What is the name given to this weapon?

A punt gun is a type of extremely large shotgun used in the 19th and early 20th centuries for shooting large numbers of waterfowl for commercial harvesting operations. These weapons are characteristically too large for an individual to fire from the shoulder or often carry by themselves, but unlike artillery pieces, punt guns are able to be aimed and fired by a single man from a mount. In this case, the mount is typically a small watercraft. Many early models appear similar to over-sized versions of shoulder weapons of the time with full-length wooden stocks with a normal-sized shoulder stock. Most later variations do away with the full-length stock--especially more modern models--and have mounting hardware fixed to the gun to allow them to be fitted to a pintle.

In the United States, this practice depleted stocks of wild waterfowl and by the 1860s most states had banned the practice. The Lacey Act of 1900 banned the transport of wild game across state lines, and the practice of market hunting was outlawed by a series of federal laws in 1918.