Offshore Pelagic Measure 3mMeasure Smart. Estimate Right. The 3m Offshore Pelagic Measure is a durable, professional grade fish measuring mat designed for serious offshore anglers. Measure fish length and estimate weight instantly while on the boat and the fish still alive in the water ideal for marlin, tuna, and other large pelagic species. Built from UV resistant vinyl with bright, easy read markings, this compact mat includes species specific length to weight conversion