J.S. Farmer & W.E. Henley, Slang and Its Analogues, Past and Present, volume 6 (1903) offers this interesting entry for scoop:
SCOOP, subs. (American).—1. A big haul; an advantage : spec[ifically] (journalists') news secured in advance of a rival, a series of BEATS [defined elsewhere in this dictionary as "anybody or anything that surpasses another"]. Also (2) on 'Change, a sudden breaking down of prices, eabling operators to buy cheaply, followed by a rise. As verb. = (1) to make a big haul : and (2) to get the better of a rival. [First two cited references:] 1882 McCabe, New York, 160. He runs seventy 'busses on this line, and scoops in three 'r four hundred a day. 1888. Detroit Free Press, 22 Sep. Mr. Terada, the editor, is in jail for fourteen months for getting a scoop on the government. ...
A 'scoop' on Wall Street
The 'Change mentioned in the second noun sense of scoop in Farmer & Henley's entry for the term is the New York Stock Exchange—and this slang usage turns out to be considerably older than you might suppose from Farmer & Henley's description. A lengthy description of what the term refers to in its Wall Street slang sense appears in "Financial Items," in the [Philadelphia, Pennsylvania] Evening Telegraph (August 4, 1868):
—The New York Herald says:—
"On the Stock Exchange the great feature of the day was a sharp raid on Erie, which resulted in a decline of 68; but the indications are that this is merely what is known in Wall street as "a scoop" preliminary to a bull movement in the stock, and those who sacrifice their Erie at the current figures will soon find that they have been cleverly victimized by a combination of unscrupulous speculators, whose immediate object is to shake all the stock they can out of the hands of weak holders, and at the same time to increase the 'short' interest. The signs are now that the raid has spent its force, and that a quick reaction will succeed. ... The Erie raid took the street entirely by surprise, and the real firmness of the market was shown in the stubbornness with which other stock yielded, notwithstanding some bull clique appeared to be in league with the Erie raiding party for the purpose of buying.
From the "New York Money Market," in the [Philadelphia, Pennsylvania] Daily Evening Bulletin (February 22, 1869), reprinted from the New York Herald:
The stock market was irregular in its fluctuation about the central figures of Pacific Mail, New York Central, Fort Wayne, and Michigan Southern. In the early portion of the week the "bears" made a raid on the market, and the ''bulls" helped them for a "scoop," basing their operations upon the difficulties surrounding the accomplishment of through connection to Chicago by the Erie Railway. A good deal of currency was also withdrawn from circulation, and affairs had a panicky look; but the clouds went by, and now that there are more encouraging signs for the success of the Chicago enterprise, the market adjourned over Tuesday with a happier feeling among operators generally.
From "Financial and Commercial," in the [New York] Sun (April 15, 1871):
The general market started off quite strong, with a slight advance in the more prominent stocks, but a feverish feeling soon became apparent during the first session of the Board, because of the very heavy sales in Union Pacific, whose upward rise had been for some time a marked feature of the street. There are many rumors current respecting the operations in this stock during the morning, but as the day advanced the whole movement appeared to have been a "scoop" game, designed for the purpose of deceiving the street as to the real movements of the new clique, who have so suddenly stepped in and checkmated the designs of the old party heretofore recognized as closely identified with the interests of that road.
And from "Slang of the Stock Board," in the Nashville [Tennessee] Union and American (January 17, 1873):
"Scoop" is a term less familiar to the public than any of the foregoing. "The scoop game," a very common one in Wall street, is played in this way. A clique of speculators, let us suppose, want to get possession of a good deal of some particular stock which they have reason to believe will soon advance in price; but, of course, they want to get it cheap, and they accomplish their object by starting a break in the stock. They instruct their brokers to offer small quantities under the market price, and keep on offering it lower and lower, until other holder of the same stock who are not in their confidence become alarmed and sell out at the best price they can get. In the meantime the clique have other brokers buying all the stock that is offered, and thus they get possession of a large amount of stock at low prices, which they can probably sell, a few days later, at a large profit. The "scoop game" is one of the most profitable that the Wall street gentlemen play.
A 'scoop' in the press
The earliest Elephind match I found for the noun "scoop" in the sense of a journalistic exclusive story is from "The Night Reporter," in the Columbia [Pennsylvania] Spy (May 28, 1870):
Some time ago on of the Chicago night reporters received a hint through a private source that there had been a serious shooting affray in a remote part of the city.Although the hour was past midnight he determined to procure the particulars for the paper of that morning. Accordingly he flew to the hack-stand, jumped into one of the vehicles always on hand, and gave orders to proceed with all dispatch to the locality indicated. On the way thither his spirits were pitched in the highest key, for lie felt morally certain that he should have a "scoop" on his brethren. On his arrival at the scene he jumped nimbly out of the carriage, but was completely dumbfounded at seeing a rival reporter jump as nimbly from the driver's seat. ...
The driver slammed the door, jumped upon his seat, and away went the carriage at a tremendous rate of speed. Again was [night reporter] No. 1 elated with the vision of a "scoop,"; again were his spirits pitched in the highest key, and as the carriage whirled rapidly along the street he drew upon his imagination for picture representative of his rival plodding wearily and dolefully in his rear. He felt some pity for him, too; but had not a game of diamond been cut diamond with them? Yes. It couldn't be helped. A "scoop" was a "scoop," and there was an end on't. In due time he got to the office, dashed away at his account, and reached the conclusion just in time for the press. Then he sought blissful repose, and dreamed of glorious "scoop" all night long.
Elephind newspaper database searches yield first occurrences of scoop as a Wall Street slang term for a type of stock price tampering from August 4, 1868, and of scoop as a newspaper term for a major exclusive news story that appears in print before the competition's coverage of the same event does from May 28, 1870. I don't know whether these overlapping slang usages are etymologically related or merely coincidental.
At least superficially, the Wall Street "scoop" suggests undercutting a stock's price in order to buy the stock later at a distressed sale price, while the journalistic "scoop" suggests getting the first shot at plunging a hand-held scoop into a barrel of something good before one's rivals have a chance to dip into the same barrel themselves. On another level, though, both slang terms seem to involve a notion of having valuable information that no one else does about an event or developing situation.
If one slang usage emerged from the other, I think it more likely that the journalism scoop derived from the stock market scoop than vice versa. But both may have arisen independently, from two fundamentally different senses of a literal scoop: a low point or depression (as in "a scoop of the sloping hills"; and an implement full of gold, meal, or some other desirable commodity.