. The 

 shad lays its eggs during the highest daily average temperature, a con- 

 dition realized about sunset, when the warmer shoal water commingles 

 with the colder channel water, establishing a balance. The priucij)al 

 spawning occurs from 5 p. m. to 10 p. m. Observations on the Potomac 

 Eiver show that of the eggs from shad caught in a seine only 11 per 

 cent were taken between midnight and noon, the percentage in the 

 morning being 14 one year and 8 another. 



The eggs in the ovaries remain in a compact mass until they ripen, 

 at first occupying but a small space, but gradually increasing until 

 they distend the whole abdomen, the average weight of the ovaries being 

 about 13 ounces. Close examination at the approach of the spawning 

 time will disclose large maturing eggs of rather uniform size and others 

 smaller and of variable size. Whether the latter are the forming eggs 

 for the next year, for two or three succeding years, or for the lifetime of 

 the fish has not been determined, nor is it knowii whether shad spawn 

 every year. The small and shrunken ovaries of a spent fish are stiU 



