Wiktionary
downrigger
n. (context fishing English) A large reel of heavily weighted steel wire fishing line used to fish with trolled bait at great depths.
Wikipedia
Downrigger
A downrigger is a device used while fishing using the trolling method, which places a lure at the desired depth. A downrigger consists of a three to six-foot horizontal pole which supports a cannonball, generally 10 to 15 pounds. by a steel cable (generally stainless steel or wire). A clip, also known as a "release" attaches a fishing line to the cannonball weight. The bait or lure is attached to the release.