Grenadiers of the World Oceans: Biology, Stock Assessment, and Fisheries

<em>Abstract.</em>—The abyssal grenadier <em>Coryphaenoides armatus </em>(Hector 1875), family Macrouridae, is a benthopelagic deep-sea species with a depth range of 282–5,180 m, with most observations and captures at depths of 2,500 m and deeper. It is one of the most abundant grenadier species in the world’s oceans but is absent from the Mediterranean Sea, Arctic Ocean, Indian Ocean north of 45°S, and has not yet been recorded from the Southern Ocean south of the Antarctic Polar Front. Typical total lengths range from 20 to 80 cm and the maximum recorded is 102 cm. Dietary items include mesopelagic fishes and cephalopods, and benthic items such as crustaceans and bivalves. The abyssal grenadier is well documented as an opportunistic scavenger and this propensity has been used to attract individuals to bait within view of submersibles and underwater camera systems to make <em>in situ </em>observations of behavior. Baited cameras have been in use to observe deep-sea scavengers since the late 1960s, with the first confirmed observation of the abyssal grenadier in 1971. More recently, baited photographic autonomous landers have been used to gain data on respiration rates, size frequency, and swimming velocity. In addition, models have been developed and refined to estimate local densities and to quantify the number of fish present at a food fall and their staying time at bait. This ultimately means that baited-camera-derived abundance estimates can be produced, and that the numbers of scavenging grenadiers and how long they remain at a small food fall can be linked to the productivity of the overlying surface waters.