delivered the opinion of the Court,

This is a suit brought by the respondent, who is also a cross-petitioner, to recover' the value of mussel shells removed from the lands of the respondent’s assignor and manufactured by the petitioners into buttons. It was brought in a Court of the State of Missouri, but was removed to the District Court of the United States. There were two counts; one simply for the conversion of the shells and a second alleging that the shells were part of the realty and that the plaintiff was entitled to treble damages, under Rev. Stats. Mo. 1909, § 5448. (Rev. Stats. Mo. 1919, § 4242.) At the trial the District Court directed a verdict for the defendants, and the judgment was affirmed by the Circuit Court of Appeals. 258 Fed. 335. The main question was disposed of on the ground that by the Statutes of Missouri, Rev. Stats. 1909, §S 6508, 6551, the title to the mussels was in the State.[*135] As to the second count it was held that the mussels were not part of the realty. Later, a rehearing'was granted, and while the Court adhered to its former opinion on the second count, it rightly, as we think, held that the statutes declaring the title to game and fish to be in the State spoke only in aid of the State’s power of regulation and left the plaintiff’s interest what it was before. See Missouri v. Holland, 252 U. S. 416, 434. It assumed that the defendants were trespassers and sent the case back for a new trial on that footing, the damages to be confined to the value of the shells at the date of conversion and not to include that subsequently added by manufacturing them into buttons. 270 Fed. 713.

The mussels were taken alive from the bottom of what seems to have.been at times a flowing stream, at. times a succession of pools, were boiled on the banks and the shells subsequently removed. As to the plaintiff’s title, it is not necessary to say that the mussels were part of the realty within the meaning of the Missouri Statutes or in such sense as to make the plaintiff an absolute owner. It is enough that there is a plain distinction between such creatures and game birds or freely moving fish,, that may shift to another jurisdiction without regard to the will of land owner or State. Such birds and fishes are not even in the possession of man. 252 U. S. 434. 2 Kent, Comm. 349. Young v. Hichens, 6 Q. B. 606. On the other hand it seems not unreasonable to say that mussels having a practically fixed habitat and little ability to move are as truly in the possession of the owner of the land in which they are sunk as would be a prehistoric boat discovered under ground or unknown property at the bottom of a canal. Elwes v. Brigg Gas Co., 33 Ch. D. 562. Reg. v. Rowe, Bell, C. C. 93. Barker v. Bates, 13 Pick. 255. This is even more obvious as to the shells, when left piled upon the bank, as they were, to[*136] await transportation. Northern Pacific R. R. Co. v. Lewis, 162 U. S. 366, 378, 382. Possession is enough to warrant recovery of substantial damages for conversion by a trespasser.' We say nothing about the character of the' stream as to navigability. The jury at least might find that there was nothing in that to prevent the application of what we have said. We are slow to believe that there were jpublic rights extending to the removal of mussels against the land owner’s will.

But it cannot be said as matter of law that those who took the mussels were trespassers; or even wrongdoers in appropriating the shells. The strict rule of the English common law as to entry upon a close must be taken tc be mitigated by common understanding with regard to the large expanses of unenclosed and uncultivated land in many parts at least of this country. Over these it 'is customary to wander, shoot and fish at will until the owner sees fit to prohibit it. A license may be implied from the habits of the country. Marsh v. Colby, 39 Mich. 626. In Missouri the implication is fortified by the limit of statutory prohibitions' to enclosed and cultivated land and private ponds. Rev. Stats. 1919, §§ 5662, 3654. There was evidence that the practice had prevailed in this region. Whether those who took these mussels were entitled to rely upon it, and whether, if entitled tb rely upon it for occasional uses, they could do so to the extent of-the considerable and systematic work that was done were questions for the jury. They could not be disposed of by the Court. The implication of a.license'of the kind that we have mentioned from, general understanding and practice does not encounter the difficulties that have been suggested in implying a license from conduct alone in cases where the same conduct after twenty years might generate an. easement, it being a plain- contradiction' to imply ad interim a license which would prevent' the acquisition of a prescriptive[*137] right. Chenery v. Fitchburg R. R. Co., 160 Mass. 211, 212.

As to the rule of damages in case the plaintiff recovers, in the absence of a decision by the Supreme Court of the, State we should not regard the mussels as part uf the realty within the meaning of the statute rélied upon in the second count, and so famas appears at present we see no reason for charging the defendants, if at all, with more than the value of the mussels at the time of conversion, as ruled below. Wetherbee v. Green, 22 Mich 311. Wooden-Ware Co. v. United States, 106 U. S. 432. Union Naval Stores Co. v. United States, 240 U. S. 284. The result is that this judgment of the Circuit Court of Appeals is affirmed, but not all the principles laid down by it, and that the case will stand for trial by jury in the District Court.

Judgment affirmed.