PROGRESS IN BIOLOGICAL INQUIRIES, 1937 21 



wliich summered in Connecticut in 1936, migrated southward in the 

 autunni, some of them as far as the sounds of North Carolina. 



These observations indicate that this species is subject to strong 

 year-class dominance and that bass migrate more than was formerly 

 suspected. It is of especial significance that the large 1934 brood was 

 produced in a year when the numbers of mature adults wei-e not only 

 no greater than during the several years preceding, but were also 

 well below average. Consequently, the restriction of the catch of ma- 

 ture striped bass in the interest of augmenting the spawning reserve 

 is of doubtful value even in such localities as Chesapeake Bay, where 

 reproduction is occasionally very successful. It is even more ques- 

 tionable whether protection of mature fish will be profitable in more 

 northern localities where the principal increments to the stocks appear 

 to come from immigration. 



This does not imply that the present practice of virtually unre- 

 stricted fishing is desirable. Results of tagging experiments indicate 

 that the fishery takes a very heavy toll of successful broods before they 

 mature. It is believed that restriction of the catch of the younger and 

 smaller fish would increase the total yield from each brood and would 

 incidentally augment the numbers of spawners. 



Shad. — The gross catch of shad has declined from nearly 50,000,000 

 pounds in 18^7 to less than 9,000,000 pounds in 1935. It is incon- 

 €eival)le that the decline in yield of this choice species does not indicate 

 diminished abundance. Since the shad is not subject to commercial 

 fishing during its period of growth in the sea, the causes of depletion 

 must be sought in human interference with spawning migrations into 

 coastal rivers. 



The following explanations of diminished reproduction have been 

 offered: (1) interference with spawning by pollution and by obstruc- 

 tion of streams by dams; (2) insufficient numbers of spawners result- 

 ing from over-fishing. It is not to be dou})ted that complete blocking 

 of the Susquehanna River by the Conowingo dam has eliminated a 

 •considerable spawning area and it is probable that severe pollution 

 in the Delaware has at least contributed greatly to a virtual disap- 

 pearance of the sliad runs in that stream. On the other hand, a num- 

 ber of rivers which are almost completely free from pollution have 

 shared in the general decline and the Hudson River, which certainly 

 cannot be said to l)e unpolluted, has staged a most spectacular re- 

 covery, the catch increasing from less than 100,000 pounds in 1917 to 

 a yield of nearly 3,000.000 pounds in 1936. 



The recovery of fishing in the Hudson River is attributed by the 

 New York Conservation Department to the measures which it has 

 adopted to insure that sufficient numbers of spawners are allowed to 

 ■escape the fishery. On the other hand, it is believed by many that 

 the shad is highly migi-atory in its habits and that the increased runs 

 in the Hudson River are merely the result of a desertion of southern 

 rivers by the stocks which usually seek them. 



The former explanation seems more likely but decision must be 

 reserved until the results of tagging experiments, scale studies and 

 other tests of the parent stream hypothesis are available. Conse- 

 quently, considerable effort will be devoted in 1938 to such observations 

 and experiments. 



