speed Baits and lures are typically trolled at speeds up to , though speeds up to can be used, particularly when boats are travelling to different fishing areas. The speed at which the lure is pulled through the water impacts on the fishing success. The optimum trolling speed varies with different species of fish, with weather conditions and the time of year, and other conditions. Chinook salmon can be successfully trolled at higher speeds than more docile lake trout. For these reasons fishermen use devices that accurately track speed. Trolling motors calibrate speed more accurately than large outboard motors. Trolling plates are also used with larger motors to slow the boat to the desired speed, although some anglers experience mixed results with plates. Trolling can be effective at surprisingly low speeds. Kayaks fitted with a deck-mounted bracket for holding a rod can be paddled to troll effectively for salmon. Recreational trolling In marine environments, trolling is used in big-game fishing to catch large offshore or open-water species such as tuna and marlin. Saltwater anglers also troll for inshore species such as bluefish, kingfish and various jacks. Rock fishermen can use an umbrella rig as a method of trolling without using a boat. Typically, an umbrella rig consists of four plastic neon green lures with a lead dragging behind. An additional lure is attached to the lead. Only the lure behind the lead need have hooks attached because this lure can appear to a stalking fish as a wounded or sick laggard in a school, making it a more likely target. A pattern of multiple baits or lures can be trolled at varying distances behind a boat. Lures can be fished straight from the rod tip (flat line), or from outriggers. Purpose designed sinkers exist to control the trolling depth on freshwater lakes. Freshwater anglers can also find trolling effective. Recreational fishermen can successfully troll lakes and reservoirs for salmon and trout. It can be the method of choice for catching the elusive muskie, and a useful technique for catching walleye, black bass and striped bass. For light and medium freshwater gamefishing, any reasonably robust casting or spinning rod can be used as a trolling rod. Effective trolling rods should be fairly stiff with a relatively fast action, since "whippy" slow action rods are frustrating to troll with. Commercial trolling Commercial trolling vessels catch fish by towing astern one or more