266 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
or 74 per cent of the length; whereas at present they are to be found in only 4,107 miles, 
a decrease of nearly 2,000 miles. This summary comprises ouly the principal rivers, 
and if minor streams and tributaries were included, the total length from which shad 
have been excluded would doubtless appear more than twice as great. In much of 
that length shad were quite numerous, the catch in many instances exceeding the yield 
in the portion to which the fisheries are now confined. The upper section of the Pee 
Dee is supposed to have yielded over 100,000 annually. In the James Eiver, according 
to the late Colonel McDonald, the annual catch of shad in the 230 miles from which 
they are now excluded “was at one time far in excess of the now (1880) entire catch 
for the whole river.” The present excluded length of the Susquehanna formerly 
yielded several hundred thousand annually. In a report of the special commissioners 
of Massachusetts appointed in 1865 to investigate the fisheries of that State, it was 
estimated that at the beginning of the present century the annual shad yield in the 
Merrimac River ranged from 500,000 to 1,000,000 in number, whereas none ascend 
that river at present. 
The limitation in the range of shad in the rivers is the result of several agencies 
in addition to the size of the stream, the most important of which are (1) natural falls, 
(2) artificial dams, (3) pollution of water, (4) agricultural operations, and (5) extensive 
fisheries. 
Natural falls exist at the escarpment line in all of the rivers having their sources 
above the coastal plane, but in only a few instances are they of sufficient height to 
form insurmountable obstacles to the range of the shad, among these being Great 
Falls on the Potomac and Bellows Falls on the Connecticut, which form absolute 
barriers to the further progress of shad that may reach these points, excluding them 
from the whole of the river above. Most of the other Atlantic coast streams having 
their sources above the coastal plane have been made impassable at a short distance 
above the escarpment line by means of artificial dams for developing water-power or 
for navigation improvements. In this class are the Savannah, the Santee, the Cape 
Fear, the James, the Susquehanna, the Housatonic, the Connecticut, the Merrimac, 
the Kennebec, and the Penobscot. The lengths from which shad are excluded appear 
in Table A on page 270. 
Access to suitable spawning areas being a physiological necessity for the main- 
tenance of the fisheries if natural reproduction is depended on, and as many of the 
spawning-groundS are located in the headwaters of the rivers, it follows that while 
the exclusion of shad from the upper sections is the immediate it is not the most 
important effect of those obstructions. It has been the common experience in all the 
shad rivers that whenever a high dam or other obstruction has been erected across 
the stream the fisheries above that point have at once ceased, and those immediately 
below have for a year or two flourished on the large number whose ascent has been 
stopped by the barrier and then they, too, have declined. It also appears that the 
extent of this decrease below the dam is largely dependent on the distance of the 
obstruction from the mouth of the river and the proportion of the spawning-grounds 
to which they are denied access, and if all the breeding-grounds have been cut off in 
a definite coastal regiou the shad have almost entirely disappeared. 
This is clearly illustrated by the conditions on the Connecticut River. The 
erection of the Holyoke dam in 1849 prevented the fish from ascending above that 
point and as they strayed about in the river below the obstruction they were taken in 
greater abundance than formerly. At the Parsonage fishery near the mouth of the 
